Volcanoes

Question 1

At what plate boundaries can volcanoes only occur?

Answer 1

Divergent and convergent

Question 2

What is the material that is ejected from the volcano called?

Answer 2

Tephra

Question 3

What are lava flows (primary)

Answer 3

Sheets of liquid rock expelled from the crown or flank of an erupting volcano.

Question 4

What are Jokulhaups (secondary)

Answer 4

Masses of water or ice suddenly released from a glacier by the heat from lava inside a volcano. Can become mudflows if the ground is unconsolidated e.g soil. Also known as glacial outbursts.

Question 5

What are pyroclastic flows (primary)

Answer 5

Dense masses of gases and fragments of lava that flow down the sides of volcanoes at great speeds. Formed when gas-saturated lava reaches the earths surface, bubbles and breaks the lava into tiny fragments (ash).

Question 6

What are lahars (secondary)

Answer 6

Volcanic mudflows commonly created when ash mixes with snow and ice from a volcano summit. Move down volcano flanks like liquid cement.

Question 7

What is tephra/ash falls (primary)

Answer 7

Explosive composite volcanoes project ash at great heights. Ash then falls to the ground covering land and property.

Question 8

What are gas eruptions (primary)

Answer 8

Water vapour and carbon dioxide are commonly released during an eruption. Poisonous sulphur dioxide and sulphur trioxide are the most common toxic gases released before, during and many years after a volcanic eruption.

Question 9

What are the primary effects of volcanoes

Answer 9

Lava flows
Pyroclastic flows
Tephra/ Ash falls
Gas eruptions

Question 10

What are the secondary effects of volcanoes?

Answer 10

Jokulhaups

Lahars

Question 11

How are volcanoes formed at convergent plate boundaries?

Answer 11

1. Pressure and tension build up as the tectonic plates move towards each other.
2. The denser plate subducts into the asthenosphere
3. The material subducted melts and adds to the mantle
4. The lithosphere/ crust begin to crack due to the pressure and tension as the plate is subducted
5. The hot molten magma rises through the cracks.
6. This hot magma erupts again and again over time as the plate is subducted.
7. This magma is fairly viscous (sticky) and the layers build up to form a composite steep sided volcano.

Question 12

How are volcanoes formed at divergent plate boundaries?

Answer 12

1. Very little pressure/friction occurs at divergent boundaries as the plates are moving apart.
2. As the plates move the crust becomes thin and often cracks occur between the two plates.
3. Magma begins to rise through these cracks in the lithosphere/crust.
4. This magma cool and this forms new lithosphere/crust
5. The rising of the magma occurs again and again over time.
6. The magma rising is very hot and therefore not very viscous (sticky).
7. The runny hot magma creates shield volcanoes which are gently sloping over a wide area.
8. Most of these volcanoes are never seen as they are deep under the ocean floor.