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Volcanic Features - Intrusive & Extrusive

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by

Austin Read

on 8 May 2013

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Transcript of Volcanic Features - Intrusive & Extrusive

Intrusive and Extrusive Volcanic Features - The high pressure inside the earth keeps rock in some parts of the mantle , semi-molten.
- when this pressure is released, the rock b becomes molten.

- Hot molten rock is known as magma.
- Because magma is less dense than the rock around it, it rises up towards the Earth's surface.

- Most magma doesn't reach the surface, but some does. The type of volcanic activity depends on where the magma ends up and is determined by the nature of material affected and the type of eruption. Intrusive Volcanic Activity Intrusive or Extrusive... - This takes place place beneath the Earth's surface.

- It includes the formation of large magma chambers and magma being forced into the crust through cracks in the rock.

- Magma in intrusive volcanic features cools, crystallizes and solidifies into igneous rocks below the surface. Slow cooling results in large crystals forming- typical of rocks such as granite and dolerite.

-The resulting features may then only become part of the landscape once later erosion removes the overlying rocks.

-There are many examples of intrusive vulcanicity in Scotland, Northern Ireland and North of England. Intrusive Volcanic Features: - Form where the magma solidifies in a fissure.

- They often form in groups called 'swarms.'

- Normally, the dyke material is more resistant than the surrounding country rock, leaving prominent wall like features on an eroded landscape.

- Erosion of less resistant dyke material leaves ditch-like features. Intrusive Volcanic Features: - Much more large-scale, and are massive in size and depth.

- Very often, dykes, sills and laccoliths will feed off the domed granite batholith before it solidifies.

- Surrounding the batholith, extreme heat and/or pressure, alters the adjacent country rock in a process called metamorphism. Extrusive Volcanic Activity - This takes place on the Earth's surface.

- The major form of this activity is volcanic eruptions of lava and other material.

- Magma in extrusive volcanic features cools, crystallizes and solidifies from surface lavas. In the contact with the air, lava cools far quicker than magma still underground- and cooling in the sea is even more rapid.

-As a consequence, the resulting igneous rocks tend to be finer grained, with small crystals, such as basalt. Extrusive volcanic features: Intrusive Volcanic Features: Sills:
- form when magma solidifes into horizontal sheets in between layers of pre-exisitng rocks. Laccoliths:
- occur when viscous magma (resistant to flow) forces overlying rock strata or layers to arch into a dome. Stock:
-a small batholith less than 40 miles squared. Maars:
- a crater lake Gaseous emissions:
- dominated by steam and highly dangerous.

Solids:
- include ash, dust and glassy cinders. May include blocks of materials such as shattered remains of solidified lava.

Liquids:
- include lava bombs (pyroclastic or tephra) which solidify mid air. May also include surface lavas (acid or basic) flowing from vents or fissures. Major extrusive features: 1) Flood/Plateau Basalt

2) Shield Volcano

3) Cinder cone

4) Composite/Strato-volcano

5) Volcanic dome

6) Caldera Major extrusive features: Rift Zones - Conspicuously do not point towards adjacent volcanoes, but instead parallel the volcano-volcano boundaries, rift-zones mark preferred directions of sub-horizontal magma excursions from the magma chamber.

- At the surface, they are characterized by numerous vents, fissures, earth cracks, cinder cones and the sources of lava flows.

- All of these are indications that magma preferentially intrudes into the rift zones and is also often stored there for up to a few years. Major Extrusive Features Maar - A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption.

- Phreatomagmatic eruption: an explosion caused by groundwater coming into contact with hot lava or magma.

- A maar characteristically fills with water to form a relatively shallow crater lake. Major extrusive features: Pyroclastic flow (nuee Ardente) - A fast-moving current of hot gas and rock (collectively known as 'tephra').

- It can reach speeds moving away from a volcano of up to 450mph, and can reach temperatures of around 1000 degrees Celsius.

- Pyroclastic flows normally hug the ground and travel downhill, or spread laterally under gravity.

- Their speed depends on the density of the current and the gradient of the slope.

- They are a common and devastating result of certain explosive volcanic eruptions. Major extrusive features: Crater/Caldera - A caldera is a couldron-like volcanic feature usually formed by the collapsed of land following a volcanic eruption.

- The word comes from Spanish caldera, meaning ''cooking pot.'' Minor extrusive features: Geysers - Throw up jets of hot water and steam at regular intervals through a vent.

-Rainwater seeps through cracks until in reaches rocks heated by molten rocks below.

- The intense heat boils the water, turning it to steam, which increases the pressure inside the crevice as bubbles of steam builds up.

- The pressure is enough to shoot water and steam upwards and out through a vent, high into the air.

- The process repeats Minor extrusive features: Fumaroles - An opening at the Earth's crust which emits steam and gases. (CO2, sulfur dioxide, hydrochloric acid and hydrogen sulphide.)

- More common than geysers.

- Continue 1000s of years after volcano has become extinct, sometimes called 'solfatara.' Minor extrusive features: Hot springs and Boiling Mud Hot springs:
- a spring that is produced by the emergeence of geothermal heated groundwater from the Earth's crust. Example: Blue Lagoon, Iceland Boiling mud pot:
-a fumerole crater with a clay-water-steam mixture.
- the water is not necessarily boiling. Dykes Batholiths Maars, Stocks, Sills, Laccoliths Volcanoes (different types)
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