Download Earthquake Causes Tsunami

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At nearly seven miles below the surface of the ocean, the bottom of the Marianas
Trench in the Pacific Ocean is the deepest place on Earth. By comparison, the top
of the highest mountain on land, Mount Everest, is about five and half miles
above sea level.
The Alps, the Himalayas and the Andes are all thought to have formed as a result
of one plate crashing into another.
The December 26 tsunamis of 2004 caused massive loss of life in countries
bordering the Indian Ocean. These enormous waves were caused by an
earthquake in a region where the Australian and Eurasian plates are colliding, off
the coast of Indonesia.
Hot links
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More on how mountains form as a result of plate collision, from Okanagan
University College
A description of how the Cascade Mountains of the U.S. are still forming as a
result of collision between the North American plate and various oceanic plates,
from the U.S. Geological Survey
From the U.S. Geological Survey: more on earthquakes and tsunamis
Plates Colliding
What happens when tectonic plates move towards each other: subduction, trenches and
mountain building.
Huge trenches
When tectonic plates with different densities collide, the denser plate sinks beneath the
other: a process known as subduction. This happens, for example, when a plate carrying a
continent (less dense) rides over an oceanic plate (more dense). The boundary between
the two plates forms a trench that can be several miles deep and tens of miles wide.
Because plates are so huge, a single trench can be thousands of miles long. All the
trenches on Earth are found in oceans.
Mountain building
Immense forces are involved when plates collide.
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As the lower plate melts is pushed down into the mantle and heats up, water and
other volatile chemicals are released from it, causing parts of the overlying mantle
to melt. Some of the resulting melt rises up through the crust, forming a chain of
volcanoes (often these are referred to as island arcs).
One plate or both can become crumpled on an immense scale (think of a rug
crumpling when it is moved up against a wall), leading to the formation of
mountain ranges. This has happened as the Indian Plate crashed into the Eurasian
plate: the Himalaya mountain range is the result. Here, there is no trench; both
plates were carrying continents in the zone of collision. Even today, the Greater
Himalaya mountain range, including Mount Everest, is rising at about 5 mm per
year as the Indian plate moves northward under Tibet at about 18 mm (three
quarters of an inch) per year.
Earthquake zones
The world's strongest earthquakes, as well as the deepest, have been recorded from zones
of plate collision. Such earthquakes occur along the western coasts of the U.S. and
Canada, where the North American plate is riding over several smaller plates.
Earthquakes in the ocean floor can cause huge waves, or tsunamis, which can be
devastating when they wash onto nearby land.
When the hot
Lava or Magma touches water, the water is boiled into steam.
This steam rises and can be seen as an eruption of air out of the
ocean. As the Magma cools, it hardens forming new \"ground\".
If the flow of magma continues and there is enough formation to
break the surface of the ocean, a new island is formed. (see
Hawaiian Islands)
If the eruption is great enough, there could be a significant increase in global temperature
caused by the steam and raising water temperature in the area. All volcanic eruptions
have an effect on global temperature. Mt St Helens increased the planet by 1.5 degrees,
now imagine an eruption like that under water? Steam Baked! When the hot LaWhat
causes a tsunami?... A tsunami is a large ocean wave that is caused by sudden motion on the ocean floor.
This sudden motion could be an earthquake, a powerful volcanic eruption, or an underwater landslide. The
impact of a large meteorite could also cause a tsunami. Tsunamis travel across the open ocean at great
speeds and build into large deadly waves in the shallow water of a shoreline.
Subduction Zones are Potential Tsunami Locations
Most tsunamis are caused by earthquakes generated in a subduction zone, an area where an oceanic plate
is being forced down into the mantle by plate tectonic forces. The friction between the subducting plate and
the overriding plate is enormous. This friction prevents a slow and steady rate of subduction and instead the
two plates become "stuck".
Image by USGS
Accumulated Seismic Energy
As the stuck plate continues to descend into the mantle the motion causes a slow distortion of the overriding
plage. The result is an accumulation of energy very similar to the energy stored in a compressed spring.
Energy can accumulate in the overriding plate over a long period of time - decades or even centuries.
Image by USGS
Earthquake Causes Tsunami
Energy accumulates in the overriding plate until it exceeds the frictional forces between the two stuck plates.
When this happens, the overriding plate snaps back into an unrestrained position. This sudden motion is the
cause of the tsunami - because it gives an enormous shove to the overlying water. At the same time, inland
areas of the overriding plate are suddenly lowered.
Image by USGS
Tsunami Races Away From the Epicenter
The moving wave begins travelling out from where the earthquake has occurred. Some of the water travels
out and across the ocean basin, and, at the same time, water rushes landward to flood the recently lowered
shoreline.
Image by USGS
va or Magma touches water, the water is boiled into steam. This
steam rises and can be seen as an eruption of air out of the
ocean. As the Magma cools, it hardens forming new \"ground\".
If the flow of magma continues and there is enough formation to
break the
surface of
the ocean, a
new island
is formed.
(see
Hawaiian
Islands)
If the eruption is
great enough,
there could be a
significant
increase in global
temperature caused by the steam and raising water temperature in the area. All volcanic
eruptions have an effect on global temperature. Mt St Helens increased the planet by 1.5
degrees, now imagine an eruption like that under water? Steam Baked!
under the ocean floor. This earthquake pushes a large volume of water to the surface, creating
proach the coast these waves get bigger and more dangerous. Tsunami waves can cause tremendous
n, landslide, or other movements of the Earth’s surface.
The earth's outer layer or crust is broken into pieces called tectonic plates which are constantly moving
towards, away from or past each other. Because continents are part of these plates, they also move. An
earthquake occurs when the rocks break and move as a result of stresses caused by plate movements.
Most earthquakes occur on the edge of plates, especially where one plate is forced under another such as
happens off Sumatra or past another as occurs in California. Some regions have more earthquakes than
others with 80% of all recorded earthquakes taking place around the edge of the Pacific Plate, in New
Zealand, Papua New Guinea, Japan, Canada, USA and South America.
Interesting Fact
Earthquake vibrations travel very fast, up to 14 kilometres per second. The fastest seismic waves take less
than 20 minutes to reach the other side of the earth, a distance of almost 13,000 kilometres!
The epicentre is the point on the Earth's surface directly above the source of the earthquake. The source,
also known as the focus, can be as deep as 700 kilometres. Smaller earthquakes occur much more
frequently than large ones and most cause little or no damage. A very large earthquake can be followed by a
series of smaller events called aftershocks during a period of adjustment which may last for several months.
Earthquakes also can cause a tsunami, or a series of waves which can cross an ocean and cause extensive
damage to coastal regions. In areas where there are steep slopes, vibrations resulting from earthquakes
may cause landslides.