Enquiry Question 1: Why are some locations more at risk from tectonic hazards?

Question 1

Seismic hazards

Answer 1

Earthquakes/tremors and associates events

Question 2

Volcanic hazards

Answer 2

Associated with eruption events

Question 3

Intra-plate earthquakes

Answer 3

earthquakes that occur away from plate boundaries (middle or interior of tectonic plates)

Question 4

Volcano

Answer 4

A vent or fissure in the Earth’s surface through which magma and gases are expelled

Question 5

Divergent plate boundary

Answer 5

constructive plate movement - found at mid-ocean ridges (mostly submarine), linked to shallow focus, low magnitude earthquakes.

Question 6

Convergent plate boundary

Answer 6

destructive plate movement - subduction or colliding plates linked to seismic and volcanic activity.

Question 7

Conservative plate boundary

Answer 7

Horizontal plate movement, linked to shallow focus seismic activity.

Question 8

SiMa

Answer 8

Oceanic crust comprising of silica and magnesium

Question 9

SiAl

Answer 9

Continental crust comprising of silica and aluminum

Question 10

Constructive plate movement

Answer 10

Tectonics plates move apart to create new lithosphere

Question 11

Destructive plate movement

Answer 11

Tectonic plates move towards each other and either subduction, or a collision, occurs

Question 12

Conservative plate movement

Answer 12

Tectonic plates slide past each other, either in opposite directions or in the same direction but at differing speeds (e.g. San Andreas fault)

Question 13

Hot spot

Answer 13

Weakness in the lithosphere, which is fed by a mantle plume, resulting in volcanic activity (e.g. Kilauea)

Question 14

Mantle Plume

Answer 14

heated lower mantle rock that rises toward the lithosphere because it is less dense than surrounding mantle rock

Question 15

Theory of Plate Tectonics

Answer 15

Earth’s lithosphere is divided into plates, and are moving due to convection currents in the mantle, slab pull, ridge push and subduction. Evidence of this has been shown through palaeomagnetism, geological and climatological evidence

Question 16

Mantle Convection

Answer 16

radioactive decay in the earth’s core emits heat which in turns heats the mantle. Magma, when heated, becomes less dense, and consequently rises towards the lithosphere. (along the geothermal gradient) At the surface, the magma begins to cool and begins to sink back towards the core, creating a current in the mantle.

Question 17

Asthenosphere

Answer 17

The solid, plastic layer of the mantle beneath the lithosphere; made of mantle rock that flows very slowly, which allows tectonic plates to move on top of it

Question 18

Palaeomagnetism

Answer 18

The study of past changes in the Earth’s magnetic field (determined from rocks, sediment or archaeological records)

Question 19

Sea floor spreading

Answer 19

the process by which new oceanic lithosphere forms as magma rises toward the surface (due to constructive plate movement at divergent plate boundaries) and solidifies

Question 20

Subduction

Answer 20

Where the thinner, more dense tectonic plate (usually oceanic crust - SiMa) descends beneath the opposing plate due to convergent plate movement.

Question 21

Slab Pull

Answer 21

the process that results when a dense oceanic plate sinks beneath a less dense plate along a subduction zone, pulling the rest of the plate that trails behind it

Question 22

Ridge Push

Answer 22

a mechanism that may contribute to plate motion; it involves the oceanic lithosphere sliding down the oceanic ridge under the pull of gravity

Question 23

Benioff Zone

Answer 23

a narrow zone of deep earthquake foci at a subduction zone

Question 24

Moho discontinuity

Answer 24

boundary between the Earth’s crust and the mantle

Question 25

P waves

Answer 25

Primary wave, first to arrive. Movement consists of compressions and rarefactions.

Question 26

S waves

Answer 26

A type of body wave, second to arrive - a shear or transverse wave - motion is perpendicular to the direction of wave propagation

Question 27

L waves

Answer 27

surface seismic waves that cause horizontal shifting of the Earth during an earthquake

Question 28

Liquefaction

Answer 28

Loose sand and silt that is saturated with water can behave like a liquid when shaken by an earthquake (source: USGS)

Question 29

Lava flow

Answer 29

masses of molten rock that pour onto the Earth’s surface during an effusive eruption. Both moving lava and the resulting solidified deposit (Source: USGS)

Question 30

Pyroclastic flow

Answer 30

A hot (typically >800 °C), chaotic mixture of rock fragments, gas, and ash that travels rapidly (tens of meters per second) away from a volcanic vent or collapsing flow front (Source: USGS).

Question 31

Tephra

Answer 31

Any type and size of rock fragment that is forcibly ejected from the volcano and travels an airborne path during an eruption (including ash, bombs, and scoria) (Source: USGS).

Question 32

Lahar

Answer 32

a hot or cold mixture of water and rock fragments that flows down the slopes of a volcano and typically enters a river valley

Question 33

Jokulhlaups

Answer 33

a glacial flash flood

Question 34

Tsunami

Answer 34

A gravitational sea wave produced by a large-scale, short-duration disturbance of the ocean floor, such as a submarine earthquake, slump, subsidence, or volcanic eruption (Source: USGS)

Question 35

Gutenberg discontinuity

Answer 35

boundary between mantle and outer core

Question 36

Lehman discontinuity

Answer 36

boundary between inner and outer core

Question 37

Mafic lava

Answer 37

lava rich in magnesium and iron, dark-colored, less viscous (flows easily), less gases are trapped leading to less explosive eruptions.

Question 38

Felsic lava

Answer 38

richer in silica thus more viscous meaning it flows slower: it is also more acidic, and more gases are trapped leading to more explosive eruptions

Question 39

Exsolve

Answer 39

When dissolved gases escape from magma

Question 40

Bubble nucleation

Answer 40

Formation of gas bubbles in magma due to exsolution

Question 41

Outgassing

Answer 41

When gases escape/are emitted from the volcano, thus releasing pressure and reducing the explosively of an eruption

Question 42

Fragmentation of lava

Answer 42

where the flow of magma undergoes a transition from a laminar flow of viscous bubbly liquid to a turbulent flow of gas carrying liquid fragments