Geology

Meteorites are fragments of rock or metal that fall to Earth from space. They are very rare, but many people find unusual rocks or pieces of metal and wonder if they might have found a meteorite. Meteorites have several properties that help distinguish them from other rocks: Density: Meteorites are usually quite heavy for their size, since they contain metallic iron and dense minerals. Magnetic...

While the USGS studies the types of rocks that can potentially form sinkholes, we don’t investigate individual sinkholes on private property. First, rule out human causes for your feature. Some sinkholes are caused by leaky underground pipes (talk to your utility company) and some are old construction pits or other buried materials that have settled. If you’re confident of a natural cause for your...

Rocks and minerals must be examined in person from all perspectives for accurate identification; they are extremely difficult to identify through photographs. You will get the best results by taking your rock or mineral to a local source where it can be handled and examined closely. Possibilities include:Your state geological surveyA natural science museumA college or university with a geology...

The National Geologic Map Database (NGMDB) is an archive of geoscience maps (including geology maps), reports, and stratigraphic information for the United States. The NGMDB contains information on more than 90,000 maps and related geoscience reports published from the early 1800s to the present day, by more than 630 agencies, universities, associations, and private companies. Much of the content...

The USGS Field Records Collection is an archive of unpublished field notes, maps, correspondence, manuscripts, analysis reports, and other data created or collected by USGS Geology Discipline scientists during field studies and other project work. The collection is located in the USGS Library in Denver, Colorado, and is available for on-premises examination during normal library hours. See the...

A soil survey is the systematic description, classification, and mapping of soils in an area. They are published by the USDA Natural Resources Conservation Service (NRCS), formerly known as the Soil Conservation Service. NRCS soil surveys are available from several sources: Some are on the NRCS website. Published soil surveys can be found at some libraries or borrowed through interlibrary loan...

At the head of the valley in Yosemite National Park - as if on a pedestal - stands Half Dome. It is smoothly rounded on three sides and a sheer vertical face on the fourth. Half Dome, which stands nearly 8,800 feet (2,682 meters) above sea level, is composed of granodiorite, and is the remains of a magma chamber that cooled slowly and crystallized thousands of feet beneath the Earth's surface. The...

A sinkhole is a closed natural depression in the ground surface caused by removal of material below the ground and either collapse or gradual subsidence of the surface into the resulting void. A pothole is usually a fairly small feature caused by failure of paving materials, usually associated with roads, parking lots, and airports. In the colder parts of the country, potholes become more abundant...

There are some very large, ancient, ‘inactive’ sinkholes in some areas of the U.S. that are thousands of years old. Alabama claims to have the largest recent collapse sinkhole. It is called the “Golly Hole” and is located in Shelby County in the central part of the state. It collapsed suddenly in 1972. The sinkhole is about 325 feet long, 300 feet wide, and 120 feet deep. Learn more: USGS Water...

Sinkholes are just one of many forms of ground collapse, or subsidence. Land subsidence is a gradual settling or sudden sinking of the Earth’s surface owing to subsurface movement of earth materials. The principal causes of land subsidence are aquifer-system compaction, drainage of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, and thawing permafrost. Land...

There is no database of sinkhole collapses for the United States, so these data are unavailable. Some individual state geologic surveys track reported collapses within their state. Many sinkhole collapses are not reported to authorities or news organizations, and many occur in rural areas where they are unobserved. Learn more: USGS Water Science School - Sinkholes

Sinkhole damages over the last 15 years cost on average at least $300 million per year. Since there is no national tracking of sinkhole damage costs, this estimate is probably much lower than the actual cost. Learn more: USGS Water Science School - Sinkholes