Major and minor forms of extrusive activity

Question 1

What are the 3 main MINOR extrusive features?

Answer 1

Geysers, hot springs and boiling mud.

Question 2

What are 2 good examples of MINOR extrusive feature sites?

Answer 2

Yellowstone National Park in the USA.

Various parts of Iceland.

Question 3

What are geysers and how are they formed?

+ EXAMPLE.

Answer 3

Water vent discharges the Earth’s surface.
Often intermittent/dangerous.
Surface water comes into contact with hot rocks - converted into steam.
Pressurised.
Fissure allows a jet of boiling water to explode onto the surface.
E.g. Old Faithful, Yellowstone National Park.

Question 4

How are hot springs formed?

+ EXAMPLE.

Answer 4

Groundwater is constantly heated by the rocks underneath the surface.
NOT pressurized so are therefore NOT explosive.
Temperatures 20-90C.
E.g. Mammoth Hot Springs.

Question 5

How is boiling mud formed?

Answer 5

Mud is mixed with heated volcanic water.
Causes it to bubble.
Acid attacks the surface and forms clay.
E.g. Yellowstone.

Question 6

When do minor extrusive features appear?

Answer 6

When an active volcano is nearing the end of its life.

Dormant volcano.

Question 7

What are the different types of volcanoes? 6

Answer 7

Fissure.
Shield.
Acid/dome.
Ash-cinder.
Composite/strato volcano.
Caldera.

Question 8

What is a lava plateaux volcano?

Answer 8

Fissure eruptions.
Basaltic - flow great distances.
Flat, layered.

Question 9

What is a shield volcano?

Answer 9

Basaltic.
Gentle sides
3 miles wide.
1,500m height.
Low gas content and silica.
E.g. Mauna Loa, Hawaii.
Constructive boundaries/hot spots.

Question 10

What is an acid/dome volcano?

Answer 10

Steep-sided - covered with rock debris.
Formed by repeated eruptions - a layered structure.
High silica and gas pressure.
Rhyolitic.
E.g. Puy Region, France.

Question 11

What is an ash-cinder volcano?

Answer 11

Formed from ash and volcanic bombs.
Steep and symmetrical sides.
E.g. Paricutin, Mexico.

Question 12

What are composite/strato volcanoes?

Answer 12

Tall, conical volcano built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash.
High viscosity - andesitic.
E.g. Mount Etna/Pinatubo.

Question 13

What are caldera volcanoes?

Answer 13

Formed from HUGE explosions - blows the summit (top) of the cone off, leaving an opening.
Rhyolitic.
May become flooded by the sea.
Lake may form.
E.g. Yellowstone.

Question 14

What are solfataras?

Answer 14

Small volcanic areas without cones, produced by gases (mainly sulphurous) escaping to the surface.
E.g. Bay of Naples in Italy.