Cave Geology Photo Index

Traditionally, the science of geology involves the study of the rocks of the earth's surface. The age of the rocks can be found by examining the fossils embedded within them. The composition can be studied by physical and chemical analysis, such as their hardness, brittleness, and whether they dissolve in acid or not. Caves can contribute to the study of surface rocks by providing access to the underground environment, often uncluttered by the physical limitations on the surface, such as plants, soil, and weathering.

More interesting to cavers, however, is the study of the cave itself: the void in the rock through which we travel. Forget how old the rock is - when did the cave itself form? How long did it take? Why is it shaped the way it is? Where is the best place to dig to find more passageways?

There are three major types of caves that are popular with explorers: solution caves, lava tubes, and boulder piles. Solution caves are formed in areas where the surface rock is especially vulnerable to attack by surface water made acid by the soil zone. Such areas are called "karst", and often have other distinguishing features besides caves, such as sinkholes, springs, and exposed rock near the surface. Minerals that often form karst surfaces are limestone, gypsum, and salt. Scientists estimate that perhaps up to 1/5 of the Earth's land surface is made up of such karst areas.

The second category, lava tubes, are formed when a specific type of volcano, called a "shield volcano", has been recently active. These tubes are generally shallow - only a few 10s of feet below the surface, and run down the slope of the volcano. They occur frequently in the areas of active volcanism, such as the Northwestern USA and the big island of Hawaii.

Boulder caves are formed when large, strong, rocks, that lack major cracks, break off mountains and pile up in jumbles in the valleys below.

Other interesting questions studied by cave geologists involve the formations and sediments found inside the cave, that formed or were transported in after the void in the rock was formed.

The map of cave distribution in the USA generally reflects the location of the karst areas as well.
Why do some passages in solution caves cut right through lots of rock layers,
while others follow a single layer for long distances?
How do these complicated spaghetti-like speleothems form? Why do they form in caves but not at the surface?
How did these complicated channels form in the ceiling of this passage?
How long did it take for these thick layers of limestone to form?

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	The map of cave distribution in the USA generally reflects the location of the karst areas as well.
	Why do some passages in solution caves cut right through lots of rock layers,
	while others follow a single layer for long distances?
	How do these complicated spaghetti-like speleothems form? Why do they form in caves but not at the surface?
	How did these complicated channels form in the ceiling of this passage?
	How long did it take for these thick layers of limestone to form?