Vulcanicity and Landforms

Vulcanicity and Landforms


# 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

* These are processes that take place on the earth's surface.
* They are subdivided in two categories:
1. Processes of degradation
2. Processes of aggradation
* 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.
* The destruction of the landscape is known as denudation. There are three processes involved:
1. Weathering
2. Erosion
3. Transportation
* The exogenetic processes require the use of agents such as running water, ice and wind.