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Extrusive Landforms • Ash and Cinder Cones- simplest type of Volcano and are formed from fragmented particles such as cinder, ash and dust and blobs of solidified magma ejected from a single vent.
SHIELD VOLCANOES • Formed from the accumulation of basic lava or basaltic lava. There sides are broad and gentle and their crater, wide.
Composite Volcanoes or Strata-Volcanoes-Caldera Cones • These volcanoes compromise of alternative layers of ash and lava flow, cinder, blocks and bombs. These are associated with convergent plate margins
CALDERA • Acidic lava plug the vents so that pressure is built up within the Volcano and this leads to violent eruptions. This causes the crater to be blown away explosively; the top of the volcano then subsides or collapses into the underlying magma forming a new depression known as a caldera.
CHANGES TO EXTRUSIVE FEATURES OVER TIME • Volcanoes- they may blow off to form Calderas, which are large steep sided basin-shaped depressions. • Calderas- water may collect in the depressions forming crater lakes.
• Rivers can establish themselves on the top of mountains cutting down the slope creating a radial drainage pattern. • Lava-Plateau Some basic lava sometimes pour out from long fissures instead of a Central vent forming a broad plateau. These can be dissected by streams to form flat top hills with steep sides seperated by steep valleys.
OTHER VOLCANIC FEATURES Hot springs- continuous outflow of ground water
GEYSERS • Violent emissions of hot water and steam at intermittent intervals. They are formed when underground water is heated above 100 degree Celsius and the super heated steam so formed, forcefully expels the water above it. The eruption occurs when steam pressure is built up.
STEAMBOAT GEYSER, YELLOWSTONE
FUMEROLES • Vents along the sides of volcanoes which, under pressure emit steam and vapour and gases such as hydrochloric acid and
VALLEY OF DESOLATION
DOMINICA EXPORTS PUMICE
Ashfall from Pinatubo, 1991; Phillipines
NEVADO DEL RUIZ • On November 13, 1985, Nevado del Ruiz erupted. Pyroclastic flows melted ice and snow at the summit which formed lahars that rushed down several river valleys. The lahars were up to 50 metres thick and travelled more than 100 kilometres.  • Many houses and towns were devastated by the lahars. The town of Armero was completely covered by debris, killing approximately 21, 000 people (out of 28, 700). The eruption caused an estimated 23, 000 deaths, 5, 000 injuries, and destroyed more than 5, 000 homes. This was the second-deadliest volcanic disaster in the 20 th century (the 1902 eruption of Mount Pelée was the worst).
NEVADO DEL RUIZ