Likely To Be Eaten By A Bottomless Pit

I was in DC last week, and in the course of bumming around, I went to a new Imax movie about caves. (Amazing Caves.)

Caves are the original IF setting; caves are also darn cool. I've written an IF game set in a cave (Hunter, in Darkness). But I didn't actually have much idea what caves were like, when I wrote it. Most of my description was second-hand Crowther and Woods. So, hey, I thought, I should see good movie footage of real caves.

(It was either that or Michael Jordan To The Max. Not a hard choice actually.)

The movie was filmed in three caves: a "traditional" limestone cave in Arizona, an ice cave in a glacier in Greenland, and an underwater cave in the Yucatan. The actual purpose of the expeditions was microbiological research -- taking samples of water from strange and isolated environments, hoping to discover peculiar organisms. But let me talk about cave environments.

Limestone caves are the ones everyone thinks of. Stalagmites, stalactites, flowstone. Bats and blind fish. You can find a million pictures.

...Remember that the pictures are illuminated by professional photographers with floodlights. The natural state of a cave is sightless, and don't you forget it -- I don't want to hear about glowing moss, either. (Mosses and lichens are photosynthetic; they require light to grow, they don't produce it. If you want to introduce a magical ecology, that's another matter, and a more complicated one.)

And caves aren't flat, either. "Twisty passages" and "chasms" and "bottomless pits" are accurate cliches. (Okay, maybe not bottomless.) The same goes for "low crawls" and "tight squeezes" -- the ceiling height wasn't designed for human convenience. Caving is a scramble, not a stroll.

Then there's the ice cave. The one in the movie was basically a vertical crack in a glacier, 500 feet deep. Descent was by rappelling straight down on ropes -- there didn't seem to be anywhere to stand. Not even at the bottom; that was a pool of liquid water, who knows how deep.

The difference between ice and stone is that ice is nearly molten, if you see what I mean. A glacier flows detectably over the course of a year; the interior is constantly under strain. And the farther down you go, the greater the stress. "Boulder-size chunks of ice blowing out of the wall with no warning," was a line from the movie. (Not an event they caught on film, I'm sorry to say.)

If it's warm outdoors -- warm enough for ice to get shiny in direct sunlight -- that means water flowing down through the glacier. The explorers in the movie had to wait for four cold days in a row before they could safely descend. Otherwise, well, it's rappelling down a vertical ice sheet with a hypothermic waterfall blasting down on your head. Good luck.

The underwater cave was by far the weirdest, visually. First of all, only suicidal lunatics go scuba-diving in caves. (Also my boss. No, wait, ...) Cave-diving is just like normal scuba-diving, except it's pitch black and they took the surface away. Alternatively: it's just like normal spelunking, except that if you get lost, you die. Doesn't this sound like fun?

Descriptive notes: you can tell where you've been, because you know those bubbles that constantly rise from scuba masks? They hit the ceiling and stick there. But you can also tell where you've been because you unreel a rope as you go. So you can follow it out. Be sure to attach plastic arrows to the rope, pointing out. You don't want to mistake the direction.

Swimming stirs up silt, and the water in the cave can turn totally opaque awfully fast. Turning around in a dead end stirs up silt even faster. Don't lose the rope.

But the strangest thing down there was a halocline -- a flat, stable boundary between seawater and fresh water. This occurred in a place where an underground river was flowing towards the sea. Seawater had backed up into the cave, and the less-dense fresh water flowed smoothly above it for a distance. You could see the boundary. It looked like... the surface of a lake. Except that people were swimming above it. And then they swam down through it. The surface rippled.

You can do this at home, actually. Fill a glass with very salty water; fill another with fresh water. Put a piece of cardboard or plastic across the fresh glass and turn it upside down. Put it above the brine glass. Pull the cardboard out. The halocline will remain. You can slosh the salt water back and forth, if you're careful.

Do this over a sink.

My perhaps-not-lunatic boss says that you can get a similar visible interface (though not so distinct) at a thermocline, where warm water overlies colder water. Or at a geologically active sea-floor site, where hydrogen sulfide is dissolved in water, again making it denser. (And poisonous. Even to skin contact. Don't stay down there long.)

But enough about cave movies. Two days later I had even more free time, so I drove two hours west, to the tourist cave zone of Virginia.

Now I freely admit that these are wussified caves, with electric lighting, levelled floors, and handrails. But you can definitely get an idea of how caves run. If you leave early from DC, you can take three hour-long cave tours in a day. This I did. I took notes, too.

Endless Caves

Very rusty, dull. (That is, the cave walls were brown-red flowstone, colored by iron oxide, and not the sparkling white of pure calcite.)

A few patches of snow-white flowstone, however. Also places where bluish limestone was exposed -- a strong contrast to the general redness.

The cave was quite dry; there hadn't been much rain the past season, so water levels were low, and some reflecting pools were entirely dry.

A barrel had been set in place below a drip, to catch the water and divert it off the walkway. I believe that was around the 1920's. At this point, the barrel is starting to be crusted with limestone, especially around the rim. Gives you an idea how fast the stuff grows.

Shield formations: a roundish horizontal plate sticking straight out from the wall. (Horizontal, or somewhat tilted.) Very strange-looking. They usually have stalactites dripping down to the floor, which support the stone, but in fact a shield grows out from the wall; the stalactites come along later. Water seeps out of a crack, and leaves thin stone lips on the crack's two edges. Now it's seeping out between the lips. So they grow, straight out. The result is a double plate. Capillary action draws the water out between the plates, so it keeps growing. If it's unsupported, it can break, of course -- possibly the plates will separate, leaving a strange tree-ring-like texture on the exposed surfaces.

Pillars and columns with inch-wide gaps in them. If the bottom of the cave is mud, it can settle under the weight of flowstone formations. Pillars crack and separate. The walls of that cave had a horizontal crack running around them, where they'd separated as well.

Three levels to the cave. Stream eats down, irregularly, leaving different levels and chasms between them.

Rimstone: "worm" effect as water flows over a wide, flat, gentle slope. Calcite builds up on irregularities, forming a network of basin-lips.

Calcite rims and shelves where water pooled. (Minerals building up at the waterline.) Lilypad formations inside dried-up pools.

Slab rooms where the roof has fallen down, splitting stone flatly. (This is where the cave walls or ceiling look like rough rock, instead of flowstone fanciness.)

A wide, very low room with many fine stal/pillars. This was the area that's a reflecting pool in times of greater water seepage. "Very low" means only a foot or two high; but as wide as any chamber in the cave.

Plant roots go surprisingly deep into the ground. Where clay was visible in the cave, sometimes it had little root-tendrils threading through it.

Lots of bats. Clinging to walls, ceilings -- not huge cinematic clouds of bats, but they were frequent. Very active in the spring. They only nest in caves; they go outdoors to feed. These bats seemed to be fairly used to people; they would fly within three feet of you.

The sound of bats screwing is sort of a sharp clicking chitter.

Moss growing in the cave -- ha! -- only where the electric lights are set. Really, a small patch of moss where each light is shining on the wall. Nowhere else. On the other hand, candles and oil lamps leave soot stains on the wall (after a time), so what are you going to do?

The cave system has not been entirely mapped; it goes at least five miles, and new sections are still being discovered. (Most of that isn't on the tour, of course.)

Shenandoah Caverns

Gravel floor (laid down by humans, not natural) -- but it has developed a film of wet clay. Very slippery. I fell down ten feet from the entrance, and spent the rest of the tour with clay all over my hands.

As in Endless, the walls are rusty-reddish.

White flowstone formations studded with large flat calcite crystals. "Spangles" up to an inch wide. Very nice.

Three levels. The cave has been entirely explored, at least as far as people can pass at all.

Spot where two underground rivers joined -- turbulence caused deep "whirlpool" weathering in the walls and ceiling. Swirls and round depressions -- looked like a tidal sinkhole, not a cave wall. The weathering extended quite a ways down the passage, as the current was swift for some distance.

Large blocks fallen, forming flat-surface caves, long after the river-passage formed. (Possibly fell during an earthquake.) Now flowstone is covering up the broken surfaces.

A very large, tall wall of flowstone formations.

Skyline Caverns

Not much flowstone.

Three levels, but the lowest is entirely submerged. (It has not been explored, as the entrances are too narrow for divers.) Three different streams flow through the cave, one falling down a thirty-foot waterfall.

The stream level varies with weather -- surface water seeping down. When I was there, one stream was nearly dry.

Seepage pools: not fed by a stream or watercourse. The water enters only through seepage from walls and ceiling. Form shallow reflecting pools.

Original exit is still visible, a narrow vertical shaft.

Anthodites: calcite needles in small sprays on the walls and ceiling. Look like sea urchins. A wide range of sizes.

These formed in small air pockets above a passage that had filled in with mud. (The air in the pockets was sealed off from the outside atmosphere.) When the cave was dug out and the anthodites exposed, they stopped growing.


Observation is good. If you want to write about caves, go look in one. If you're actually an adventurer, and not a wimp like me, go caving. Report back. We're curious what it's like beyond the handrails.

Updated April 3, 2001.

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