January 4, 2022 • 43 mins
In this classic episode of Stuff to Blow Your Mind, Robert and Joe explore the science and history of sinkholes. How have these impressive geographic features impacted our world, and what can they reveal about the past? (originally published 1/14/2021)
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Episode Transcript
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Speaker 1 (00:05):
Hey, are you welcome to Stuff to Blow your Mind?
My name is Robert Lamb and I'm Joe McCormick, and
today we're bringing you an episode from the vault. This
is our part one of our episode on sink Holes,
which originally aired on January. We hope you enjoy Welcome
(00:25):
to Stuff to Blow Your Mind production of My Heart Radio.
Hey you welcome to Stuff to Blow your Mind. My
name is Robert Lamb and I'm Joe McCormick, and today
we're gonna be talking about sink holes. This is actually,
I think, in a way a listener request topic that
(00:47):
turned out to be very interesting. But it's, uh, it's
sort of leap frogging off of some some previous episodes
we did. Rob did the did the sink Whole journey
begin when we were talking about the star Lac from
Return of the Jedi. I think that is the original context.
I think that was the original point at which we
begin to hear listener males about the idea of in
a sink Whole episode, because we talked about the star
(01:09):
Lac and then we talked about some ideas and was
it meso American uh? Mythology concerning uh entities of the
ground that swallow things up. Oh, that could be it. Well,
I know we ended up talking about the Bible, which
will revisit in a minute here. But one of the
questions that came up was, you know that scene in
movies where there's an earthquake and and then suddenly a
(01:32):
crack opens up in the middle of the street and
it's you know, miles deep, and it just swallows people
down into it. Uh. The question was like, does that
kind of thing really happen? Does during an earthquake? Does
the earth open up and open these deep pits and
chasms that people fall down and disappear into. And our
previous answer to that was, well, not really, or it
(01:53):
seems like that's that's extremely rare if it ever happens.
That's not like a common feature of what happens to
the surf is topology during an earthquake. But sinkholes, a
listener pointed out, or a very different story, and sinkholes
could explain many of these stories, uh, from from mythology
and all that of the earth opening up and swallowing people.
We can get back into that in a bit. But
(02:13):
you actually turned up a really interesting photo essay about
a fascinating sudden opening of a sinkhole. Uh just earlier
this year, that's right. Well, actually it was last year, remember,
oh god, Yeah, I haven't turned the calendar fully yet.
It's still it's still It's like that year is kind
of like the the other world in hell Raisers. So
(02:36):
it's got chains with hooks and them, and they shoot
out of the walls and so the hooks are still
in my brain, but I'm slowly methodically rebuilding my body
to escape. All right, Well, this is this story takes
us back to April. So Um. What happened is a
whole opened up in the front yard of a home
in Black Hawks, South Dakota. Uh, specifically in a housing
(02:58):
development there that is called perfectly enough, the Hideaway Hills development.
That just doesn't sound great. I mean no offense to
the people who live there, but it doesn't sound like
a place I want to go. It sounds like a
place where, I don't know, where you like retreat after
you've committed a crime. What was the housing development on
arrested development, Sudden Valley or Sudden Yeah Appa, so Um,
(03:25):
Like you pointed out, there's an incredible photo essay photos
series on this on board Panda about this. If you
look up board Panda Black South Dakota sinkhole, you will
find it because uh this photo essay, if you will,
it takes us through a journey by a local caving
group called Pahsapa Grotto as they decided to venture down
(03:47):
into this hole that opened up in this front yard
to explore the world beneath the suburbs. Now, this sinkhole,
it turns out it's going to be very different than
most of the sinkholes we're talking about in this episode.
Most sink holes open up over some kind of void
that is formed in the rock below, and as we'll
get into a lot of that usually has to do
(04:08):
with water and hydrology. But in this case, the void
in the rock below the neighborhood was was more was
of a more artificial persuasion, right. That's because there was
an abandoned gypsum mine beneath the housing development, and so
the cavers had they had to lower down in on ropes,
you know, had to use like actual caving equipment into
(04:28):
the dark and sometimes flooded tunnels beneath reportedly over two
thousand feet across in a hundred and fifty feet wide
this tunnel um complex. Uh, and they encountered the remains
of what looks like an old, like nineteen fifties automobile. Uh.
There's just a whole world down there, like a whole
uh Minoan maze beneath this you know, rather mundane looking
(04:51):
housing development. It's like two levels of weird. So first
of all, it's yes, the suburban you know, neighborhood, and
then just in the middle of somebody's front yard a
pit opens up, so that's the sinkhole. But then it's
that the sinkhole goes to this maze. And yeah, like
you said, there's like an old Chevy convertible down there,
And I'm wondering, why is that down there? Did somebody
(05:11):
drive it into the mind before the mind was sealed up? Yeah,
I don't know. Like, it's just it's a place full
of questions, is a place full of the past, of mysteries.
And so the article itself gets into some of the
community fall out over all this. But but what I
love about this episode is it illustrates for us this
divide between the surface world so tightly manicured and controlled
(05:32):
so much of the time, and a world beneath that
we have only a shaky understanding of like something out
of a mash up between Poltergeist and The Descent. You know,
a gateway to that hidden underworld might open up at
any moment and reveal its secrets to us, invite us in,
perhaps swallow us entirely, and then we'll be part of
(05:53):
that underworld. Because if we're being you know, perfectly rational
without any supernatural ideas like that, that idea alone is terrifying.
You know that the earth might open up and we
might fall, you know, into a pit. But then if
you begin to layer in beliefs and superstitions, then yeah,
become this whole becomes a portal to other realms. Yeah, exactly.
(06:15):
Now we've talked about natural features in the landscape taking
on religious significance before, Like in we did a couple
of episodes called The Sacred Mountain, which was about mountain
peaks that were considered to be holy or supernatural or
the dwelling places of gods or places that Win explored.
People often reported having supernatural experiences, They're like One of
the things that came out of that was the the
(06:36):
often reported third man syndrome, feeling that mountain climbers sometimes
have very high up but we talked about possible ways that,
like the effects of the sun or that altitude sickness
could contribute to that um. But there are also ways
in which sinkholes can take on similar types of religious significance,
can have a similar mythological appeal, And one great example
(06:59):
is we is some of the sinkholes are also known
as sinnotes that we see throughout Mesoamerican religion in the
Yucatan Peninsula and among the ancient Mayan people. But I
guess well, we'll come back to that more later. I
wanted to get to this question about the the idea
that the earth can open up and swallow you. It's
an image that seems like to perfectly fit ancient myths
(07:21):
and texts. You would imagine passages like this appearing in
you know, Babylonian texts or something. It definitely appears in
the Hebrew Bible, for example, in the Book of Numbers,
there's a passage where Moses is speaking to people and
he's trying to demonstrate that he was in fact sent
by the Lord and he uh he, he says, and
basically he makes a promise that hey, if the Lord
(07:42):
has sent me he'll he'll send a sign, and you'll
know it, because there will be this group of people
that will be swallowed up alive into a pit that
opens up suddenly in the earth. For very these wicked
people who have rejected the Lord. And the passage says
in Uh in the Book of Numbers. Now it came
to pass, as he finished speaking all these words, that
the ground split apart under them, and the earth opened
(08:03):
its mouth and swallowed them up with their households, and
all the men of Cora, with all their goods. So
they and all those with them went down alive into
the pit. The earth closed over them, and they perished
from among the assembly. And so I wonder, I mean, obviously,
with passages like this, I wonder if it's this kind
of thing that inspired that scene in every movie that
(08:24):
has an earthquake in it where suddenly a bottomless pit
opens up in the ground and people get sucked into it. Yeah,
you know, this could also be graboids. If I think,
if they want to make another Tremor's film, which they will,
I'm sure they should go for you know, some biblical
flare here, go for an Old Testament Tremor's movie with
with Moses being our central character, and that's a very
(08:45):
good direction. Now, one thing I want to say, because
I feel like I have to bring this up every
time we talk about geo mythology. Uh, there's this question
of is this story in the Bible based on something
that someone in history witnessed witnessing a real world geological event,
perhaps a sudden collapse of a settled area due to
a sinkhole. Uh. And as I pretty much always do
(09:06):
whenever we talk about geomethology, I want to emphasize that
fantastic imagery and in myths and legends and religious text
doesn't necessarily need to be explained by someone actually having
seen something physical in the world. I think we can
sometimes go overboard looking for naturalistic explanations of this kind
to explain what somebody thought they saw that appears in
(09:27):
a story. You know, people are highly imaginative, and sometimes
stories are just stories. But there's always also the possibility
that stories like these could be based on people hearing
stories about having seen I don't know, there was a
there was a castle or a building or something like
that that was just swallowed up into the earth, which
if you didn't have any kind of geological understanding with
(09:47):
which to to to interpret that. It would certainly seem
to be a you know, a supernatural event. I don't
I don't know how else you would interpret it. Yeah,
because I think one of the things that really drives
home and when we we see examples of sync holes
and we hear stories like this, we see cinematic interpretations,
is that idea that the that terra firma is not
(10:08):
that firm, is not that fixed, that it could change,
that the that the firm ground beneath our feet could
suddenly give way, you know, like that alone is just
this kind of uh, you know, horrifying idea that that
it that it easily applies as a metaphor to everything
else in our in our life. You know, that the
thing that is the order that we depend upon might
(10:32):
go away at any moment. Yeah, it's interesting to think about,
like a vertical spectrum of of ways the natural world
can intrude on our lives and how most of the
stuff that we're that we're used to thinking about taking
into consideration, worrying about as as possible threats, all basically
takes place like on the surface of the earth. And
that you know, when you go to the vertical ends
(10:53):
of that spectrum, you've got like impacts from space coming
from above, sinkholes up and opening up from below, and
these fen I'm gonna intrude on that day to day
understanding of physical forces. Yeah, so it's it's no surprise.
We were talking about this before the podcast started rolling
here that if you start looking around for sinkholes online,
you'll find just so many galleries, top ten lists, lots
(11:16):
of click bait about sinkholes. Like sinkholes are kind of
they're kind of like a like they're kind of like
true crime, you know there um there. You also see them,
like I was noticing, like very tabloid sites sites that
otherwise they're not going to really have anything related to geology,
but they'll have sinkholes. You know, it'll be celebrity gossip,
(11:38):
um and you know, maybe some conspiracy theories. But then also, uh,
big old holes opening up in the earth. Chump boxes
are full of sinkholes. Have you ever noticed this? These
are the like the link um grids at the bottom
of blogs and whatnot. Yeah. Yeah, so, like you know,
like most websites on the Internet these days are just
being more and more infected by ads that a since
(12:00):
really take the form of malware. But if you scroll
down to the bottom of most articles or any text
image based website, you'll usually see one of these boxes
that's full of just like extremely tacky, distasteful images that
are either like something that's kind of sexually suggestive and
a gross way, or something that is uh sort has
(12:20):
some kind of like health vibe, Like it looks like
infected skin or holes in skin, or some kind of
bite or something like the kind of a necrotic bite
that you might imagine someone would get in their worst
nightmares from a brown recluse, you know that kind of thing. Um. Yeah,
they they tie into our like deepest, most primal fears
(12:42):
and desires, just pure eroticism or just pure in necrotic
damage or indeed holes opening up in the earth. You know,
it's got to be something extreme like that to make
it into that grid of horror. Yeah. The toilet with
the rat coming up through it, remember that one. Oh,
I think I've seen that when I was a common
chumbox image or the like. You know, doctors say never
(13:04):
eat this vegetable, but they don't tell you what it is. Yeah, yeah, yeah,
sometimes it is. Um. It. It's economic as well. You know,
there'll be some sort generally it's like a picture of
an old person and just a few like alarming words
about you know, investments and retirement or something. Right, but
that is the world. Well, sinkholes are actually in their
own way. I mean, of course they can be horrifying,
(13:26):
they can be destructive to human life, but they are
also fascinating in their own way. In the natural way,
they are wonderful. Uh. There can be beautiful uh legends
and stories attached to them, and so I don't know,
I feel like they are the most uh naturally beautiful
thing that that fits in the chum box. I mean
(13:46):
the rat and the toilet can't compete. I mean the
rat and the toilet. We could do an episode on
that as well. But yeah, I agree, the sinkholes need
to be rescued from the chum box. Uh. And and
that's kind of what we're doing in in this episode
of Stuff to Blow Your Mind and the possible second
episode of Follan. Alright, so sinkholes are formed in a
(14:10):
number of ways, but most naturally occurring sinkholes, like most
other things on planet Earth, in the end, come back
to the power of water. Water, of course, is the
molecule of life, largely because of its power as a
master solvent, and in much the same way really that
water created life on Earth, probably it also creates many
(14:31):
of Earth's most astounding geologic features. And so this is
how we we get sinkholes for the most part. So
as carbon dioxide in the air or in the soil
mixes with rain water, that mixture forms a weak acid
with the with the chemical formula H two c O three.
So what you've got there is you've got your H
(14:51):
two oh the water, and then you've got your C
O two the carbon dioxide. They react, they make a
compound with two hydrogens, one carbon and three oxygen's. And
this weak acid formed in the atmosphere or in the
soil is known as carbonic acid, and it is the
primary reason that caves exist. Now most caves in the world,
(15:11):
not all, but most are formed by the drainage of
acidified water through what you might call soluble rock and uh.
Soluble rock are types of rock that can react chemically
with this water and be dissolved and carried away. Now
they're they're multiple kinds of soluble rock, including minerals like
(15:33):
salt and gypsum, But probably the most important, or at
least the most charismatic, is limestone, which is in itself
a fascinating and even mind boggling rock. And sometimes I
really do think a lot about limestone, and maybe people
are aren't inclined to be as impressed by it as
I am. But if you don't believe me that limestone
(15:54):
is amazing, I think it's worth considering that if you
live in an area of the world you know this
primary resting on limestone, which in the United States would
include huge portions of like Florida and the coastal southeast,
big parts of the Midwest. If you live in a
place like that dominated by this this carbonate rock, you
are walking around every day on rock that is probably
(16:16):
mostly built out of dead bodies. Limestone can be formed
in a number of ways. Some of those ways are
a biotic, but one of the major processes that forms
limestone is the gradual deposition of the shells and other
hard calcium carbonate body parts of animals and other tiny
organisms in the oceans and rivers and lakes where they
(16:38):
accumulate on the bottoms of these water sources over millions
of years, and apparently feces also in general, waste products
can contribute as well. So the calcium based body parts
of algae and coral and oysters and all kinds of
creatures of the sea settle in the deep, and then
they're pressed down and paved over by time and pressure
(17:01):
until they become layers of sedimentary rock. I really just
think about that. Sometimes limestone is largely made out of
life that has died and become rock, like the fallen
creatures of Earth pile up and become part of the
crust of the Earth itself. Wow, it's like it's like
the Medusa's layer, right, all these like the petrified bodies. Oh,
(17:24):
that's I wish I had thought of that when we
were doing our Medusa episodes. Except I guess in the
Medusa Garden that they keep their form right here. They
just sort of like go back to whence they came.
They become part of this mass. But anyway, it's via
rocks like this that we get so many of the
naturally occurring sinkholes on the Earth. So how do they form? Well,
(17:45):
imagine that there is a storm, it rains here in
an area with some kind of soluble rock. Let's say
it's a it's a carbonate rock, it's like limestone, and
rainwater collects on the surface of the earth and then
runs downhill. And if that rainwater drains down in two
cracks insoluble rock like limestone, things begin to happen much
in the same way that you can dissolve table salt
(18:07):
or sugar and a glass of water. The crystal contents
of these soluble rock surfaces are gradually dissolved in and
carried away by that acidified water. And over tens or
hundreds of thousands of years, that dissolution of the rock
by acidic water can turn what might have started as
this tiny stress fracture in a chunk of bedrock into
(18:28):
an underground cavern large enough for a human to climb into.
And of course, as the centuries go on, these these
voids created by the drainage pathways of water can just
get bigger and bigger. They can form underground rivers that
form larger and larger voids. And it's this dissolution of
soluble rock by water that usually leads to the creation
(18:49):
of sinkholes. Uh though these voids in the rock, I
think sometimes maybe geologists will get picky about this, these
voids in the rock are not technically themselves sinkhole, and
we would normally think of them as voids or just
caves right there, their caves in the rock. Um. Rather,
a sinkhole is more of a topographical designation. It's a
(19:10):
topographical concept about the ground and the surface of the earth.
So according to the U S Geological Survey, a sinkhole
is quote an area of ground that has no natural
external surface drainage. So like in one of these areas,
if it rains, water just pools in and there's nowhere
on the surface level that allows this water to run out.
(19:33):
So if the water leaves, it's either evaporating into the
air or it's draining out through somewhere in the bottom. Sinkholes,
of course, can form gradually over hundreds or hundreds of
thousands of years, often of steady dissolution, or they can
form quite suddenly. For example, when the ground over a
void in the limestone below is suddenly just suddenly there's
(19:54):
not enough for it to support its own weight, and
then it just collapses and reveals the void that had
been there for so long. Uh. And we know that
the sudden appearance of a sinkhole can have these devastating
effects on human settlements and uh whatever is lying on
the surface, which will get into more later, but it
can also have strange, otherworldly effects simply on the geological
(20:15):
and hydrological landscape itself. And I wanted to share one
amazing example that I came across while I was reading
up for this episode. This was the opening paragraph in
an article for The New Yorker by David Owen. There
was an article about sinkholes called Notes from Underground, and this,
this paragraph really gave me chills when I got to
the end of it. So, uh, if you don't mind,
(20:37):
I just want to share this here. In the fall
of nine, much of Lake Jackson, a four thousand acre
natural body of water just north of Tallahassee and a
popular site for fishing, water skiing, and recreational boating, disappeared
down a hole like a bathtub, emptying into a drain trophy.
Bass became stranded in rapidly shrinking eddies, enabling children to
(21:02):
catch them with their hands and toss them into picnic coolers,
and many of the lake's other fish, turtles, snakes, and
alligators vanished into the earth at various times. During the
next few years, the lake partially refilled, redrained, and refilled again.
Jonathan Arthur, who is Florida's state geologist and the director
(21:23):
of the Florida Geological Survey, was among several people who,
during a dry period descended a ladder into the main opening,
which was about eight feet in diameter. Quote, you could
climb down twelve feet or so and then walk under
the lake bed. He told me recently, I hadn't gone
very far before my red flags went up, and I
(21:43):
was like, maybe I won't go any farther. So that image,
it combined with the way it's phrase that that really
gave me goose bumps. Yeah. Yeah, the idea of yeah,
I mean, it really feels like like a place you
do not belong. The you know, the the cave beneath
the lake that is uh yeah, that that that could
potentially fill back up at any moment. Well. And also,
(22:04):
I mean, I think anybody who, especially people who do
like scuba diving and stuff, are made uniquely aware of
the dangers of of being in places that combine water
and overhead rock. Like Yes, absolutely that that can be
an especially dangerous and and suddenly dangerous surprisingly dangerous combination
(22:27):
of features. Yeah, I mean, even if you are an
experience cave diver, cave diving is dangerous. Uh so um so, yeah,
that is a dangerous realm to to go down into,
for sure. Now, I figured it would be worth talking
about a few of the different ways that natural sinkholes form. Um. Obviously,
things will be a little bit different if you're talking
(22:48):
about sinkholes, you know, created by human activity, though human
activity can also contribute to some of the things I'm
about to talk about. But but if you're talking about
natural sinkholes in a carbonate rock like limestone. Um. There
are three main pathways that were highlighted in uh in
several sources, in my major source here just being the U. S.
(23:09):
Geological Survey, who has great materials about this, um and
so the first one is dissolution sinkholes. These are relatively
gentle sinkholes. You can think of it as a kind
of top down sinkhole. Here, what you should picture is
that you've got a thin layer of what would be
called overburden, and overburden just means whatever stuff's on top
(23:30):
of the rock that makes up the ground. So this
means soil could be sand, could be clay, pebbles, rocks,
other material resting on top of the rock layer on
the surface. Now, in a dissolution sinkhole, rain comes down
and it collects in a depression in the soluble rock
and just continues to dissolve and deepen that depression over
(23:52):
time as water gradually percolates down into cracks or joints
in the rock below. These tend to form very gradually,
so you can picture kind of a a gentle sort
of dip or pond in the rock that water is
going into, and slowly, over time it's draining down into
the rock below through some cracks or other types of openings,
(24:12):
and as it does so, it is dissolving more and
more of the rock and carrying it away. The next
type would be cover subsidence sinkholes, and this is where
you've got a lower level of soluble rock that gets
dissolved by the process we've already talked about, you know,
water running through it opening up a void in the rock.
And in this case, if the soil or overburden that
(24:36):
is above that layer of rock has certain physical characteristics,
I think, especially if it's like a more free flowing
kind of granular sediment like sand. Basically, the overburden or
the soil above kind of gradually pours down into the
void that opens up. You can imagine it being kind
of like sand pouring down from the top half of
(24:57):
an hour glass into the bottom half, and and that
that overburden pours down fills the void up partially. But
as it does so, it's sort of like creates a depression,
of visible depression in the surface of the overburden. And
these types of pits tend to develop pretty gradually and
not be all that deep or all that dangerous. Right,
(25:18):
You've probably seen pits like this before. You're just walking
through a field and suddenly there's just a depression in
the ground. Very possibly what's going on there is this
cover substance sinkhole. The soil is just kind of draining
into a void in the rock below. Now, of course,
it's worth noting in all of this, even these milder
(25:38):
forms of the sinkhole can certainly be destructive if you
have some sort of humanum structure built atop of it,
or a road, etcetera, which is sometimes the case, right,
But these first two have the benefit of not being sudden.
You know that they're going to take time to develop.
The third category, this is the real monster that could
(25:59):
inspire the geo myth potentially. This is the cover collapse, sinkhole,
and these are the ones that can potentially happen in
an instant and at least in the United States, they
tend to be most common in places where the overburden
is mostly clay. So again, you start the same way
that the last one did. Avoid opens up in the
underlying layer of soluble rock, and then the lower levels
(26:24):
of the overburden gradually drained down into the cavity in
the rock. And as this happens, what you get is
a cavity gradually opening up from from below and climbing
up into the overburden or the soil itself. So imagine again,
you've got to rock with a cavity or avoid in it,
and then maybe a layer of clay, and so the
(26:46):
clay on the bottom starts to seep down into that
cavern below and it just opens up a bigger and
bigger void in the clay. And eventually what's going to
happen there is that that void in the clay reaches
a point where where the collapsing roof of the void
breaches the surface, which means whatever is on the surface
falls into the hole. And that surface might well be
(27:08):
a road or a lake bed, or the ground under
a building. And this is the example where we can
see sudden collapses that can be deadly and destructive and
terrifying because suddenly what you thought was solid ground is
revealed to have long had had to void beneath it,
and suddenly it can't support whatever is on it anymore,
and it all goes down into the void. It's basically
(27:29):
like a trap door effect. You know, that's the that's
the terrifying part about it. You know, that's like suddenly
there is this opening beneath this and and people, you know,
can can build things without having any idea that that's
what's down there. Yeah, I mean, we've we've gotten to
the point where if we know what we're looking for,
especially you know, we we have more tools at our disposal,
uh for detecting sink holes and potential sink holes, and
(27:53):
in keeping track of of existing sink holes that maybe
expanding but but expanding have expanded. But yeah, for the
most part, like that that the the idea here is
that you don't know what's going to happen, and then
suddenly there's this chasm there in the earth. Now. Another
thing that's interesting to me about sinkholes is that we
often think about geological events like earthquakes and volcanoes as
(28:16):
what people sometimes call acts of God, you know, natural
events that occur for reasons vastly beyond our control and
that we can do nothing to stop. But there is
some indication that human activity may have more impact on
some massive geological events than once thought, and it certainly
appears to have an effect on the proliferation of sinkholes
(28:37):
in particular. In other words, sinkhole collapses can it seems
absolutely be invited by human behavior, as will probably discuss
more as we go on, but in broad strokes, it
appears that sinkhole collapses can be induced by uh. So,
one thing is human construction and other changes in the
top level terrain, especially how that affects water drainage. So
(28:57):
you're moving earth around and changing the way that water
drains on the surface. That can lead to sinkle collapses.
But also pumping of groundwater is a huge thing here.
You pump out groundwater from deep underground uh the pressure
of the natural water that's in the ground helps keep
the soil above it in place. So if you take
(29:19):
that water out, you lower the groundwater level, you can
cause collapses of the overburden lying over now evacuated aquifer voids.
Another thing that seems kind of relevant to that story
you started with. Remember the sinkle collapse that turned out
to lead to a mine down below in South Dakota.
The mine was a gypsum mine. So gypsum is a
(29:41):
major mineral that's that's in the ground there. We've been
focusing a lot on limestone, but one thing to note
that I did read also from the U. S Geological
Survey was that other types of underlying rock layers, such
as minerals like salt and gypsum, those can sometimes dissolve
and form voids much fast to than even sedimentary carbonate
(30:03):
rocks like limestone. So limestone will form these voids with
water running through it over you know, thousands of years,
but apparently assault and gypsum, potentially with the right circumstances,
can form large voids in in a matter of you know,
days or months. Than well, let's get into some examples
(30:27):
of sinkholes. Uh. And granted there are so many sinkholes
that have either existed for you know, thousands of years
or have just popped up in you know, recent decades.
But I want to start with one that I imagine
is instantly coming to a number of your minds. And
you're you're, especially when we were talking earlier about click
(30:47):
baity uh sinkholes, and that would be the two thousand
seven and especially the two thousand ten Guatemala City sinkholes. Um.
And they're they're worth mentioning for a couple of reasons. So, so,
first of all, there are some very dramatic photographs of
this thing. Photographs so dramatic that they they look photoshop.
You know, they don't look real. Absolutely, it looks like
(31:11):
something out of a movie. Yeah. It looks like a
hole has been like a cylindrical hole has been bored
into this city escape and it just descends into absolute darkness.
It is. It's a terrifying image. Um. And And and
when this these occurred, I mean, these were dramatic, traumatic events,
These were deadly occurrences. That two thousand seven sinkhole killed
(31:32):
five people and required the evacuation of more than a thousand.
The two thousand ten sinkhole swallowed a three story factory
and killed fifteen people. And in both cases, uh, it
seems to there seemed to have been a at least
a trio of causes. So there was the impact of
tropical Storm Agatha as well as the Pacaya volcano eruption,
(31:55):
but also leakage from sewer pipes and all of this.
So we're together to erode uncemented volcanic act, limestone and
other pyroclastic deposits beneath the city. And this case is
actually so visually alarming. There's a Snopes article about it,
not because there seems to be like a lot of
(32:15):
misinformation about the event itself. Uh, but it gets picked
up continually on social media as if it just happened,
as if it just happened, you know, this week or today,
as opposed to a decade ago. Right, So the photo
is real, the story is real, but it's but what
needs to be debunked is that people want to just
like reintroduce it as newly relevant over and over again
(32:38):
because it will always get attention. It's so dramatic looking. Yeah. Uh.
There is also a good Atlas Obscure article about it,
though I have to point out that the Atlas Obscure article.
I think this is a feature of just things that
they have cataloged on the site. But it says sorry,
great Guatemalan sinkhole is permanently closed, which which is it
(33:00):
is a weird sentence to read. Now. Meanwhile, up here
in North America we have our own sinkholes of note.
For instance, there are two giant West Texans sinkholes in
Wink and Kerment, Texas. They're located about a mile apart,
and these are similar to the Guatemalan sinkholes, and that
we have definite uh uh connection to human activities. These
(33:20):
were caused by oil and gas extraction in the area,
especially during the heyday of nineteen twenty six through nineteen
sixty four. Uh Wink Sinc. Number One opened in nineteen
eighty and Wink Sinc. Number Two open twenty two years
later in two thousand and two. And I was looking
at a two thousand sixteen Southern Methodist University study where
(33:41):
they were they were taking a look at these sinkholes
and the fact that they seem to be expanding because
the ground there is still unstable due to changing groundwater
levels and dissolving minerals um. However, like I said, are
they were now able to use stuff like satellite monitoring
to keep a better track of sinkhole development and progress.
But again, this is a case someone to what we
(34:02):
were describing earlier, where we've taken stuff out of the
ground and in doing so we have disrupted like the
you know, the natural balance of things down they're making uh,
sinkholes more likely to occur. Looking at a picture of
the wink sinkholes, Uh, just not as impressive as some
of these because the water level seems to have been
filled up pretty close to the top. So it looks
(34:24):
like just a weird pit in the middle of the
desert that could be like a lake. It's just you know,
water in it. But uh, but I imagine if you
that water were to drained out, it would look pretty
pretty messed up. Yeah. Plus, the bar is pretty high
for spectacular looking sinkholes, as we'll continue to see as
we discuss other sinkholes in the in in this episode
(34:44):
in the one to follow. Well, so I was wondering,
what's the what's the deepest known sinkhole on planet Earth? Oh, well,
if we want to go to the deepest, uh, then
we have to go to China. That is where we
encounter China's um. This is the the the Shijia uh
Tien King or the Heavenly Pit, and it's it's named
(35:06):
for a nearby village and then uh Tien King just
means heavenly pit. And it's located near Chuanshing in southwest China.
It's apparently six hundred and twenty six meters or two
thousand and fifty four ft long. It is five hundred
and thirty seven meters or a thousand, six hundred sixty
two feet wide, and it is between five hundred eleven
(35:28):
and six hundred and sixty two meters deep or between
one thousand, six hundred and seventy seven to two thousand,
one hundred and seventy two ft deep, So it's deep
that it is an enormous hole. And this is one
that I recommend looking at pictures of because it's is
really splendid looking. It's beautiful because it um. You have
the it's it's you have this this this double um.
(35:51):
It's like a double pit. There's like the initial pit
and then the pit below. You have vertical walls going
down to a little area that tapers off and then
or vertical walls going down even further that there's some
rich vegetation around it. Um, it's it's really beautiful to
look at, and indeed it is a tourist attraction if
you travel there. There apparently two thousand, eight hundred steps
(36:13):
constructed that allow visitors to journey all the way down
to the bottom of that second nested pit, which I
was reading. I think it takes you're gonna spend like
a couple of hours doing that. I think I read
that this is also a limestone pit, and yeah, one
of the great things about it is pits of the
size and of of this age. You know, it's been
around for a long time where the surface life has
(36:35):
just poured down into it, so you know, it looks
almost like the forest is spilling into the pit. And
of course that you know, it's a habitat for many animals.
I think I saw a report that maybe rare like
the clouded leopard had been spotted there. I think, oh, interesting. Yeah,
you see time and time again reading about different sinkholes
(36:57):
that they inevitably become uh an interesting place to look
at biodiversity. And we'll get we'll get more into that later.
But yeah, these are these end up being. You know,
they're not just especially ones that have been there for
a considerable amount of time. They're not just holes in
the earth. They don't remain voids. Nature feels that void,
and it does so in very remarkable ways. Now, there
(37:18):
are numerous um heavenly pits in this region of China,
and I can only imagine that there are some really
interesting traditions and legends about these geologic features. But I
have to admit that I could not find any of them,
at least none that had been translated into English. So
if anybody out there has that information, I would love
to hear about it, because a sinkhole like this is
(37:41):
just it's just too amazing. And it's been around way
too long. It's been around since ancient times, so there
have to be some cool traditions and legends regarding its
origin and things that live there, et cetera. Yeah, like you,
I was looking for similar things and I couldn't find
any any any cultural context for it. But I would
love to if you know out there now there is
(38:02):
another Chinese sinkhole of note that does have some cool
legend applied to it, and that is a dragon hole
in the Paracel Islands. It's nine four feet deep two
hundred and nine so this is out in the ocean.
It's also known as the Young Lu Dragon Hole, named
for the fifteenth century Mean dynasty Young Lu Emperor Um.
(38:25):
It's also known as the Eye of the South China Sea.
And the tradition here is that this is where the
Monkey King Uh Soon Will Kong finds his golden cudgel
in Journey to the West, So this would be his
magical staff. If you've ever seen a movie with the
with the Monkey King in it or seeing images of
the Monkey King, this is his big, amazing fighting staff.
(38:47):
So he actually gets it from this pit. Well that
is that is what that they've sort of taken the
story and said, oh, this must be the pit, okay,
because in the story he has to retrieve it from
the underwater kingdom of of our Guang, the Dragon King
of the East Sea, and uh yeah, this this amazing
magical staff, the the compliant golden hooped rod or has
(39:09):
it also been translated as the as you will gold
banded cudgel? Um? Oh I see compliant or as you will? Yeah, yeah,
it's um. They're also there's legends that this may have
been you the Great's measuring stick for determining the depths
of the Great Flood, So it has that would make
sense that you know, that would be underwater because there's
this connection to the depths, and so anyway, he dives
(39:32):
down into this hole and retrieves it. Now is this, Uh,
this is a picture of this pit that you've attached
here for us to look at. Yes, so again, it's
out out in the water, and it's just like a
sudden deep section of the of the water, a hole
in the sea floor that contains you know, dark depths.
You may have seen pictures of sinkholes in tropical oceans
(39:54):
like this before, for example, if you've ever seen a
picture of the Great Blue Hole, which as I think
isn't believe. Um, yes, because so the way that looks
from above is that, yeah, you'll see a sort of
just ring of dark blue surrounded by much lighter blue. Uh.
As as I guess that just reflects the sudden difference
in depth. Yeah, exactly, it's this is very much in
(40:16):
keeping with the Great Blue Hole, just maybe less dramatic looking,
but still extremely beautiful. Now in s is reported by
Danny Lewis for Smithsonian mag dot com researchers discovered uh
like something like forty nine sinkholes clustered close together while
serving the chin Ling Bashan Mountains in China's uh Uh
(40:36):
Shaunzi Province, the largest being one thousand, seven hundred and
six ft or five hundred and nineteen meters wide and
a thousand and fifty or three hundred and twenty feet deep.
So um, yeah, it's uh we keep finding these things,
you know, or in many cases, rediscovering them, and every
time discoveries like this you're made. You know, it's not
(40:56):
just an interesting geologic curio, it's a fresh operatunity to
gaze back in time to understand geology, biology, and even
the climate of the region in in times past. Oh yeah,
because this is an interesting thing. You were pointing out
when we started looking at this, that sinkholes are often
used as a kind of scientific time capsule, That there
(41:18):
are ways that sinkholes can tell us things about the
past that the surface can't do quite as easily. Absolutely,
and I think we'll start our next episode by diving
into that, discussing the ways that sinkholes are are very
often time capsules that we can unlock that we can
we can venture into not just to you know, to
to to be in awe of the of the you know,
(41:40):
this dramatic environment around us, but to uncover the secrets
of the Earth and the secrets of the ecosystem. I
can't wait. We got a lot of cool stuff to
talk about. Next time we can talk about UH. Sinkholes
in religions, sinkholes in space, sinkholes as time capsules. It's
gonna be great, That's right. And in the meantime, if
you want to check out other episodes of Stuff to
(42:00):
Blow your Mind, you know where to get them. You
can get them in the Stuff to Blow your Mind
podcast feed and you'll find that wherever you get your podcast,
Just rate, review and subscribe UH to support us. We
have core episodes of Stuff to Blow Your Mind every
Tuesday and Thursday. On Mondays and Wednesdays, we have What's
Seen an episode of the Artifact. We have some listener
mail trickling in every week, and on Friday's we do
(42:22):
a little weird House Cinema. That's our chance to discuss
a weird movie. You know, not not lean into the
science too much, but more lean into the weird. Huge
Thanks as always, to our excellent audio producer Seth Nicholas Johnson.
If you'd like to get in touch with us with
feedback on this episode or any other, to suggest topic
for the future, just to say hello, you can email
(42:43):
us at contact at stuff to Blow your Mind dot com.
Stuff to Blow your Mind. It's production of I Heart Radio.
For more podcasts for my Heart radiocause at the I
Heart Radio app, Apple Podcasts, or wherever you listening to
your favorite shows. U
Hey, are you welcome to Stuff to Blow your Mind?
My name is Robert Lamb and I'm Joe McCormick, and
today we're bringing you an episode from the vault. This
is our part one of our episode on sink Holes,
which originally aired on January. We hope you enjoy Welcome
(00:25):
to Stuff to Blow Your Mind production of My Heart Radio.
Hey you welcome to Stuff to Blow your Mind. My
name is Robert Lamb and I'm Joe McCormick, and today
we're gonna be talking about sink holes. This is actually,
I think, in a way a listener request topic that
(00:47):
turned out to be very interesting. But it's, uh, it's
sort of leap frogging off of some some previous episodes
we did. Rob did the did the sink Whole journey
begin when we were talking about the star Lac from
Return of the Jedi. I think that is the original context.
I think that was the original point at which we
begin to hear listener males about the idea of in
a sink Whole episode, because we talked about the star
(01:09):
Lac and then we talked about some ideas and was
it meso American uh? Mythology concerning uh entities of the
ground that swallow things up. Oh, that could be it. Well,
I know we ended up talking about the Bible, which
will revisit in a minute here. But one of the
questions that came up was, you know that scene in
movies where there's an earthquake and and then suddenly a
(01:32):
crack opens up in the middle of the street and
it's you know, miles deep, and it just swallows people
down into it. Uh. The question was like, does that
kind of thing really happen? Does during an earthquake? Does
the earth open up and open these deep pits and
chasms that people fall down and disappear into. And our
previous answer to that was, well, not really, or it
(01:53):
seems like that's that's extremely rare if it ever happens.
That's not like a common feature of what happens to
the surf is topology during an earthquake. But sinkholes, a
listener pointed out, or a very different story, and sinkholes
could explain many of these stories, uh, from from mythology
and all that of the earth opening up and swallowing people.
We can get back into that in a bit. But
(02:13):
you actually turned up a really interesting photo essay about
a fascinating sudden opening of a sinkhole. Uh just earlier
this year, that's right. Well, actually it was last year, remember,
oh god, Yeah, I haven't turned the calendar fully yet.
It's still it's still It's like that year is kind
of like the the other world in hell Raisers. So
(02:36):
it's got chains with hooks and them, and they shoot
out of the walls and so the hooks are still
in my brain, but I'm slowly methodically rebuilding my body
to escape. All right, Well, this is this story takes
us back to April. So Um. What happened is a
whole opened up in the front yard of a home
in Black Hawks, South Dakota. Uh, specifically in a housing
(02:58):
development there that is called perfectly enough, the Hideaway Hills development.
That just doesn't sound great. I mean no offense to
the people who live there, but it doesn't sound like
a place I want to go. It sounds like a
place where, I don't know, where you like retreat after
you've committed a crime. What was the housing development on
arrested development, Sudden Valley or Sudden Yeah Appa, so Um,
(03:25):
Like you pointed out, there's an incredible photo essay photos
series on this on board Panda about this. If you
look up board Panda Black South Dakota sinkhole, you will
find it because uh this photo essay, if you will,
it takes us through a journey by a local caving
group called Pahsapa Grotto as they decided to venture down
(03:47):
into this hole that opened up in this front yard
to explore the world beneath the suburbs. Now, this sinkhole,
it turns out it's going to be very different than
most of the sinkholes we're talking about in this episode.
Most sink holes open up over some kind of void
that is formed in the rock below, and as we'll
get into a lot of that usually has to do
(04:08):
with water and hydrology. But in this case, the void
in the rock below the neighborhood was was more was
of a more artificial persuasion, right. That's because there was
an abandoned gypsum mine beneath the housing development, and so
the cavers had they had to lower down in on ropes,
you know, had to use like actual caving equipment into
(04:28):
the dark and sometimes flooded tunnels beneath reportedly over two
thousand feet across in a hundred and fifty feet wide
this tunnel um complex. Uh, and they encountered the remains
of what looks like an old, like nineteen fifties automobile. Uh.
There's just a whole world down there, like a whole
uh Minoan maze beneath this you know, rather mundane looking
(04:51):
housing development. It's like two levels of weird. So first
of all, it's yes, the suburban you know, neighborhood, and
then just in the middle of somebody's front yard a
pit opens up, so that's the sinkhole. But then it's
that the sinkhole goes to this maze. And yeah, like
you said, there's like an old Chevy convertible down there,
And I'm wondering, why is that down there? Did somebody
(05:11):
drive it into the mind before the mind was sealed up? Yeah,
I don't know. Like, it's just it's a place full
of questions, is a place full of the past, of mysteries.
And so the article itself gets into some of the
community fall out over all this. But but what I
love about this episode is it illustrates for us this
divide between the surface world so tightly manicured and controlled
(05:32):
so much of the time, and a world beneath that
we have only a shaky understanding of like something out
of a mash up between Poltergeist and The Descent. You know,
a gateway to that hidden underworld might open up at
any moment and reveal its secrets to us, invite us in,
perhaps swallow us entirely, and then we'll be part of
(05:53):
that underworld. Because if we're being you know, perfectly rational
without any supernatural ideas like that, that idea alone is terrifying.
You know that the earth might open up and we
might fall, you know, into a pit. But then if
you begin to layer in beliefs and superstitions, then yeah,
become this whole becomes a portal to other realms. Yeah, exactly.
(06:15):
Now we've talked about natural features in the landscape taking
on religious significance before, Like in we did a couple
of episodes called The Sacred Mountain, which was about mountain
peaks that were considered to be holy or supernatural or
the dwelling places of gods or places that Win explored.
People often reported having supernatural experiences, They're like One of
the things that came out of that was the the
(06:36):
often reported third man syndrome, feeling that mountain climbers sometimes
have very high up but we talked about possible ways that,
like the effects of the sun or that altitude sickness
could contribute to that um. But there are also ways
in which sinkholes can take on similar types of religious significance,
can have a similar mythological appeal, And one great example
(06:59):
is we is some of the sinkholes are also known
as sinnotes that we see throughout Mesoamerican religion in the
Yucatan Peninsula and among the ancient Mayan people. But I
guess well, we'll come back to that more later. I
wanted to get to this question about the the idea
that the earth can open up and swallow you. It's
an image that seems like to perfectly fit ancient myths
(07:21):
and texts. You would imagine passages like this appearing in
you know, Babylonian texts or something. It definitely appears in
the Hebrew Bible, for example, in the Book of Numbers,
there's a passage where Moses is speaking to people and
he's trying to demonstrate that he was in fact sent
by the Lord and he uh he, he says, and
basically he makes a promise that hey, if the Lord
(07:42):
has sent me he'll he'll send a sign, and you'll
know it, because there will be this group of people
that will be swallowed up alive into a pit that
opens up suddenly in the earth. For very these wicked
people who have rejected the Lord. And the passage says
in Uh in the Book of Numbers. Now it came
to pass, as he finished speaking all these words, that
the ground split apart under them, and the earth opened
(08:03):
its mouth and swallowed them up with their households, and
all the men of Cora, with all their goods. So
they and all those with them went down alive into
the pit. The earth closed over them, and they perished
from among the assembly. And so I wonder, I mean, obviously,
with passages like this, I wonder if it's this kind
of thing that inspired that scene in every movie that
(08:24):
has an earthquake in it where suddenly a bottomless pit
opens up in the ground and people get sucked into it. Yeah,
you know, this could also be graboids. If I think,
if they want to make another Tremor's film, which they will,
I'm sure they should go for you know, some biblical
flare here, go for an Old Testament Tremor's movie with
with Moses being our central character, and that's a very
(08:45):
good direction. Now, one thing I want to say, because
I feel like I have to bring this up every
time we talk about geo mythology. Uh, there's this question
of is this story in the Bible based on something
that someone in history witnessed witnessing a real world geological event,
perhaps a sudden collapse of a settled area due to
a sinkhole. Uh. And as I pretty much always do
(09:06):
whenever we talk about geomethology, I want to emphasize that
fantastic imagery and in myths and legends and religious text
doesn't necessarily need to be explained by someone actually having
seen something physical in the world. I think we can
sometimes go overboard looking for naturalistic explanations of this kind
to explain what somebody thought they saw that appears in
(09:27):
a story. You know, people are highly imaginative, and sometimes
stories are just stories. But there's always also the possibility
that stories like these could be based on people hearing
stories about having seen I don't know, there was a
there was a castle or a building or something like
that that was just swallowed up into the earth, which
if you didn't have any kind of geological understanding with
(09:47):
which to to to interpret that. It would certainly seem
to be a you know, a supernatural event. I don't
I don't know how else you would interpret it. Yeah,
because I think one of the things that really drives
home and when we we see examples of sync holes
and we hear stories like this, we see cinematic interpretations,
is that idea that the that terra firma is not
(10:08):
that firm, is not that fixed, that it could change,
that the that the firm ground beneath our feet could
suddenly give way, you know, like that alone is just
this kind of uh, you know, horrifying idea that that
it that it easily applies as a metaphor to everything
else in our in our life. You know, that the
thing that is the order that we depend upon might
(10:32):
go away at any moment. Yeah, it's interesting to think about,
like a vertical spectrum of of ways the natural world
can intrude on our lives and how most of the
stuff that we're that we're used to thinking about taking
into consideration, worrying about as as possible threats, all basically
takes place like on the surface of the earth. And
that you know, when you go to the vertical ends
(10:53):
of that spectrum, you've got like impacts from space coming
from above, sinkholes up and opening up from below, and
these fen I'm gonna intrude on that day to day
understanding of physical forces. Yeah, so it's it's no surprise.
We were talking about this before the podcast started rolling
here that if you start looking around for sinkholes online,
you'll find just so many galleries, top ten lists, lots
(11:16):
of click bait about sinkholes. Like sinkholes are kind of
they're kind of like a like they're kind of like
true crime, you know there um there. You also see them,
like I was noticing, like very tabloid sites sites that
otherwise they're not going to really have anything related to geology,
but they'll have sinkholes. You know, it'll be celebrity gossip,
(11:38):
um and you know, maybe some conspiracy theories. But then also, uh,
big old holes opening up in the earth. Chump boxes
are full of sinkholes. Have you ever noticed this? These
are the like the link um grids at the bottom
of blogs and whatnot. Yeah. Yeah, so, like you know,
like most websites on the Internet these days are just
being more and more infected by ads that a since
(12:00):
really take the form of malware. But if you scroll
down to the bottom of most articles or any text
image based website, you'll usually see one of these boxes
that's full of just like extremely tacky, distasteful images that
are either like something that's kind of sexually suggestive and
a gross way, or something that is uh sort has
(12:20):
some kind of like health vibe, Like it looks like
infected skin or holes in skin, or some kind of
bite or something like the kind of a necrotic bite
that you might imagine someone would get in their worst
nightmares from a brown recluse, you know that kind of thing. Um. Yeah,
they they tie into our like deepest, most primal fears
(12:42):
and desires, just pure eroticism or just pure in necrotic
damage or indeed holes opening up in the earth. You know,
it's got to be something extreme like that to make
it into that grid of horror. Yeah. The toilet with
the rat coming up through it, remember that one. Oh,
I think I've seen that when I was a common
chumbox image or the like. You know, doctors say never
(13:04):
eat this vegetable, but they don't tell you what it is. Yeah, yeah, yeah,
sometimes it is. Um. It. It's economic as well. You know,
there'll be some sort generally it's like a picture of
an old person and just a few like alarming words
about you know, investments and retirement or something. Right, but
that is the world. Well, sinkholes are actually in their
own way. I mean, of course they can be horrifying,
(13:26):
they can be destructive to human life, but they are
also fascinating in their own way. In the natural way,
they are wonderful. Uh. There can be beautiful uh legends
and stories attached to them, and so I don't know,
I feel like they are the most uh naturally beautiful
thing that that fits in the chum box. I mean
(13:46):
the rat and the toilet can't compete. I mean the
rat and the toilet. We could do an episode on
that as well. But yeah, I agree, the sinkholes need
to be rescued from the chum box. Uh. And and
that's kind of what we're doing in in this episode
of Stuff to Blow Your Mind and the possible second
episode of Follan. Alright, so sinkholes are formed in a
(14:10):
number of ways, but most naturally occurring sinkholes, like most
other things on planet Earth, in the end, come back
to the power of water. Water, of course, is the
molecule of life, largely because of its power as a
master solvent, and in much the same way really that
water created life on Earth, probably it also creates many
(14:31):
of Earth's most astounding geologic features. And so this is
how we we get sinkholes for the most part. So
as carbon dioxide in the air or in the soil
mixes with rain water, that mixture forms a weak acid
with the with the chemical formula H two c O three.
So what you've got there is you've got your H
(14:51):
two oh the water, and then you've got your C
O two the carbon dioxide. They react, they make a
compound with two hydrogens, one carbon and three oxygen's. And
this weak acid formed in the atmosphere or in the
soil is known as carbonic acid, and it is the
primary reason that caves exist. Now most caves in the world,
(15:11):
not all, but most are formed by the drainage of
acidified water through what you might call soluble rock and uh.
Soluble rock are types of rock that can react chemically
with this water and be dissolved and carried away. Now
they're they're multiple kinds of soluble rock, including minerals like
(15:33):
salt and gypsum, But probably the most important, or at
least the most charismatic, is limestone, which is in itself
a fascinating and even mind boggling rock. And sometimes I
really do think a lot about limestone, and maybe people
are aren't inclined to be as impressed by it as
I am. But if you don't believe me that limestone
(15:54):
is amazing, I think it's worth considering that if you
live in an area of the world you know this
primary resting on limestone, which in the United States would
include huge portions of like Florida and the coastal southeast,
big parts of the Midwest. If you live in a
place like that dominated by this this carbonate rock, you
are walking around every day on rock that is probably
(16:16):
mostly built out of dead bodies. Limestone can be formed
in a number of ways. Some of those ways are
a biotic, but one of the major processes that forms
limestone is the gradual deposition of the shells and other
hard calcium carbonate body parts of animals and other tiny
organisms in the oceans and rivers and lakes where they
(16:38):
accumulate on the bottoms of these water sources over millions
of years, and apparently feces also in general, waste products
can contribute as well. So the calcium based body parts
of algae and coral and oysters and all kinds of
creatures of the sea settle in the deep, and then
they're pressed down and paved over by time and pressure
(17:01):
until they become layers of sedimentary rock. I really just
think about that. Sometimes limestone is largely made out of
life that has died and become rock, like the fallen
creatures of Earth pile up and become part of the
crust of the Earth itself. Wow, it's like it's like
the Medusa's layer, right, all these like the petrified bodies. Oh,
(17:24):
that's I wish I had thought of that when we
were doing our Medusa episodes. Except I guess in the
Medusa Garden that they keep their form right here. They
just sort of like go back to whence they came.
They become part of this mass. But anyway, it's via
rocks like this that we get so many of the
naturally occurring sinkholes on the Earth. So how do they form? Well,
(17:45):
imagine that there is a storm, it rains here in
an area with some kind of soluble rock. Let's say
it's a it's a carbonate rock, it's like limestone, and
rainwater collects on the surface of the earth and then
runs downhill. And if that rainwater drains down in two
cracks insoluble rock like limestone, things begin to happen much
in the same way that you can dissolve table salt
(18:07):
or sugar and a glass of water. The crystal contents
of these soluble rock surfaces are gradually dissolved in and
carried away by that acidified water. And over tens or
hundreds of thousands of years, that dissolution of the rock
by acidic water can turn what might have started as
this tiny stress fracture in a chunk of bedrock into
(18:28):
an underground cavern large enough for a human to climb into.
And of course, as the centuries go on, these these
voids created by the drainage pathways of water can just
get bigger and bigger. They can form underground rivers that
form larger and larger voids. And it's this dissolution of
soluble rock by water that usually leads to the creation
(18:49):
of sinkholes. Uh though these voids in the rock, I
think sometimes maybe geologists will get picky about this, these
voids in the rock are not technically themselves sinkhole, and
we would normally think of them as voids or just
caves right there, their caves in the rock. Um. Rather,
a sinkhole is more of a topographical designation. It's a
(19:10):
topographical concept about the ground and the surface of the earth.
So according to the U S Geological Survey, a sinkhole
is quote an area of ground that has no natural
external surface drainage. So like in one of these areas,
if it rains, water just pools in and there's nowhere
on the surface level that allows this water to run out.
(19:33):
So if the water leaves, it's either evaporating into the
air or it's draining out through somewhere in the bottom. Sinkholes,
of course, can form gradually over hundreds or hundreds of
thousands of years, often of steady dissolution, or they can
form quite suddenly. For example, when the ground over a
void in the limestone below is suddenly just suddenly there's
(19:54):
not enough for it to support its own weight, and
then it just collapses and reveals the void that had
been there for so long. Uh. And we know that
the sudden appearance of a sinkhole can have these devastating
effects on human settlements and uh whatever is lying on
the surface, which will get into more later, but it
can also have strange, otherworldly effects simply on the geological
(20:15):
and hydrological landscape itself. And I wanted to share one
amazing example that I came across while I was reading
up for this episode. This was the opening paragraph in
an article for The New Yorker by David Owen. There
was an article about sinkholes called Notes from Underground, and this,
this paragraph really gave me chills when I got to
the end of it. So, uh, if you don't mind,
(20:37):
I just want to share this here. In the fall
of nine, much of Lake Jackson, a four thousand acre
natural body of water just north of Tallahassee and a
popular site for fishing, water skiing, and recreational boating, disappeared
down a hole like a bathtub, emptying into a drain trophy.
Bass became stranded in rapidly shrinking eddies, enabling children to
(21:02):
catch them with their hands and toss them into picnic coolers,
and many of the lake's other fish, turtles, snakes, and
alligators vanished into the earth at various times. During the
next few years, the lake partially refilled, redrained, and refilled again.
Jonathan Arthur, who is Florida's state geologist and the director
(21:23):
of the Florida Geological Survey, was among several people who,
during a dry period descended a ladder into the main opening,
which was about eight feet in diameter. Quote, you could
climb down twelve feet or so and then walk under
the lake bed. He told me recently, I hadn't gone
very far before my red flags went up, and I
(21:43):
was like, maybe I won't go any farther. So that image,
it combined with the way it's phrase that that really
gave me goose bumps. Yeah. Yeah, the idea of yeah,
I mean, it really feels like like a place you
do not belong. The you know, the the cave beneath
the lake that is uh yeah, that that that could
potentially fill back up at any moment. Well. And also,
(22:04):
I mean, I think anybody who, especially people who do
like scuba diving and stuff, are made uniquely aware of
the dangers of of being in places that combine water
and overhead rock. Like Yes, absolutely that that can be
an especially dangerous and and suddenly dangerous surprisingly dangerous combination
(22:27):
of features. Yeah, I mean, even if you are an
experience cave diver, cave diving is dangerous. Uh so um so, yeah,
that is a dangerous realm to to go down into,
for sure. Now, I figured it would be worth talking
about a few of the different ways that natural sinkholes form. Um. Obviously,
things will be a little bit different if you're talking
(22:48):
about sinkholes, you know, created by human activity, though human
activity can also contribute to some of the things I'm
about to talk about. But but if you're talking about
natural sinkholes in a carbonate rock like limestone. Um. There
are three main pathways that were highlighted in uh in
several sources, in my major source here just being the U. S.
(23:09):
Geological Survey, who has great materials about this, um and
so the first one is dissolution sinkholes. These are relatively
gentle sinkholes. You can think of it as a kind
of top down sinkhole. Here, what you should picture is
that you've got a thin layer of what would be
called overburden, and overburden just means whatever stuff's on top
(23:30):
of the rock that makes up the ground. So this
means soil could be sand, could be clay, pebbles, rocks,
other material resting on top of the rock layer on
the surface. Now, in a dissolution sinkhole, rain comes down
and it collects in a depression in the soluble rock
and just continues to dissolve and deepen that depression over
(23:52):
time as water gradually percolates down into cracks or joints
in the rock below. These tend to form very gradually,
so you can picture kind of a a gentle sort
of dip or pond in the rock that water is
going into, and slowly, over time it's draining down into
the rock below through some cracks or other types of openings,
(24:12):
and as it does so, it is dissolving more and
more of the rock and carrying it away. The next
type would be cover subsidence sinkholes, and this is where
you've got a lower level of soluble rock that gets
dissolved by the process we've already talked about, you know,
water running through it opening up a void in the rock.
And in this case, if the soil or overburden that
(24:36):
is above that layer of rock has certain physical characteristics,
I think, especially if it's like a more free flowing
kind of granular sediment like sand. Basically, the overburden or
the soil above kind of gradually pours down into the
void that opens up. You can imagine it being kind
of like sand pouring down from the top half of
(24:57):
an hour glass into the bottom half, and and that
that overburden pours down fills the void up partially. But
as it does so, it's sort of like creates a depression,
of visible depression in the surface of the overburden. And
these types of pits tend to develop pretty gradually and
not be all that deep or all that dangerous. Right,
(25:18):
You've probably seen pits like this before. You're just walking
through a field and suddenly there's just a depression in
the ground. Very possibly what's going on there is this
cover substance sinkhole. The soil is just kind of draining
into a void in the rock below. Now, of course,
it's worth noting in all of this, even these milder
(25:38):
forms of the sinkhole can certainly be destructive if you
have some sort of humanum structure built atop of it,
or a road, etcetera, which is sometimes the case, right,
But these first two have the benefit of not being sudden.
You know that they're going to take time to develop.
The third category, this is the real monster that could
(25:59):
inspire the geo myth potentially. This is the cover collapse, sinkhole,
and these are the ones that can potentially happen in
an instant and at least in the United States, they
tend to be most common in places where the overburden
is mostly clay. So again, you start the same way
that the last one did. Avoid opens up in the
underlying layer of soluble rock, and then the lower levels
(26:24):
of the overburden gradually drained down into the cavity in
the rock. And as this happens, what you get is
a cavity gradually opening up from from below and climbing
up into the overburden or the soil itself. So imagine again,
you've got to rock with a cavity or avoid in it,
and then maybe a layer of clay, and so the
(26:46):
clay on the bottom starts to seep down into that
cavern below and it just opens up a bigger and
bigger void in the clay. And eventually what's going to
happen there is that that void in the clay reaches
a point where where the collapsing roof of the void
breaches the surface, which means whatever is on the surface
falls into the hole. And that surface might well be
(27:08):
a road or a lake bed, or the ground under
a building. And this is the example where we can
see sudden collapses that can be deadly and destructive and
terrifying because suddenly what you thought was solid ground is
revealed to have long had had to void beneath it,
and suddenly it can't support whatever is on it anymore,
and it all goes down into the void. It's basically
(27:29):
like a trap door effect. You know, that's the that's
the terrifying part about it. You know, that's like suddenly
there is this opening beneath this and and people, you know,
can can build things without having any idea that that's
what's down there. Yeah, I mean, we've we've gotten to
the point where if we know what we're looking for,
especially you know, we we have more tools at our disposal,
uh for detecting sink holes and potential sink holes, and
(27:53):
in keeping track of of existing sink holes that maybe
expanding but but expanding have expanded. But yeah, for the
most part, like that that the the idea here is
that you don't know what's going to happen, and then
suddenly there's this chasm there in the earth. Now. Another
thing that's interesting to me about sinkholes is that we
often think about geological events like earthquakes and volcanoes as
(28:16):
what people sometimes call acts of God, you know, natural
events that occur for reasons vastly beyond our control and
that we can do nothing to stop. But there is
some indication that human activity may have more impact on
some massive geological events than once thought, and it certainly
appears to have an effect on the proliferation of sinkholes
(28:37):
in particular. In other words, sinkhole collapses can it seems
absolutely be invited by human behavior, as will probably discuss
more as we go on, but in broad strokes, it
appears that sinkhole collapses can be induced by uh. So,
one thing is human construction and other changes in the
top level terrain, especially how that affects water drainage. So
(28:57):
you're moving earth around and changing the way that water
drains on the surface. That can lead to sinkle collapses.
But also pumping of groundwater is a huge thing here.
You pump out groundwater from deep underground uh the pressure
of the natural water that's in the ground helps keep
the soil above it in place. So if you take
(29:19):
that water out, you lower the groundwater level, you can
cause collapses of the overburden lying over now evacuated aquifer voids.
Another thing that seems kind of relevant to that story
you started with. Remember the sinkle collapse that turned out
to lead to a mine down below in South Dakota.
The mine was a gypsum mine. So gypsum is a
(29:41):
major mineral that's that's in the ground there. We've been
focusing a lot on limestone, but one thing to note
that I did read also from the U. S Geological
Survey was that other types of underlying rock layers, such
as minerals like salt and gypsum, those can sometimes dissolve
and form voids much fast to than even sedimentary carbonate
(30:03):
rocks like limestone. So limestone will form these voids with
water running through it over you know, thousands of years,
but apparently assault and gypsum, potentially with the right circumstances,
can form large voids in in a matter of you know,
days or months. Than well, let's get into some examples
(30:27):
of sinkholes. Uh. And granted there are so many sinkholes
that have either existed for you know, thousands of years
or have just popped up in you know, recent decades.
But I want to start with one that I imagine
is instantly coming to a number of your minds. And
you're you're, especially when we were talking earlier about click
(30:47):
baity uh sinkholes, and that would be the two thousand
seven and especially the two thousand ten Guatemala City sinkholes. Um.
And they're they're worth mentioning for a couple of reasons. So, so,
first of all, there are some very dramatic photographs of
this thing. Photographs so dramatic that they they look photoshop.
You know, they don't look real. Absolutely, it looks like
(31:11):
something out of a movie. Yeah. It looks like a
hole has been like a cylindrical hole has been bored
into this city escape and it just descends into absolute darkness.
It is. It's a terrifying image. Um. And And and
when this these occurred, I mean, these were dramatic, traumatic events,
These were deadly occurrences. That two thousand seven sinkhole killed
(31:32):
five people and required the evacuation of more than a thousand.
The two thousand ten sinkhole swallowed a three story factory
and killed fifteen people. And in both cases, uh, it
seems to there seemed to have been a at least
a trio of causes. So there was the impact of
tropical Storm Agatha as well as the Pacaya volcano eruption,
(31:55):
but also leakage from sewer pipes and all of this.
So we're together to erode uncemented volcanic act, limestone and
other pyroclastic deposits beneath the city. And this case is
actually so visually alarming. There's a Snopes article about it,
not because there seems to be like a lot of
(32:15):
misinformation about the event itself. Uh, but it gets picked
up continually on social media as if it just happened,
as if it just happened, you know, this week or today,
as opposed to a decade ago. Right, So the photo
is real, the story is real, but it's but what
needs to be debunked is that people want to just
like reintroduce it as newly relevant over and over again
(32:38):
because it will always get attention. It's so dramatic looking. Yeah. Uh.
There is also a good Atlas Obscure article about it,
though I have to point out that the Atlas Obscure article.
I think this is a feature of just things that
they have cataloged on the site. But it says sorry,
great Guatemalan sinkhole is permanently closed, which which is it
(33:00):
is a weird sentence to read. Now. Meanwhile, up here
in North America we have our own sinkholes of note.
For instance, there are two giant West Texans sinkholes in
Wink and Kerment, Texas. They're located about a mile apart,
and these are similar to the Guatemalan sinkholes, and that
we have definite uh uh connection to human activities. These
(33:20):
were caused by oil and gas extraction in the area,
especially during the heyday of nineteen twenty six through nineteen
sixty four. Uh Wink Sinc. Number One opened in nineteen
eighty and Wink Sinc. Number Two open twenty two years
later in two thousand and two. And I was looking
at a two thousand sixteen Southern Methodist University study where
(33:41):
they were they were taking a look at these sinkholes
and the fact that they seem to be expanding because
the ground there is still unstable due to changing groundwater
levels and dissolving minerals um. However, like I said, are
they were now able to use stuff like satellite monitoring
to keep a better track of sinkhole development and progress.
But again, this is a case someone to what we
(34:02):
were describing earlier, where we've taken stuff out of the
ground and in doing so we have disrupted like the
you know, the natural balance of things down they're making uh,
sinkholes more likely to occur. Looking at a picture of
the wink sinkholes, Uh, just not as impressive as some
of these because the water level seems to have been
filled up pretty close to the top. So it looks
(34:24):
like just a weird pit in the middle of the
desert that could be like a lake. It's just you know,
water in it. But uh, but I imagine if you
that water were to drained out, it would look pretty
pretty messed up. Yeah. Plus, the bar is pretty high
for spectacular looking sinkholes, as we'll continue to see as
we discuss other sinkholes in the in in this episode
(34:44):
in the one to follow. Well, so I was wondering,
what's the what's the deepest known sinkhole on planet Earth? Oh, well,
if we want to go to the deepest, uh, then
we have to go to China. That is where we
encounter China's um. This is the the the Shijia uh
Tien King or the Heavenly Pit, and it's it's named
(35:06):
for a nearby village and then uh Tien King just
means heavenly pit. And it's located near Chuanshing in southwest China.
It's apparently six hundred and twenty six meters or two
thousand and fifty four ft long. It is five hundred
and thirty seven meters or a thousand, six hundred sixty
two feet wide, and it is between five hundred eleven
(35:28):
and six hundred and sixty two meters deep or between
one thousand, six hundred and seventy seven to two thousand,
one hundred and seventy two ft deep, So it's deep
that it is an enormous hole. And this is one
that I recommend looking at pictures of because it's is
really splendid looking. It's beautiful because it um. You have
the it's it's you have this this this double um.
(35:51):
It's like a double pit. There's like the initial pit
and then the pit below. You have vertical walls going
down to a little area that tapers off and then
or vertical walls going down even further that there's some
rich vegetation around it. Um, it's it's really beautiful to
look at, and indeed it is a tourist attraction if
you travel there. There apparently two thousand, eight hundred steps
(36:13):
constructed that allow visitors to journey all the way down
to the bottom of that second nested pit, which I
was reading. I think it takes you're gonna spend like
a couple of hours doing that. I think I read
that this is also a limestone pit, and yeah, one
of the great things about it is pits of the
size and of of this age. You know, it's been
around for a long time where the surface life has
(36:35):
just poured down into it, so you know, it looks
almost like the forest is spilling into the pit. And
of course that you know, it's a habitat for many animals.
I think I saw a report that maybe rare like
the clouded leopard had been spotted there. I think, oh, interesting. Yeah,
you see time and time again reading about different sinkholes
(36:57):
that they inevitably become uh an interesting place to look
at biodiversity. And we'll get we'll get more into that later.
But yeah, these are these end up being. You know,
they're not just especially ones that have been there for
a considerable amount of time. They're not just holes in
the earth. They don't remain voids. Nature feels that void,
and it does so in very remarkable ways. Now, there
(37:18):
are numerous um heavenly pits in this region of China,
and I can only imagine that there are some really
interesting traditions and legends about these geologic features. But I
have to admit that I could not find any of them,
at least none that had been translated into English. So
if anybody out there has that information, I would love
to hear about it, because a sinkhole like this is
(37:41):
just it's just too amazing. And it's been around way
too long. It's been around since ancient times, so there
have to be some cool traditions and legends regarding its
origin and things that live there, et cetera. Yeah, like you,
I was looking for similar things and I couldn't find
any any any cultural context for it. But I would
love to if you know out there now there is
(38:02):
another Chinese sinkhole of note that does have some cool
legend applied to it, and that is a dragon hole
in the Paracel Islands. It's nine four feet deep two
hundred and nine so this is out in the ocean.
It's also known as the Young Lu Dragon Hole, named
for the fifteenth century Mean dynasty Young Lu Emperor Um.
(38:25):
It's also known as the Eye of the South China Sea.
And the tradition here is that this is where the
Monkey King Uh Soon Will Kong finds his golden cudgel
in Journey to the West, So this would be his
magical staff. If you've ever seen a movie with the
with the Monkey King in it or seeing images of
the Monkey King, this is his big, amazing fighting staff.
(38:47):
So he actually gets it from this pit. Well that
is that is what that they've sort of taken the
story and said, oh, this must be the pit, okay,
because in the story he has to retrieve it from
the underwater kingdom of of our Guang, the Dragon King
of the East Sea, and uh yeah, this this amazing
magical staff, the the compliant golden hooped rod or has
(39:09):
it also been translated as the as you will gold
banded cudgel? Um? Oh I see compliant or as you will? Yeah, yeah,
it's um. They're also there's legends that this may have
been you the Great's measuring stick for determining the depths
of the Great Flood, So it has that would make
sense that you know, that would be underwater because there's
this connection to the depths, and so anyway, he dives
(39:32):
down into this hole and retrieves it. Now is this, Uh,
this is a picture of this pit that you've attached
here for us to look at. Yes, so again, it's
out out in the water, and it's just like a
sudden deep section of the of the water, a hole
in the sea floor that contains you know, dark depths.
You may have seen pictures of sinkholes in tropical oceans
(39:54):
like this before, for example, if you've ever seen a
picture of the Great Blue Hole, which as I think
isn't believe. Um, yes, because so the way that looks
from above is that, yeah, you'll see a sort of
just ring of dark blue surrounded by much lighter blue. Uh.
As as I guess that just reflects the sudden difference
in depth. Yeah, exactly, it's this is very much in
(40:16):
keeping with the Great Blue Hole, just maybe less dramatic looking,
but still extremely beautiful. Now in s is reported by
Danny Lewis for Smithsonian mag dot com researchers discovered uh
like something like forty nine sinkholes clustered close together while
serving the chin Ling Bashan Mountains in China's uh Uh
(40:36):
Shaunzi Province, the largest being one thousand, seven hundred and
six ft or five hundred and nineteen meters wide and
a thousand and fifty or three hundred and twenty feet deep.
So um, yeah, it's uh we keep finding these things,
you know, or in many cases, rediscovering them, and every
time discoveries like this you're made. You know, it's not
(40:56):
just an interesting geologic curio, it's a fresh operatunity to
gaze back in time to understand geology, biology, and even
the climate of the region in in times past. Oh yeah,
because this is an interesting thing. You were pointing out
when we started looking at this, that sinkholes are often
used as a kind of scientific time capsule, That there
(41:18):
are ways that sinkholes can tell us things about the
past that the surface can't do quite as easily. Absolutely,
and I think we'll start our next episode by diving
into that, discussing the ways that sinkholes are are very
often time capsules that we can unlock that we can
we can venture into not just to you know, to
to to be in awe of the of the you know,
(41:40):
this dramatic environment around us, but to uncover the secrets
of the Earth and the secrets of the ecosystem. I
can't wait. We got a lot of cool stuff to
talk about. Next time we can talk about UH. Sinkholes
in religions, sinkholes in space, sinkholes as time capsules. It's
gonna be great, That's right. And in the meantime, if
you want to check out other episodes of Stuff to
(42:00):
Blow your Mind, you know where to get them. You
can get them in the Stuff to Blow your Mind
podcast feed and you'll find that wherever you get your podcast,
Just rate, review and subscribe UH to support us. We
have core episodes of Stuff to Blow Your Mind every
Tuesday and Thursday. On Mondays and Wednesdays, we have What's
Seen an episode of the Artifact. We have some listener
mail trickling in every week, and on Friday's we do
(42:22):
a little weird House Cinema. That's our chance to discuss
a weird movie. You know, not not lean into the
science too much, but more lean into the weird. Huge
Thanks as always, to our excellent audio producer Seth Nicholas Johnson.
If you'd like to get in touch with us with
feedback on this episode or any other, to suggest topic
for the future, just to say hello, you can email
(42:43):
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