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Lava Flow and Crystals
Name: Samuel M.
Status: Student
Age: 15
Location: N/A
Country: N/A
Date: March 2001
Question:
HI, is it possible for somebody to explain how the flow
rate of lava is affected by the quantity of crystallized material within it.
Replies:
Lava, by its nature, is molten. It does not become crystalline until it
cools from a liquid to a solid. So, there are theoretically no crystals in
lava.
However, there are two types of lava, wet and dry. When lava is
underground, it is referred to as magma. For volcanos that occur on the
edge of a tectonic plate, such as on the west coasts of North and South
America, the continental plates are overriding the oceanic plates. As the
ocean floor is subducted under the continental plate, a substantial portion
of seawater is carried with it. Eventually, the oceanic plate is pressed so
far below the surface that the rock and seawater become heated enough to
melt and turn into magma.
While this magma is enormously hot, because it is also under extreme
pressure, it remains liquid. It then begins rising towards the surface,
slowly creating mountain ranges. When this type of magma does eventually
reach the surface and erupt, the hot water and other gases almost
immediately convert from a liquid to superheated steam. This creates a
catastrophic explosion of poisonous gases and ash. When the steam condenses
into water, great floods of mud roar away from the eruption, creating more
destruction. Examples of this type of eruption are Pompeii, Krakatoa, and
Mount St. Helens.
Dry eruptions typically occur in mid-plate volcanos. Examples of this type
of volcano are in Hawaii. Because the lava comes through weak spots in the
plate, it does not contain the large amount of water the wet lava contains.
Consequently, the lava is the stereotypical glowing red liquid that rolls
slowly downhill without the explosive effects of a wet eruption. While
still destructive and hazardous, these types of volcanos are far less
dangerous than the other type.
For more information, almost any basic geology textbook will have more
information on this topic.
Andrew Johnson
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Update: June 2012
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