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Some of the best scenic features in the Black Hills
can be found underground.
Hi.
I'm Ranger Dan, and welcome to Jewel Cave National Monument.
In this podcast, we'll be showcasing
some of the rare and unusual formations you might see
while you're on a cave tour.
Caves around the world are often adorned
with strange and beautiful formations produced
through a slow process of deposition.
Jewel Cave is no different.
It's well-known for its diversity of cave features,
properly called speleothems.
The different formations include flowstone, stalactites,
stalagmites, columns, helictites, soda
straws, frostwork, popcorn, gypsum needles,
and gypsum flowers.
Flowstone formations are composed
of sheet-like deposits of calcite,
forming where water flows down the walls or over cave floors.
In Jewel Cave, visitors often see
draperies, a type of flowstone, caused by calcite-rich water
flowing along an overhung surface.
Some are small, while others create
a large chandelier-like feature in lofty passages.
In some areas like the formation room,
decorative flowstone has occurred
on rocks creating a smooth surface that
gives a pillow-like appearance.
Although somewhat rare inside Jewel Cave,
stalactites are formations that hang from the ceiling.
A great way to remember their name
is stalactites hold tight to the ceiling.
On the other hand, a stalagmite is a formation
that rises from the floor of the cave due to calcium deposits
dripping down from the ceiling.
You can remember their name this way.
Stalagmites, you might trip over them.
If stalactites and stalagmites come together,
they create a column.
A helictite is perhaps one of the strangest formations
in the cave.
They form by seeping water and capillary action
rather than by dripping water.
In fact, it is unusual to see drops of water
on the ends of helictites.
They have a curving or angular form
that looks as if they were grown in environments
with zero gravity.
A soda straw is a speleothem in the form of a hollow tube.
Soda straws grow in places where water leaches slowly
through cracks in the ceilings of caves.
As you might expect, a soda straw
can turn into a stalactite if the hole at the bottom
is blocked or if the water begins
flowing on the outside surface of the hollow tube.
In soda straws as each drop hovers at the tip,
it deposits a ring of mineral at its edge.
It then falls, and a new drop takes its place.
Each successive drop of water deposits a little more
mineral before falling.
And eventually, a tube is built up.
Soda straws are some of the most fragile of speleothems.
Jewel Cave is also known for its frostwork formations.
Delicate needle-like growths of calcite or a related mineral,
aragonite, are sometimes shaped like frostwork.
The small formations tend to grow
outward from the cave walls.
The origin of frostwork is often debated
by cavers and geologists.
In Jewel Cave and nearby Wind Cave,
frostwork seems to concentrate in passages
with above average airflow where it is thought evaporation
plays a role in its formation.
Cave popcorn is a visitor favorite
and can be seen along the Scenic Tour route.
It forms by precipitation.
Water seeping through cave walls or splashing onto them
leaves deposits when carbon dioxide loss causes
its minerals to precipitate.
It seems as though most popcorn is white in color.
However, some color differences may be caused
by impurities in the water.
For those that go caving inside Jewel Cave,
two final favorites include gypsum needles and gypsum
flowers.
Gypsum crystals are common in some
of the drier parts of the cave.
Gypsum, a mineral containing both calcium and sulfur,
sometimes takes the form of needle-like crystals
that radiate from clusters on the cave floor.
In other cases, gypsum resembles puffs of cotton or forms
clusters of curved or coiled crystals called gypsum flowers.
They truly are some of the more unique cave features
within the monument.
Every cave is different.
Every cave offers different formations.
The best way to appreciate an underground environment
is to explore and discover its hidden scenery.
What makes caves so special is that their features are often
still changing.
What one person looks at, another
looks past to something else.
For the monument, the cave continues
to make the strange familiar and the familiar strange.
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