volcanoes Flashcards
is continental crust high or low density?
low
is oceanic crust high or low desnity?
high
what occurs when oceanic crust is destroyed?
new oceanic crust is formed elsewhere
what plates is iceland on?
north american and eurasian
how do oceanic ridges form?
- as 2 plates pull apart magma rises
- the hotter, expanded crust forms a ridge
- a central valley may occur as a section of crust subsides into the magma below
how did iceland form from an oceanic ridge?
- liquid magma erupted from a split in the crust (lower pressure area)
- as the magma rises and cools, a volcano can rise until it reaches the surface
what is a rift valley?
a low land between highlands which is sinking as the crust pulls apart
what might occur to the East African rift valley?
if the valley continues to sink due to the tectonic forces, it may eventually flood and become an ocean
give 3 geographical features of a constructive plate margin
- new crust
- rift valleys
- shield volcanoes
give 3 geographical features of a destructive plate margin
- composite volcanoes
- deep ocean trenches
- earthquakes
give a geographical feature of a conservative plate margin
- earthquakes
what is an island arc?
a curved chain of volcanic islands at a plate margin
how are island arcs formed?
- an oceanic plate subducts
- the oceanic plate melts
- the magma rises causing volcanic islands
- due to tectonic movement, subduction occurs elsewhere next, creating a volcano in a different place
what is a hot spot?
an area which is above a mantle plume
what is a mantle plume?
a spot where rock is heated via the earths core which then rises through the crust
what is tephra?
large pieces of rock ejected by a volcano
what is a vent?
the tunnel in a volcano where the magma rises
what is a crater (volcano)?
an opening where the magma escapes the volcano
what is the magma chamber?
a store of hot, molten rock within a volcano
what plate margin are composite volcanoes found?
destructive (viscous lava)
what plate margin are shield volcanoes found?
constructive (runny lava)
describe:
active
dormant
extinct volcanoes
- erupted in living memory
2, erupted in historical records - will not erupt
give 4 features of composite volcanoes
- destructive pm
2.narrow base + steep sides - explosive eruptions
- viscous + acidic lava ( andesitic)
give 4 features of shield volcanoes
- constructive pm
- low explosiveness
- wide base, shallow sides
- runny, less acidic lava (basaltic)
what is a lahar?
a flow of rainwater/snow mixed with ash
give 4 features of basaltic lava (shield)
- 1200 degrees c
- flows like a river ( keeps gas longer)
- 45-52% silica
- produces gently sloping landforms
give 4 features of andesitic lava (composite)
remember temperature
7/11 rule
- 800 degrees c
- 52-63% silica
- cools fast/ viscous (loses gas fast)
- produces steep sides
give 4 comparisons between S and C volcanoes
- S = Basaltic lava C= Andesitic lava
- S= gentle slope C= steep sided
- S= frequent, less explosive C= less frequent, more explosive (gas build up)
- S= Constructive pm C= destructive PM
what are the 3 types of eruption?
- Plinian
- Hawaiian
- Strombolian
describe Plinian eruptions
- most dangerous type of eruption
- high silica content
- high gas content causes explosiveness as it depressurises
- pyroclastic flows
describe Hawaiian eruptions
- low silica and gas content
- less dangerous and explosive
- reduced amount of tephra
- basaltic lava flow rather than pyroclastic
describe strombolian eruptions
- least dangerous eruption type
- lava flung 15-90m in air in bursts
- short bursts of lava means effects are less dangerous
- viscous lava (andesitic)
what is a pyroclastic flow?
a fast moving current of gas and volcanic matter
