Volcanoes Flashcards
Volcano
Vents at the surface of the earth through which magma and volcanic materials are ejected
Composite volcanoes
Tall, conical shapes and are composed of alternate layers of lava and ash
Caldera
A large volcanic crater that has undergone collapse, following an eruption
Shield volcano
They have gentle slopes of less than 10 degrees and a roughly circular shape around a circular vent
Fissure eruption
Where magma reaches the surface along long, linear crack or fissures
Fumarole
Opening in or near a volcano, through which hot gases emerge
VEI
A measure of the explosiveness of a volcanic eruption, allowing them to be compared. It is a 0 to 8 index of increasing explosivity
Describe how columnar joint form
tensional forces set up in igneous rock as it cools steadily and contracts. Forces pull open a series of joints form a hexagonal pattern.
Explain how pillow lava form from submarine eruptions
Lava erupted under water. Outer skin cools very rapidly where as inside stays molten. Pressure fromm more lava causes the front to break through to form a new pillow shape.
Describe the eruption cycle of a volcano
Period of no activity- magma chamber filling, differentiation may take place and pressure is building.
Pressure exceeds mass of overlying rock- explosion blasting away part of top of volcano, pyroclastic material escapes
Final stage- lava reaches surface and forms layer on top of pyroclasts. Gas pressure decreases, lava supply reduces and cools in vent plugging volcano
Describe how calderas form
Series of violent eruptions of pyroclastic flows, ash and pumice removing lots of magma. Magma chamber starts to empty and volcano starts to collapse into weakened area below, compressing remaining magma so eruptions are more violent. Entire cone collapses
isopachyte
A line joining points of equal thickness of a deposit such as ash. The maps may be called isopach maps
What happens to volcanic gases during an eruption?
They exolve due to pressure release. Main gas is water vapour. Gases combine with hydrogen and water to produce toxic compounds. Rain can be very acidic near volcano
What is the risk of lava flows? x3
Move slowly and rarely kill, can destroy property and agricultural land
What is the risk of blast damage?x4
very destructive near volcanoes, people in danger zone killed, trees flattened, buildings destroyed
What is the risk of ash fall? x2
Affects areas far from volcano, damage properties- mass of ash causes roof collapse
What is the risk of pyroclastic flows? x5
Very hot, travel quickly, mostly confined to valleys, kill many , unpredictable
What is the risk of lahars? x4
Move rapidly, may be very destructive, limited to valleys, may affect areas far from volcanoes
What is the distribution of pyroclasts by grain size?
Coarse bombs and blocks are dropped close to the vent
Finer pyroclastic material is carried further away possibly hundreds or thousands of km
ash gets finer and thinner with distance from vent
What is the distribution of pyroclasts by wind?
Where wind blows in the prevailing direction ash will mainly be deposited on leeward side of volcano. Rising columns of ash can get high into stratosphere. Jet streams in upper troposphere can transport ash around the world. Higher the wind velocity the further the as goes.
Effusive
Term used to describe the fluid, non-explosive, basaltic lava
Scoria
A volcanic rock that is usually mafic but can be intermediate in composition
