by Carl Strang
At present there are no caves to visit in northeast Illinois, unless one counts tiny Devil’s Cave on the Fox River. As far as I know there are none in the bedrock beneath us, though some of that bedrock is dolomite, which once was limestone, so we could in places have little caves under the hundred feet, more or less, of glacial till.
In order to appreciate the potential that a major cave can achieve, we need to travel. Today’s photos come from the Lehman Caves in eastern Nevada’s Great Basin National Park, which I visited in 2003. Most caves form in limestone, which dissolves slowly in the slightly acidic groundwater derived from rainfall. Rainwater picks up acid-forming carbon dioxide from the air and organic acids from the soil as it percolates down. Should time and circumstance drain the cave of much or all of its water, the stage is set for a new phase of activity.
Over time, the oozing water builds the stalactites, and in places drips to the floor and creates stalagmites.
Stalactites continue to elongate.
Eventually the stalactite and stalagmite may meet, forming a column.
As water continues to flow, the column can achieve an impressive diameter and configuration.
Some caves have unusual formations that go outside this standard sequence.
Apart from the small caves which may or may not be in the bedrock beneath us, our major local connection to caves is in the shelter that southern caves provide in winter for most of our bats.
Caves are the permanent homes for other organisms, whose survival is dependent upon import of nutrients from the outside. Some of that importing is done by the bats, which deposit guano from their ceiling roosts. At this moment, some cave invertebrate to our south is benefiting from a bit of fresh northeast Illinois guano dropped by a bat that grabbed a meal in our area on its way south.
We have two local kinds of ecosystems analogous to those in caves, likewise reliant on import of energy and nutrients to support their economies. Soil ecosystems are based in large part on the dead vegetable matter of the previous growing season, and in fact many of the small cave specialists clearly evolved from soil decomposer ancestors. Streams, though lacking such clear ties to caves, are small compared to the landscape through which they flow, and thus their character depends upon material and physical influences that come into them from all sides.