http:www.nationalgeographic.comforcesofnature

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http//www.nationalgeographic.com/forcesofnature/
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The Environmental Interactions Section requires
you to display knowledge of the following

• World Distribution of Earthquakes, Volcanoes and
  tropical storms.
• How Earthquakes, Volcanoes and tropical storms
  are formed.
• A case study looking at the damage caused by each
  disaster and the aid received by emergency
  organisations
• Earthquake Mexico City 1985
• Volcano Mt.St Helens 1980
• Tropical Storm Hurricane Mitch 1998

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Where They Happen
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How They Happen
Divergent convergent sliding
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How They Are Recorded
Sensitive seismographs are the principal tool for
studying earthquakes. A seismograph is a simple
pendulum. When the ground shakes, the base and
frame of the instrument move with it, but
intertia keeps the pendulum bob in place. It
will then appear to move, relative to the shaking
ground. As it moves it records the pendulum
displacements as they change with time, tracing
out a record called a seismogram.
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A
B
A is an earthquake of magnitude 5.6. The
magnitude of B is 1.9.
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How They Are Measured

• The Richter Scale, named after Dr. Charles F.
  Richter of the California Institute of
  Technology, is the best known scale for measuring
  the magnitude of earthquakes.
• The scale is logarithmic so that a recording of
  7, for example, indicates a disturbance with
  ground motion 10 times as large as a recording of
  6.
• A quake of magnitude 2 is the smallest quake
  normally felt by people.
• Earthquakes with a Richter value of 6 or more are
  commonly considered major great earthquakes have
  magnitude of 8 or more on the Richter scale.

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Mexico City

• The 1985 Mexico City earthquake was one of the
  most devastating earthquakes in the history of
  the Americas. On Thursday, September 19, 1985, at
  719 AM local time, Mexico City was struck by an
  earthquake of magnitude 8.1 on the Richter scale.
  The epicentre of the earthquake was off the
  Pacific coast of the Mexican state of Michoacán,
  a distance of 350 km, in the Cocos Plate
  subduction zone. It was felt as far away as Los
  Angeles, California.
• As a result of the earthquake, according to
  official government statistics, at least 20,000
  people were killed, 30,000 injured, and 100,000
  left homeless. 416 buildings were destroyed and
  over 3,000 seriously damaged.

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VOLCANOES
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Constructive plate boundaries are found where two
plates are moving apart. The moving semi-liquid
rocks in the mantle are pulling the crust in two
different directions, so that it cracks and
splits.This allows liquid rock from the mantle
(magma) to rise into the crust through the cracks
and reach the surface as a volcanic eruption.
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Destructive plate margins are found where two
plates move together.The surface rock crumple
and crack and are squeezed up into mountains.
At the same time, the heavier plates forces
down into the mantle. Here it melts and the
liquid rock makes its way through the cracks to
the surface, as a volcanic eruption.
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Mount St Helens

• The 1980 eruption of Mount St. Helens was a
  major catastrophic volcanic eruption. An
  earthquake at 832 a.m. on May 18, 1980, caused
  the entire weakened north face to slide away,
  suddenly exposing the partly molten, gas- and
  steam-rich rock in the volcano. The rock
  responded by exploding into a very hot mix of
  pulverized lava and older rock that sped toward
  Spirit Lake so fast that it quickly passed the
  avalanching north face.A volcanic ash column rose
  high into the atmosphere and deposited ash in 11
  U.S. states. At the same time, snow, ice, and
  several entire glaciers on the mountain melted,
  forming a series of large lahars (volcanic
  mudslides) that reached as far as the Columbia
  River
• By the time the ash settled, 57 people and
  thousands of animals were dead, hundreds of
  square miles reduced to wasteland, over a billion
  U.S. dollars in damage had occurred (2.74
  billion in 2007 dollars), and the face of Mount
  St. Helens was scarred with a huge crater on its
  north side

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Stages in the formation of a tropical storm
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Hurricane Mitch

• Hurricane Mitch formed in the western
  Caribbean Sea on October 22 and was one of the
  deadliest and most powerful hurricanes on record
  in the Atlantic basin, with maximum sustained
  winds of 180 mph (290 km/h).
• Deaths due to catastrophic flooding made it
  the second deadliest Atlantic hurricane in
  history nearly 11,000 people were killed with
  over 8,000 left missing by the end of 1998. The
  flooding caused extreme damage, estimated at over
  5 billion.

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Hundreds of weather stations on land and at sea
record the weather as the hurricane approaches
and passes over, giving information on its
wind-speed, wind direction, temperature and
pressure.
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Radiosonde Balloons are sent into the hurricane
carrying weather instruments and they send back
information on temperature, pressure and
humidity.
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Radar is used to find out where the rain is
falling and its intensity.
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Satellites take photographs of the hurricane so
that its speed and direction can be tracked.
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Specially-designed aircraft fly into hurricanes
and record wind-speed, wind direction and
temperature.
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Computers in the National Hurricane Centre in
Miami, USA process all this data and, based on
how previous hurricanes have behaved (stored in
their memory), they predict the hurricane's
speed, strength and direction over the next few
days.