Caves in Maryland

Take a virtual tour of 18 Maryland caves by browsing to A Gallery of Maryland caves

While not as numerous or spectacular as caverns in Kentucky, Tennessee, or the Virginias, Maryland's caves are interesting and valuable resources. Caves are important habitats for a variety of plants and animals, some of which are endangered. Caves are often an integral part of the natural drainage system which collects and purifies ground water. Other caves are the source of drinking water for communities. As cultural resources, many Maryland caves have long and interesting histories. They have served as shelters for prehistoric populations, sources of minerals for commerce, and even as cold storage for dairy products. Some caverns contain fossils remains of ancient sea creatures and Ice Age mammals. For a detailed study of Maryland caves, see Educational Series Report 3: Caves of Maryland.

One Maryland cave, Crystal Grottoes in Boonesboro (Washington County), is open to the public. Crystal Grottoes is about an hour drive from Baltimore and Washington D.C. It is well worth the pleasant drive, and there are many other interesting places to see in the vicinity including Antietam Battlefield, Harpers Ferry and Washington Monument State Park. Crystal Grottoes is located at 19821 Shepherdstown Pike, Boonesboro (301 432-6336). For more information on Crystal Grottoes see the Crystal Grottoes page.

At least 53 caves occur in Maryland. Most of these are located in western Maryland, in Washington, Allegany, Garrett and Frederick Counties. There are no known caves on the Eastern Shore or southern Maryland. The reason for this uneven distribution is due primarily to two geologic factors: bedrock type and drainage. Caves usually form when ground water slowly dissolves slightly soluble minerals in limestone and marble. The water flows through the rock because gravity forces it along cracks, called joints, in the rock. The limestone minerals, mostly calcite and dolomite, dissolve in slightly acidic water. Rain water is naturally slightly acid because it absorbs atmospheric carbon dioxide to make a very dilute solution of carbonic acid. When rain water passes through soil, it can become even more acidic by absorbing more carbon dioxide and other organically-derived acids. This acidic water then filters down to the limestone bedrock where it flows through pores and joints. Over thousands of years, this process enlarges the voids and spaces in the limestone, forming caves. Maryland's caves occur mostly in limestone and marble. Exposures of these rocks are limited to the central and western parts of the state. Therefore, most of Maryland's caves are found in those regions. These caves are probably less than 10 million years old

The landscape that develops over limestone and marble regions is often shaped by the same geochemical process that forms caves. Sinking streams, sinkholes, and springs are often found in areas underlain by limestone. This type of topography is called karst. While visually interesting, karst topography can be a potential hazard. Sinkholes can develop unexpectedly and rapidly, swallowing up cars, houses and whole towns. For more information on karst and karst terrane hazards, see MGS Factsheet 11: Foundation Engineering Problems and Hazards in Karst Terranes.

The mild temperatures and high humidities found in most Maryland caves are relatively constant throughout the year. This kind of environment makes caverns an ideal habitat for many animals. A variety of spiders, insects, amphibians, reptiles, fish and mammals make caves their seasonal or permanent homes. Salamanders, wood rats and several types of bats are particularly attracted to caves. These animals currently suffer from loss of habitat in Maryland due to development. Caves offer refuge to these creatures when forests and farmland are destroyed and surface streams are diverted and polluted. Other animals including cave crickets and cave moths live primarily in the subterranean world. In the past, aboriginal human populations used caves for shelter and religious ceremonies. More recently, some of these caves have been mined as a source of metal ores, and nitrates for gunpowder. Maryland caves have a rich natural and cultural history that requires careful preservation and study.