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HAZARDS GENERATED BY VOLCANIC ACTIVITY - Coggle Diagram
HAZARDS GENERATED BY VOLCANIC ACTIVITY
Types of volcano
Effusive
Types of eruption
Hawaiian eruptions
Central activity, runny basaltic lava travels down, gases escape easily with occasional pyroclastic activity
Icelandic lava eruptions
Persistent fissure eruption, large volume of basaltic lava build up horizontal plains
Products
Lava plateau
Basic lava erupting from fissures covering large areas with free flowing lava, uniform relief
Sheild volcano
Wide base with gently sloping sides, successive flows can accumulate to widen the volcano. Formed by frequent gentle eruptions of runny lava
Plate type
Divergent
Lava type
Basalt
Explosive
Type of eruption
Plinian eruptions
Gas rushes up through sticky lava and blasts ash/debris in large explosions, large gas clouds and pyroclastics that rush down
Vesuviun eruptions
Powerful blasts of gas creating ash clouds, lava flows
Vulcanian eruptions
Violent gas explosions that blast lava, large amounts of ash and pumice, occurs when viscous lava solidifies quickly
Strombolian eruptions
Frequent gas explosions with blasting fragments of running lava forming cones, very explosive lots of pyroclastic activity
Products
Strato-volcano/composite volcano
Concave symmetrical profile with central vent, layers of rock from previous eruptions, complex internal networks of which form minor intrusive igneous features (sills/dykes/parasitic cone). Magma builds up in vents
Gas bubbles also form as they reach the vent, rapid expansion tears the magma and volcano violently erupts producing ash.
Enough gas can produce sticky slow moving lava which travels a short distance before solidifying creating new layers and a steeper slope
Caldera
Craters left behind after an eruption, destroying the cone emptying the magma chamber, without the support of which the sides collapse
Cinder Cone volcano
One central vent, no layers. Steep conical hill made of tephra. Bowl shaped crater
Lava type
Rhyolite/andesite
Plate type
Convergent
Hot spots
Fixed, intraspecific-plate areas of intense volcanic activity- magma from a mantle plume reaches the surface
E.g Hawaii as the pacific plate has moved over the Hawaiian hot spot, basalt has acccumulated creating islands, the plate eventually moves away from the hot spot and the source of magma is lost
Supervolcanoes
Volcanoes that erupt more than 1000km3 of material in a single event forming giant calderas most recent was 27,000 years ago can causes global climate change
E.g Yellowstone, Wyoming 75km caldera
Magma types
Basalt
52% silica content
1000-1200 degrees c
low viscosity (fluid)
1-2% gas content
less explosive
Andesite
60% silica content
900-1100 degrees c
3-4% gas content
Rhyolite
70%+ silica content
650-800 degrees c
High viscosity (thick)
4-6% gas content
most explosive
Measuring volcanic activity
Magnitude
Amount of material erupted
Volcanic explosivity index
Combines magnitude and intensity into a single number, each increase represents a tenfold increase in explosivity
Intensity
Speed at which material is erupted
During eruptions
Lava flows
Basaltic lava can cover 800m, burying everything in it’s path, can squeeze out of vents and form domes
Pyroclastic flows
500degrees c+ gases ash and rock can travel 100km/h following the con tours of the ground destroying/vapour using everything, inhalation causes instant death
Pyroclastic surge is less dense
Tephra
Material including pumice and ash, can destroy engineers and airways. Buildings can collapse due to the weight (ash fall)
Create eruption columns where it rapidly ruses into the air creating an ash cloud
Toxic gas
Carbon dioxide, carbon monoxide and suplhur dioxide no smell or colour can affect breathing and cause acid rain
CO2 is heavier than air so can be trapped in low areas
Fluorine can be trapped in ash and contaminate water
Lahar
Wet mud flow, water or melted ice mix with ash and rock, can travel 50km/h burying everything
Floods
Eruptions beneath ice cause melting, water accumulates and is released at once
Tsunamis
Eruptions of island volcanoes can displace causing extremely fast tsunami waves
Long term climate change
Ash can block sunlight, sulphuric acid can reflect solar insolation