Volcanoes Flashcards
Which boundaries do volcanoes form on
Constructive and destructive
Aswell as hotspots in the Centre of some plates
How do volcanoes form
-the upwelling of hot molten material from the core/mantle boundary
- OR from the top of a huge mantle plume just under the crust
Fill in:
The shape of volcanoes is mainly related to the __ _ __ erupted
Type Of Lava
what type of volcanoes are yellowstone and taupa
Super volcanoes
what happens to volcanic hazards when magnitude increases
volcanic hazards increases
TRUE OR FALSE are composite cones more dangerous than shield volcanoes
TRUE
what factor causes the shape of volcanoes
the type of lava
characteristics of composite volcanoes
composite volcano rises higher with a greater gradient than shield volcanoes
Produces a much greater ash cloud than shield
Has a quick eruptions
Has a longer period of time between eruptions
Narrow base
The magma is andesitic and likely melted from oceanic crust
Crate can be blocked causing violent eruptions
what are the characteristics of shield volcanoes
Wide base
Gentle slope, less than 10 degrees
Magma rises directly from asthenosphere
Magma is basaltic
Gentle eruption - mainly lava occasionally ash from rare explosive eruptions
define primary hazard
when a volcano erupts (immediate)
what are the 4 primary hazard of volcanic eruptions
Lava flows
Emissions of gases and steam
Pyroclasts/tephra - ash, volcanic bombs
Pyroclastic flows
define secondary hazard
a hazard that occurs after the eruption
what are the 2 secondary hazards of volcanoes
jokulhaup
lahar
what does the speed of flow of lava depend on
viscosity, temperature, silica content, and the volcanoes incline
what lava is associated with composite volcanoes
andesitic lava
what type of lava is associated with shield volcanoes
basaltic lava
what type of lava is associated with super volcanoes
rhyolitic lava
what is the hottest type of lava
basaltic lava
what are the flow characteristics of andesitic lava
slow, intermediate viscosity, traps gases
what are flow characteristics of basaltic lava
runny, low viscosity, thin, gases escape
what are the flow characteristics of rhyolitic lava
thick, high viscosity, slow, gases are trapped
the eruption energy of basaltic lava
gentle, effusive
the eruption energy of andesitic lava
violent, moderately explosive
the eruption energy of rhyolitic lava
very violent, cataclysmic
is it true that gases can still be released even years after the volcanic eruption
TRUE
Gases are released in and around volcanoes before, during and for many years after volcanic eruptions.
what are the 2 main gases released by volcanoes
water vapour
sulphur dioxide
what can water vapour cause during eruptions
heavy rainfall or even lahars in some situations
what can sulphur dioxide cause during eruptions
Forms fine particles that get carried as high as the stratosphere. These solid particles reflect radiation from the Sun back into space, so cooling the Earth.
what are the gases released by volcanoes
water vapour
sulphur dioxide
fluorine gas
carbon dioxide
what can fluorine gas cause during eruptions
can be poisonous in high concentrations and can contaminate farmland or water supplies.
what are pyroclasts
volcanic materials that are solid
what are the 3 groups of pyroclasts
volcanic ash
lapilli
volcanic bombs/blocks
how are the 3 groups of pyroclasts catagorised
via size of the pyroclasts
what size is volcanic ash
less than 2mm
what size is lapilli
2mm - 64mm
what size are volcanic bombs/blocks
greater than 64mm
how can ash cause hazards
its disruptive rather than devastating. Heavy ash can collapse roofs, damage crops and vegetation and affect people’s breathing.
what are pyroclastic flows
a dense mixture of superheated tephra and poisonous gases moving rapidly down the sides of a composite cone volcano
how fast can pyroclastic flows travel
at speeds of up to 700 km/h
an example of pyroclastic flows
for example, Chances Peak on Montserrat in 1997
what can pyroclastic flows cause
leave behind thick layers of volcanic deposits (ignimbrite), up to 200 m thick
may cause secondary hazards such as river flooding if they temporarily dam them
example Pinatubo, Philippines 1991
what are lahars
consist of water mixed with volcanic deposits flowing rapidly along existing valleys.
how are lahars caused
heavy rainfall
- a result of humid air being seeded with volcanic ash which accelerates condensation, the formation of clouds and rain
emptying of a crater lake; or through the melting of snow and ice due to the heat from an eruption at high altitude
what are the dangers of lahars
their fast velocity, the amount of material carried and the great distances they can travel.
what is a jokulhlaup
A jokulhlaup is a flood of meltwater from underneath an ice cap or glacier.
how does a jokulhlaup form
This happens when a volcano erupts underneath the ice and melts the ice so that it forms a lake, either in a crater or at the crater side where it is dammed by the ice.
The warm meltwater will have sufficient volume to lift the ice away from the bedrock. When this happens the water bursts out underneath the ice carrying with it glacial moraines and blocks of ice.
dangers of Jokulhlaup
The speed and volume of the event will wash away anything in its path and change the route of river channels.
how do scientists measure eruptions
VEI (volcanic explosivity index)
what factors does VEI use to measure a volcanoes eruption
Amount and height of volcanic material erupted
How long the eruption lasts
Qualitative descriptive terms (e.g gentle, explosive)
what scale does VEI use
logarithmic
0 (non explosive) to 8 ( extremely explosive)
how do scientists predict eruptions, what signs do they look for
Small earthquakes
Changes to the volcanoes surface
Changes to the volcanoes tilt
a problem with predicting eruptions
they are never 100% accurate
