Volcanoes Flashcards
Volcanic zones
Hot spot
Convergent pb
Divergent pb
Where plates break up
Where are the largest and most active volcanoes found?
Pacific ring of fire
New Zealand along east Asia, across to Atlantic and south along north and South America
Active volcanoes
Currently erupting/showing signs of unrest
1,500 active volcanoes
50-70 erupt ever year
Eg. Mount Etna
Dormant volcanoes
Not currently erupting/ not expected to erupt in the near future
High probability they will erupt again eventually
Eg. Mount Pinatubo
Extinct volcanoes
Not erupted in historical times
Probably won’t erupt in future as no longer has lava supply
Eg slemish mountain (Antrim)
Why do volcanoes erupt?
- Upper mantle + subducted plates melt to become thick, flowing substance (magma)
- Magma - lighter than surrounding solid rock so it forces its way up towards crust
- Collects in a magma chamber (area of fractured rock in lithosphere)
- Gases + steams held under v high pressure in magma. As magma rises, gases expand further helping to drive up magma
- Eventually forces its way through a crack/hole in surface (eruption occurs)
- When magma on surface - lava
Volcanic material - lava (basic)
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
Volcanic materials - lava (acidic)
Acidic lava
- high silica content so viscous + pasty
- flows for short distance before cooling and solidifying
- steep sided landforms
- eg. Mount pinatubo
Volcanic material - pyroclastic (flow)
- 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
Volcanic material - pyroclastic (cloud)
- 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
Volcanic material - pyroclastic (lahar)
- 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
Volcanic gases
-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
Volcanic landforms - extrusive
Central vent eruptions
Fissure eruptions
Hot spot eruptions
Central vent eruptions
- 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
Central vent eruptions - composite volcano
- 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
Central vent eruption - lava dome
- 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
Central cent eruption - Caldera
- 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
Fissure eruptions
- 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
Fissure eruptions - lava plateau
- 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)
Where do fissure eruptions occur?
Where two plates are pulling apart
(Right now - on the floor of the Atlantic Ocean - American and Eurasian plates are separating)
- mid Atlantic ridge
Hot spot eruptions
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
Hot spot eruptions pt 2
- 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
Hot spot eruptions pt 3
- 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
Volcanic landforms - intrusive
Plutons
-batholiths
- laccoliths
- sills
- dykes
