Tectonic Processes and Hazards

Question 1

Distribution of Earthquakes/Volcanic eruptions: Where? Key term? Percentage?

Answer 1

Destructive/Convergent plate boundaries- 70-80% of all Earthquakes. Mainly in the “Ring of Fire”, pacific ocean (predominantly affecting Asia).

5% of Earthquakes are Intra-earthquakes.

Question 2

Define Intra-earthquake

Answer 2

A earthquake which occurs in a minor plate; aka not along a plate boundary.

Question 3

Define Accretion wedge

Answer 3

The accumulation of material at the point of subduction.

Question 4

Define Asthenosphere

Answer 4

Upper mantle layer; Semi-molton and 2000km wide.

Question 5

Define Continental Crust

Answer 5

Crust forming the continents of the lithosphere; average 35km thick.

Question 6

What is continental drift?

Answer 6

Movement of tectonic plates due to convection currents rising to the asthenosphere and being forced sideways pulling the crust apart (or together) as it sinks due to gravity. Slab pull is now thought as the primary driving force of this.

Question 7

Define Convection currents

Answer 7

Circulation of magma within the mantle. Magma is heated by radioactive processes in the core and cools at the surface; circulating between the two places.

Question 8

What is a epicentre and focus? Difference?

Answer 8

Epicentre (Hypocentre)- Point on the surface, directly above the earthquakes origin.

Focus- Where the pressure/seismic energy is released.

Question 9

What is a hotspot? Example?

Answer 9

Volcanoes found away from the plate boundary due to a magma plume closer to the surface. These tend to create island arcs such as Hawaii.

Question 10

Define Jokulhaup

Answer 10

Glacial flood caused by a glacier near a volcano melting due to heat of an eruption.

Question 11

Define Lahar

Answer 11

A flow of mud and debris (aka mudslide).

Question 12

Define Lithosphere

Answer 12

The upper crust of the earth (above the asthenosphere). Average thickness of 100km.

Question 13

3 types of seismic wave. Most destructive? Order that they come in?

Answer 13

P (Primary) waves- First to reach the surface; Longitudinal (straight line) with minimal damage. Pass through Solids & liquids.

S (Shear/Secondary) waves- Second to reach the surface; Transverse meaning they move sideways in a back and forth motion. Only pass through solids.

L (Love) waves- Last to reach the surface; mainly causes the damage from an earthquake ie building collapse due to movement which is up and down.

Question 14

Define Liquefaction

Answer 14

Process that generates liquid from a solid. Ie land turns to a liquid during a earthquake.

Question 15

Formation of a Tsunami

Answer 15

1) There is earth movement at the subduction zone; usually a earthquake which occurs under water. This energy travels up in seismic waves and causes a water column displacement due to the rapid movement of the sea bed.
2) A series of waves travel outwards from the column at heights believed to be at less than 3 foot.
3) Once the waves approach land, the energy compresses into a smaller space; creating an elliptical shape and an enormous height.

Question 16

What is a mid-ocean ridge? example?

Answer 16

Parting oceanic plates at a constructive plate boundary creates a ridge, with new land at the base of the oceanic valley. For example, the mid-Atlantic ridge.

Question 17

What scale is used to measure earthquake energy release?

Answer 17

MMS (moment magnitude scale). Considered the most accurate measure of earthquake energy release. Logarithmic; meaning it increasing in x10 per 1.

Alternatively, the Richter scale could be used.

Question 18

What is paleomagnetism?

Answer 18

The study of alternating polarisation over time. This creates new land when the poles swap direction meaning as magma cools the magnetic elements within rocks like Iron align with the magnetic field, showing clear evidence of alteration.

Question 19

Define Pyroclastic flow

Answer 19

Mixture of gases and rock fragment at high temperatures travelling at rapid speeds.

Question 20

Define slab pull

Answer 20

The force contributing to the movement of tectonic plates due to the weight of the plate.

Question 21

What is subduction? Where does this happen? Another word for this?

Answer 21

Subduction is the process of a plate being forced below another (usually oceanic below continental due to being denser). This happens at the subduction zone, also known as the Benioff zone (however this focuses more on the region of subduction rather the general area).

Question 22

What is the scale used for measuring volcanic activity?

Answer 22

VEI (volcanic explosivity index) measures magnitude of a volcanos eruption. Again, logarithmic (x10 per 1).

Question 23

Define Island Arc. How do they form?

Answer 23

Island arcs are a series or volcanoes, usually in the shape of an arc, that are formed consecutively as a plate moves across a magma plume.

Question 24

What is a natural hazard and how is this different to a disaster?

Answer 24

Natural hazard: A event which COULD cause economic, environmental and social impacts on a large scale.

Disaster: An event which disrupts the normal ways of a community.

Hazard is theoretical (most remaining dormant) however once this becomes active the hazard turns into a disaster; as it causes damage.

Question 25

What is the hazard risk equation?

Answer 25

Risk= Hazard x vulnerability