Vulcanicity

Question 1

Vulcancity benefits

Answer 1

Lava flows can create land

Igneous rocks contain valuable mineral deposits

Lava and ashes weather quickly into fertile soils

Tourist attractions

Question 2

Global distribution of volcanoes

Answer 2

Destructive, constructive margins and hot spots

Most are located in linear patterns around the edge of the Pacific Ocean and this is known as the ring of fire.

Question 3

Volcano formation at destructive margins

Answer 3

E.g where the Nazca plate is being forced beneath the South African plate

Convection currents in the asthenosphere causes the denser oceanic plate to move towards the lighter continental plate and it is subducted along with a large amount of water. This ocean water mixes with the magma which is formed due to the intense heat and this friction and it rises and erupts.

Subsequent eruptions cause a volcano to cause

Question 4

Volcano formation at constructive margins- two sections of oceanic crust

Answer 4

2 sections of oceanic plate move apart due to convection currents.

The plates move apart allows magma to reach the surface and in some places, submarine volcanoes are formed.

These volcanoes are found along or close to oceanic ridges such as the Atlantic ridge

Question 5

Volcano formation at constructive margins- 2 sections of continental plate

Answer 5

2 sections of crust move apart due to convection currents pulling the crust in different directions, creating faults and weaknesses .

This allows magma to rise to be surface and solidifies

Question 6

Volcano formation at hotspots

Answer 6

Formed due to a rising plume of superheated magma which thins and heats the crust, allowing magma to reach the surface.

Overtime, layers of lava builds up to form volcanoes

E.g Hawaii is a hot spot volcano in the centre of the Pacific plate

Question 7

Active volcanoes

Answer 7

Have erupted in living memory

Question 8

Dormant volcanoes

Answer 8

Have erupted within historical record

E.g mount Etna, Italy

Question 9

Inactive volcanoes

Answer 9

Haven’t erupted in the last 25,000 years

Question 10

Volcanoes definition

Answer 10

Openings in the earths crust through which lava, ash and gases erupt

Question 11

Extrusive volcanic landforms definition

Answer 11

Magma is extrusive volcanic features cools, crystallises and solidifies at the surface with air.

Therefore, the igneous rocks tend to be finer grained with small crystals such as basalt

The lava cools far quicker than magma underground

Question 12

Materials erupted by volcanoes

Answer 12

Gaseous emissions- dominated by steam but also more dangerous gases such as carbon monoxide and calories

Solids- ash, dust and glassy cinders

Liquids- tephra which solidify in mid air. Tephra ranges in size such as large lava bombs and in its finest form of hair like trails called lapilli.
Surface lavas- acid or basic

Question 13

Name the 3 types of lava

Answer 13

Basaltic

Andesitic

Rhyolithic

Question 14

Basaltic lava

Answer 14

From ex from the upward movement of mantle material

Low silica which makes it more fluid that a
Lows gas bubbles to escape on the way up, preventing sudden explosive activity

Question 15

Andesitic lava

Answer 15

Formed at destructive margin

Silica rich (viscous)

Lava often solidifies before reaching the surface, leading to a build up of pressure and a violent explosion

Question 16

Rhyolithic lava

Answer 16

Formed at destructive and collision margins

Same characteristics as andesitic lava

Question 17

Vent volcano openings

Answer 17

Usually create cone shaped landforms

Question 18

Fissure opening volcanoes

Answer 18

A long crack in the crust which allows lava to spill out over a large area

Question 19

Basic shield volcanoes

Answer 19

Gently sloping cones from layers of less viscous lava

Question 20

Composite volcanoes

Answer 20

Layers of ash and lava

Pyramid shaped

Question 21

Acid volcanoes

Answer 21

Steep sides, convex cones consisting of viscous lava

Acidic lava causes a plug in the volcano

Question 22

Calderas

Answer 22

Form when the build up of gases inside the volcano is so big that explosions occur which clears out all the magma and remove the peak of the cone and leave an enormous crater

Question 23

Ash and cinder cones

Answer 23

Formed from ash, cinder and volcanic bombs

Question 24

How can volcanoes be classified based on the violence of the eruption

Answer 24

Examples

Hawaiin volcano- constructive, lava flows gently, basaltic magma, eruption height of 2km

Vulcanian volcano- destructive, eruption height of 20km

Question 25

Intrusive volcanic landforms

Answer 25

Magma cools below the surface within the first.

The resulting features may only become part of the landscape once later erosion removes the overlying rocks

Question 26

Batholiths

Answer 26

Formed when large masses of magma cool and solidify

They are often done shaped and exposed by later erosion

Question 27

Dykes

Answer 27

Vertical intrusions with horizontal cooling cracks

They cut across the bedding plane of the rocks into which they have been intruded

Often occur in groups known as dyke swarms

Question 28

Sills

Answer 28

Horizontal instrusions with vertical cooling cracks

Question 29

Geysers

Answer 29

Occur when water, heated by volcanic activity explode onto the surface

It is an intermittent, forceful discharge of superheated water ejected from the surface

E.g old faithful, Yellowstone national park, USA

Ground water collects in conduits
Magma within the crust heats the water
As the water is heated, pressure builds up until an explosion occurs

Question 30

Hot springs/ boiling mud

Answer 30

Hot thermal springs aren’t under pressure and so don’t explode at the surface.
Water collects in pools
E.g the blue lagoon, Iceland

Where hot water on its way upwards mixes wig mud and minerals near the surface, a bubbling boiling mud may form

Question 31

Fumarole

Answer 31

Low pressure outlets of steel

Founded in areas where super heated water turns to steam as it cpndenses on the surface

Mainly steam and carbon dioxide

If the gas is sulphurous, fumaroles are called solfataras

Question 32

Vulcanicity hazards

Answer 32

Lava flows burn and bury crops

Flooding can result from lava flows

Submarine, coastal or island eruptions can cause tsuniamis

Ash falls disrupt transport, pollutes the air, causes breathing difficulties

Pyroclastic flow can destroy life and property

Volcanic dust absorbs solar energy and so lowers atmospheric temps