Other Geological Hazards

Carbon Dioxide

Elevated concentrations of CO2 and depressed concentrations of O2 in building spaces is an arising environmental hazard in western Pennsylvania and other areas of the Appalachian coalfields. This problem was restricted to blackdamp (a gas composed of a mixture of CO2 and nitrogen) from abandoned deep mines in the past, but serious CO2 hazards related to surface mining activity have emerged in recent years.

Staff geologist Christopher D. Laughrey and Pennsylvania Department of Environmental Protection's Fred J. Baldassare provide information on this problem in a paper (PDF format – 5.2MB) entitled “Some applications of isotope geochemistry for determining sources of stray carbon dioxide gas.” This paper is made available from the American Association of Petroleum Geologists journal Environmental Geosciences, v. 10, no. 3 with their permission. The Pittsburgh Geological Society also has information about carbon dioxide migration and other geohazards.


Flooding is well known as a hazard across Pennsylvania. Although flooding is controlled by the landscape and precipitation, it’s the use of the land and its modification that tend to worsen flooding situations. The Pittsburgh Geological Society provides information about floods and other geohazards. The U. S. Geological Survey's Pennsylvania Water Resources District Office is a good source of information on current hydrologic conditions in Pennsylvania.

Methane Gas

In some areas of Pennsylvania (especially areas of coal mining and gas well activity), stray methane gas in the subsurface can be a hazard.  Under certain conditions, methane can migrate to private water supply wells and ultimately into a house or structure.  Unmitigated, methane can build to explosive concentrations.  A proper well vent allows methane to vent to the atmosphere rather than build up to explosive levels.  The risk of an explosion from stray methane varies from location to location based on site-specific conditions.  In Greene County in 1997, a methane explosion destroyed a home. Methane gas had migrated through an improperly vented water well into the house.  The Pittsburgh Geological Society provides information about the migration of natural gas and other geohazards.


Radon is a naturally occurring, colorless, odorless, inert, but radioactive gas, with a half-life of 3.8 days. It is a decay product of the most abundant naturally occurring isotope of uranium, U238, and has radium as its immediate radioactive parent. Uranium and radon are found nearly everywhere in very small concentrations. Radon and its daughter products decay by the emission of alpha particles, essentially helium nuclei (two protons and two neutrons) carrying a charge of +2. Because of their large mass and charge, alpha particles travel only a short distance through body tissue, and have the capability of causing extensive damage when they encounter living tissue. The risk of lung cancer is understood to be proportional to the amount of exposure to radon decay products in air. — Pennsylvania Geology, vol. 18, no. 2.

It is estimated 40 percent of homes in Pennsylvania have radon levels above EPA's action guideline of 4 pCi/l. For more information, visit the Pennsylvania Department of Environmental Protection's web page on radon. Also, see the U. S. Geological Survey web site on radon, including “The Geology of Radon.”

Survey Publications or staff articles on radionuclides

Cecil, L. D., Smith, II, R. C., Reilly, M. A., and Rose, A. W., 1987, Radium-228 and radium-226 in ground water of the Chickies Formation, Southeastern Pennsylvania, in Radon, Radium, and Other Radioactivity in Ground Water, Graves, B. (editor), Lewis Publishers, p 437-447.

McCauley, J. F., 1961 (2nd printing, 1983), Uranium in Pennsylvania, Pennsylvania Geological Survey, Mineral Resource Report 43, 71 p., 9 pls.

Smith, II, R. C. and Hoff, D. T., 1984, Geology and mineralogy of copper-uranium occurrences in the Picture Rocks and Sonestown quadrangles, Lycoming and Sullivan Counties, Pennsylvania, Pennsylvania Geological Survey, Mineral Resource Report 80, 271 p., 4 pls., geol. and min. resource map, scale 1:24,000.

Smith, II, R.C., Reilly, M. A., Rose, A. W., Barnes, J. H., and Berkheiser, S. W., April 1987, Radon: A profound case, Pennsylvania Geology, vol. 18, no. 2, p 3-7.

Subsidence Caused by Underground Mining

Subsidence associated with the underground extraction of coal is a geologic hazard with a human twist. After coal is removed from the ground, over time the roof of the mine begins to collapse. The sagging of rock layers may propagate to the surface. Land subsidence can be devastating to a building’s foundation, and also can alter ground water and surface water flow.

For more information on land subsidence, contact the Survey, or visit the Department of Environmental Protection’s mine subsidence insurance and “Subsidence Agent Program” web pages. The Pittsburgh Geological Society also provides information about land subsidence from mining and other geohazards.