Vulcanicity Flashcards
Vulcancity benefits
Lava flows can create land
Igneous rocks contain valuable mineral deposits
Lava and ashes weather quickly into fertile soils
Tourist attractions
Global distribution of volcanoes
Destructive, constructive margins and hot spots
Most are located in linear patterns around the edge of the Pacific Ocean and this is known as the ring of fire.
Volcano formation at destructive margins
E.g where the Nazca plate is being forced beneath the South African plate
Convection currents in the asthenosphere causes the denser oceanic plate to move towards the lighter continental plate and it is subducted along with a large amount of water. This ocean water mixes with the magma which is formed due to the intense heat and this friction and it rises and erupts.
Subsequent eruptions cause a volcano to cause
Volcano formation at constructive margins- two sections of oceanic crust
2 sections of oceanic plate move apart due to convection currents.
The plates move apart allows magma to reach the surface and in some places, submarine volcanoes are formed.
These volcanoes are found along or close to oceanic ridges such as the Atlantic ridge
Volcano formation at constructive margins- 2 sections of continental plate
2 sections of crust move apart due to convection currents pulling the crust in different directions, creating faults and weaknesses .
This allows magma to rise to be surface and solidifies
Volcano formation at hotspots
Formed due to a rising plume of superheated magma which thins and heats the crust, allowing magma to reach the surface.
Overtime, layers of lava builds up to form volcanoes
E.g Hawaii is a hot spot volcano in the centre of the Pacific plate
Active volcanoes
Have erupted in living memory
Dormant volcanoes
Have erupted within historical record
E.g mount Etna, Italy
Inactive volcanoes
Haven’t erupted in the last 25,000 years
Volcanoes definition
Openings in the earths crust through which lava, ash and gases erupt
Extrusive volcanic landforms definition
Magma is extrusive volcanic features cools, crystallises and solidifies at the surface with air.
Therefore, the igneous rocks tend to be finer grained with small crystals such as basalt
The lava cools far quicker than magma underground
Materials erupted by volcanoes
Gaseous emissions- dominated by steam but also more dangerous gases such as carbon monoxide and calories
Solids- ash, dust and glassy cinders
Liquids- tephra which solidify in mid air. Tephra ranges in size such as large lava bombs and in its finest form of hair like trails called lapilli.
Surface lavas- acid or basic
Name the 3 types of lava
Basaltic
Andesitic
Rhyolithic
Basaltic lava
From ex from the upward movement of mantle material
Low silica which makes it more fluid that a
Lows gas bubbles to escape on the way up, preventing sudden explosive activity
Andesitic lava
Formed at destructive margin
Silica rich (viscous)
Lava often solidifies before reaching the surface, leading to a build up of pressure and a violent explosion
Rhyolithic lava
Formed at destructive and collision margins
Same characteristics as andesitic lava
Vent volcano openings
Usually create cone shaped landforms
Fissure opening volcanoes
A long crack in the crust which allows lava to spill out over a large area
Basic shield volcanoes
Gently sloping cones from layers of less viscous lava
Composite volcanoes
Layers of ash and lava
Pyramid shaped
Acid volcanoes
Steep sides, convex cones consisting of viscous lava
Acidic lava causes a plug in the volcano
Calderas
Form when the build up of gases inside the volcano is so big that explosions occur which clears out all the magma and remove the peak of the cone and leave an enormous crater
Ash and cinder cones
Formed from ash, cinder and volcanic bombs
How can volcanoes be classified based on the violence of the eruption
Examples
Hawaiin volcano- constructive, lava flows gently, basaltic magma, eruption height of 2km
Vulcanian volcano- destructive, eruption height of 20km
Intrusive volcanic landforms
Magma cools below the surface within the first.
The resulting features may only become part of the landscape once later erosion removes the overlying rocks
Batholiths
Formed when large masses of magma cool and solidify
They are often done shaped and exposed by later erosion
Dykes
Vertical intrusions with horizontal cooling cracks
They cut across the bedding plane of the rocks into which they have been intruded
Often occur in groups known as dyke swarms
Sills
Horizontal instrusions with vertical cooling cracks
Geysers
Occur when water, heated by volcanic activity explode onto the surface
It is an intermittent, forceful discharge of superheated water ejected from the surface
E.g old faithful, Yellowstone national park, USA
Ground water collects in conduits
Magma within the crust heats the water
As the water is heated, pressure builds up until an explosion occurs
Hot springs/ boiling mud
Hot thermal springs aren’t under pressure and so don’t explode at the surface.
Water collects in pools
E.g the blue lagoon, Iceland
Where hot water on its way upwards mixes wig mud and minerals near the surface, a bubbling boiling mud may form
Fumarole
Low pressure outlets of steel
Founded in areas where super heated water turns to steam as it cpndenses on the surface
Mainly steam and carbon dioxide
If the gas is sulphurous, fumaroles are called solfataras
Vulcanicity hazards
Lava flows burn and bury crops
Flooding can result from lava flows
Submarine, coastal or island eruptions can cause tsuniamis
Ash falls disrupt transport, pollutes the air, causes breathing difficulties
Pyroclastic flow can destroy life and property
Volcanic dust absorbs solar energy and so lowers atmospheric temps
