volcanoes

Question 1

what causes the formation of a volcano at a constructive margin?

Answer 1

• magma rises filling space left by plates
• this can form ocean ridges underwater
• rift valleys are formed on land as the plates pull apart
• therefore magma breaks through the surface

Question 2

what causes the formation of a volcano at a destructive margin?

Answer 2

• at subduction zones, plates are pulled underneath eachother.
• the denser plate forms magma
• magma comes under pressure in the upper asthenosphere and rises to the surface

Question 3

what is the distribution of volcanoes?

Answer 3

• can occur at construction and destructive plate margins because they form new crust
• can also be found at the middle of plates due to mantle plumes and hotspots

Question 4

what are mantle plumes?

Answer 4

• vertical columns of hot magma that rise from the mantle
• they are caused by radioactive decay
• they melt and weaken the crust to force their way through it to form a new volcano (hotspot volcanoes)
• mantle plume stays stationary and the crust moves over it, repeating the process again

Question 5

what are primary hazards of volcanoes?

Answer 5

• lava flows
• pyroclastic flows
• volcanic gases
• tephra

Question 6

what are secondary hazards of volcanoes?

Answer 6

• lahars
• jokulhlaups

Question 7

what is a lava flow and pyroclastic flow?

Answer 7

lava flow:
- flows from volcanic vent
- high temp, low viscocity

pyroclastic flow:
- superheated gas, ash, volcanic rock
- created in volcano crater
- travels at high speeds, cause a lot of destruction

Question 8

what are volcanic gases and tephra?

Answer 8

volcanic gases:
- water vapour, carbon dioxide and sulphur
- colourless and odorless
- poisonous, can cause breathing difficulties

tephra:
- pieces of rock ejected into the air during an eruption
- can damage buildings/people
- can produce atmospheric hazes reducing crop yields, and it’s harmful to breathe in

Question 9

what is a lahar and a jokulhlaup?

Answer 9

lahar:
- mudflow, water mixed with ash and slit from heavy rainfall/rivers
- can bury/destroy natural habitats as it moves very quick

jokulhlap:
- flood caused by glacial meltwater from subglacial lake
- melts due to heat from volcanic eruption
- releases a sudden deluge of water known as a glacial outburst
- contains ice fragments and moraine