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Volcanoes and lava
I will start out with volcanoes then lava. First an example of a composite volcano is Mt. Saint Helens! Our volcano! These volcanoes are many miles wide and several thousand feet high. They consist of layers of solid lava flows mixed with layers of sand- or gravel-like volcanic rock called cinders or volcanic ash.
A cinder cone volcano these volcanoes consist mostly of loose grainy cinders and no lava. They are smaller than the usual composite volcano. A shield volcano is what makes up the islands of Hawaii. The lava is frozen and big craters at the top.
Now onto lava! Low water/low silica is a type of lava that is really runny not like water but more like hot wax or warm honey. When these types of lavas erupt they can flow for long distances before solidifying.
Low water/high silica lava is very "pasty" like soft clay and hardly flow at all ending up with a tall, narrow pile of lava. This type of lava is high in silica, or quartz, and tends to stick together.
High water/low silica lava has low viscosity and bubbles and froths a great deal right at the surface. It produces tiny cinders and larger "bombs" of lava that quickly cool and fall back to the ground. This type of eruption creates a spectacular "fire fountain" at the top. The remaining lava quietly flows away.
The last type of lava is high water/high silica this type of lava is inside the mountain known as Mt. Saint Helens! As the lava oozes to the surface, the gases quickly form bubbles that turn the lava into a red-hot froth that explodes out of the ground. A hot grayish cloud of superheated steam and tiny particles called ash is what makes up the explosion.
Article posted October 15, 2009 at 12:00 AM •
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