Lechuguilla Cave, part of Carlsbad Caverns in New Mexico, is the nation's deepest at 1,567 feet. Together, these two caves attract more than 2,000,000 visitors annually. The most common caves are solution caves. They form when soluble carbonate rock, such as limestone, dolomite, marble, or gypsum, is dissolved by groundwater.
Limestone makes up the majority of caves in the United States.
In addition to soluble carbonate rock, two additional factors must be present for caves to form. The acidified water trickles down into the bedrock moving horizontally between layers of rock and vertically into joints in the rock. All the while, it is very slowly dissolving the calcite, the main mineral in limestone. Understand more about the relationship between acids and bases in Riverdeep's Chemistry Gateways activity, Properties of Acids and Bases. Review the products of the photosynthetic process in Riverdeep's Biology Gateways activity, An Overview of Photosynthesis.