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geog a level physical > volcanoes > Flashcards

volcanoes Flashcards

1
Q

is continental crust high or low density?

A

low

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2
Q

is oceanic crust high or low desnity?

A

high

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3
Q

what occurs when oceanic crust is destroyed?

A

new oceanic crust is formed elsewhere

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4
Q

what plates is iceland on?

A

north american and eurasian

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5
Q

how do oceanic ridges form?

A
  1. as 2 plates pull apart magma rises
  2. the hotter, expanded crust forms a ridge
  3. a central valley may occur as a section of crust subsides into the magma below
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6
Q

how did iceland form from an oceanic ridge?

A
  1. liquid magma erupted from a split in the crust (lower pressure area)
  2. as the magma rises and cools, a volcano can rise until it reaches the surface
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7
Q

what is a rift valley?

A

a low land between highlands which is sinking as the crust pulls apart

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8
Q

what might occur to the East African rift valley?

A

if the valley continues to sink due to the tectonic forces, it may eventually flood and become an ocean

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9
Q

give 3 geographical features of a constructive plate margin

A
  1. new crust
  2. rift valleys
  3. shield volcanoes
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10
Q

give 3 geographical features of a destructive plate margin

A
  1. composite volcanoes
  2. deep ocean trenches
  3. earthquakes
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11
Q

give a geographical feature of a conservative plate margin

A
  1. earthquakes
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12
Q

what is an island arc?

A

a curved chain of volcanic islands at a plate margin

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13
Q

how are island arcs formed?

A
  1. an oceanic plate subducts
  2. the oceanic plate melts
  3. the magma rises causing volcanic islands
  4. due to tectonic movement, the crust shifts over the hot spot
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14
Q

what is a hot spot?

A

an area which is above a mantle plume

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15
Q

what is a mantle plume?

A

a spot where rock is heated via the earths core which then rises through the crust

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16
Q

what is tephra?

A

large pieces of rock ejected by a volcano

17
Q

what is a vent?

A

the tunnel in a volcano where the magma rises

18
Q

what is a crater (volcano)?

A

an opening where the magma escapes the volcano

19
Q

what is the magma chamber?

A

a store of hot, molten rock within a volcano

20
Q

what plate margin are composite volcanoes found?

A

destructive (viscous lava)

21
Q

what plate margin are shield volcanoes found?

A

constructive (runny lava)

22
Q

describe:
active
dormant
extinct volcanoes

A
  1. erupted in living memory
    2, erupted in historical records
  2. will not erupt
23
Q

give 4 features of composite volcanoes

A
  1. destructive pm
    2.narrow base + steep sides
  2. explosive eruptions
  3. viscous + acidic lava ( andesitic)
24
Q

give 4 features of shield volcanoes

A
  1. constructive pm
  2. low explosiveness
  3. wide base, shallow sides
  4. runny, less acidic lava (basaltic)
25
Q

what is a lahar?

A

a flow of rainwater/snow mixed with ash

26
Q

give 4 features of basaltic lava (shield)

A
  1. 1200 degrees c
  2. flows like a river ( keeps gas longer)
  3. 45-52% silica
  4. produces gently sloping landforms
26
Q

give 4 features of andesitic lava (composite)

remember temperature
7/11 rule

A
  1. 800 degrees c
  2. 52-63% silica
  3. cools fast/ viscous (loses gas fast)
  4. produces steep sides
27
Q

give 4 comparisons between S and C volcanoes

A
  1. S = Basaltic lava C= Andesitic lava
  2. S= gentle slope C= steep sided
  3. S= frequent, less explosive C= less frequent, more explosive (gas build up)
  4. S= Constructive pm C= destructive PM
28
Q

what are the 3 types of eruption?

A
  1. Plinian
  2. Hawaiian
  3. Strombolian
29
Q

describe Plinian eruptions

A
  1. most dangerous type of eruption
  2. high silica content
  3. high gas content causes explosiveness as it depressurises
  4. pyroclastic flows
30
Q

describe Hawaiian eruptions

A
  1. low silica and gas content
  2. less dangerous and explosive
  3. reduced amount of tephra
  4. basaltic lava flow rather than pyroclastic
31
Q

describe strombolian eruptions

A
  1. least dangerous eruption type
  2. lava flung 15-90m in air in bursts
  3. short bursts of lava means effects are less dangerous
  4. viscous lava (andesitic)
32
Q

what is a pyroclastic flow?

A

a fast moving current of gas and volcanic matter

33
Q
A

geog a level physical (6 decks)

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