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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Chart showing the Earth’s magnetic feild
Almost certainly not. Since the invention of the magnetometer in the 1830s, the average intensity of the magnetic field at the Earth's surface has decreased by about ten percent. We know from paleomagnetic records that the intensity of the magnetic field decreases by as much as ninety percent at the Earth's surface during a reversal. But those...
Earth-inter and outer core
The Earth's outer core is in a state of turbulent convection as the result of radioactive heating and chemical differentiation. This sets up a process that is a bit like a naturally occurring electrical generator, where the convective kinetic energy is converted to electrical and magnetic energy. Basically, the motion of the electrically...
Image: College Geomagnetic Observatory
In a sense, yes. The Earth is composed of layers having different chemical compositions and different physical properties. The crust of the Earth has some permanent magnetization, and the Earth’s core generates its own magnetic field, sustaining the main part of the field we measure at the surface. So we could say that the Earth is, therefore, a "...
Migratory flights simulated by the IBM
Yes. There is evidence that some animals, like sea turtles and salmon, have the ability to sense the Earth's magnetic field (although probably not consciously) and to use this sense for navigation.
Image: Trilobite Fossil (Phacops rana africana)
No. There is no evidence of a correlation between mass extinctions and magnetic pole reversals. Earth’s magnetic field and its atmosphere protect us from solar radiation. It’s not clear whether a weak magnetic field during a polarity transition would allow enough solar radiation to reach the Earth's surface that it would cause extinctions. But...
Large waves crashing on rocks at beach.
Although both are sea waves, a tsunami and a tidal wave are two different and unrelated phenomena. A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon, and Earth ("tidal wave" was used in earlier times to describe what we now call a tsunami.) A tsunami is an ocean wave triggered by large earthquakes...
A home, severely damaged by the tsunami that hit Sumatra on December 26, 2004, sits atop debris.
Although earthquake magnitude is one factor that affects tsunami generation, there are other important factors to consider. The earthquake must be a shallow marine event that displaces the seafloor. Thrust earthquakes (as opposed to strike slip) are far more likely to generate tsunamis, but small tsunamis have occurred in a few cases from large (i...
Image: Tsunami Carried Boat
Tsunamis are ocean waves triggered by: Large earthquakes that occur near or under the ocean Volcanic eruptions Submarine landslides Onshore landslides in which large volumes of debris fall into the water  Scientists do not use the term "tidal wave" because these waves are not caused by tides. Tsunami waves are unlike typical ocean waves generated...
Tsunami Evacuation Route
NOAA (National Oceanic and Atmospheric Administration) maintains the U.S. Tsunami Warning Centers, which work in conjunction with USGS seismic networks to help determine when and where to issue tsunami warnings. If an earthquake meets certain criteria for potentially generating a tsunami, the pop-up window and the event page for that earthquake on...
Tsunami-evacuation sign in the city of Nehalem, Oregon
Large tsunamis have occurred in the United States and will undoubtedly occur again. Significant earthquakes around the Pacific rim have generated tsunamis that struck Hawaii, Alaska, and the U.S. west coast. One of the largest and most devastating tsunamis that Hawaii has experienced was in 1946 from an earthquake along the Aleutian subduction...
Color graphic showing lava flow hazard zones
Lava-flow hazard zones on Hawai'i Island reflect the long-term hazard of lava flows, not the short term hazard. Rate of lava coverage—not how recently lava covered an area—is the basis of long-term lava flow hazard. Zone 1: "Includes the summits and rift zones of Kīlauea and Mauna Loa (left) where vents have been repeatedly active in historic time...
Mauna Loa 1984 eruption with lava flow
An option is to contact the State of Hawaii Department of Commerce and Consumer Affairs. The USGS Lava-Flow Hazard Zone Map is meant to convey relative volcanic hazard rather than risk. A volcanic hazard is a destructive event that can occur in a given area or location, such as a lava flow or a volcanic earthquake, along with the probability of...