Hazards: Physical

Question 1

How was the earth formed?

Answer 1

Accretion (gravitational attraction and collision of meteorites.Meteorite collision, radioactive decay and planetary compression caused temperatures to rise above 2000C the melting point of ironEarth cooled > layers formed > heaviers materials sank and lighter rocks rose above.

Question 2

What are the two reasons why the earth’s core is so hot?

Answer 2

Primordial heat (left over from the formation of the planet)
Radiogenic heat (radioactive decay).

Question 3

What is the asthenosphere?

Answer 3

Semi-molten mantle, nearer the core that plates move on.

Question 4

What is the lithosphere?

Answer 4

Crust and rigid upper section of the mantle

Question 5

Give three differences between oceanic and continental crust.
Oceanic

Answer 5

6-10km (thinner)
Less than 200 million years old (younger)
Denser (3.0)
Basalt, SIMA (silicon, magnesium and oxygen)

Question 6

Give three differences between oceanic and continental crust.
Continental

Answer 6

30-70km (thicker)
Over 1500 million year old
Less dense (2.6)
Granite, SIAL (silicon, aluminium and oxygen).

Question 7

What are the main elements of the inner core?

Answer 7

iron, nickel

Question 8

What is the state of the inner core?

Answer 8

Solid

Question 9

What is the average temperature of the inner core?

Answer 9

over 6000C

Question 10

What are the main elements of the outer core?

Answer 10

Iron and nickel

Question 11

what is the state of the outer core?

Answer 11

liquid

Question 12

what is the temperature of the outer core?

Answer 12

4000-5000C

Question 13

What are the main elements of the mantle?

Answer 13

SIAL SIMA

Question 14

What is the state of the mantle?

Answer 14

semi-molten

Question 15

What is the temperature of the mantle?

Answer 15

3000C

Question 16

What is are the main elements of the crust?

Answer 16

Silicon, aluminium, potassium, sodium, oxygen

Question 17

What is the state of the crust?

Answer 17

solid

Question 18

What theory did Alfred Wegener suggest?

Answer 18

Continental drift

Question 19

Two pieces of biological evidence from Alfred Wegener?

Answer 19

Fossilized plants and animals from the same period found in disparate areas:
Fossil brachiopods found in Indian limestone and similar fossils in Australia

Question 20

Two pieces of geographical evidence from Alfred Wegener?

Answer 20

Fit of continents together
Evidence of late-carboniferous glaciation (290 million years ago) deposits that are found in South America, Antarctica and India. These cannot be explained by current position must have formed together and then moved

Question 21

What is sea floor spreading?

Answer 21

Theory that the ocean floor was created at mid-ocean ridges and has then been gradually expanding sideways due to volcanic activity.Plates must be being destroyed somewhere to accommodate the increase in their size at mid-oceanic ridges.

Question 22

What evidence did Vine and Matthews use to support their theory?

Answer 22

Mirroring patterns of paleomagnetism either side of ocean ridges.

Question 23

Outline the process of convection currents in the asthenosphere:

Answer 23

Hot spots in the earth’s core create thermal plumes in the asthenosphere.
Hot magma rises as it is less dense, it spreads out underneath the lithospheric plates.
This basal drag (friction/lateral pressure) moves the plates.
Magma cools becoming more dense and sinking, creating a continuous cycle.

Question 24

Outline the process of Gravitational sliding at ocean ridges:

Answer 24

At constructive plate boundaries magma rises to the surface to form a new crust.
Rising magma is very hot and heats surrounding rocks which expand and become elevated above the surrounding sea floor forming a slope.
As the new crust cools and becomes denser, gravity causes it to move downslope away from the mid-oceanic ridge.
This puts pressure on the tectonic plates causing them to move apart. The process repeats.

Question 25

Outline the process of slab pull at ocean trenches:

Answer 25

At destructive plate boundaries the subducting oceanic plate (usually composed of basalt) is denser than surrounding material.Downward gravitational force acts upon the cold dense descending plate as it sinks into the mantle.This pulls the rest of the plate behind it.

Question 26

How do plates move at a constructive plate boundary?

Answer 26

Apart

Question 27

How do plates move at a destructive plate boundary?

Answer 27

plates move towards each other

Question 28

How do plates move at a conservative plate boundary?

Answer 28

plates move alongside each other in opposite directions or the same direction at different speed

Question 29

Outline the formation of ocean ridges:

Answer 29

Plates diverge in oceanic areas (due to convection currents and gravitational sliding) - sea floor spreading.As plates move apart this leaves cracks and fissures, lines of weakness that allows magma from the mantle to escape from the highly pressurised interior of the planet. This magma fills the gap and eventually erupts onto the surface and cools as new land. Creating ridges of undersea mountains and volcanoes.

Question 30

Formations associated with constructive plate boundaries [3]:Outline the formation of rift valleys:

Answer 30

When plates diverge beneath land, rising magma causes the continental crust to bulge and fracture, forming fault lines,As the plates keep moving apart the crust between the parallel faults drop down to form a rift valley.The crust here is thinner due to tension in the crust causing the plate to thin as it starts to split. Through this thinning crust, magma forces its way to the surface to from volcanoes

Question 31

Outline the processes at oceanic-continental destructive plate boundaries

Answer 31

Denser oceanic plate subducts under the less dense continental plate > downwarping forms an ocean trench. As the oceanic plate descends friction with the plate above and increasing pressure and heat in the asthenosphere, melts the subducting ocean plate at the benioff zone. Some of this molten material works its way up through the continental plate above through fissures, as molten material is less dense than the asthenosphere.Magma eventually re-emerges at the surface to create explosive composite volcanoes (explosive as they have silica-rich andesitic lava). Sediments on the edge of the continental crust cumple upwards as the oceanic plate subducts forming fold mountains. As one plate is subducted, plates can become stuck > pressure builds up > suddenly jerk past each other > earthquakes.

Question 32

Outline the processes at oceanic-oceanic destructive plate boundaries.

Answer 32

Denser oceanic plate subducts under the less dense oceanic plate > downwarping forms an ocean trench. As the oceanic plate descends friction with the plate above and increasing pressure and heat in the asthenosphere, melts the subducting ocean plate at the benioff zone. Some of this molten material works its way up through the less dense oceanic crust through fissures. Magma eventually re-emerges at the surface to create an island arc of explosive composite volcanoes.

Question 33

Outline the processes at continental-continental destructive plate boundaries.

Answer 33

Neither plate subducts into the mantle because of their similar density. Instead, the two plates crumple into one another and fold upwards into fold mountains.As neither is subducted there are no volcanoes but the pressure build up can cause earthquakes.

Question 34

Outline the processes at conservative plate boundaries

Answer 34

Two plates move alongside each other (in opposite directions or the same direction at different speeds). Plates get stuck (‘lock’) due to friction and pressure builds up.Plates suddenly jerk past each other or crack forming fault lines, this releases the pressure sending shockwaves through the earth’s crust as earthquakes

Question 35

Give three characteristics of a hotspot:

Answer 35

Stationary area of crust
High heat flow (rising magma plume due to concentration of radioactive elements below the crust).
Thinner crust (low pressure and high heat allow magma plume to melt and thin the lithosphere)Located away from plate boundaries

Question 36

Give two examples of hotspots

Answer 36

Hawaiin hotspotReunion hotspot (deccan traps)

Question 37

Outline the formation of a hotspot

Answer 37

Intense radioactivity (due to concentration of radioactive elements) below the crust creates a magma plume (column of extra-hot upwelling lava).Plume from the asthenosphere rises upwards and high heat and low pressure allows molten rock to melt the plate above (so plate is thinner than average) and push through the crust above.Lava breaks through the surface forming active volcanoes above the plume.The magma plume remains stationary but the tectonic plate moves. Upwelling lava creates a steady succession of new volcanoes.Volcano above the hotspot is active and the remainder form a chain of islands of extinct volcanoes. The oldest volcanoes put pressure on the crust causing subsidence and marine erosion results in old volcanoes becoming seamounts.