Volcanoes Flashcards
What is magma?
Molten rock below the surface
What is lava?
Molten rock above the surface
What does extrusive mean?
When lava and other materials reach the surface
What does intrusive mean?
Material that is injected into the crust
What is igneous rock?
Rocks formed from cooled magma
What is pyroclastic material?
Material ejected from the volcano as fragments
What are fissure eruptions?
1) Lava erupts from an elongated fissure of the main central vent
2) Lava fills up hollows creating a dome shape
3) Cooling produces columnar jointing
•Comprised of basalt
•E.g. Giants causeway, N Ireland
What are dome volcanoes?
1) Lava from central vent and acid lava quickly solidifies forming a steep sided convex cone with many layers
•E.g. Mt St Helens, USA
What are shield volcanoes?
1) Lava flows from central vent and spreads over a large area before solidifying giving it a cone-like appearance with long, gentle sloping sides with many layers
•E.g. Mauna Loa, Hawaii
What are ash and cinder cones?
1) Fine ash and cinder are ejected from central vent, layering up creating a shallow sided, concave cone
•E.g. Mt Etna, Italy
What is caldera volcano?
1) Gas builds up in the magma chamber causing an explosion
2) Sides of the crater subside
3) Craters can be flooded by the sea creating lagoons
What are magma plumes?
•Vertical columns of extra-hot magma that rises up from the mantle
• Volcanoes can form above magma plumes
•Can create chains of island e.g. Hawaii
How are magma plumes formed?
1) Radioactive decay in the Earth’s core heats the lower mantle, creating plumes of magma with thermal currents
2) These currents can cause plate movement or burn through the lithosphere, creating a hotspot volcano
3) The hotspots stay fixed whilst the plate above moves causing a chain of extinct volcano -> Bends in the chain can show plate movement
What do active volcanoes mean?
Erupted in living memory like Mt Etna, Italy
What do dormant volcanoes mean?
Erupted in historic record like Mt Kilimanjaro, Tanzania
What do extinct volcanoes mean?
Will not erupt ever again like Ben Nevis, Scotland
How to measure volcanic eruptions?
Measured using volcanic explosivity index which measures the volume of ejected material
-No characteristic mark on the scale
-Low end -> Hawaii and Icelandic eruptions
-High end -> Super volcanic eruptions
Info bout Basaltic lava:
-Found at constructive margins
-Hot 1200°C, runny and low viscosity -> Flows for a long time
-Low silica content 45-52%
-Flows like rivers of molten rock as it takes longer to cool
-Keeps it’s gas content so it’s more mobile
-Produces extensive, gently sloping landforms
-Volcanoes erupting basaltic lava do so frequently and continuously
-Relatively gentle but frequent eruptions
-Not violet
-Lava and steam erupts
-Underwater = ocean ridges formed e.g. disused along mid-Atlantic ridge
-On land = rift valleys, magma can rise making land thinner so it can break the surface
-Hot spots = Maura Loa, Hawaii - forming gentle sided shield volcanoes
Info about Andesitic lava:
-Found at destructive margins
-Cooler (800 °C) and high viscosity so flows more slowly over shorter distance
-High silica content 52-63%
-Erupt intermittently and are short-lived
-Flows short distances as soon cools and solidifies
-Steep-sided, localised features
-Less frequent eruptions but are violent because of gas build up
-Pyroclastic - as, rock, gases and steam + lava ejected
-Subduction zones = melting of the plates forms magma, which rises to volcano surface. Because this lava is viscous it forms blockages in the volcano vents, causing pressure to build which is cleared by violent eruptions
-Island arcs = Mt. Pelee, Martinique
How do you predict volcanoes?
-Measure seismic activity and ground deformations
-Changes in CO2 and O2 signify imminent eruptions
-Bulges on volcano sides
Pyroclastic flow
-Mixture of super-heated gas, ash, lava and volcanic rock
-Travels downslope
-High speeds of 80-200Km/h
-Travels around 10-15Km
-Relatively little warning due to speeds which can cause widespread death and destruction
-Temperatures of 350-1000°C
- occurring at subduction zones, commonly with andesitic lava
Pyroclastic flow impacts:
-Widespread destruction and death due to high speeds e.g. burning and burial under debris as it carries away anything in its path
-Extreme temperatures can ignite fires
-Ice and snow can melt due to extreme temperatures
-Risk of serious burns
-Causes floods and lahars
Nuee ardente
-Means glowing cloud
-Contains more dense material
-Normally found 50Km from source
Tephra
-Rock fragments ejected during an eruption, large fragments land close to the source whereas small fragments can travel great distances
-Ash can cause breathing difficulties, block sunlight and alter temperatures
