Earth Science: Origins and Geology – Volcanoes
The active life of the inner Earth is brought to the surface and made apparent by volcanoes and thermal springs. Volcanic activity affects the global climate and can pose great dangers to the nearby population. However, volcanoes are also an important source of soil nutrients, and thermal springs have long been prized for their therapeutic qualities.
Anatomy of Volcanoes
Volcanoes have existed ever since Earth’s beginning 4.5 billion years ago. Although volcanic eruptions are destructive to the animal and plant world, lava and volcanic ash also add enriching minerals to the soil.
Volcanoes are fed by unseen magma chambers: pockets of molten rock that lie about half a mile beneath Earth’s crust. If a chamber’s pressure exceeds a certain threshold, its agma begins to rise through fissures and cracks, ultimately forming a volcanic vent. The magma may remain underground, or the vent may open at the surface, either above ground or through the ocean floor, spilling magma out of the crust as lava.
This rising of molten rock to the surface is known as volcanism, and the solidification of magma under Earth is called subvolcanism. There are several different types of volcanos. Linear volcanoes (also called volcano cones or cinder cones) eject lava through linear shafts. In central volcanoes, lava flows from a central, tubelike vent. The lava flows of shield volcanoes are viscous, but those of stratovolcanoes, or composite cones, are less so.
Magma
The composition of molten rock, or magma, determines the type of each volcano’s eruption. Magma with silica (SiO2) levels greater than 66 percent is called acid magma while basic magma is about 52 percent silica. Magma releases gases as it rises, which decreases its pressure—acting in much the way car- bon dioxide does when a soda bottle is opened. The higher the magma rises, the greater the amount of degasification that occurs.
The enormous pressure exerted by the gas released from the magma forces the magma up the volcanic vent, blasting it out onto the Earth’s surface in the form of a volcanic eruption. Because acid magma’s viscosity keeps it from escaping as easily as basic magma does, eruptions of acidic volcanoes—when they do occur—are the most explosive.
SUPER VOLCANO
Approximately 5 miles (8 km) beneath Yellowstone National Park in the United States lies a 37 mile (60 km) long, 25 mile (40 km) wide, and 6 mile (10 km) deep magma chamber that contains about 5,800 cubic miles (24.000 km’) of magma.
If this volcano erupted again, it could cause earthquakes and tsunamis, as well as catastrophic effects on the Earth’s climate.