9.1 Hazards resulting from tectonic processes

Question 1

What is a hazard?

Answer 1

A threat that could injure people or damage the built environment.

Question 2

What is a hazard event?

Answer 2

The occurrence or realisation of a hazard and its effects.

Question 3

What is a disaster?

Answer 3

A hazard that causes so much damage and injury that help is needed to recover.

Question 4

What is risk?

Answer 4

The probability of a hazard causing harmful consequences.

Question 5

What is resilience?

Answer 5

How well a population recovers from disaster.

Question 6

What is soil liquefaction?

Answer 6

When weak rocks act as a liquid and flow, due to ground shaking. Leads to the sinking of buildings. It occurs when groundwater is near the surface and soft sediment mixes with water.

Question 7

What are tsunamis?

Answer 7

High, long period waves in the ocean, resulting from a sudden displacement of the seabed along a fault. They have long wavelengths so are hard to monitor.

Question 8

What are primary earthquake hazards?

Answer 8

Shaking - sends out P, S and surface waves.

Surface faulting

Question 9

What is a hotspot?

Answer 9

Volcanoes which sit above isolated plumes of rising magma. A jet of hot material rises from deep within the magma.

Question 10

What is partial melting?

Answer 10

When some minerals melt before others, altering the composition of molten rock.

Question 11

Why does viscous magma create more explosive volcanoes?

Answer 11

In fluid magma, bubbles rise to the surface.

In viscous magma, gases are trapped so pressure is built up more.

Question 12

What is a mantle plume?

Answer 12

Stationary area of hot mantle which rises. The plume is narrow but the top spreads out under the plate to form a bulbous head.

Question 13

What is seismic tomography?

Answer 13

An ‘x-ray’ of the earth to give an image of areas where shock waves pass through slowly or quickly.

Question 14

What is a seismometer?

Answer 14

Records the elastic vibrations of seismic waves and creates a graph called a seismogram.

Question 15

What is the richter scale?

Answer 15

10 point logarithmic scale

Measures the height of the largest wave.

Question 16

What are the advantages of the richter scale?

Answer 16

Easy comparison of EQ magnitudes.

Highly accurate of magnitudes less than 4.

Question 17

What are the disadvantages of the richter scale?

Answer 17

Relative measure - compares one size of EQ to another.

Becomes inaccurate at large magnitudes.

Question 18

What is the moment magnitude scale?

Answer 18

Uses elements of Richter scale. Logarithmic.

Question 19

What are the advantages of the MM scale?

Answer 19

Independent of recording instruments. Highly accurate for EQs above magnitude 4.

Question 20

What are the disadvantages of the MM scale?

Answer 20

Not accurate for EQs with magnitude less than 4.

Takes longer to determine.

Question 21

What is the Mercalli scale?

Answer 21

A 12 point scale that measures the intensity of the event and the physical damage it creates.
Very subjective.

Question 22

What is the focus?

Answer 22

The point of origin of an EQ underground.

Question 23

What is the epicentre?

Answer 23

Point on the earth’s surface that is directly above the focus.

Question 24

What is sheer stress?

Answer 24

When pressure and stress build up as the plates are forced to try to move.

Question 25

What is a P wave?

Answer 25

A primary body wave that travels underground and arrives at the detector first. Its waves are longitudinal and push-compressional.

Question 26

What are S waves?

Answer 26

Secondary body waves that travel underground. These waves are transverse, several times larger than P waves, and arrive at the detector second. They travel through material by shearing or changing its shape in the direction perpendicular to the direction of travel.

Question 27

What is a love wave?

Answer 27

A surface wave. It has horizontal movement and a long wavelength.

Question 28

What are surface waves?

Answer 28

Waves that travel just below the surface. They move more slowly than body waves, but are often the more destructive type of wave.

Question 29

What is a Raleigh wave?

Answer 29

A surface wave with rolling vertical movement. Very destructive.

Question 30

What are seismic waves?

Answer 30

Waves of elastic energy.

Question 31

What is an Icelandic eruption?

Answer 31

Fluid basalts issue quietly from fissures at mid-ocean ridges.

Question 32

What is a Hawaiian eruption?

Answer 32

Fluid basalts issue from vaults and volcanoes. Gases escape easily and quietly with occasional gas spurts.

Question 33

What is a strombolian eruption?

Answer 33

Less fluid lava and gases escape with moderate explosions. Lava bombs.

Question 34

What is a Vulcanian eruption?

Answer 34

More violent eruptions as more viscous lava solidify quickly and trap gases. Ashes and cinders emitted.

Question 35

What is a Vesuvian eruption?

Answer 35

Viscous magma gains high gas content during long inactivity. Violent eruptions send wide ash cloud.

Question 36

What is a Plinian eruption?

Answer 36

Very violent explosion of gas, ash and pumice. Results in narrower cloud.

Question 37

What is a Pelean eruption?

Answer 37

Highly viscous magma and long inactivity cause an explosion out of weakness in the side of the volcano. Top gets blocked due to dormancy and solidification.

Question 38

What is Aa?

Answer 38

Thick but fast basaltic lava, formed when a lot of lava erupts quickly. Surface breaks into rough clinkers as it moves. Moves with sudden surges of speed, destroying anything it touches.

Question 39

What is Pahoehoe?

Answer 39

Slow flowing lava, formed when low volumes are ejected more slowly. Solidifies while moving and flows further than aa lava.

Question 40

What is a nuee ardente?

Answer 40

A very hot, incandescent cloud composed of gas and tiny fragments of solid material. Moves rapidly down slopes. Categorised by their ashes which glow in the dark. Caused when viscous magma causes a solid plug to grow in the vent of a volcano so that lava has to explode sideways out of a weakness if the flank of the volcano.

Question 41

What is pyroclastic material?

Answer 41

Solid particles that reach the ground in pyroclastic falls.

Question 42

What is tephra?

Answer 42

Airborne pyroclastic material.

Question 43

Give the names for the different types of solid material in size order.

Answer 43

Ashes, cinders, lapilli, volcanic blocks

Question 44

What are volcanic bombs?

Answer 44

Round fragments of solid lava, formed as molten lava cools while spinning through the air.

Question 45

What are pyroclastic flows?

Answer 45

When hot, dry rock fragments and gases move rapidly away from the vent down slopes by gravity. Very dense.

Question 46

What are lahars?

Answer 46

Volcanic mudflows.