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Volcanic eruptions

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Deep inside the Earth, magma rises upwards, gathers in pools within or below the crust and tries to get to the surface. Cracks provide escape routes and the magma erupts as a volcano. Steam and gas form clouds of white smoke, small fragments of rock and lava blow out as volcanic ash and cinder, and small hot bombs of lava shoot out and harden. Not all lava is the same. It may be thick and sticky or thin and runny. Lava thickens or viscosity determines the type of volcanic eruption and the kind of rock that forms when the lava hardens. Some volcanoes are active, erupting at any time; some are dormant or cold, waiting to erupt; others are dead or extinct. ...read more.


In Indonesia more people live on the islands with active volcanoes than on the islands with none. The volcano Mount Saint Helens is one of 15 in the Cascade Range of the north-west United States- an area where the Juan de Fuca plate is subducting beneath the North American plate. On 20 March 1980, a string of earthquakes north-west of the mountain peak signalled the slow awakening of the volcano, which had been dormant since 1857. A week later, a small eruption shot ash and steams into the air. Groups of scientists arrived with instruments to monitor the volcano. By early May, a bulge developed on the cone. This indicated magma rising in the volcano's vent. ...read more.


to the east. Ash fell like black snow in parts of Montana, Idaho, Oregon and Washington, and covered streets, cars and buildings. Cats and dogs downwind from the eruption turned pale grey from the ash that floated from the sky. But ash does not melt like snow and it has to be cleared. Most ended up in landfills. Mudflows Thick sticky mud caused by melting snow and ice sped down the North Toutle River Valley into communities below. Trees More than six million trees were uprooted or flattened by rock blasted from the volcano. After a massive salvage operation to clear the logs, seedlings were planted to replace the forests. Plinian Plume Minutes after the first explosion a second eruption produced a large Plinian column of ash and gas that rose to a height of 20 km (12 miles). This phase of the volcanic eruption continued for nine hours. ...read more.

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