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Mr. Penner

abby alshukhaiti

on 16 April 2010

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Transcript of Geography

VOLCANOS Types Composite Composite volcanoes, also called strato volcanoes, are formed by alternating layers of lava and rock fragments. This is the reason they are called composite.

Strato-volcanoes often form impressive, snow-capped peaks which are often exceeding 2500m in height, 1000sq.km in surface, and 400km3 in volume.

Between eruptions they are often so quiet they seem extinct. To witness the start of a great eruption requires luck or very careful surveillance. Cinder Cinder cones are built from lava fragments called cinders. The lava fragments are ejected from a single vent and accumulate around the vent when they fall back to earth.

Cinder cones grow rapidly and soon approach their maximum size. They rarely exceed 250m in height and 500m in diameter. Shield island arc island arc is a type of archipelago formed as one oceanic tectonic plate subducts under another and produces magma at depth below the over-riding plate. An island arc that develops along the edge of a continent (for example, large parts of the Andes/Central American/Canadian mountain chain) may be known as a volcanic arc, though most people find the distinction of little benefit. Shield volcanoes are huge in size. They are built by many layers of runny lava flows. Lava spills out of a central vent or group of vents. A broad shaped, gently sloping cone is formed. This is caused by the very fluid, basaltic lava which can't be piled up into steep mounds. Intrusive Forms Batholith a large emplacement of igneous intrusive rock that forms from cooled magma deep in the earth's crust. Batholiths are almost always made mostly rock-types, such as granite, quartz monzonite, or diorite. Dike A vertical or semi-vertical wall-like igneous intrusion which cuts vertically in the bedding planes of a rock. Dikes often form in swarms. Sill An horizontal or semi-horizontal intrusion of magma that spreads
between the layers of sedimentary rocks. Lacolith A laccolith is a small area that broke away from the main area of magma but did not have the pressure to break through the surface. The area of the laccoith was undergound until it cooled into hard granite. Extrusive Forms Plateau Extensive area of flat upland, usually bounded by an escarpment on all sides but sometimes enclosed by mountains. Plateaus are extensive, and together with enclosed basins they cover about 45% of the Earth's land surface. The essential criteria for a plateau are low relative relief and some altitude. Crater A bowl-shaped depression at the mouth of a volcano or geyser. Caldera A bowl-shaped circular depression caused by the destruction of the peak of a volcano Stages Dromant A volcano which shows little to no activity but is not extinct.
(Mount Fuji, Japan) Active A volcano that is active and erupts regularily. May or may not cause damage depending on location. (Mount Sakurajima, Japan) Extinct A volcano that shows no signs of activity
at all. (Mount Kenya, Africa) Molten Material Magma Molten or partially molten rock from which igneous rocks form, usually consisting of silicate liquid. Magma migrates either at depth or to the Earth's surface, where it is ejected as lava. The interactions of several physical properties, including chemical composition, viscosity, content of dissolved gases, and temperature, determine the characteristics of magma. Lava Magma that has been ejected or that has
oozed out of a volcano is now lava. Andesitic: Thick lava that is rich in silica. Erupts from violent
volcanos and is slow moving.

Basaltic: Thin running lava that is rich in magnesium. It is constructive
and fast moving. Nuee Ardente When viscous magma, containing much gas, is erupted under reasonably low pressure, a glowing cloud containing ash and pumice may be thrown into the air, this cloud will fall back onto the earth like an avalanche before it can cool off. Pyroclastic Material Pyroclastic material is another name for a cloud of ash, lava fragments carried through the air, and vapor. Such a flow is usually very hot, and moves rapidly due to buoyancy provided by the vapors. Pyroclastic flows can extend miles from the volcano, and devastate life and property within their paths. Lahar Lahars form from debris avalanches that contain water from snow and ice which, when released, mixes with loose debris to form a lahar
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