Types of Volcanoes and Volcanic Hazards

Earth and Space Science

Types of Volcanoes

1. Shield volcanoes - Lava flows a great distance before having a chance to cool- Forms a very broad volcano with gentle sloping sides as more lava flows over previously cooled lava

Shield volcanoes

Types of Volcanoes

2. Composite cone- explosive and violent eruptions as pressure builds up in the sticky/gooey/viscous magma, and the lava oozes out or ash and cinders shoot out from vents- forms layers of lava and ash- tall with steep sides due to the lack of ability of the lava to flow very far

Composite cone

Types of Volcanoes

3. Cinder cone- magma with a lot of trapped gases- violent eruptions that shoot out lava and ash at the same time- this lava and ash cools as it falls and forms very steep sides to the volcano- generally short lived volcanoes and become dormant soon

Cinder cone

Types of Volcanoes

4. Caldera - a volcanic vent which collapsed after the erupting magma left an empty chamber under the ground- forms a large depression or hole, usually larger than the original vent

Caldera

Volcanic Hazards

• There are many materials that escape from erupting volcanoes.

Volcanic Flow Hazards1. Lava flows• Streams of molten rock that comes from vents

and fissures in the Earth’s crust

Lava flows

• They destroy almost everything in their path

Lava flows• Factors affecting flow rate: slope of the hill,

viscosity, cooling rate of the lava as lava cools it becomes more viscous

and less able to flow

Lava flows

• The outer crust cools quickly and lava can still flow through it like a tube

Volcanic Flow Hazards2. Pyroclastic Flows• High-density mixtures of hot ash, rock

fragments, and hot gases that rush down the sides of volcanoes

Pyroclastic Flows• Occur in

explosive eruptions

Pyroclastic Flows

• Can move at speeds up to 350 km/h

Pyroclastic Flows• Extremely dangerous and destroy almost

everything in their path

Volcanic Flow Hazards3. Lahar• A wet, cement-

like mixture of water, mud and volcanic rock fragments that flows down the slopes of a volcano

Lahar• Can carry rock debris ranging from clay to

gravel to boulders

Lahar• May be triggered by eruptions melting snow

and ice, and/or releasing a small lake and the water mixing with the eruption debris

Lahar• Rain soaked debris may also start a lahar

during or after an eruption

Lahar• Lahars can bury entire villages under meters

of mud

Volcanic Airborne Releases• Tephra – all pieces of volcanic rock and ash

that are ejected in the air

Volcanic Airborne Releases

Classified by size - Volcanic bombs – pieces bigger than 64 mm

Volcanic Airborne Releases

Classified by size - Lapilli – pieces between 64 mm and 2 mm

Volcanic Airborne ReleasesClassified by size - Ash – pieces smaller than 2 mm

Volcanic Airborne Releases

• Volcanic bombs and lapilli usually fall on or near the top of the volcano due to their size, while ash can travel hundreds to thousands of kilometers