1.3 Physical processes causing hazards

Question 1

what is a hypocentre?

Answer 1

the point at which the earthquake actually happens

Question 2

what is the epicentre?

Answer 2

directly above the hypocentre (on the Earths surface)

Question 3

what are seismic waves?

Answer 3

• waves that transmit the energy released by an earthquake
• 3 types- P, S, L

Question 4

what is a fault?

Answer 4

• a fracture in the rocks that make up the earths crust

Question 5

what are primary or p waves?

Answer 5

• vibrations caused by compression
• travel fastest

Question 6

what are secondary or s waves?

Answer 6

• slower, vibrate at right angles to direction of travel, cannot pass through water
• up and down

Question 7

what are long or l waves?

Answer 7

• surface waves, vibration in horizontal plain- high amplitude
• side to side

Question 8

what are primary hazards?

Answer 8

• caused by the direct interaction of seismic wave energy with the ground- usually surface rupture or ground shaking

Question 9

what are secondary hazards?

Answer 9

• caused as a consequence of the ground shaking e.g. ground settlement, liquefaction and landslides

Question 10

what is soil liquefaction?

Answer 10

• shaking from the earthquake destabilises the soil by increasing the space between grains
• with its structure lost, the soil flows like a liquid

Question 11

what does the richter scale measure?

Answer 11

• measure the amount if energy released (magnitude)
• logarithmic scale e.g. a magnitude 5 is 10x more powerful than a 4
• biggest ever- 9.5, Chile 1960

Question 12

what does the mercalli scale measure?

Answer 12

• measures the effects of an earthquake
• scale 1-12 based on observations

Question 13

what are the three ways volcanoes are formed from?

Answer 13

• hotspot volcano
• constructive boundaries
• destructive boundaries

Question 14

what are the 4 types of volcanoes?

Answer 14

• lava dome
• shield
• composite
• cinder cone

Question 15

what measures volcanoes?

Answer 15

• the volcanic explosive index (VEI)
• 0-8, logarithmic scale
• dependent on- the amount snd height of material ejected, length of eruption

Question 16

what is a lava flow?

Answer 16

• streams of molten rock that pours or oozes from an erupting event
• a primary hazard

Question 17

what is a pyroclastic flow?

Answer 17

• a dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing at great speed.
• a primary hazard

Question 18

what is a tephra?

Answer 18

• also known as ash fall, tephra is a solid material of varying grain size ejected into the atmosphere
• a primary hazard

Question 19

what are volcanic gases?

Answer 19

• the fluid gas phase released by active volcanoes, composed of mainly water, carbon dioxide and sulphur dioxide
• a primary hazard

Question 20

what are lahars?

Answer 20

• a hot or cold mixture of water and rock fragments that flow quickly down the slopes of a volcano
• a secondary hazard

Question 21

what are jokulhlaups

Answer 21

• floods caused by the sudden release of water and rocks when glacial ice is melted by the volcanic eruption
• a secondary hazard