Volcanoes Flashcards
Active volcano
Erupts regularly/likely to erupt soon
Mount Etna
Dormant volcano
Hasn’t erupted in recent history but is likely to erupt again Mnt Kilimanjaro
Extinct volcano
Hasn’t erupted in recent history + isn’t expected to erupt again
Mount Slemish
Acidic lava
Convergent boundaries
High silica content
800 C
High viscosity - moves slowly
Cools hard + fast
Gasses trapped - violent explosion
Forms steep sided slopes
Basic lava
Divergent boundaries
Low silica content
1,200 C
Low viscosity- moves quick
Cools + hardens slowly
Gases escape - gentle eruption
Forms gentle slopes
Tephra
Ash, dust + rock fragments emitted into the atmosphere
When tephra flows down the slopes of a volcano it is known as…
pyroclast
Pyroclastic flows
Can reach 500km/h + 1,000km
Power of the explosion crushes rocks in the vent. The pulverised rock + ash form air bubbles. Pyroclast can kill post eruption
Gases emitted in volcanic eruption
Carbon dioxide + sulfur
Oceanic-oceanic collision
Volcanic island eg. Philippines
Oceanic-continental collision
volacanic arcs eg. Cotapaxi (nazca subducts) in Ecuador
Divergent
Magma rises through fissures, no crust melting, gasses released eg. Mid Antlantic Ridge
Hotspots
away from boundaries, usually oceanic. Areas where the mantle is hotter, so it melts through the plate to form a volcano. Fixed point in the mantle, crust moves over it, oldest island = furthest away. Eg. Hawaiian islands
Composite cones /stratovolcanoes
convergent boundaries.
Explosive eruptions => alternating layers of acidic lava and pyroclastic material.
E.g. Mount St. Helens
Cinder cones
Smallest/most common type of volcano.
Made from pyroclastic material
Steep sides and a wide crater.
1 eruption => destroys their structure.
Calderas
Formed when composite cones explode violently.
Eruption factures rock => rock collapses in magma chamber => forms depression.
eg Yellowstone w 75 km caldera
Shield volcanoes
Form at divergent boundaries or over hotspots from gentle eruptions of basic lava
Volcano base >100 km diameter.
E.g. Mauna Loa and Mauna Kea, Hawaii
Lava plateau
Formed when basic lava releases to surface from fissure eruptions + flows over a large area before cooling/solidifying.
Repeated eruptions => build-up layer by layer
Antrim Derry plateau
60 million years old North American+ Eurasian diverged, fissures formed, large lava flows continued for 2 million years forming a 1.8km thick plateau, lava cooled+contracted, into hexagonal basalt columns, e.g. the Giant’s Causeway, Co. Antrim.
Batholiths
during periods of fold mountain building magma rises through the crust, melts surrounding layers of rock => pocket underneath the new fold mountains, magma cools to granite over millions of years.
> 100 km2 w thin cover of metamorphic rock
Leinster batholith
The Leinster Batholith> 1,500 km² 400 million years old
North American and Eurasian plates collided.
Thin layer of metamorphic rock protects granite from erosion, e.g. the Sugarloaf Mountain in Co. Wicklow is protected by quartzite
Sills
Magma forces through layers of sedimentary rock, cools slowly to form horizontal layer of granite.
Dykes
Magma forces through layers of sedimentary rock, cools slowly to form thin vertical layer of granite.
Laccoliths
Magma forces through layers of sedimentary rock, pressure forces rock to bulge upwards, magma cools to form small, dome-shaped layer of granite.
