volcanoes - types & volcanic hazards
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VOLCANOES
Presented by:Abinash Acharya
• It is point on the earth’s crust where magma forces its way to the surface due to pressure.
• Ash and gases may also escape during a typical volcanic eruption.
What is a volcano?
Location Of Volcanoes
Layout Of A Volcano
Types Of VolcanoesAcid Volcanoes• Highly explosive
• Magma/lava is viscous (thick)
• Found where oceanic crust is subducted under continental crust
Basaltic Volcanoes• Less explosive*
• Magma/lava less viscous (runny)
• Found at rift zones (constructive boundaries) and hotspots
Acid Volcanoes
Lava Domes
• Formed of layers of lava high in silica
• Lava is viscous and does not flow very far
• Rounded Form• Composed completely of
lava
Stratovolcanoes
• Also called composite volcanoes
• Formed of layers of lava and ashes
• Lava is viscous• Distinct cone shape
LAVA DOMES-EXAMPLE
Mount Chaiten, Chile
STRATOVOLCANO-EXAMPLE
Mount St. Helen, US (Before and after)
Basaltic Volcanoes• Also known as shield volcanoes
• Consists of widespread layers of lava and have low viscosity
• Silica content is low
• Low form spread over a great distance
Basaltic Volcano-Example
Eyjafjallajökull, Iceland
Calderas Volcanoes• Collapsed Volcanoes• Magma chamber has emptied and the ground
has sunk• Often becomes a lake• New volcanoes can form, or pressure can build
from below, lifting the ground• If acidic, this can cause a catastrophic eruption
in the form of a ’Super Volcano’
Calderas-Example
Mount Pinatubo, Phillipines
Hotspots
• Tectonic plate moves over a magma plume• Occasionally erupts, creating a volcano
Major Hotspots
Volcanic Explosivity Index (VEI)TYPE DESCRIPTION EXAMPLEHawaiian Gentle KilaueaStrombolian Explosive StromboliVulcanian Severe NabroPeléan Cataclysmic Mt.PeléePlinian Paroxysmal St.HelensPlinian/Ultra-Plinian Colossal KrakatoaUltra-Plinian Super-Colossal TamboraSupervolcanic Mega-Colossal Yellow Stone
Number 8 has never been experienced in human historyThe list has been simplified. See correct details here:
http://www.unc.edu/~rowlett/units/scales/VEI.html
Volcanic Activity Index
Volcanic Hazards
Most hazards during eruptions are caused by what comes out of a volcano. In the next few slides, we’ll be seeing the different types of volcanic hazards.
Volcanic Hazards – Lava Flows• Mostly associated with basic volcanos• Slow moving 1 – 5 km/h• Low risk to human life• Cover large areas and destroy large amounts of
infrastructure
Hazards – Pyroclastic Flows• Hot clouds of ash and gas• Move downhill, close to the ground, following
valleys• High speed – up to 500 km/h• As far as 30 km• Up to 7000 C• Highly dangerous
Hazards - Lahars
• Occur on high volcanos covered in snow and ice, or wet mud/soil
• Eruption causes snow to melt, or lava mixes with mud
• Flows downhill like wet concrete
Hazards – Ash Clouds
• Slow moving• Weight of ash can collapse buildings• Destroys crops, pollutes water• Affects air traffic• Can enter high atmosphere and cause cooling – disrupting
climate
Hazards – Lava Bombs
• Molten rocks thrown out of volcano• Pummice – smaller rocks• Travel short Distances• Can Start Fires
Benefits Of Living Near a Volcanic Region
• Aesthetic beauty eg. Mount Fuji, Japan• Mining of minerals and diamonds• Geothermal energy and hot springs• Highly fertile soils – soft rocks and high
mineral content
Predicting Volcanic Eruptions
• Monitoring seismic disturbances (tremors)
• Changes in volcano profile (shape)
• Chemical changes in groundwater
• Emissions of gases• Thermal monitoring
(temperature)
History Of Eruptions• 1800 BC – destruction of Bronze age
settlements – then several more times• 79 AD – destruction of Pompeii• At least 40 times until the last eruption in 1944
– witnessed by allied troops towards the end of WWII
• = once every 40-50 years
Reducing The Risks
• Round-the-clock monitoring of the volcano: Tremors, gases, changes in water
• Identifying hazard areas: Weak spots, secondary vents, predicting routes of pyroclastic flows
• Creating an evacuation plan: Zoning, warning systems, public education
References
• http://greenfieldgeography.wikispaces.com/IGCSE+Plate+Tectonics+and+GCSE+Plate+Tectonics
• http://volcano.oregonstate.edu/
• http://www.physicalgeography.net/fundamentals/chapter10.html
• http://volcanoes.usgs.gov/hazards/index.php
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