You’ve probably heard in the news about volcanic eruptions, or you might remember when Mount St. Helens erupted in 1980.
(Volcanoes can alter the landscape of a town, county, even country!)
Perhaps you’ve even seen an active volcano. Although they are often a destructive force, volcanoes are an amazing facet of creation. They come in a variety of shapes, sizes, and eruption types.
Volcanoes erupt when magma, red-hot liquid rock, seeps up through a vent in the earth.
More violent eruptions occur when pyroclastic material – a mixture of magma, rocks, ash, and hot gases – is exploded upward by pressure caused by underground gases and magma.
When magma flows above the surface of the earth, it is called lava. Usually lava changes from bright red to duller red, gray, or black as air causes it to cool and solidify.
Volcanic eruptions vary in size and display. There are six common types of eruptions, with differing features:
There are also different shapes and sizes of volcanoes.
Stratovolcanos are usually very high, with pointy tops. They are formed by repeated explosions, usually Plinian, and by slow-moving lava. Eruptions from these volcanoes are usually very large but occur infrequently.
Mount Vesuvius, which buried the Roman city of Pompeii in 79 AD (creating an instant fossil record) is a stratovolcano.
Shield-type volcanoes are usually spread out over a large area and have gently sloping sides. They are caused by minor explosions (usually Hawaiian) and erupt more frequently than stratovolcanoes. Most of the major volcanoes in Hawaii are shield volcanoes.
Scoria Cones are the most common volcano type, usually caused by Strombolian eruptions. They are shaped like upside-down cones, with slightly squished tops. Scoria cones usually erupt only once.