Earthquakes and Volcanoes
The Earth's crust is constantly moving throughout the world. It moves in some places more often than in other places. The Earth's crust moves when blocks of the earth abruptly slip past one another. This results in an Earthquake. Earthquakes are related to cracks in the crust called faults.
Faults may have formed from an earlier earthquake or while an earthquake is occurring. During an earthquake the crust is in motion on either side or both sides of the fault.
The earthquake vibrations travel through the crust and the farther people are away from the earthquake the harder it is to feel the vibrations. The location below where the earthquake starts is called the hypocenter, and the area directly above it on the surface of the earth it is called the epicenter.
A seismograph is a device that records the motion at locations all around the crust. The size of an earthquake is called its magnitude. There is one magnitude for each earthquake that takes place. The lower the magnitude of an earthquake the less damage is done to a town or city. Large earthquakes can destroy entire towns and cities. Earthquakes in the United States are more likely to occur along the West Coast, but they can also occur in the Midwest and along the East Coast.
An underwater earthquake can cause a tsunami. A tsunami is a large ocean wave which can reach the coastlines and cause major damage and flooding. Earthquakes may also be the cause of some volcanoes to become active and erupt.
A volcano is a rupture on the crust of the Earth that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. The hot molten rock deep below Earth's surface is called magma and it rises upward. If the magma reaches the surface of the Earth it may flow out as lava, or it is hurled out when the volcano erupts. Magma is liquid rock inside the volcano; lava is liquid rock on the outside of the volcano.
Scientists have classified volcanoes into three main categories: active, dormant, and extinct. With an active volcano there is the possibility the volcano will erupt, and most likely recently erupted. A dormant volcano is a volcano is one that has not erupted in a very long time but there is possibility that it may erupt sometime in the future. The third type, the extinct volcano, is one that erupted thousands of years ago and there is no possibility of another eruption.
The Earth is home to approximately 1500 volcanoes which are considered active, and about 100 of those are under the oceans. Many active volcanoes in the United States are found in Hawaii, California, Alaska, Oregon, and Washington. Erupting volcanos have been known to wipe out entire forests, trigger tsunamis, flash floods, earthquakes, mudflows, avalanches, mudslides, and rock falls. However, volcanos that erupt can also create new islands once the hot lava cools off, especially those near the coast or below the ocean's surface.
In summary, an earthquake caused by a fault in the earth's crust, and a volcano, caused by a rupture on the crust of the Earth, are related to each other and both can cause major damage and destruction. An earthquake can also cause a tsunami, which is a giant ocean wave. There are three types of volcanos: active, dormant, and extinct. Earthquakes and volcanos are both considered natural disasters.