Volcanoes are vents in the Earth's crust. From this vent ashes, molten rock, and gas erupt. Most volcanoes are formed near the tectonic plate boundaries. These are formed when the ocean floor is moved into the mantle of the earth, which is
the rocky layer beneath the earth’s crust. At this time the accumulated rock form volcanic cones. During this process blocks of rocks push and pull past one another causing friction that once released melts rocks and produces hot magma. When this magma rises to the surface volcanic eruptions occur. Volcanoes can occur in three major types. These types are cinder cone, shield, and composite. (Southwestern Advantage, 2011) Cinder cone volcanoes are created from explosive eruptions. During this type of volcano much of the rock lands near the vent of the volcano during the eruption, this builds the cone up to the shape of a peak. These volcanoes do not typically have long life spans because the gas that is released is released at a much quicker rate. Shield volcanoes are formed more in the shape of a flattened dome. During this type of volcano the lava is typically water-like in texture and therefore spreads farther and wider. Composite volcanoes are formed from a combination of fragments from cinder cone eruptions and shield eruptions. This volcano is the steepest in stature. The composite volcano is formed over long periods of time and therefore and grow quite tall in height. The composite volcanoes also tend to erupt quite explosively and can pose extreme danger to both life and property. |
Mt. Fuji in Japan is an example of a composite volcano. This volcano formed as a result of the Asian and the Pacific plates colliding with each other as a result of Plate Tectonics.
(Southwestern Advantage, 2011) Mt. St. Helens in Washington State is yet another known volcano that still stands today. This volcano is known as a composite volcano as well. One of the most known eruptions of Mt. St. Helens occurred on March 27, 1980. After several of days of earthquake activities that shook away much of the land around the volcano, the volcanic core and extreme heat was exposed to the atmosphere and in turn began to violently erupt and explode for approximately 10 hours. During this eruption it was said that around 60 people lost their lives. One of these deaths was a volcanologist by the name of David Johnston.(pictured above) Johnston had been sitting at the feet of Mt. St. Helens hours before her eruption. Unfortunately the rapid explosion took Johnston’s life. (Southwestern Advantage, 2011) http://sthelenshero.homestead.com/DavidJohnston.html |