Transcript Types of Volcanoes and Volcanic Hazards

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