A volcano is an opening in the Earth's crust, which allows magma, gases and other substances to escape the mantle. Many volcano eruptions will create a mountain, with many layers of lava - each from a separate eruption. These build up, forming a cone shape. When magma reaches the surface, it becomes lava.
Volcanoes form when magma escapes the Earth through a vent. This generally happens at plate boundaries.
At Compressional(destructive) boundariesEdit
At Tensional(constructive) boundariesEdit
- Gentle slope
- Wide base
- Frequent eruptions
- Lava flows easier - travels longer distances before cooling
- Usually non-violent
- Example: Loa, Kilauea
- Steep sided
- Narrow base
- Alternate layers of acid lava and ash
- Subsidiary cones/vents may form
- Often violent
- For example: Etna, Vesuvius, Mt. Fuji
VOLCANIC ERUPTION MECHANISMS :
1. Gas released under decompression causing magmatic eruptions.
2. Thermal contraction from chilling or contact with water causing phreatomagmatic eruptions.
3. Ejection of entrained particles during stream eruptions causing phreatic eruptions.
Volcanic materials generaly includes of lava, rock fragments and gases. Rock fragments are solid materials of all sizes explosively ejected from a volcano into the atmoshpere eg. ash, cinder. Gases such as CO2, SO2,N2 are made from steam and usually carries the dust forming dark smoke.
Benefits of volcanic eruptionsEdit
1. Lands that contain lava and ash are fertile and rich in nutrients which can be useful for agriculture.
2. When lava cools, some crystals are fomed creating glass. Perlite, a volcanic glass, can be heated in furnaces and made into light concreate.
3. Volcanoes create amazing sceneries which attract tourists especially the Shield Volcanoes.
4. High level of heat and activity inside the Earth can provide opportunities for generating geothermal energy.
5. Volcanoes also provide valuable resources such as zinc, sulphur (La Soufriere, Dominica), copper and lead.