Vocanoes And Hot Spots Flashcards
What is a magma plume?
Magma plumes are the areas of hot, upwelling mantle.
A hotspot develops above the plume in the crust. Magma generated by the hot spot rises through the rigid plates of the lithosphere and produces active low viscosity volcanoes in the earths surface.
Eg the Hawaiian Island chain.
What happens as Continental volcanos move away from a hotspot?
They cool, subside and become extinct.
Describe magma plumes
• Radioactive decay in the Earth’s core heats the lower mantle, creating plumes of magma with thermal currents.
• these currents can cause plates to move, or may burn through the lithosphere, creating a Hot Spot Volcano
• the Hot Spot stays fixed whilst the plate above moves, creating a chain of extinct volcanos
• bends in the chain can show plate movement
What is meant by active?
Have erupted in living memory
Eg Mt. Etna, Italy
What is meant by dormant?
Have erupted within historic record
Eg Mt. Kilimanjaro, Tanzania
What is meant by extinct?
Will not erupt again
Eg Ben Nevis, Scotland
Describe basaltic lava
• hot (1200C) and runny, low viscosity
• low silica content
• flows as rivers of molten rock as takes longer to cool
• keeps its gas content so more mobile
• produces extensive, gentle sloping landforms
• relatively gentle but frequent eruptions
• lava and steam erupted
• found at constructive plate margins
Eg fissures along Mid-Atlantic Ridge
Eg over hot spots - Mauna Loa, Hawaii
Describe andesitic lava
• viscous, cooler (800C) flows more slowly for shorter distances
• higher silica content
• flows very short distances as soon cools and solidifies
• loses gas quickly so becomes more viscous
• steep-sided, localised features
• less frequent eruptions but are violent because of gas build up
• pyroclastics - ash, rock, gases and steam and lava ejected
• found at destructive margins where oceanic crust is destroyed, melts and rises
Eg subduction zones Mt. St Helens
Eg as island arcs Mt. Pelee, Martinique
What does the VEI (Volcano Explosivity Index) measure?
The volume of erupted material
(Volcanic explosivity)
What are the primary impacts of a volcanic eruption?
• lava flows
• tephra (solid material) - eg ash and volcanic bombs
• pyroclastic flow (over 800C) - gas and tephra travelling at 700km/h
• volcanic gas (CO2, CO, SO2 and Cl2) - poisonous
What are the secondary impacts of a volcanic eruption?
• Lahars (volcanic mudflow) - hot, melted snow and ash flowing at high speeds. Can kill people.
• Acid rain - gases eg SO2 combines with rain. Kills plants, fish and contaminates water.
• Tsunamis - earthquakes associated with volcanoes.
• Flooding - in glaciated landscapes through the melting of ice
• climate change - ash blocks solar radiation and creates cooling effect.
Give 4 ways to predict volcanic eruptions
• history (time/frequency of previous eruptions)
• look at gases released - may increase on lead up to eruption
• ground swelling
• ground water level changes
Give 2 methods of protection against volcanic eruptions.
• Prior warning (alert systems eg red=evacuate)
• divert lava - eg direct into manmade channels or controlled explosions to allow lava to be diverted to lessen impact.
Give short term responses for a volcanic eruption
• Food, shelter and water
• provide provision emergency services
Give long term responses for a volcanic eruption
• rebuilding infrastructure (eg roads, electricity and buildings)
• protection methods
