Volcanic Eruptions
Published on Feb 03, 2016
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In Hawaii there are many myths about Pele, the goddess of volcanoes. According to legend, when Pele is angry, she cause a volcanic eruption. Pele's hair forms when lava sprays out of the ground like water fro, a fountain. When it cools, the lava stretches and hardens into thin strands as shown in the picture.
Beneath a volcano, magma collects in a pocket called the magma chamber. The magma moves upward through a pipe, a long tube in the ground that connects the chamber to Earth's surface. You can see the features in the picture behind.
Molten rock and gas leave the volcano through an opening called a vent. A lava flow is the area covered by lava as it pours out of a vent. A crater is a bowl-shaped area that may form at the top of a volcano around the central vent.
Photo by Konabish ~ Greg Bishop
As magma rises toward the surface, the pressure of the surrounding rock on the magma decreases. The dissolved gases begin to expand, forming bubbles. As pressure falls within the magma, the size of the gas bubbles increases greatly. When an volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out of the vent.
Photo by paul bica
Geologists classify volcanic eruptions as quiet or explosive. A volcano erupts quietly if it's magma is low in silica. ( low silica has low viscosity and flows easily.) quiet eruptions can produce both pahoehoe and aa.
The Hawaiian islands were formed from quiet eruptions.
A volcano erupts explosively if it's magma is high in silica. ( high silica magma has high viscosity, making it thick and sticky.) The trapped gases build up pressure until they explode. That's what happened during the eruption of St. Helens.
A Pyroclastic flow occurs when as explosive eruption hurls out a mixture of hot gases, ash, cinders, and bombs. During a quiet eruption, lava flows from vents, setting fire to and then burying everything in its path. In an explosive volcano, it can belch out hot clouds of deadly gases as well as ash, cinders, and bombs. Eruptions can cause landslides and avalanches.
Photo by gnuckx
Geologists try to determine a volcano's past and whether it will erupt again. Geologists often use the terms active, dormant, or extinct to describe a volcano's stage of activity. An active volcano is one that is erupting or shows signs that it may erupt in the near future. A dormant volcano is like a sleeping bear, scientists expect the dormant volcano to awaken in the future and become active agin. An extinct or dead volcano is unlikely to erupt again.
Photo by inkknife_2000 (2.5 million + views)
Geologists have been more successful with predicting volcanic eruptions than predicting earthquakes. Geologists use tilt meters and other instruments to detect slight changes in elevation and tilt caused by magma moving underground. The upward movement of magma triggers these quakes.
Photo by Mal B
