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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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