VOLCANOES

Question 1

crater

Answer 1

basin above a volcano’s vent.

Question 2

caldera

Answer 2

a bowl-shaped structure that resembles a crater, but it is much larger (km in scale) and forms when a volcano collapses in on itself.

Question 3

materials produced by volcanic eruptions

Answer 3

gas, lava, and fragmented debris called tephra.

Question 4

Volcanic Gas

Answer 4

Magma contains gas. At high pressures, the gases are dissolved within magma. However, if the pressure decreases, the gas comes out of solution, forming bubbles.

The main component of volcanic gas emissions is water vapour, followed by carbon dioxide (CO2), sulphur dioxide (SO2), and hydrogen sulphide (H2S).

Question 5

lava

Answer 5

high viscosity = high silica/polymerisation + lots of gas bubbles.
low viscosity = the opposite.

Question 6

lava tubes

Answer 6

tunnels within older solidified lava flows.
lava within tubes can flow for 10s of km because the tubes insulate the lava from the atmosphere and slow the rate at which the lava cools.

Question 7

lava dome

Answer 7

caused by highly viscous magma

Question 8

volcanic ash

Answer 8

particles less than 2 mm in diameter

Question 9

lapilli

Answer 9

Fragments with dimensions between 2 mm and 64 mm

Question 10

Blocks

Answer 10

larger than 64 mm.
solid fragments of the volcano that form when an explosive eruption shatters the pre-existing rocks.

Question 11

Bombs

Answer 11

larger than 64 mm.
lava is thrown from the volcano and cools as it travels through the air.

Question 12

Pumice

Answer 12

forms from gas-filled felsic lava.

Question 13

scoria

Answer 13

forms from gas-filled felsic lava.

Question 14

Shield volcanoes

Answer 14

largest especially in diameter.

they have gentle hill-like shape because they are built of successive flows of low-viscosity basaltic lava.

Question 15

Composite volcanoes

Answer 15

second largest.
Unlike shield volcanoes, composite volcanoes have a distinctly conical shape, with sides that steepen toward the summit.

The change in the slope reflects the accumulation of tephra fragments near the volcano’s vent. Composite volcanoes typically erupt higher viscosity andesitic
and rhyolitic lavas, which do not travel as far from the vent as basaltic lavas do. This results in volcanoes of smaller diameter than shield volcanoes.

short geological life span - form quickly and pyroclastes erode quickly.

Question 16

Cinder cones

Answer 16

smallest.
Cinder cones have straight sides, unlike upward-steepening composite volcanoes, or rounded shield volcanoes.

straight sides and are typically less than 200 m high. Most are made up of fragments of scoria (vesicular rock from basaltic lava) that were expelled from the volcano as gas-rich magma erupted. Because cinder cones are made up almost exclusively of loose fragments, they have very little strength. They can be eroded away easily, and relatively quickly.