Mammoth Caves (Kentucky, USA): Cave System
1. Zoom from Iguazu Falls to Mammoth Caves
2. Next Geologic Wonder is right in the middle of the US: Mammoth caves. The
odd nature of a cave is that you can be right over one, and even live there
your whole life, and have no idea it is there. You can’t miss a waterfall, but a
cave can be very hard to find.
3. A cave is missing rock. But it can be more than that too. Next two lectures
will look at two aspects of caves
a. This lecture: remarkable missing rock; giant networks of cave
passages; giant caverns, enormous holes than extend deep into the
ground
b. The next one will focus on some of the remarkable formation that we
find in caves, forming after the caves themselves were made.
4. Mammoth Caves are big. It is hard to imagine how big they are: currently at
392 miles (630 km). The next largest cave network – South Dakota’s Jewel
Cave: 150 miles. Not even close. [Show some pictures of Jewel Cave]. And
hundreds of miles of other passages are nearby How does something like this
happen?
a. Most caves are in limestone – very abundant rock (we met it in the
Grand Canyon)
b. Though limestone is only about 10-15% of all sedimentary rocks,
there are large portions of the continents that have vastly wide sheets
of limestone somewhere at or under the ground. True for most of
Eastern US
c. Dissolution of CaCO3 by acidic water (carbonic acid; tannic acids)
d. Location of water table (saturated underneath; but fluctuates over
time)
e. Caves form when water table is above them – passages of water
develop, but it is a runaway effect – more water, more erosion
f. Water table is high at certain times, such as runoff from melting ice
sheets at end of Ice Ages – caves form
g. Water table drops, and you can see caves. Iterative process.
Impossible to tell how old some of the caves like Mammoth are – up to
hundreds of millions of years, but could be much younger
h. Missouri – more than 7000 mapped caves. Might be interconnected –
very hard to tell.
i. In Kentucky, the limestone is capped by a stiff sandstone layer that
has kept the cave stable and prevented the ground from eroding down
too quickly, protecting the cave network.
5. Show the network map – very hard to map – 3D structure, but no lights, and
can’t use GPS!
a. Tell some of Bob Osburn’s stories (He is in my department; regularly
leads weekend cave exploration visits mapping out new cave
segments
b. Describe some of the features. Where the overlying sandstone cap is
intact, no water leaks in from above, so the passageways have no
stalactites or other formation. But where it is broken and water gets
in, there are the classic formations, as at Frozen Niagara.
c. Some of the passageways are vast. Some, that connect huge portions
of the caves, are barely wide enough for a skinny person to squeeze
through.
d. It takes a certain personality to explore caves, crawling miles through
tiny dark passages, sometimes with the rock above pushing down on
top of you.
6. Caves often have interesting histories, because people may develop the land
above, and then when the cave passages are discovered, there may be
conflicts over who actually owns the cave. Sometimes hard to figure out!
Mammoth cave, partly because of its great size, has had a particularly
interesting history.
a. Mummified remains of early native Americans – (Patty Jo Watson, of
WashU, in the 1950s) – so well preserved, they could even find out
what they ate (hunter-gatherers) (Native Americans had long uses the
caves far a variety of purposes – like in Cooper’s Last of the Mohicans)
b. Land purchased in late 1700s by Valentine Simons, who immediately
started mining it for its saltpeter (potassium nitrate), which is a key
ingredient of gunpowder.
i. Very important source of saltpeter during War of 1812, when
the British blockaded American ports, cutting off imports.
c. But after the war, prices of saltpeter and other minerals fell, and
mining in the cave ceased.
d. This was the start of the cave, and many nearby, being used for
tourism – especially with the discovery of a native American mummy.
Cave changed hands many times, but it a slave who gave the tours,
Stephen Bishop, who made the first maps of the cave and started
naming features of the cave.
e. At one point they even tried to use the cave as a hospital for
tuberculosis victims, hoping the “vapours” would cure them
(unsuccessfully, of course) – and Stephen Bishop and others would
end up catching and dying of tuberculosis.
f. In the late 1800s, with travel opened up by the railroads, Mammoth
Caves became an international Geologic Wonder, and many famous
people came to visit.
i. Famous actor Edwin Booth (brother of John Wilkes) – a cave
named “Booth’s Amphitheater”
ii. Famous violinist Ole Bull gave a concert there – now a room
called “Ole Bull’s Concert Hall”
g. A severe competition between different caves for tourists, including
planting misleading signs, telling tourists that another cave had been
closed, etc.
h. Mammoth Cave National Park was commissioned in 1926, but legal
challenges surrounding personal properties overhead continued until
1941, when it became official.
i.
Since then, continued exploration has not only found new and
unknown passages, but also found the links between many of the
other competing caves, creating the massive network that exists
today.
7. Today, the Park runs a set of tours to many parts of the cave (describe)
8. The cave is also a natural wonder – it has a unique ecosystem, that is very
delicate and changes very slowly.
a. Bats, blind and albino salamanders, etc.
9. Top 5:
a. Hang Son Doong Cave (Vietnam) – made famous by the National
Geographic feature – 200 m high, 150 m wide for 5 km – largest cave
in the world; just discovered in 1991; fast flowing river inside
b. Deer Cave (Borneo) – 170m wide and 120m tall for a kilometer! (2nd
largest)
c. Cave of Swallows (Mexico) – largest vertical shaft (370 m, from the
high side of the cave mouth); the Chrysler Building in NYC would fit
easily inside (just the top of the tower of the Empire State Building
would stick out the top); widens to the bottom; have sent a hot air
balloon down; people rappel down – takes about 20 min; It takes 10 s
to freefall, so people skydive down it with a parachute.
d. Skocjan Caves (slovenia) – vast underground canyon (3.5 km long,
140 m high, 10 to 60 m wide, with a huge river running through it)
e. Special Mention: Voronya cave (Abkhazia, Georgia) – world’s deepest
cave; 2080 m (1.3 miles!!)
Questions:
1) Many cave systems often have channels that follow straight lines? How do
you think these might have initially formed?
2) Why is limestone the most common host rock for caves?