Hazards

Question 1

Wegeners theory

Answer 1

Continental drift

During the Carboniferous period Pangea existed and over time the continents separated

Question 2

Geological evidence of continental drift

Answer 2

Fit of the continents
Mountain chains and some rock sequences on either sides of the oceans show great similarity eg northeast Canada and northern Scotland
Evidence from 290 million years ago of the effects of glaciatiob in South Africa, South America, Australia and India and Antarctica suggest that these land masses were once joined

Question 3

Biological evidence for continental drift

Answer 3

Similar fossil branchiopods (marine shellfish) found in Australian and Indian limestones

Similar fossil reptiles found in South America

Fossils from rocks younger than the Carboniferous period in places such as Australia and India showing fewer similarities suggesting they followed different evolutionary paths

Question 4

What is the lithosphere

Answer 4

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

Approximately 80-90km thick
Divided into plates

Question 5

Characteristics of the mantle

Answer 5

Surrounds the core
Composed of silicate rock rich in iron and magnesium 
Semi molten
Less dense rock
Temperature reaches 5000 degrees 
Generates convection currents

Question 6

Characteristics of the crust

Answer 6

Rocks composed of silicon, oxygen, aluminium and potassium

Thinnest layer

Is made up of two types - oceanic and continental

Oceanic - made of basaltic rock
Continental - made of igneous, metamorphic and sedimentary rock

Question 7

Characteristics of the asthenosphere

Answer 7

A layer in the earth mantle in which rocks are easily deformed

It is several hundred km thick

Lies between the lithosphere which has a high viscosity and is much more resistant to deformation

Tectonic plates move on the semi molten asthenosphere

Question 8

Characteristics of the core

Answer 8

Solid inner part
Densest part of the planet
Rich in iron and Nickel
Outer core - semi molten

Question 9

How do tectonic plates move

Answer 9

The most likely cause of plate movement is the existence of convection currents in the asthenosphere

Heat comes from a combination of radioactive decay in the core and residual primary heat

The convection currents cause magma to circulate and this moves the lithosphere

Question 10

Tectonic plates

Answer 10

Pacific, African, Eurasian, North America, South America, Antarctic and I do-Australian

Question 11

Difference between continental and oceanic crust

Answer 11

Continental - less dense, 30-70 km thick, over 1500 million years old

Oceanic - more dense, 6-10 km, less than 200 million years old

Question 12

Example of tectonic plates

Answer 12

African plate - convergent margin, moves around 21.5mm per year

Question 13

Example of oceanic plates

Answer 13

Pacific plate - convergent, divergent and transform margins, moves around 50-100mm per year

Question 14

Oceanic/continental convergent

Answer 14

Where oceanic and continental plates meet the dense oceanic plate is forced under the lighter continental one - subduction. The continental crust being more buoyant is not subduction but uplifted, buckled and folded forming fold mountains

Ocean trench formed at point of subduction

Subduction plate is heated and melts causing it to rise

Question 15

Oceanic oceanic convergent

Answer 15

When oceanic crust converges with oceanic crust, subduction still occurs, as one plate is likely to be slightly older and slightly sensed than the other

This creates a deep ocean trench

On the non subduction plate, a volcanic island arc forms from the rising magma generates from the subduction plate

Question 16

Continental continental convergent

Answer 16

Neither is subducted because of their thickness

The plates are initially separated by an ocean floor that is being subducted under one continent

As the ocean floor continues to be subducted the two continents come closer together until the eventually collide

This causes food mountains eg the Himalayas

Question 17

Divergent plate boundaries

Answer 17

Plates are separating and new lithosphere is forming

Divergent boundaries are places where crust is extended, thinned and fractured as magma rises to the surface where it appears as pillow lava

Most commonly occur along the crests of oceanic ridges - mid Atlantic ridge

Question 18

Where else are divergent boundaries formed

Answer 18

Under continents in the early stages of continental break up

When magma wells beneath a continent the crust is initially elevated, stretched and thinned producing fractures, faults rift valleys and volcanic activity - Red Sea separating the Arabian peninsula from Africa and the gulf of California

Question 19

P waves

Answer 19

Primary - travel fastest and arrive first - can produce warning for heavy ground shaking to follow

Can travel through any type of wave

Rarely causes any damage

Question 20

L waves

Answer 20

Longer the wavelength than p and S waves

Surface waves

Travel along the surface of the earth

Cause the most damage

Question 21

S waves

Answer 21

Secondary - travel slower than p waves

Do not travel in liquid

Question 22

Warning time

Answer 22

The warning time is about one second for every five miles of distance to the focus of the earthquake, which gives automated systems plenty of time to respond and enough time to react

Question 23

Tsunamis

Answer 23

Larger version of a normal wave with a peak and trough but consist because of the movement of energy through water

Tsunamis are caused by energy originating under water from a volcanic eruption, landslide of most commonly an underwater earthquake

Question 24

Vulnerability

Answer 24

Concerned with the ability of a person or community to withstand exposure to and risks from a hazard such as an earthquake. People are most vulnerable when relatively small physical changes have major socio-economic implications