WALKING THROUGH THE UNDERGROUND:
Caves, Caverns, and the World of Eternal Night
This is about natural caves and caverns, not
artificial catacombs and mines. Catacombs and mines have a human
logic to their construction. Natural caves are random and illogical,
thoroughly unpredictable and often inconvenient in their form.
(If you want to read a fantasy novel that
uses real caves as an obstacle, try The Weirdstone of Brisingamen.
I'd read it more often if that section wasn't so frightening.)
Most caves are formed by water cutting through
stone. The few that are not are
- jumble "caves," voids in piles
of boulders. They are like a casual heap of blocks. Earth movements
or landslides can collapse them. They have none of the pretty
features of "real caves" and are usually above the
real ground level. They are usually next to the slopes the boulders
tumbled down. When they occur in moraines left by retreating
glaciers, they often represent a spot where a large chunk of
ice remained a while. When it finally melted, the rocks falling
in on the space locked together. See, even these can be water-formed
in a backward way.
- volcanic caves, like lava tubes, result when
lava hardens on the outside, but the still-liquid insides run
out afterwards. Think of it like draining a cordial cherry and
leaving only the chocolate coating. These can be surprisingly
complex, while featuring lots of shattered volcanic glass (obsidian)
and leather-shredding rock textures.
- fissure caves, caused by rock splitting.
The fissure may or may not reach the top of the rock. These are
never extensive or complicated.
All the rest are eroded by water, like most
Ice caves form in glaciers by the same method:
meltwater running through fissures, eroding them larger.
The most extensive and prettiest caves will
be found in limestone: Kentucky, the Yucatan, Germany. In fact,
95% of all caves are in limestone. Cavers (who hate the name
"spelunker") will delight in any hole in the ground,
eager to crawl in and see where it goes. Pretty formations are
nice, but many would far rather find the deepest, longest, most
extensive, or newest cave. Many of the miles listed in a cavern
system's extent is not tourist trail. It's crawling through nature's
drainpipes. However, the general rule has always been that what
counts as cave is something a human can get to, or through. Naturally,
top cavers are skinny and often short.
Caverns can have individual rooms too large
to light and photograph. The record to date is 162,700 square
meters in the Sarawak Chamber of the cave Lubang Nasib Bagus,
As of March 2013, the deepest cave in the
world is Voronya
cave in the Arabika massif in the Caucasus mountains in the Republic
of Georgia, at 6824 feet/2080 meters deep. Lamprechtsofen
in the Leoganger Steinberge massif, in the Northern Calcareous
Alps, Austria, is #2, currently explored to 5354 feet/1632 meters.
The US has Lechuguilla Cave, 1632 feet/497
meters deep, and 101 miles/156.5km long. It was only discovered
in 1986, and has a potential to go as deep as any. (You can see
a map of it, color-coded for depths, here.)
Kazumura Cave runs a vertical 3602 feet with
over 40 miles of explored passages, making it the most extensive
lava cave in the world.
The largest, most extensive cave system
is the Mammoth Cave/Flintridge system in Kentucky, 360 miles/5906
kilometers of explored passages, but only going down to 379 feet/115.5
Caves send offshoots in many directions. The
deeper or longer the cave, the harder it is to mount an expedition
to stay underground long enough to explore many. New passable
cave may be found at any time.
Sound like you know what you're talking about
by using the caver's vocabulary. This recaps the information
that appeared in an article of mine published in Dragon
magazine #249: isn't D&D all about underground places?
This antique engraving
of part of the Gailenruth caverns demonstrates that most real
caverns are not neat catacombs with ten-foot-square passages:
they have holes and drops, high places and low, all quite random.
If you followed the links to the maps of the deepest caves, you
saw what looked like diagrams of a handful of threads left hanging
in near-zero-G. The only constant is a tendency to run downward.
However, since this isn't open ground, sometimes the only route
for water is to fill a gap then be forced up a rising crack by
the pressure of the water still trying to come down.
Some areas of some caverns are flooded, so
that cave scuba has become a special part of caving. As long
as a system still has water moving through it, if only a drop
at a time, it is considered "live," still forming.
Systems are "dead" when they have dried out. A dead
cave is often easier to get through, lacking water hazards. In
live caves, you may encounter rushing torrents, rapids, and towering
waterfalls, besides placid dark pools and lakes of unknown depth
A cave is any gap. A large or complex
cave is also known as a cave system. Open cave
is any part that is exposed to the immediate outside world, whether
or not a person can reach the opening or pass through it. A cavern,
when not just a synonym for cave, is a large or highly decorated
cave, the kind you can walk tourists through.
Limestone caves are the reason for karst
regions. Karst topography is marked by lots of sinkholes,
pits in the ground ranging from the size of a bathtub to one
you could lose a house in (a sinkhole in Florida once did open
up under a house: new housing developments watering their lawns
to get them green can wash out the ceiling of an unsuspected
cave). When a cave ceiling collapses, you get a sinkhole. This
collapse is called breakdown, and may still leave the
actual cave forty feet below the surface, or open it to the outside.
The area collapses doesn't have to be paper thin.
Any passage that leads from the outside into
a cave system can be called an adit.
the uppermost part of any opening, floors the bottom,
walls the sides. A passage is an opening longer
than it is tall or wide, especially when tall enough to walk
in, a natural hallway. A smaller passage, requiring crawling,
may be called a lead [leed]. A crawl is any low
passage, even if it's thirty feet wide. A cave that opens out
beyond the passages around it, a wide spot in the road, is a
chamber. Generally narrow passages are called corridors
when mostly straight and leading between chambers.
or dry, are one of those places where water got forced upward
and cut a passage. A normal siphon is a U-shape that dips
down and goes up again, also called a duckunder. An inverted
siphon goes up then down again, rather sharply. A wet siphon
will look like a pool or hole filled with water: you won't know
it goes anywhere until you get into it to explore. A wet inverted
siphon will only be found underwater. It is possible for one
end to be underwater in a pool and the top of it, above the water
level of the pool, dry, and the farther side drained. A siphon
and an inverted siphon right after each other makes for vertically
S-shaped passages. How difficult these are to pass depends on
if they are a close squeeze or you can walk upright along the
known as flowstone, is the stuff of cavern fantasies. All the
beautiful fantastical formations are made of this. Simply, water
coming through limestone dissolves it. Each drop carries its
microscopic burden of lime. Anywhere it dries out, it deposits
this iota of stone. Over time, centuries, it can form remarkable
shapes. Similar speleothems can be formed out of water carrying
any mineral: you may have seen concrete dripstone or rustsicles.
Where dripstone forms from the floor upward,
like candle wax built up in a stack, it's a stalagmite
(stalaGmites Grow up from the Ground). Where
it forms from the ceiling like icicles, it's a stalactite
(stalaCtites Come down from the Ceiling).
When stalactite and stalagmite meet, you get a column.
A very skinny stalactite may be called a straw. Dripstone
can form along a fracture line into sheets of rock, called drapery.
A pool of water evaporates along its surface.
This can result in fragile cave rafts being formed on
its surface. If cave raft anchors to the sides, it forms shelfstone
(if the pool dries out from under the shelf, it can make
very fragile footing). Otherwise, when it grows too heavy, it
will sink and become part of the bottom of the pool. Small pools
that are frequently dripped into may develop little balls of
limestone, called cave pearls. Baconstone is limestone
that is white or yellow, streaked with red from iron oxide. When
this forms drapery that can be lit from behind, it is particularly
beautiful. There may also be cave flowers, calcite crystals
that form in clusters.
There Be Light
Writers taking characters underground often
create artificial light sources so it's the equivalent of going
into a building with no windows but a lighting system. These
have included glowing ceilings left by The Ancients or the ever-popular
phosphorescent lichen or fungi.
Let's address the business they're always
trying to avoid: carrying your own light sources and how long
Bernard Mason provided us with the information
everyone wants and can't find: what "a torch" is and
how long it burns. He describes a stick about 1'/30cm long and
3/4"/18cm in diameter. The end is soaked and coated with
pine pitch (brighter, hotter flame) or tallow (soft animal fat,
giving a dimmer light).
Remember the 1-hour limit they stick you with
in D&D? Mason, who used torches in the woods in the days
before flashlights, says one such torch "burns all night."
Let's call that a 6-hour minimum, 12-hour maximum, 9-hour average
(it could easily be the longer limit: someone want to make some
and time the burn?). So as long as you can keep a torch lit,
you won't have to carry stacks of them with you for a trip of
a day or two. Each weighs about a pound (less than half a kilo).
An ordinary Alpine candle-lantern, with glass
cylinder; 2" diameter; telescoped, 4" high, open 6
1/2" high, brass with bail hanger up 10" high, weighs
half a pound, less than a quarter kilo, without candle. It uses
1.5 ounce candles (.04 kilo), 3 1/8" long, 1 1/8" diameter.
Each of them burns 9 hours. So this is probably close to a torch's
end mass of fuel.
Surely some of you keep emergency candles
in the house for power outages. The cheap ones at the supermarket
are rated to burn 12 hours, and weigh no more than two ounces.
We also picked up stats on a traditional oil
lantern, black enamel with shutters, silvered reflector, 8.5"
high, 2.75" diameter, lens 3.75". Empty, it weighs
a bit over a pound, exactly half a kilo. It holds about a half-pound
of lantern oil. It will burn on one filling for 10-12 hours,
and lights up an area 40-60 yards/meters around.
One entertaining thought is that your lighting
may use up all the oxygen. In certain dead-end passages, this
may be a problem, or if you're caught in a cave-in. However,
natural caverns normally have natural airflows.
In some odd passages, this can be quite a stiff breeze, but normally
it is just a draft, circulating air. Natural caves don't get
the firedamp of coalmines. For starters, they aren't in coal
formations. But if you send your characters into old coalmines,
be sure to check on their particular perils.