Earth's Systems and Resources - Environmental Science - page 10

Source: U.S. Geological Survey
Earthquakes
At times, pressure builds up at plate boundaries because of friction from plate movement, and stress is created.
When this stress is ultimately discharged, energy is released throughout the Earth's crust, causing vibrations, or
earthquakes. Often, earthquakes are caused by movement of the lithospheric plates and occur at plate bounda-
ries. The focus of an earthquake is the location at which the earthquake originates within the Earth. Above the
focus is the epicenter, which is the first place on the Earth's surface affected by the earthquake.
The types of faults from which earthquakes can occur include strike-slip, normal, and reverse. Strike-slip
faults occur where the plates slide past one another horizontally. Normal faults are caused by tension from a
pulling-apart motion. Reverse faults are caused from compression.
Earthquakes themselves do not generally kill people, but their effects on human-built structures do. Because an
earthquake is a vibration of the Earth caused by a sudden release of energy, this movement transfers into build-
ings, roadways, and other infrastructures. The consequences of structural failure in constructed facilities ulti-
mately cause harm. Tsunamis are seismic sea waves generated from undersea earthquakes or volcanic erup-
tions and are an exception to this statement, though. They are not dangerous while traveling through the ocean,
but they can cause massive destruction once they reach a coastline, which can be thousands of miles from the
location of the earthquake or volcano.
Volcanoes
Volcanoes are openings in the Earth's surface that allow magma, gases, ash, cinder, and other volcanic material
to escape from the mantle. A volcano's structure includes a magma chamber, which contains a pool of magma
deep within the earth; a pipe (conduit) that brings lava, gases, and other materials from the magma chamber to
the surface; and a vent, which is the opening through which lava and other material escapes. Some volcanoes
also have a crater, or depression, at the mouth,
Because of the ever-changing interior of the Earth, volcanoes have various stages and remain active for a peri-
od of time. An active volcano is either presently erupting or will eventually erupt because of a large amount of
seismic and thermal activity occurring within it. A dormant volcano is inactive but could potentially erupt
again. An extinct volcano is not erupting and most likely will never erupt again.
Types of volcanoes
Three main types of volcanoes have been identified:
• Shield volcanoes are large with broad sides, gradual slopes, and usually a crater at the top. They typically
erupt slowly, with lava oozing from the vent or multiple vents. Examples include Mauna Loa in Hawaii,
Mount Wrangell in Alaska, and Skjaldbreiður in Iceland.
• Composite volcanoes (strato volcanoes) are tall, symmetrical, and steep. They're built of alternating lay-
ers of ash, lava, and cinders. Examples include Mount Hood in Oregon, Mount Lassen and Mount Shasta
in California, Mount Fuji in Japan, Arenal in Costa Rica, Mount Cotopaxi in Ecuador, Mount Etna in
Italy, and Mount Rainier and Mount St. Helens in Washington. Eruptions of composite volcanoes can be
either explosive or lava extruding; therefore, predicting the type of eruption and its severity is difficult.
• Cinder cone volcanoes are usually made of lava that erupts in the form of cinders, which are blown into
the air and then settle around the opening of the volcano, ultimately forming a small, steep-sided moun-