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 Types of Volcanoes

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 Hazards 1. 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 Hazards 2. 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 Hazards 3. 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 Releases Classified 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