FAQ's about Geology

To view maps of volcanoes visit the USGS online store at Maps>Hazards or Education Products>Earthquakes, Volcanoes, and Landslides.

A rock is an aggregate of one or more minerals; or a body of undifferentiated mineral matter.

No. The San Andreas Fault System, which crosses California from the Salton Sea in the south to Cape Mendocino in the north, is the boundary between the Pacific Plate and North American Plate. The Pacific Plate is moving in northwest with respect to the North American Plate at approximately 46 millimeters per year (the rate your fingernails grow). The strike-slip earthquakes on the San Andreas Fault are a result of this plate motion. The plates are moving horizontally past one another, so California is not going to fall into the ocean. However, Los Angeles and San Francisco will one day be adjacent to one another!

For further information, see: Earthquakes, Megaquakes, and the Movies.

There are no official definitions for generic terms as applied to geographic features. Such definitions as exist derive from the particular needs and applications of organizations using them. The Geographic Names Information System (GNIS) database utilizes 63 broad categories of feature types originally defined solely to facilitate retrieval of entries with similar characteristics from the database.

These categories generally accord with dictionary definitions, but not always or in all respects. The differences are thematic and highly perceptive. For example, a lake is classified in the GNIS as a "natural body of inland water," a definition that may not apply in other contexts. We have found 54 other generic terms with characteristics similar to a lake, and all are classified as lake, including features called ponds. It might be generally agreed that a pond is smaller than a lake, but even this is not always true.

All "linear flowing bodies of water" are classified as streams in the GNIS. At least 121 other generic terms fit this broad category, including creeks and rivers. Observers might contend that a creek must flow into a river, but such hierarchies do not exist in the Nation's namescape. Near the USGS offices in Northern Virginia, Little River flows into Goose Creek. Many controversies exist, such as mountain and hill, which we call "summit" along with 194 generic terms with similar characteristics. Cities, towns and other entities with human habitation are classified as populated places.

The British Ordnance Survey once defined a mountain as having 1,000 feet of elevation and less was a hill, but the distinction was abandoned sometime in the 1920's. There was even a movie with this as its theme in the late 1990's - The Englishman That Went Up a Hill and Down a Mountain. The U.S. Board on Geographic Names once stated that the difference between a hill and a mountain in the U.S. was 1,000 feet of local relief, but even this was abandoned in the early 1970's. Broad agreement on such questions is essentially impossible, which is why there are no official feature classification standards.

Fool's Gold can be one of three minerals; the most common mineral mistaken for gold is pyrite, chalcopyrite may also appear gold-like, and weathered biotite mica can mimic flake gold.

For additional information go to: http://energy.cr.usgs.gov/oilgas/noga/ (choose Williston/Bakken in the interactive map to see all available documents).

Browse the following websites for more information:

• US Recent Earthquakes
• World-wide Recent Earthquakes
• World-wide Earthquakes in the Last 7 Days
• NEIC QED list
• Global Earthquake Information - IRIS Seismic Monitor
• United States - ANSS

A landslide is defined as, the movement of a mass of rock, debris, or earth down a slope. (Cruden, 1991). Landslides are a type of "mass wasting" which denotes any down slope movement of soil and rock under the direct influence of gravity. The term "landslide" encompasses events such as rock falls, topples, slides, spreads, and flows (Varnes, 1996). Landslides can be initiated by rainfall, earthquakes, volcanic activity, changes in groundwater, disturbance and change of a slope by man-made construction activities, or any combination of these factors. Landslides can also occur underwater, causing tidal waves and damage to coastal areas. These landslides are called submarine landslides.

Failure of a slope occurs when the force that is pulling the slope downward (gravity) exceeds the strength of the earth materials that compose the slope. They can move slowly, (millimeters per year) or can move quickly and disastrously, as is the case with debris-flows. Debris-flows can travel down a hillside of speeds up to 200 miles per hour (more commonly, 30 – 50 miles per hour), depending on the slope angle, water content, and type of earth and debris in the flow. These flows are initiated by heavy, usually sustained, periods of rainfall, but sometimes can happen as a result of short bursts of concentrated rainfall in susceptible areas. Burned areas charred by wildfires are particularly susceptible to debris flows, given certain soil characteristics and slope conditions. More information can be found in USGS Fact Sheet numbers FS-071-00, Landslide Hazards (English Version), and FS-072-00, Peligros de Deslizamientos (Spanish Version).

Information on debris flows can be found in our Publications section.

Sources of Information for this FAQ:

(1). Cruden, D.M., 1991. A Simple Definition of a Landslide. Bulletin of the
International Association of Engineering Geology, No. 43, pp. 27-29.

(2). Varnes, D.J., 1996. Landslide Types and Processes, in Turner, A. K., and R.L. Schuster, Landslides: Investigation and Mitigation, Transportation Research Board Special Report 247, National Research Council, Wasington, D.C.: National Academy Press.

Nowadays, thanks to the advent of science, it has been shown there is no connection between weather and earthquakes. Earthquakes are the result of geologic processes within the earth and can happen in any weather and at any time during the year. Earthquakes originate miles underground. Wind, precipitation and barometric pressure changes affect only the surface and shallow subsurface of the Earth. Earthquakes are focused at depths well out of the reach of weather, and the forces that cause earthquakes are much larger than the weather forces. Earthquakes occur in all types of weather, in all climate zones, in all seasons of the year, and at any time of day.

Oil has been produced from the Bakken Formation since the 1950's and, as of March 2009, cumulative oil production from the Bakken Formation totaled about 164 million barrels (up from 149 million barrels in December 2008 and 135 million barrels in September 2008). This production comes from about 1,849 wells. Please see our slideshow presentation for context at: http://energy.usgs.gov/flash/Bakken_slideshow.swf.

For additional information go to: http://energy.cr.usgs.gov/oilgas/noga/ (choose Williston/Bakken in the interactive map to see all available documents).

In 1931, there were about 350 stations operating in the world; today, there are more that 4,000 stations and the data now comes in rapidly from these stations by telex, computer and satellite. This increase in the number of stations and the more timely receipt of data has allowed us and other seismological centers to locate many small earthquakes which were undetected in earlier years, and we are able to locate earthquakes more rapidly.

The NEIC now locates about 12,000 to 14,000 earthquakes each year or approximately 50 per day. Also, because of the improvements in communications and the increased interest in natural disasters, the public now learns about more earthquakes. According to long-term records (since about 1900), we expect about 18 major earthquakes (7.0 - 7.9) and one great earthquake (8.0 or above) in any given year. However, let's take a look at what has happened in the past 32 years, from 1969 through 2001, so far. Our records show that 1992, and 1995-1997 were the only years that we have reached or exceeded the long-term average number of major earthquakes since 1971. In 1970 and in 1971 we had 20 and 19 major earthquakes, respectively, but in other years the total was in many cases well below the 18 per year which we may expect based on the long-term average.

A temporal increase in earthquake activity does not mean that a large earthquake is about to happen. Similarly, quiescence, or the lack of seismicity, does not mean a large earthquake is going to happen.

See NEIC's Earthquake Statistics webpage for the tables of earthquake counts by magnitude and year.

Please see the Bakken Formation fact sheet at http://pubs.usgs.gov/fs/2008/3021/. There is a table on page 2 of the fact sheet that provides 5%, 50%, 95%, and mean probabilities of oil, gas, and natural gas liquids. As of March 2009, cumulative oil production from the Bakken Formation totaled about 164 million barrels (up from 149 million barrels in December 2008 and 135 million barrels in September 2008).

For additional information go to: http://energy.cr.usgs.gov/oilgas/noga/ (choose Williston/Bakken in the interactive map to see all available documents).

There are about 1500 potentially active volcanoes worldwide, aside from the continuous belt of volcanoes on the ocean floor. About 500 of these have erupted in historical time. Many of these are located along the Pacific Rim in what is known as the "Ring of Fire." In the U.S., volcanoes in the Cascade Range and Alaska (Aleutian volcanic chain) are part of the Ring, while Hawaiian volcanoes form over a "hot spot" near the center of the Ring.

1. Niihau
2. Kauai
3. Oahu
4. Molokai
5. Lanai
6. Maui
7. Kahoolawe
8. Hawaii (Big Island)

Of the 193,000 metric tons of gold discovered to date, 62% is found in just four countries on earth. All the gold discovered thus far would fit in a cube 22 meters on a side.

The earliest reference we have to unusual animal behavior prior to a significant earthquake is from Greece in 373 BC. Rats, weasels, snakes, and centipedes reportedly left their homes and headed for safety several days before a destructive earthquake. Anecdotal evidence abounds of animals, fish, birds, reptiles, and insects exhibiting strange behavior anywhere from weeks to seconds before an earthquake. However, consistent and reliable behavior prior to seismic events, and a mechanism explaining how it could work, still eludes us. Most, but not all, scientists pursuing this mystery are in China or Japan.

Volcanoes are mountains, but they are very different from other mountains; they are not formed by folding and crumpling or by uplift and erosion. Instead, volcanoes are built by the accumulation of their own eruptive products -- lava, bombs (crusted over lava blobs), ashflows, and tephra (airborne ash and dust). A volcano is most commonly a conical hill or mountain built around a vent that connects with reservoirs of molten rock below the surface of the Earth. The term volcano also refers to the opening or vent through which the molten rock and associated gases are expelled. -- From: Tilling, 1985, Volcanoes: USGS General Interest Publication.

1975: For example, on November 29, 1975, a large magnitude-7.2 earthquake struck the Big Island of Hawaii at 4:48 a.m. It was centered about 28 kilometers southeast of Kilauea Volcano's summit caldera at a depth of 5 kilometers; the earthquake occurred within the volcano's south flank. The earthquake was preceded by numerous foreshocks, the largest of which was a 5.7 magnitude jolt at 3:36 a.m. the same morning, and was accompanied, or closely followed, by a tsunamis, massive ground movements, hundreds of aftershocks, and a short-lived eruption in Kilauea's summit caldera.

The eruption began at 5:32 a.m. from a 500-meter long fissure on the caldera floor and ended by 10:00 p.m. According to scientists at the USGS Hawaiian Volcano Observatory, the eruptive activity "was apparently triggered by the 7.2 magnitude earthquake. The small volume and brief duration of the eruption suggest that the shallow magma might not have reached the surface under its own buoyant energy without a triggering mechanism apparently provided by the violent ground shaking."

1868: The largest historic earthquake (estimated between 7.5 and 8.1) on the Big Island occurred beneath the south flank of Mauna Loa Volcano on April 2, 1868. The earthquake was followed by a small eruption from Kilauea's southwest rift zone and from a fissure on the caldera wall that flooded the adjacent Kilauea Iki crater with lava. Also, within Kilauea's caldera, part of the floor subsided about 90 meters. This activity occurred nearly simultaneously with an eruption from the southwest rift zone of Mauna Loa volcano.

Source:

Macdonald, Gordon A., Abbott, Agatin T., and Peterson, Frank L., 1983 (2nd edition), Volcanoes in the Sea -- The geology of Hawaii: Honolulu, University of Hawaii Press, 517 p.

More Historic Examples

Mount Pinatubo, Philippines

Mount Pinatubo's huge explosive eruption on June 15, 1991, occurred within 11 months of a magnitude 7.8 earthquake that occurred about 100 kilometers northeast of the volcano. Many scientists have since asked, "Was the eruption triggered by, or otherwise related to the earthquake that had occurred on July 16, 1990?" A recent study by scientists of the Philippine Institute of Volcanology and Seismology and the U.S. Geological Survey Study suggests that there was indeed a relationship between the two events.

The study suggests that the "failure stress along faults of the Pinatubo area" after the big earthquake "were probably not a cause of Pinatubo's awakening. However, compressive stress on the magma reservoir and its roots was about 1 bar, possibly enough to squeeze a small volume of basalt into the overlying dacitic reservoir.

Alternately, strong ground shaking associated with the Luzon earthquake might have done the same or triggered movement along previously stressed faults that in turn allowed magma ascent."

Source:

Bautista, B.C., Bautista, L.P., Stein, R.S., Barcelona, E.S., Punongbayan, R.S., Laguerta, E.P., Rasdas, A.R., Ambubuyog, G., and Amin, E.Q., Relationship of Regional and Local Structures to Mount Pinatubo Activity in: Newhall, C.G., Punongbayan, R.S. (eds.) Fire and mud: Eruptions and lahars of Mt. Pinatubo, Philippines, Philippine Institute of Volcanology and Seismology, Quezon City and University of Washington Press, Seattle p. 351- 370.

Restless Calderas

A recent study of the historic activity at calderas from around the world showed that "caldera unrest occurred at least 79 times in close temporal association with regional earthquakes or, in a few instances, with swarms of regional earthquakes. By close temporal association we mean within a time span that is short in relation to the usual recurrence intervals of both the regional earthquakes and the unrest, usually within a few months or less."

"Fifty regional earthquakes (most M 6 and above) were followed within hours to months of unrest at nearby calderas... Twenty seven of these episodes culminated in eruptions, and three others are continuing without eruptions as yet (Rabaul, Wrangell, and Yellowstone)." Rabaul caldera in Papua New Guinea erupted in 1994.

The authors also found that "at least 27 regional earthquakes occurred within 100 kilometers of a restless caldera during or shortly after caldera unrest" and concluded "that magma bodies beneath young calderas often react to changes in regional tectonic strain, and that unrest at calderas is sometimes a general, long-range precursor to regional earthquakes."

Source:

Newhall, Christopher, G., and Dzurisin, Daniel, 1988, Historic Unrest at Large Calderas of the World: U.S. Geological Survey Bulletin 1855, vol 1, p. 19-20.

Karymsky Volcano, Russia

For a recent example, see the May 1996 report on Karymsky Volcano on the Kamchatka Peninsula in Russia from the Smithsonian Institution's Bulletin of the Global Volcanism.

A "continuous" oil accumulation means that the oil resource is dispersed throughout a geologic formation rather than existing as discrete, localized occurrences, such as those in conventional accumulations. The next largest "continuous" oil accumulation in the U.S is in the Austin Chalk of Texas and Louisiana, with an undiscovered estimate of 1.0 billions of barrels of technically recoverable oil.

In 2000, the USGS assessed undiscovered technically recoverable oil and gas in Saudi Arabia at 87 billion barrels (USGS 2000 World Petroleum Assessment: http://energy.cr.usgs.gov/WEcont/regions/reg2/r2saud.pdf). The Energy Information Administration records current proven oil reserves (those expected to be recovered) in Saudi Arabia as 269 billion barrels (http://www.eia.doe.gov/cabs/Saudi_Arabia/Profile.html).

Meanwhile, North America was slowly pulled westward away from the rift zone. The thick continental crust that made up the new east coast collapsed into a series of down-dropped fault blocks that roughly parallel today's coastline. At first, the hot, faulted edge of the continent was high and buoyant relative to the new ocean basin. As the edge of North America moved away from the hot rift zone, it began to cool and subside beneath the new Atlantic Ocean. This once-active divergent plate boundary became the passive, trailing edge of westward moving North America. In plate tectonic terms, the Atlantic Plain is known as a classic example of a passive continental margin.

Sediments eroded from the Appalachian and other inland highlands were carried east and southward by streams and gradually covered the faulted continental margin, burying it under a wedge, thousands of feet thick, of layered sedimentary and volcanic debris. Today most Mesozoic and Cenozoic sedimentary rock layers that lie beneath much of the coastal plain and fringing continental shelf remain nearly horizontal or tilt gently toward the sea.

Excerpt and Graphic from: USGS/NPS Geology in the Parks Website, Atlantic Plain Province, August 2001