Hotspots and supervolcanoes Flashcards Preview

A Level Geography - Plate tectonics and associated hazards > Hotspots and supervolcanoes > Flashcards

Flashcards in Hotspots and supervolcanoes Deck (19):
1

How can a hot spot be described?
+ EXAMPLE.

A small area of the Earth’s crust where an unusually high heat flow is associated with volcanic activity.
Away from plate boundaries e.g. Hawaiian islands - localised hot spot within the Pacific plate.

2

How do hot spots *sometimes* create volcanoes?
+ EXAMPLE.

Excess of radioactive decay at the core.
Plastic rock plume (asthenosphere) pushes upwards.
Pressure drops and the plastic rocks become molten.
Lava breaks through surface, an active volcano is created above the hot spot - PLUME VOLCANOES.
Stationary - Pacific plate moves over it, a line of volcanoes is created (moving northwest).
The one above the hot spot is active.
Thinner crust here.
The rest - extinct volcanoes - EMPEROR SEAMOUNT.

3

What are some examples of volcanic activity that occur AWAY from the plate boundaries?

Oceanic features - Hawaiian Islands.
Continental features - Yellowstone super volcano.
Emperor seamount chain.

4

How was the Emperor seamount chain created?
+ what does it prove?

Oldest seamount - 70 million years.
5,000m+ long.
Stationary hot spot - Pacific plate moves over it - volcano line is created (5 inches per year).
The one above the hot spot is active, with the rest being extinct volcanoes.
Oldest - so much pressure on the crust - subsidence.
With marine erosion - reduced to seamounts below sea level.
Kilauea - largest active hotspot volcano - still rumbling - yet to move completely off the hot spot.
*proves that the Earth's crust is moving (Wegener)*

5

How was the Yellowstone supervolcano discovered?

Evidence of a prehistoric disaster.
200 rhinos, camels etc. in Nebraska- all had died abruptly 10 million years ago.
Ash - choked these animals to death.
Only a volcano could have produced so much ash, but there are NO volcanoes in Nebraska.
A supervolcano called Bruneau Jarbridge, 1600km away from the Nebraska fossils - led to SUPERVOLCANO discovery.
One eruption covered half of America with 2m of ash.

6

What was the last supervolcano eruption?

THE TOBA SUPER ERUPTION - 74,000 years ago, Indonesia.
Ash thrown out - 3000km - created global cooling.
Crater larger than the city of London.
Created Lake Toba - 100km long, 50km wide.
3000km3 of material.
Could reduce global temperatures by 5C - enough to spark an ice age.

7

What is a supervolcano and why are they so hard to spot?

A big bang eruption - affects everyone on the planet.
Ground - very hard to spot.
Calderas are so large - can only be spotted from space.

8

Where can supervolcanoes be located around the world?

Indonesia, New Zealand, South America.
Extinct - Glen Coe in England.
Yellowstone - still active - American National Park - 3 million+ people visit every year.

9

How are supervolcanoes formed?

Magma column rising through a vent into the crust.
Magma gets stuck and pools - melts rock for thousands of years.
Pressure build up.
Eruption eventually happens - drains the magma lake. Land above collapses down over - caldera.

10

How explosive are supervolcanoes?

VEI - 8.
Each leap up the scale represents an increase of explosive scale of 10 times the power.
Mount St Helens - VEI 5.

11

Why do people still visit Yellowstone if it's a supervolcano?

100km across.
Hot springs, geysers, geothermal.
Small eruptions - occurred every 20 to 30,000 years.
Difficult to prepare = never seen one.

12

What is the theory behind Yellowstone?

Yellowstone hotspot.
Magma moves upwards in the Mantle, melting the crust - creates huge magma chamber.
Static hot spot - Earth’s crust moves over it.
2 million years ago - hot spot settled under Yellowstone.

13

How often does Yellowstone erupt?

1.3 million years ago and 64,0000 years ago.
600,000-700,000 years cycle.

14

How did gases show that the Yellowstone magma was rising?

2003 - ground temperatures were at boiling point.
More frequent geyser eruptions.
New vents released hot volcanic gasses/mud - killed trees.
5 bison died.
High levels of carbon dioxide/hydrogen sulphide - death by gas poisoning.
Both gases come from magma.

15

How did ground deformation show that the Yellowstone magma was rising?

Ground movement - scientists use GPS and INSAR.
Measures distance between the satellite in space and the ground - can compare images over time.
1996 - uplift near the Norris Geyser Basin.
Land has uplifting over the past 7 years.
If it is magma - expected small/huge eruption.

16

What were the signs of a Yellowstone hydrothermal explosion?

An underwater eruption.
Bulge in the lake floor and explored it with a remote camera - found that the sediments arte lifting up

17

How were earthquakes used to help monitor Yellowstone?

1,000 to 3,000 small earthquakes.
22 seismometers.
Measured earth tremors - created from the magma movement in the magma chamber.
Detected seismic waves passing through rocks.
Waves pass through rock/magma at different speeds.

18

What did the scientists discover about the Yellowstone magma from using the seismometers?

Magma chamber - BIG THREAT.
80km long.
40km wide.
8km deep.
Not all liquid.

19

What would happen if Yellowstone was to erupt?

Affects whole world - disaster.
Magma will push the dome up.
Earthquakes - allows fissures to crack the surface.
Lava escapes.
Columns of ash - ejected 10s of kilometres into the air.
Pyroclastic flows.
Ash = Great Plains - would stop grain production - US economic activity would be affected.
Altered global climate - stopping the growing season.