Volcanoes

How do Volcanoes form? Volcanoes form when hot material from the

mantle rises and leaks into the crust. The hot material, called magma, rising from

lower ground, gathers in a reservoir called the magma chamber.

Eventually, but not always, the magma erupts onto the surface and forms lava.

Formation of a Volcano

This is a drawing of magma making it's way up through the crust, causing the volcano to expand

prior to eruption.

Where do Volcanoes form? At Subduction zones Along Hot Spots/plumes The opening in Earth’s surface which allow

material to escape is called a vent.

What is Hot Spot? An area in the middle of a lithospheric plate where

magma rises from the mantle and causes eruptions at the Earth's surface.

If the hot spot forces magma to the surface during an eruption, it may create a volcano.

Continual eruptions could eventually build a whole island on the surface. (Ex. Hawaii)

The hot spot is stationary and the plate moves over it.

Hot spots cont…… Hot spots may cause the formation of

geysers or hot springs, rather than lava based eruptions.

Hot Spot

Types of Volcanic Eruptions Explosive: Short, violent eruptions that

break lava into smaller pieces (cinders and ash)

Effusive: Slow, continual eruptions of lava

Categories for Volcanoes Active

Has erupted in the last 100 years Dormant

Has erupted in the last 1000 years Extinct

Hasn’t erupted in over 1000 years

Types of Volcanoes Composite/StratoVolcanoes Formed by Alternating layers of lava and

ash Typically steep sided and have a high

elevation. Explosive Eruptions Ex. Mount Fuji, Japan

Mount St. Helens, WA

Types of Volcanoes cont…..

Shield Volcanoes Formed by continuous eruption of lava over

long periods of time. Usually very large at the base and not very

steep. Effusive eruptions Ex. Mauna Loa and Kilauea in Hawaii

Example of Shield Volcano

Types of Volcanoes Cindercone Formed from the eruption of lava fragments

called cinders. Usually form quite rapidly and are tall and

steep sided. Not as tall as Strato and not as wide as

Shield Ex. Mount Paricutin in Mexico

Cindercone

Types of Volcanic Hazards Lava: Two categories based on appearance Aa Pahoehoe

Lava--Pahoehoe Lava that has a smooth, ropy surface. Typically slow moving and cooling

Pahoehoe

Volcanic Hazards Aa Lava: Rigid, spiky lava Fast cooling, viscous

Aa lava

Volcanic Hazards Tephra: Material that is ejected from the volcano Size decreases as distance from volcano

increases Ex. Cinders, ash, bomb Damage can include: lightening, respiratory

problems, interference with aircraft, destruction of vegetation, building collapse

Volcanic Hazards Poisonous Gases Gas developed as magma heats water

vapor Typical gases released: Carbon Dioxide,

Sulfur Dioxide, Carbon Monoxide, Hydrochloric Acid

Poisonous in large amounts

Volcanic Hazards Pyroclastic Flow Fluidized masses of rock fragments and

gases that move rapidly in response to gravity

Very fast and cause more death than any other hazard

Pyroclastic flows can incinerate, burn, and asphyxiate people.

Pyroclastic Flow

Pyroclastic Flow

http://www.geo.mtu.edu/volcanoes/hazards/primer/pyro.html

Volcanic Hazards Lahar Form from debris avalanches that contain

water from snow and ice which, when released, mixes with loose debris to form a lahar

Massive flooding Extremely dangerous for people living close

to a volcanic eruption

Lahar