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