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Geog Xmas 2023 > Volcanoes > Flashcards

Volcanoes Flashcards

1
Q

Volcanic zones

A

Hot spot
Convergent pb
Divergent pb
Where plates break up

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2
Q

Where are the largest and most active volcanoes found?

A

Pacific ring of fire
New Zealand along east Asia, across to Atlantic and south along north and South America

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3
Q

Active volcanoes

A

Currently erupting/showing signs of unrest
1,500 active volcanoes
50-70 erupt ever year
Eg. Mount Etna

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4
Q

Dormant volcanoes

A

Not currently erupting/ not expected to erupt in the near future
High probability they will erupt again eventually
Eg. Mount Pinatubo

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5
Q

Extinct volcanoes

A

Not erupted in historical times
Probably won’t erupt in future as no longer has lava supply
Eg slemish mountain (Antrim)

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6
Q

Why do volcanoes erupt?

A
  1. Upper mantle + subducted plates melt to become thick, flowing substance (magma)
  2. Magma - lighter than surrounding solid rock so it forces its way up towards crust
  3. Collects in a magma chamber (area of fractured rock in lithosphere)
  4. Gases + steams held under v high pressure in magma. As magma rises, gases expand further helping to drive up magma
  5. Eventually forces its way through a crack/hole in surface (eruption occurs)
  6. When magma on surface - lava
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7
Q

Volcanic material - lava (basic)

A

Basic lava
- low in silica so very runny
- can flow from volcanoes in big rivers for dozens of km before solidifying
- forms extensive but gently sloping landforms
- eg Antrim-Derry plateau

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8
Q

Volcanic materials - lava (acidic)

A

Acidic lava
- high silica content so viscous + pasty
- flows for short distance before cooling and solidifying
- steep sided landforms
- eg. Mount pinatubo

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9
Q

Volcanic material - pyroclastic (flow)

A
  • mixture of dry rock fragments and hot gases
  • moves away from vent of volcano and flows down its flanks at hurricane force speed (700km/hr)
  • deadliest of all volcanic events
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10
Q

Volcanic material - pyroclastic (cloud)

A
  • consists of dust and ash
  • blasted high into the sky during an eruption
  • can remain there for a long time and can be transported round the world by winds
  • eg. 2010 ash cloud from Iceland disrupted air traffic across Northern Europe
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11
Q

Volcanic material - pyroclastic (lahar)

A
  • volcanic mud flow
  • if the ash and dust get mixed with rain/steam(from melted snow) a flow of thick mud results
  • can flow down slopes of up to 200km/hr
  • eg. Mount pinatubo
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12
Q

Volcanic gases

A

-Magma contain gases
- driving force that saludes most eruptions
- large eruptions = can release huge amounts of gas into the atmosphere in short time
- harmless = water vapour/steam
- hazardous = carbon dioxide, sulphur dioxide and chlorine
- acid rain can be produced

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13
Q

Volcanic landforms - extrusive

A

Central vent eruptions
Fissure eruptions
Hot spot eruptions

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14
Q

Central vent eruptions

A
  • when volcanic material spews from a vent/opening in earth
  • central vent is connected to a magma chamber
  • lava and other volcanic materials (ash, cinders etc) pour out and build up around vent
  • cone shaped mountain formed
  • steep sided depression (crater) found at top of volcano (formed during eruption
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15
Q

Central vent eruptions - composite volcano

A
  • consists of alternate layers of lava and pyroclastic material
  • most of these materials fall near vent so a steep cone builds up
  • lava helps bind lose pyroclastic material
    -eg. Mount Vesuvius
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16
Q

Central vent eruption - lava dome

A
  • form when acidic, viscous lava erupts
  • as it’s pasty, unable to flow far
  • lava piles up around vent and forms a dome shape with high, steep sides
  • can explode violently releasing huge amounts of hot rock and ash
  • eg. Mount St Helens
17
Q

Central cent eruption - Caldera

A
  • forms when large quantities of molten magma and gases are blown out onto surface (violent eruptions)
  • if enough magma ejected, magma chamber becomes partially emptied
  • chamber is not unable to support cone above which collapses in
  • large depression (caldera)
  • eg. Yellow stone National park
18
Q

Fissure eruptions

A
  • magma rises, will find easiest route to reach the surface
  • if rises up through long crack/fissure, fountains of lava can form a curtain of fire
  • can be up to 10km long
  • eruption takes form of curtain of fire with lava barely rises about ground level
19
Q

Fissure eruptions - lava plateau

A
  • Fissure eruptions produce large amounts of basic lava and are less explosive
  • as lava spreads out, covers large areas of land
  • up to 50m thick, 50km from source
  • successive flows build up to form a flat landscape (lava plateau)
  • ^^^ flat topped landform that rises above surrounding area
  • eg. Antrim Derry plateau (65 mya)
20
Q

Where do fissure eruptions occur?

A

Where two plates are pulling apart
(Right now - on the floor of the Atlantic Ocean - American and Eurasian plates are separating)
- mid Atlantic ridge

21
Q

Hot spot eruptions

A

Hot spots - zones where they is usually hot mantle beneath the plates
- plume = a column of hot molten rock rises from deep within mantle
- plume eventually breaks through crust

22
Q

Hot spot eruptions pt 2

A
  • lava erupts and builds up into a large volcanic cone plate directly above hot spot
  • built of basic lava, the cones are wide and have gently sloping sides
23
Q

Hot spot eruptions pt 3

A
  • the plume stays still while the plate above moves
  • the plate carries older volcanoes away from the hot spot
  • eventually become extinct + hot spot continues to create new volcanoes
  • volcanoes increase in age with their distance from hot spot
  • eg. Hawaiian islands
24
Q

Volcanic landforms - intrusive

A

Plutons
-batholiths
- laccoliths
- sills
- dykes

25
Q

Batholiths

A
  • largest plutons
  • dome shape with steeply sloping sides
  • formed many km below surface as large amounts of magma pushed its way up to the crust
  • molten magma cooled and solidified very slowly, rocks are coarse, grained and have large crystals
  • granite
  • eg. Leinster batholith
26
Q

Laccoliths

A
  • dome like structures with flat floor
  • formed when magma pushes between the rock strata
  • the pressure forced the overlaying strata to bulge upwards
  • magma cooled and solidified
27
Q

Sills

A
  • horizontal sheets of volcanic rock that are parallel to rock strata
  • formed quite close to the surface where they’re was less pressure from overlying rock
  • magma forced into bedding planes and cool ed and solidified
28
Q

Dykes

A
  • thin, verticals sheets of volcanic rock that run perpendicular to the rock strata
  • formed when magma was forced into vertical fractures/ faults in the rock
  • cooled and solidified
29
Q

Predicting volcanic activity

A

Changes in shape of volcano
- as magma rises, cone pushed outwards
Heat and gases
- “ “ “, rocks around heat. If any snow/ice around, could trigger flooding/ lahars
- any large increase in amount of gas release - magma closer
Seismic activity
- magma chamber generates heat. Heat cracks surrounding rocks. Tremors

30
Q

Positive effects - fertile soil

A
  • ash + cinders are rich in minerals
  • people move back to volcanic regions after eruptions - vegetation
  • lava (when weathered + eroded) also makes fertile soil
  • eg. New Zealand (dairy and kiwi)
31
Q

Positive effects - tourist attractions

A
  • positive effect on local economies by providing employment (accommodation, transport, guiding, souvenir production)
  • eg. Mount Vesuvius, Pompeii
32
Q

Positive impacts - geothermal energy

A

—-> (geothermal cards)

33
Q

Negative effect - destruction + death

A
  • can cause large scale d + d
  • eruption can cause mudflows and lahars that can bury villages and kill people
  • towns at bottom of volcanoes at risk
  • eg. Nevado del Ruiz (Columbia) 1985
34
Q

Negative effects - air traffic disruptions

A
  • flights cancelled all around the world
  • travellers can be left stranded
  • ash clouds risk damaging engines
35
Q

Negative effects - poisonous gases

A
  • can cause death
  • eg. Carbon dioxide (odorless and heavier than air)
  • can displace oxygen
  • eg. Lake Nyos (Cameroon)
36
Q

Antrim-Derry plateau

A
  • basalt
  • formed from fissure eruption
  • giants causeway
37
Q

The Leinster batholith

A
  • Dublin mountains, Wicklow mountains + blackstairs mountains
  • granite

Geog Xmas 2023 (4 decks)

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