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In 1980, what is known as an andesitic volcano in the Coast Ranges of North America named Mount Saint Helens, erupted in a white hot blast of gas and ash that quickly engulfed and destroyed everything in its path. Across the Pacific Ocean on Hawaii a different type of volcano throws up a runny type of lava in a display of wildly beautiful fiery fountains. These gentle giants are known as basaltic volcanoes and are regarded as tourist attractions.

Volcanoes are formed when two of earth's plates collide creating a curved chain of islands. Since the ocean floor is constantly renewing, hot materials well up along lines of weakness from the earth's interior. These materials solidify to form a panel or plate that moves away and is destroyed in other regions. This is known as the study of plate tectonics. Some plates collide creating land masses and mountains. Volcanic mountains tend to form along plate margins in response to the movement between two plates. They occur in areas where the movement of the earth is bringing hot materials to the surface due to weakness produced by folding or faults of a block mountain. As they erupt that lava and ash is thrown out of the volcano increasing the height of the mountain. These weakened areas are called hot spots and are known to be areas where the activity in the earths mantle is strong.

Basaltic type volcanoes spew lava that hardens into a fine grained rock know as basalt. They erupt quietly, sending out large volumes of black runny lava that usually covers a large area. Most of these volcanoes are located at the bottom of the sea. When the lava produces an oceanic ridge which rises above sea level, a broad island is formed made entirely of basaltic or shield volcanoes. These produce a flat lava flow that can flow for many miles and build up a shield like volcano on the thick masses produced by earlier lava flows.

The andesitic volcano is quite different from the basaltic volcano. It produces a much thicker, stiffer lava and forms steep sided volcanoes. Because the lava is thicker, it solidifies much faster sometimes blocking a volcanic vent. Pressure builds behind the blocked vent until a violent explosion blasts away the block. This blast usually takes part of the mountain with it, as was the case with Mount Saint Helen's. The lava from andesitic volcanoes is made of plate materials melted by the friction of one plate being crunched beneath another. It contains more of the silica chemical for this reason. Silica is what makes gray or brown andesitic lava harder to melt and thicker.