Types of Volcanoes and Volcanic Hazards Earth and Space Science
Dec 23, 2015
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