Assess the range of hazards caused by explosive volcanic eruptions. (12
marks)
Composite volcanoes (found mainly on convergent plate margins) cause
explosive volcanic eruptions that are violent and damaging - the denser
oceanic plate is subducted and melts in the mantle. They cause a range of
primary and secondary hazards that vary in severity. Primary hazards are
caused directly as a result of the volcanic eruption itself, while secondary
hazards are caused indirectly by the volcanic eruption. I will assess and
evaluate the range in severity of both primary and secondary hazards.
Lava flows are an example of a primary hazard that (in my opinion) has
low severity compared to other. Lava flows are streams of lava that have
erupted onto the Earth’s surface, they have very high temperatures up to
1170o C. Lava from composite volcanoes (that cause violent eruptions) is
acidic lava that is very viscous (thick) so as a result moves very slowly
(approx. 2-3 mph). Because the lava moves slowly, there is sufficient time
for people nearby to move out of the way and make their way to safety
(the average person will walk twice the speed of the lava travelling
towards them, making lava flows a less sever hazard when concerned
about social damages); this makes lava flows less damaging because they
pose no severe threat to human life. This is a localised, short-term impact
of violent volcanic eruptions, people are only impacted if they are very
close to the volcano at the time of the eruption which therefore makes
lava flows less severe because only a small amount of people will be
impacted for a short amount of time. However, lava flows can be
damaging because they will burn and damage anything in their paths;
this will cause economic damage to property and infrastructure. Overall, I
don’t believe lava flows to be the most sever hazard caused by explosive
volcanic eruptions because the impacts are localised to the area of the
volcanic eruption itself.
Lahar’s are secondary hazards that in my opinion have a high severity and
cause large amounts of damage both socially and economically. Lahars
are masses of rock, mud, and water that travel quickly down a volcano.
They are caused when an eruption quickly melts snow and ice. They are a
very sever hazard because they move too quickly for people to outrun,
which causes loss of life (social impact). For example in 1985, 23,000
people died as a result of a lahar on the Nevado del Ruiz volcano in
Columbia - which is the deadliest lahar ever recorded. Lahars are very
damaging socially and economically making them one of the most sever
hazards as a result of volcanic eruptions. Social damages are caused
because it is very difficult to avoid fatalities in lahars as they happen so
suddenly and quickly, consequently there is loss of life and high death toll.
There are also large amounts of economic damage caused because
infrastructure will need to be rebuilt following the destruction caused by
lahars, which will be very costly. The reason lahars are more severe and
damaging than lava flows, is because they produce a much higher death
toll and result in higher social impacts than lava flows.
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