Revision:Vulcanicity and Landforms

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• Vulcanicity is the process through which gases and molten rock are either extruded on the earth's surface or intruded into the earth's crust.
• Magma is the molten rock originating from the upper plastic layer of the mantle. When it gets to the surface and loses its gases, it is known as lava.
• Pyrocrasts are the ashes, cinders and small particles of magma during an explosive volcanic eruption.

Intrusive Igneous Landforms

1. Batholiths: Largest mass of magma crumbling in the crust. An example is the Stone Mountain of Georgia.
2. Sills: Sheets of magma intruded onto bedding planes of sedimentary rocks.
3. Dykes: Wall like features formed when magma cuts across several bedding planes.
4. Pipes: The stems of volcanoes.
5. Laccoliths: Dome shaped layers of magma formed when magma encounters rock more resistant at its sides than its center.
6. Lopoliths: Bowl shaped layers of magma formed when magma encounters rock more resistant at its center than its sides.

Extrusive Igneous Landforms

1. Composite Volcano: A cone shaped feature formed by alternating layers of lava and ash. Sometimes, a volcano erupts so violently, its crater is blown off enlarging the top depression. This is then known as a caldera. If filled with water, it is known as a Caldera Lake.
2. Lava Plateau: This is an upland with a generally level summit made up off successive layers of lava and ash.

Types of Volcanoes

1. Active: This is a volcano that has erupted within the last 500 years and still shows signs of activity.
2. Dormant: This is a volcano that has not erupted within the last 500 years but still shows signs of activity such as hot springs. An example is Mt. Kilimanjaro.
3. Extinct: This is a volcano that has not erupted within the last 500 years and shows no signs of activity. An example is Mt. Kenya.

Exogenetic Processes

1. These are processes that take place on the earth's surface.
2. They are subdivided in two categories:
   1. Processes of degradation
   2. Processes of aggradation
3. Processes of aggradation are those that build up material. Processes of degradation are those that destroy what has been built up by endogenetic/aggradation processes.
4. The destruction of the landscape is known as denudation. There are three processes involved:
   1. Weathering
   2. Erosion
   3. Transportation
5. The exogenetic processes require the use of agents such as running water, ice and wind.

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