What are volcanoes? <ul><li>Volcanoes are a result of the Earth trying to lose its internal heat. If the Earth's interior was cold, there would be no volcanoes </li></ul><ul><li>Deep inside Earth, between the molten iron core and the thin crust at the surface, there is a solid body of rock called the mantle. When rock from the mantle melts, moves to the surface through the crust, and releases gases, volcanoes erupt." </li></ul>
Are all volcanoes the same? All volcanoes are not the same as some occur at Divergent Plate Boundaries , some occur at Convergent Plate Boundaries and some occur at Hot Spots Volcanoes at Divergent Plate Boundaries. At Divergent Plate Boundaries as convection currents drive the plates apart magma rises from the mantle to form new crust. If this process occurs with enough force it can create a volcano like this one in Heimaey near Iceland.
Volcanoes at Convergent Plate Boundaries At convergent plate boundaries the denser oceanic crust is forced under the lighter continental crust (SUBDUCTION). As the plate is forced into the mantle it begins to melt. Magma then rises up through the continental crust forming a volcano. At convergent plate boundaries volcanoes tend to erupt violently like Mt St Helen’s did in 1980.
Summary table of differences between volcanoes Type of volcano = Composite cones or Cinder cones (Steeper slopes made from layers of old eruptions) Type of volcano = Shield (Have a broad base and gently sloping sides) Erupted material includes pyroclastic flow that contains volcanic blocks, lapilli and ash Erupted material includes lava that can form lava fountains or lava rivers Eruption is explosive and very dangerous Eruption tends to be quieter and less dangerous Erupts when plates collide and subduction occurs leading to magma rising through a mountain Erupts when plate move apart and magma rises from mantle Convergent Plate Boundary Divergent Plate boundary
The majority of volcanic eruptions occur near plate boundaries. There are some exceptions. For example, the Hawaiian Islands, which are entirely of volcanic origin. They have formed in the middle of the Pacific Ocean more than 3,200 km from the nearest plate boundary, at what are known as Hot Spots Volcanoes at Hot Spots
These happen around relatively small, long-lasting, and exceptionally hot regions -- called hotspots -- Intermittently magma rises up through a hole in the crust and erupts onto the surface. As plates move new volcanic islands are created above the stationary hot spot. These volcanoes tend to be Shield volcanoes. Volcanoes at Hot Spots
Volcanic hazards Pyroclastic Flow : Fast flowing clouds of Volcanic ash and rock. Gas : Often poisonous gases released from the mantle during an eruption. Volcanic bombs : Large volcanic rocks Lapilli/Tephra : Small volcanic stones Lava : Liquid rock that reaches very temperatures. Landslides : Collapsing mountain material. Lahaar : A fast flowing river of volcanic Mud. Acid rain: Rain mixed with volcanic gasses that can damage crops.