Types of Volcanoes and Volcanic Hazards Earth and

Types of Volcanoes and Volcanic Hazards Earth and Space Science

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

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 Types of Volcanoes

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

3. Lahar • A wet, cement-like mixture of water, mud and volcanic rock fragments that flows down the slopes of a volcano Volcanic Flow Hazards

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