Volcanoes

Question 1

What plate margins can volcanoes occur at and why?

Answer 1

Constructive and destructive because there’s a source of magma

Question 2

What type of volcano happens at a constructive margin?

Answer 2

Shield volcano

Question 3

Why type of volcano happens at destructive margins?

Answer 3

Composite

Question 4

What are the characteristics of volcanos at a destructive margin?

Answer 4

They are the most destructive and explosive but tend to be more infrequent

Question 5

What are volcanoes like at constructive margins?

Answer 5

Generally less explosive and more effusive as they create rift volcanoes

Question 6

What is a hotspot?

Answer 6

An area of the mantle from where heat rises as a thermal plume from deep in the earth. High heat and low pressure at the base of the lithosphere enables rock to melt causing eruptions through a weak crust.

Question 7

What type of lava is produced by volcanoes at hotspots?

Answer 7

Basaltic lava

Question 8

What happens as a plate moves over a hotspot?

Answer 8

The volcano is carried away with the plate and then a new volcano is formed, creating a chain of volcanoes, atolls and sea mounts e.g. Hawaii

Question 9

What determines how violent a volcanic eruption is?

Answer 9

The amount of dissolved gas in magma and how easily the gas can escape

Question 10

How many active volcanoes are there today?

Answer 10

1900

Question 11

How are volcanoes measured?

Answer 11

The volcanic explosivity index

Question 12

What is the scale of the VEI and what type of scale is it?

Answer 12

Logarithmic scale that uses a scale from 0 (no explosive) to 8 (extremely large)

Question 13

What does the VEI take into account when it measures volcanoes?

Answer 13

The amount of volcano material ejected
The height of the volcano material ejected
How long the eruption lasts
Qualitative descriptions

Question 14

What do scientists look for when predicting a volcano?

Answer 14

Small earthquakes caused by magma rising to the surface
Changes to the surface of the volcano- as the magma pushes upwards, pressure builds and it causes the surface to swell
Changes to the tilt of the volcano

Question 15

What are lava flows like?

Answer 15

Streams of lava can be very hot, reaching 1170 degrees and take years to cool completely
While they destroy everything in their path, they generally aren’t a threat to humans as they move so slowly that people can outrun them.

Question 16

What makes lava flow faster?

Answer 16

A steeper slope and less viscosity which is determined by the amount of silicon dioxide in it

Question 17

What was one of the greatest lava disasters of all time?

Answer 17

1873, when molten material was issued from the Lakagigar fissure for 5 moths. An estimated 22% of the population died from the resulted famine

Question 18

What are volcanic gases and how do they pose a threat?

Answer 18

Magma contains dissolved gases that are released in the atmosphere during a volcanic eruption. They include water vapour, carbon dioxide, carbon monoxide, hydrogen and sulphur dioxide
Most deaths are associated with carbon dioxide as it’s more dangerous due to its colourless and odourless nature and can accumulate in valleys
They can travel thousands of miles

Question 19

What was one of the greatest death causing events from volcanic gases?

Answer 19

In 1986, emissions of CO2 from Lake Nyos in Cameroon killed 1,700 people

Question 20

What are pyroclastic flows and how do they cause a threat to people?

Answer 20

They are a mixture of dense hot rock, lava, ash and gases ejected from a volcano. They destroy everything they touch and move very quickly- can reach temperatures of 700 degrees and speeds of 100km per hour
They result from the frothing of molten magma in the volcano vent. As the bubbles burst, pyroclastic material is ejected

Question 21

What are tephra and ash falls and how do they pose a threat to people?

Answer 21

This is pieces of volcanic rock and ash that blast into the air during an eruption. The larger pieces tend to fall nearer to volcanoes and can cause injury or death, whereas the smaller pieces travel long distances.
Where ash lands, it creates poor visibility, slippery roads, roofs may collapse under its weight, fires may start and engines may be clogged up

Question 22

What are Lahars and how do they pose threat to people?

Answer 22

Lahars are volcanic mudflows made of masses of rock, mud and water that travel quickly down the side of the volcano. They are caused by the melting of snow and ice of heavy rainfall that can erode loose tephra
They are also fast meaning people cannot outrun them

Question 23

What is an example of a deadly Lahar?

Answer 23

The town of Armero was engulfed in a lahar that has travelled 74km from the Nevado del Ruiz in Columbia, killing 23,000 in just a few minutes

Question 24

What are jokulhulps?

Answer 24

A glacial outburst flood, caused by the heat of a volcano melting snow and ice. They occur very suddenly

Question 25

How many people have died over the last 300 years as a result of volcano action?

Answer 25

260,000

Question 26

What lava is the coolest lava and what tenperature is it?

Answer 26

Rhyolitic lava- 650-800 degrees

Question 27

Which lava is the hottest lava and what temperature is it?

Answer 27

Basaltic lava 1000-1200 degrees

Question 28

How hot is andesitic lava?

Answer 28

800-1000 degrees

Question 29

What is the order of the gas content in each of the lavas?

Answer 29

Basaltic- least- 0.5-2%
Intermediate- andesitic- 3-4%
Highest
Rhyolitic -4-6%

Question 30

How viscous are each of the lavas?

Answer 30

Basaltic- thin and runny as gases can escape
Andesitic- slow- intermediate viscosity
Rhyolitic- very slow- high viscosity

Question 31

What is the eruption energy of each of the different lavas?

Answer 31

Basaltic- gentle and effusive
Andesitic- violent and moderately explosive
Rhyolitic- very violent, cataclysmic

Question 32

Where do you find Rhyolitic lava?

Answer 32

Super volcanoes or composite cone ones

Question 33

Where do you find andesitic lava?

Answer 33

Composite cone volcanoes and subduction zones

Question 34

Where do you find basaltic lava?

Answer 34

Ocean hot spots, mid ocean ridges and shield volcanoes