Tectonics and the Natural Disasters they Cause

Geophysical hazards

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Tectonics and the Natural Disasters they cause
Background Information:
The theory of continental drift originated in 1910 as a result of the discoveries of
Alfred Wegener. It was heavily opposed to at first due to the lack of evidence to
support Wegener's new ideas. After lying dormant for half a century, the theory of
continental drift was reintroduced in the 1960s, due to the recent discovery of the
sea floor. It was then renamed as the theory of plate tectonics. However, it is an
evolving theory, as there is still much yet to be discovered.
The basics about plate tectonics:
According to much research and observation, Earth's surface is divided into 6 large
plates and several small ones. These plates are estimated to be 6 to 10 miles thick,
and are made of the same material as the fluid mantle, with temperature as the only
difference. The temperatures are approximated at 4oC on the upper surface of the
plate and 600oC (near melting point) on the bottom surface.
There are two types of crust, Continental crust and Oceanic crust. As their names
suggest, the former forms the continents upon which we live, and the latter
underlies the oceans. Oceanic crust is heavy, whereas Continental crust is light. This
weight difference is the key to the occurrence of subduction zones.
The movement of Earth's plates, also called its tectonic activity, is the result of
convection currents in Earth's mantle (the semi-molten layer beneath the crust).
There are three major types of tectonic plate activity that cause natural disasters
such as volcanic eruptions, earthquakes, and tsunamis. These three types of
movement cause ridges, transform faults, and trenches.
Spreading centres:
Spreading centres are responsible for the formation of ridges, and are constructive
margins. They occur when plates move away from each other. The gap created by
this movement is then filled with the liquid material from the mantle, located
underneath the plate. The mantle's matter is liquid due to the extremely elevated
temperatures (600oC and over). This matter gradual cools and solidifies to solid rock
as it reaches the sea floor. Spreading centres have formed many underwater
mountain ranges.

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Transform faults:
Transform faults are a result of two plates moving alongside each other in opposite
directions at their boundaries. This creates a conservative margin. A brilliant
example of a transform fault is the San Andreas Fault of California, USA.
Subduction zones:
Subduction zones are the third and final main type of tectonic plate activity, and
create what is known as a trench. They produce destructive margins. A subduction
zone is formed where an oceanic plate and a continental plate are moving towards
each other.…read more

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Earthquakes:
The most violent earthquakes
occur at collision margins,
by means of the rapid
collision of two continental
plates.
At destructive margins also
earthquakes happen due to
the friction between the two
plates in a subduction zone.
Conservative margins such as the San Andreas Fault in California also cause
earthquakes. This is because there is a huge amount of friction caused by the rubbing
of the two tectonic plates that are moving in opposite directions.
Tsunamis:
Tsunamis are not the direct result of tectonic
activity.…read more

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Christchurch, New Zealand
earthquake:
The earthquake that struck New Zealand
on 22nd of February 2011 has been
described as "the country's deadliest
natural disaster in 80 years." Christchurch
is one of New Zealand's largest cities.
Boxing Day Tsunami:
As its name suggests, the Boxing Day Tsunami happened on the 26th December
2004. The word `tsunami' comes from the Japanese meaning 'harbour wave.' In this
particular instance, the huge wave that was caused by a strong earthquake left a trail
of destruction.…read more

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