They release enormous amounts of energy and create eruption columns of gas and ash that can rise up to 50 km (35 miles) high at speeds of hundreds of meters per second. Ash from an eruption column can drift or be blown hundreds or thousands of miles away from the volcano. Creating such hazard as occurred at Mount St. Helens in 1980. which produced falls of ash, scoria and lava bombs miles from the volcano, and pyroclastic density currents that razed forests, striped soil from the bedrock and obliterated anything in its paths. These type of eruptions are known as Plinian and are hard to predict as they are
Due to high temperatures in the mantle of around 3000 degrees centigrade, this oceanic crusts melts and then rises due to the convection currents in the aesthenosphere . As it joins with trapped seawater and sediment, it melts the overlying continental crust, and the magma plumes rise to the surface. They contain more silica so are more viscous, which plugs up the volcano, meaning pressure build up. This is why these volcanoes are so explosive. Another type of plate boundary are constructive, which is the margin between two diverging plates where new magma
The oldest ash deposits were erupted at least 40,000 years ago onto an eroded surface that's still older volcanic and sedimentary rocks. Intermittent volcanism continued after the glaciers disappeared, and nine main pulses of pre-1980 volcanic activity have been recognized. Two months before the big explosion there was a 4.1 magnitude earthquake that hit underneath Mount Saint Helens, then seven days after that a 250 foot hole was in the mountain and released a plume of ash. The entire area was evacuated. Then on May 18, 1980 it happened, 57 people were killed, over 7,000 animals were killed as well.
They can cause widespread destruction, such as the 1980 eruption of Mt St Helens. Lahars are a secondary effect of a volcanic eruption and are cement-like mudflows consisting of volcanic ash and water. They often occur in the days following an eruption when people are at their most vulnerable and with the capacity to travel up
Compare and evaluate two contrasting eruptions and evaluate how damaging they were. I am going to compare the Eyjafjallajokull eruption of 2010 and the Chaiten eruption of 2008. Both eruptions were damaging in different ways: The town of Chaiten is in Chile, an LEDC, and the Chaiten volcano had not erupted for 9500 years prior to May 2, 2008. Chaiten is part of the longest chain of Fold Mountains in the world, the Andes Mountains, and sits above the Peru-Chile subduction zone. In this convergent boundary, the denser Nazca Plate is being subducted beneath the less dense continental lithosphere of the South American tectonic plate.
The mountain grows from three to five millimeters each year. The upper portion of the mountain is made up of volcanic and sedimentary deposits of what once was one or more island arcs of the Pacific Plate dating back to the Jurassic and Cretaceous periods, between 90 and 190 million years ago. During this time, the Pacific Plate was subducting beneath the North American continent. These deposits were scraped off the top and accreted onto the North American Plate. This resulted in the highly distorted and fractured basalt and serpentine of the Mount Diablo Ophiolite and meta sediments of the Franciscan complex around the summit.
At destructive plate margins, the oceanic plate goes under the continental plate due to it’s more dense, which is a process known as subduction. The oceanic plate moves down into the mantle entre the benioff zone where it’s melted and destroyed because a pool of magma formed. The magma then rises through the cracks in the crust called vents and it erupts on the surface forming a volcano. There are also different types of volcano for examples composite volcanoes, shield volcanoes and dome volcanoes. For constructive plate margins, the magma rises up into the gap that created by the plate move apart to form a volcano.
Eventually, the friction is overcome and the blocks slip abruptly, releasing pent-up energy with a huge “snap”—an earthquake” (The Plate Tectonic Model – Page 107). Plates diverge at volcanic zones by the ocean basins. These are long huge cracks were lava rises from below and freezes into the Lithosphere (About.com – Geology). In which plates move past each other is call a transform boundary. These are not that common as the converge or diverge plates and the most common one is the San Andreas fault of California [About.com – Geology].
Examples of regional metamorphic rocks include schist and gneiss. Thermal metamorphic rocks, also known as contact metamorphic rocks, are formed by extreme heat along with quite a bit of pressure. The pressure pushes the molten rock against the Earth's surface, causing it to recrystallize. Examples of thermal metamorphic rocks are marble and sandstone
Igneous rocks can form in two environments that are very different. All igneous rocks came from magma. Changing from magma to rock the magma either freezes or crystallizes. When it cools fastly the crystals are small, but when it takes a long time to cool the crystals are large. Magma can complaetely crystallize into a crystal or even a diamond.