Volcanoes

Question 1

Volcano

Answer 1

Vents at the surface of the earth through which magma and volcanic materials are ejected

Question 2

Composite volcanoes

Answer 2

Tall, conical shapes and are composed of alternate layers of lava and ash

Question 3

Caldera

Answer 3

A large volcanic crater that has undergone collapse, following an eruption

Question 4

Shield volcano

Answer 4

They have gentle slopes of less than 10 degrees and a roughly circular shape around a circular vent

Question 5

Fissure eruption

Answer 5

Where magma reaches the surface along long, linear crack or fissures

Question 6

Fumarole

Answer 6

Opening in or near a volcano, through which hot gases emerge

Question 7

VEI

Answer 7

A measure of the explosiveness of a volcanic eruption, allowing them to be compared. It is a 0 to 8 index of increasing explosivity

Question 8

Describe how columnar joint form

Answer 8

tensional forces set up in igneous rock as it cools steadily and contracts. Forces pull open a series of joints form a hexagonal pattern.

Question 9

Explain how pillow lava form from submarine eruptions

Answer 9

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.

Question 10

Describe the eruption cycle of a volcano

Answer 10

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

Question 11

Describe how calderas form

Answer 11

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

Question 12

isopachyte

Answer 12

A line joining points of equal thickness of a deposit such as ash. The maps may be called isopach maps

Question 13

What happens to volcanic gases during an eruption?

Answer 13

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

Question 14

What is the risk of lava flows? x3

Answer 14

Move slowly and rarely kill, can destroy property and agricultural land

Question 15

What is the risk of blast damage?x4

Answer 15

very destructive near volcanoes, people in danger zone killed, trees flattened, buildings destroyed

Question 16

What is the risk of ash fall? x2

Answer 16

Affects areas far from volcano, damage properties- mass of ash causes roof collapse

Question 17

What is the risk of pyroclastic flows? x5

Answer 17

Very hot, travel quickly, mostly confined to valleys, kill many , unpredictable

Question 18

What is the risk of lahars? x4

Answer 18

Move rapidly, may be very destructive, limited to valleys, may affect areas far from volcanoes

Question 19

What is the distribution of pyroclasts by grain size?

Answer 19

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

Question 20

What is the distribution of pyroclasts by wind?

Answer 20

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.

Question 21

Effusive

Answer 21

Term used to describe the fluid, non-explosive, basaltic lava

Question 22

Scoria

Answer 22

A volcanic rock that is usually mafic but can be intermediate in composition