Frequently Asked Questions

Natural Hazards

The USGS monitors and conducts research on a wide range of natural hazards to help decision-makers prepare for and respond to hazard events that threaten life and property.

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Population Exposed to Potentially Damaging Earthquake Groundshaking
The duration of an earthquake is related to its magnitude but not in a perfectly strict sense. There are two ways to think about the duration of an earthquake. The first is the length of time it takes for the fault to rupture and the second is the length of time shaking is felt at any given point (e.g. when someone says "I felt it shake for 10...
Photo of scientist sitting at a computer with seismograms on the wall behind him.
When an earthquake occurs, one of the first questions is "where was it?" The location may tell us what fault it was on and where damage (if any) most likely occurred. Unfortunately, Earth is not transparent and we can't just see or photograph the earthquake disturbance like meteorologists can photograph clouds. When an earthquake occurs, it...
Devastation of 1906 San Francisco Earthquake
For earthquakes that occurred between about 1890 (when modern seismographs came into use) and 1935 when Charles Richter developed the magnitude scale, people went back to the old records and compared the seismograms from those days with similar records for later earthquakes. For earthquakes prior to about 1890, magnitudes have been estimated by...
USGS Forecast for Ground Shaking Intensity from Natural and Induced Earthquakes in 2017
Magnitude scales, like the moment magnitude, measure the size of the earthquake at its source. An earthquake has one magnitude. The magnitude do not depend on where the measurement is made. Often, several slightly different magnitudes are reported for an earthquake. This happens because the relation between the seismic measurements and the...
Volcano erupting and spewing a huge cloud of rock and ash into the sky.
The largest subaerial (on land) landslide in Earth's recorded history was connected with the 1980 eruption of Mount St. Helens volcano in Washington state, USA. That landslide had a volume of 2.8 cubic kilometers (0.67 cubic miles) of material and the landslide traveled about 22.5 kilometers (14 miles) down the North Fork Toutle River. Average...
Cumulative number of earthquakes with a magnitude of 3.0 or larger in the central and eastern United States, 1973-2014
Earthquake size, as measured by the Richter Scale is a well known, but not well understood, concept. The idea of a logarithmic earthquake magnitude scale was first developed by Charles Richter in the 1930's for measuring the size of earthquakes occurring in southern California using relatively high-frequency data from nearby seismograph stations....
Image: Installing Antenna and Solar Panel for Seismic Station
Earthquakes are recorded by a seismographic network. Each seismic station in the network measures the movement of the ground at that site. The slip of one block of rock over another in an earthquake releases energy that makes the ground vibrate. That vibration pushes the adjoining piece of ground and causes it to vibrate, and thus the energy...
Aerial view of the caldera of Mt Tambora, island of Sumbawa, Indonesia.
The term "supervolcano" implies a volcanic center that has had an eruption of magnitude 8 on the Volcano Explosivity Index (VEI), meaning that at one point in time it erupted more than 1,000 cubic kilometers (240 cubic miles) of material. In the early 2000s, the term “supereruption” began being used as a catchy way to describe VEI 8 eruptions....
Buffalo at Yellowstone National Park
Almost all earthquakes at Yellowstone are brittle-failure events caused when rocks break due to crustal stresses. Though we've been looking at Yellowstone for years, no one has yet identified "long-period (LP) events" commonly attributed to magma movement. If LP events are observed, that will NOT mean Yellowstone is getting ready to erupt. LP...
Image: The Grand Canyon of the Yellowstone by Lucien Powell
Contrary to popular belief, Yellowstone was not named for the abundant rhyolite lavas in the Grand Canyon of Yellowstone that have been chemically altered by reactions with steam and hot water to create vivid yellow and pink colors. Instead, the name was attributed as early as 1805 to Native Americans who were referring to yellow sandstones along...
Image: Active Lava Flow
The most recent volcanic activity at Yellowstone consisted of rhyolitic lava flows that erupted approximately 70,000 years ago. The largest of these flows formed the Pitchstone Plateau in southwestern Yellowstone National Park. Learn more: Yellowstone Eruption History The evolution of the Yellowstone Plateau Volcani Field: Past, present, and...
Image: Footprints in Ash from 1790 Kilauea Volcano Eruption
If another large, caldera-forming eruption were to occur at Yellowstone, its effects would be worldwide. Such a giant eruption would have regional effects such as falling ash and short-term (years to decades) changes to global climate. Those parts of the surrounding states of Montana, Idaho, and Wyoming that are closest to Yellowstone would be...