volcanoes

Question 1

is continental crust high or low density?

Answer 1

low

Question 2

is oceanic crust high or low desnity?

Answer 2

high

Question 3

what occurs when oceanic crust is destroyed?

Answer 3

new oceanic crust is formed elsewhere

Question 4

what plates is iceland on?

Answer 4

north american and eurasian

Question 5

how do oceanic ridges form?

Answer 5

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

Question 6

how did iceland form from an oceanic ridge?

Answer 6

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

Question 7

what is a rift valley?

Answer 7

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

Question 8

what might occur to the East African rift valley?

Answer 8

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

Question 9

give 3 geographical features of a constructive plate margin

Answer 9

1. new crust
2. rift valleys
3. shield volcanoes

Question 10

give 3 geographical features of a destructive plate margin

Answer 10

1. composite volcanoes
2. deep ocean trenches
3. earthquakes

Question 11

give a geographical feature of a conservative plate margin

Answer 11

1. earthquakes

Question 12

what is an island arc?

Answer 12

a curved chain of volcanic islands at a plate margin

Question 13

how are island arcs formed?

Answer 13

1. an oceanic plate subducts
2. the oceanic plate melts
3. the magma rises causing volcanic islands
4. due to tectonic movement, subduction occurs elsewhere next, creating a volcano in a different place

Question 14

what is a hot spot?

Answer 14

an area which is above a mantle plume

Question 15

what is a mantle plume?

Answer 15

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

Question 16

what is tephra?

Answer 16

large pieces of rock ejected by a volcano

Question 17

what is a vent?

Answer 17

the tunnel in a volcano where the magma rises

Question 18

what is a crater (volcano)?

Answer 18

an opening where the magma escapes the volcano

Question 19

what is the magma chamber?

Answer 19

a store of hot, molten rock within a volcano

Question 20

what plate margin are composite volcanoes found?

Answer 20

destructive (viscous lava)

Question 21

what plate margin are shield volcanoes found?

Answer 21

constructive (runny lava)

Question 22

describe:
active
dormant
extinct volcanoes

Answer 22

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

Question 23

give 4 features of composite volcanoes

Answer 23

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

Question 24

give 4 features of shield volcanoes

Answer 24

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

Question 25

what is a lahar?

Answer 25

a flow of rainwater/snow mixed with ash

Question 26

give 4 features of basaltic lava (shield)

Answer 26

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

Question 26

give 4 features of andesitic lava (composite) | remember temperature 7/11 rule

Answer 26

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

Question 27

give 4 comparisons between S and C volcanoes

Answer 27

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

Question 28

what are the 3 types of eruption?

Answer 28

1. Plinian 2. Hawaiian 3. Strombolian

Question 29

describe Plinian eruptions

Answer 29

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

Question 30

describe Hawaiian eruptions

Answer 30

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

Question 31

describe strombolian eruptions

Answer 31

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)

Question 32

what is a pyroclastic flow?

Answer 32

a fast moving current of gas and volcanic matter