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Himalayas
Niall, Vineet, Delvin
Introduction
• Himalayas formed around 20-40 million years ago.
Prior to the Eurasian and Indo-Australian plate colliding
they were separated by the Tethys Sea. When the IndoAustralian plate collided with the Eurasian plate, the
light sediments from the seabed were forced up,
forming the Himalayan mountain range.
• Every 100 years India moves 200 cm north against the
Asian plate. This colliding force builds up pressure
continually for several years and this pressure is
released in the form of earthquakes from time to time.
• Collision Plate Boundary:
In this case:
The Indian Plate is colliding head-on
with the Eurasian Plate. Both plates
are comprised of continental
lithospheric crust, so there is no
appreciable distinction in density. Both
have a density of approximately 2.7
g/cm³. This as opposed to ocean crust
with a mean density of 3.3 g/cm³. The
plates try to compete in the plate-toplate collision but the equal densities
of the two plates cannot push one
under the other very deep like that in a
subduction zone. The result is largescale thickening of the continental
crust in the region at and surrounding
the collision boundary.
There are tremendous temperatures
attained at a continental plate-to-plate
collision boundary. However, the crust
is simply too thick, and too “squashed
together” to allow anything to squeeze
up and break through to the surface as
volcanic eruptions.
What are the processes involved?
• The process begins as two continents (different bits of continental
crust), separated across a tract of ocean (and oceanic crust),
approach each other, while the oceanic crust is slowly consumed at
a subduction zone. The subduction zone runs along the edge of one
of the continents and dips under it, raising volcanic mountain chains
at some distance behind it. Continental crust is subducted with
difficulty, but is subducted to depths of 90-150 km or more. Normal
subduction continues as long as the ocean exists, but the
subduction system is disrupted as the continent carried by the
down going plate enters the trench. Because it contains thick
continental crust, this lithosphere is less dense than the underlying
asthenospheric mantle and normal subduction is disrupted. The
volcanic arc on the upper plate is slowly extinguished. Resisting
subduction, the crust buckles up and under, raising mountains
where a trench used to be.
What patterns of hazards are
produced?
• Four major earthquakes have occurred in the
Himalayan region in the past 100 years. The
famous earthquake that hit Nepal in 1933 A.D.
killed thousands of people in Nepal and
northern India. Several earthquakes have
occurred since that time.
• The Indian Himalayas have experienced some significantly strong
earthquakes in the last few decades.
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Kinnaur Earthquake (1975)
This earthquake struck in the early afternoon of January 19, 1975. It caused havoc
in parts of the Kinnaur, Lahaul and Spiti regions of India. It is believed to have been
caused by movements along a fault known as the Kaurik fault. This quake killed
hundreds of people and caused severe damage to property. A massive landslide
was triggered off by this earthquake near Maling in the Spiti Valley. Another giant
landslide blocked the Paro chu River near Sumdo. Many smaller occurrences of
slope failure were caused by this earthquake. As a result, communications
remained disrupted for several days and helicopter services had to be pressed into
operation to bring relief to the worst-affected areas.
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Uttarkashi Earthquake (1991)
In the early morning hours of October 14, 1991, a severe earthquake shook
Uttarkashi and Chamoli districts of Garhwal. It caused widespread loss of life and
property. This earthquake also affected other parts of Garhwal and Kinnaur. The
regions remained cut off from the rest of the world for several days due to the
debris. Landslides occurred at several locations, and it took a significant amount of
time for people to recover from this incident.
From this data, not only do we see a pattern that only Earthquakes can and have
occurred at this plate boundary, but there are patterns within the impacts. The same
secondary impacts arise such as landslide and property damage.
The time period between each Earthquake is very hard to predict as it ranges from
every 5-20 years there is an Earthquake.
• Until recently it was believed that four magnitude 8
earthquakes had occurred in the past 100 years. The first of
these events (1897) is now known not to have occurred in
the Himalaya but beneath Shillong, the second (1905) has
been recalculated to have been smaller (M=7.8) and were it
to recur today would do so in a M=7.5 earthquake.
• The number of great earthquakes known in the past several
centuries appears inadequate to accommodate the 16-18
mm/year of Himalayan convergence observed.
• We conclude that several M>8 earthquakes may be
overdue. Due to increased populations and urbanization in
the Ganges plain, the death toll from any one of these
earthquakes could now exceed 1 million.
What Impacts have there been?
• One of the biggest impacts of earthquakes in
the Himalayan regions is deaths. It has
recently been reported, that an estimated
800,000-900,000 people could die if an
earthquake of magnitude 8+ occurs. This is
because the areas near the Himalayas are
extremely populous (Northern India, Pakistan
and Nepal).
2005 Kashmir Earthquake:
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8th October.
Magnitude 7.6
Focus: 26 km deep. Epicentre: 100 km north of Islamabad.
100,000 deaths (18th most of any earthquake).
138,000 injured 3.5 million homeless.
$6-7 billion in damage.
Over $5.4 billion in aid.
US Army and RAF deployed to assist.
5 Crossing points opened between India and Pakistan to
allow humanitarian and medical aid into the most affected
regions.
2001 Gujarat Earthquake:
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January 26th.
7.7 magnitude
20,000 deaths (largest affected areas were only villages!)
167,000 injured. 400,000 homes destroyed (40% of all
homes).
60% of food and water stocks destroyed.
$5.5 billion in damage
8 schools and 2 major hospitals destroyed.
Red Cross, opened up a medical facility due to the
destruction of the hospitals.
Indian Military brought in to find survivors and organise a
clean up.