Plate Tectonics And Associated Hazards- Plate movement

Question 1

Mantle

Answer 1

Surrounds the core. Most of the mantle (asthenosphere) is semi molten.

Question 2

Lithosphere

Answer 2

Consists of the crust and the rigid upper section of the mantle

Question 3

Asthenosphere

Answer 3

This is below the lithosphere and is semi molten.

Question 4

Oceanic crust

Answer 4

Thinner
Younger
Denser
Basalt rocks known as sima

Question 5

Continental crust

Answer 5

Thicker
Older
Less dense
Mainly granite rocks known as sial

Question 6

Pangea

Answer 6

An ancient supercontinent (the theory which suggests that all contingents were once all joined together)

Question 7

Alfred Wegener

Answer 7

In 1912, he published a theory suggesting that all the continents were once all joined together in a supercontinent called Pangea.

He said that all the land masses drifted apart until they occupied their current positions.

Question 8

Evidence of continental drift

Answer 8

Jigsaw fit- some continents seem to fit together if placed beside each other (Africa and South America)

Geological evidence- rocks of the same age and type and displaying the same formations are found in South East Brazil and South Africa.

Biological evidence- similar fossil formations are found on either side of the Atlantic

Question 9

Problem with Wegeners theory

Answer 9

His theories were unable to explain how continental movement could have taken place.

Question 10

Core

Answer 10

Two parts: a semi molten outer core and a solid inner core.

Temperatures can reach 5000 degrees C

The heat generates convention currents within the mantle

Question 11

Palaeomagnetism

Answer 11

The study of the record of he earths magnetic field in rocks.

Every 400,000 years or so, the earths magnetic field switches polarity. The rocks that form the ocean crust show this alternating polarity.

As the lavas solidify, the particles provide a permanent record of the earths polarity at the time.

The result is a series of magnetic ‘stripes’

Question 12

Convection currents

Answer 12

The heat from the core causes the mantle to be heated at its base. The hot rock rises towards the crust. As it rises, it moves further away from its heat source at the core and it starts to cool down. When it reaches the crust, it is forced out sideways. It continues to cool and as it cools, it begins to sink back down towards the core.

Question 13

Constructive plate margins landforms

Answer 13

Mid oceanic ridges
Rift valleys
Volcanoes

Question 14

Destructive plate margins landforms

Answer 14

Oceanic trenches
Told mountains 
Volcanoes 
Earthquakes 
Island arcs

Question 15

Mid oceanic ridges

Answer 15

An underwater mountain range.

Convection currents move the plates apart which leaves cracks and fissures and lines of weaknesses that allow magma to escape.

Eventually magma fills the gap and eventually erupts on the surface and cools as new land

Question 16

Rift valleys

Answer 16

A Rift Valley is a lowland region created by the process of sea floor spreading.

Eg the Great African Rift Valley

They are formed when the lithosphere stretches, causing it to fracture into sets of parallel faults.

The land between these faults then collapses into deep, write valleys which are separated by upright blocks of land called horsts

Question 17

Ocean trenches

Answer 17

Ocean trenches are deep areas of sea which form at destructive plate margins.

2 plates move together due to convection currents and the denser ocean crust is subducted underneath the continental crust.

An ocean trench marks the point at which the plate is being subduction.

Eg the Chille-Peru trench which is over 8km deep

Question 18

Active volcanoes

Answer 18

Have erupted in living memory

Question 19

Intermittent/ dormant volcanoes

Answer 19

Have erupted within historical record

Question 20

Inactive volcano

Answer 20

Haven’t erupted in the last 25000 years

Question 21

Distribution of volcanoes

Answer 21

Most volcanic activity is associated with tectonic process and are mainly located along plate margins in belts.

Along the ‘ring of fire’ that surrounds the Pacific ocean

Over hot spots such as the one in the middle of the Pacific Ocean which has formed the Hawaiin islands

Question 22

Benefits of volcanoes

Answer 22

Lava flow can create land

Igneous rocks contain valuable mineral deposits

Lava and ashes weather quickly into fertile soils

Volcanoes can be great tourist attractions

Question 23

Volcanic hazards

Answer 23

Lava flows burn and bury crops

Flooding results from lava flows

Submarine, coastal or island eruptions can cause tsuniamis

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

Violent eruptions of pyroclastic flow destroys life and property

Volcanic dust absorbs solar energy and so lowers atmospheric temperature

Question 24

How volcanoes occur at destructive margins

Answer 24

Convection currents in the asthenosphere cause the plates to move together.

The denser oceanic plate is being moved towards the thicker lighter continental plate.

The subduction plate begins to melt due to friction and heat in the mantle. This occurs in the Benioff zone. Water from the ocean above also descends and mixes with magma to make it more acidic and viscous.

Lighter, gaseous magma under pressure rises up through weaknesses in the continental crust above.

The magma erupts at the surface as lags along with ash and gases.

Subsequent eruptions over time cause a volcano to form from layers of ash and lava.

Question 25

Why volcanoes occur at constructive margins (oceanic-oceanic)

Answer 25

Convection currents in the aesthenosphere pull the two oceanic plates apart.

This allows magma to reach the surface and solidify to form new crust and volcanoes in some places.

Question 26

Why volcanoes occur at hotspots

Answer 26

In places like Iceland, hotspots lead to the formation of volcanoes where a rising plume of superheated magma thins and heats the crust, allowing magma to reach the surface.

Over time, layers of lava build up to form volcanoes.

Question 27

Why volcanoes occur at contrastive margins (continental-continental)

Answer 27

Convection currents beneath continental crust pulls the crust in opposite directions, creating faults and weaknesses.

Magma rises to the surface and solidifies as lava flows.

Question 28

Material erupted from a volcano

Answer 28

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

Solids- included ash, dust and glassy cinders.

Liquids- Tephra which solidify in mid air. Tephra ranges in size such as large lava bombs and in its fine form of hair like trails called lapilli. Also surface lavas which can be acidic or basic

Question 29

Basaltic lava

Answer 29

Formed from the upward movement of mantle material.

Magma is low in silica which makes it a more fluid magma that allows gas bubbles to expand on the way up- preventing sudden explosive activity

Question 30

Andesitic lava

Answer 30

Formed at destructive margins where crust is being destroyed.

Formed from silica rich magma that is very visous

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

Gases don’t escape from the viscous lava so pressure builds up.

Question 31

Rhyolithic lava

Answer 31

Formed at destructive and collision margins

Same characteristics as andesitic lava (bit thicker)

Question 32

Volcanic islands

Answer 32

Where there is a split in the crust, a lower pressure zone is created where lava can erupt to form submarine volcanoes.

If these eruptions continue, volcanoes may develop until they reach the surface, forming volcanic islands.

Question 33

Island arcs

Answer 33

Island arcs are curved chains of volcanic islands.

Subduction processes result in the formation of volcanoes which over millions of years, pile up lava on the ocean floor until a submarine volcano rises avoid sea level to form an island volcano.

Such volcanoes are typically strung out in curved chains called island arcs.

The magma that forms island arcs are produced by the partial me,ting of the descending large and or the overlying oceanic lithosphere