Plate Tectonics

Question 1

Inner core

Answer 1

Can reach over 6000°C. In spite of heat and pressure, inner core is solid and contains iron with around 20% nickel content.

Question 2

Outer core

Answer 2

Found at depth of 2900 km and can reach up to 5500°C. It is semi molten and is composed of mostly iron. We know it is semi molten as seismic waves cannot pass through it.

Question 3

Mantle

Answer 3

Thickest later at around 2300 km thick. Consists of silicate materials that are rich in iron and magnesium. The upper part is rigid and is welded to the overlying crust. Most of the mantle is semi molten with temperatures reaching 5000°C.

Question 4

Crust

Answer 4

Thinnest layer composed of tectonic plates.

Question 5

Oceanic crust

Answer 5

Covers 65% of the earth's surface
6 km thick average. 
Denser 2.9g/cm3
Newer 200 million years old
Contains Basalt, gabbro and sima.

Question 6

Core

Answer 6

6350 km down and is the densest part of the planet.

Question 7

Continental Crust

Answer 7

Thicker 30-70km average
Less dense 2.7g/cm3
Older 3.7 billion years old
Contains granite and sial

Question 8

Lithosphere

Answer 8

The crust and the upper part of the mantle

Question 9

Asthenosphere

Answer 9

Partial liquid layer in mantle below lithosphere. Part of mantle which lithosphere floats on.

Question 10

Mohorovicic discontinuity

Answer 10

Division between mantle and crust in lithosphere.

Question 11

Gutenburg discontinuity

Answer 11

Division between mantle and core.

Question 12

Tectonic Plate

Answer 12

A section of the lithosphere which moves due to convection currents in the mantle.

Question 13

The theory of plate tectonics

Answer 13

Idea that the earth’s lithosphere is made up of many plates that are moved around by convection currents.

Question 14

Continental Drift

Answer 14

In 1912, Alfred Wegener suggested that all continents were pervasively joined to form a super continent (pangea) before drifting apart to form Laurasia and Gondwanaland and then eventually the continents we have today.

Question 15

Constructive Plate Margin

Answer 15

Where two plates diverge
Eurasian plate and North American plate.
Mid-Ocean Ridges (when underwater), Rift valleys (when under land)
Seismically and volcanically active.

Question 16

Destructive plate margin

Answer 16

Where two plates converge.

Question 17

Oceanic-continental destructive margin

Answer 17

Nazca plate and South American plate.
Deep sea trenches, young volcanoes
Seismically and volcanically active

Question 18

Oceanic-oceanic destructive margin

Answer 18

Pacific plate and Philippine plate
Deep sea trenches, island arcs
Seismically and volcanically active

Question 19

Continental-continental destructive margin

Answer 19

Indo-Austrailian plate and Eurasian plate.
Fold mountains
Seismically active

Question 20

Conservative plate margin

Answer 20

When two plates move past each other.
North American plate and Pacific plate.
Low ridges, fault lines
Seismically active

Question 21

Hotspot

Answer 21

Areas of intense volcanic activity where heat is very localised underneath the earth’s crust that aren’t near to any plate margins.

Question 22

Intrusive volcanic activity

Answer 22

Takes place beneath the earth’s surface where magma forced into the crust doesn’t break through. Typically composed of granite and dolerite

Question 23

Extrusive volcanic activity

Answer 23

Takes place on the earth’s surface when magma forced into the crust breaks through.

Question 24

Dykes

Answer 24

Intrusive volcanic feature. A vertical wall-like intrusion of igneous rock.

Question 25

Sills

Answer 25

Intrusive volcanic feature. Horizontal intrusions of igneous rock.

Question 26

Batholiths

Answer 26

Intrusive volcanic feature. Gigantic mass of igneous rock such as granite.

Question 27

Laccolith

Answer 27

Intrusive volcanic feature. A mass of igneous rock that has been intruded between rock strata causing uplift in the shape of a dome.

Question 28

Pyroclastic flows

Answer 28

High-density mixtures of hot, dry rock fragments and hot gases that move away from the vent that erupted them at high speeds. Most pyroclastic flows consist of two parts: a basal flow of coarse fragments that moves along the ground, and a turbulent cloud of ash that rises above the basal flow.

Question 29

Lahars

Answer 29

Hot or cold mixture of water and rock fragments flowing down the slopes of a volcano and (or) river valleys.

Question 30

Geyser

Answer 30

Minor form of extrusive activity. A type of hot spring where hot water and steam are ejected from the surface in a fountain. Form in areas of intense volcanic activity.

Question 31

Fumaroles

Answer 31

Minor form of extrusive activity. Low pressure outlets of steam and gas. Emit steam, carbon dioxide but also CO. HCl and sulphur gases.

Question 32

Hot springs and boiling mud

Answer 32

Minor form of extrusive activity. Source of stream flows near to area of recent intrusive volcanic activity so water is heated. Groundwater heated below surface may contain minerals dissolved from contact with hot rocks that build up on surface as colourful boiling mud deposits.

Question 33

Seismic waves

Answer 33

Waves of energy that travel through the Earth’s layers, and are a result of an earthquake, explosion, or a volcano that gives out low-frequency acoustic energy.

Question 34

Richter scale

Answer 34

Measure magnitude of an earthquake. Its a logarithmic scale where each unit represents a 10 fold increase in amplitude (strength) and a 30 fold increase in energy. Magnitude proportional to energy released.

Question 35

Mercalli scale

Answer 35

Measures the intensity of the event and its impact. 12 point subjective scale based on eyewitness accounts where 1 is detected only by instruments and 12 is complete destruction. 8.5 on Richter scale = 12 on Mercalli.

Question 36

Primary waves

Answer 36

Fastest waves that reach surface first. 330m/s in air, 1450m/s in water.
Push and pull earth in direction of travel
Compressional, hig frequency waves
Travel through any material.

Question 37

Secondary waves

Answer 37

Slower than P waves (half as fast)
Waves move earth at right angles to direction of travel
High frequency transverse waves- very damaging
Travel through solids but not liquids (core) so can;t be measured at point opposite focus.

Question 38

Surface waves

Answer 38

Slowest of seismic waves and come in two varieties

Love waves and Raleigh waves.

Question 39

Love waves

Answer 39

Travel slowest on earth’s surface but do most damage
Side to side motion with shearing effect
Strength drops with increasing depth of earthquake.
Only travel through solids.

Question 40

Raleigh waves

Answer 40

Radiate from epicentre at low frequency
Travel through liquids and solids
Rolling motion similar to a wave that cause shaking.

Question 41

Benioff zone

Answer 41

Zone of melting of a subducted plate. 100km-700km. Melting caused by extreme heat and friction