Volcanic Hazards

Question 1

What is meant by a primary hazard?

Answer 1

Hazards that are directly related to the volcano and its eruption (e.g. lava flows, ash falls and gas clouds)

Question 2

What is a pyroclastic flow?

Answer 2

A mixture of hot rock, lava, ash, and gases arising from a volcanic eruption that moves at rapid speed along the ground

Question 3

What is tephra?

Answer 3

Rock fragments ejected during volcanic eruptions

Question 4

What is a nuee ardente?

Answer 4

A dense, rapidly moving cloud of hot gases, ashes and lava fragments from a volcanic eruption (a type of pyroclastic flow)

Question 5

What is meant by a secondary hazard?

Answer 5

Hazards that occur due to the occurrence of another, primary hazard. They are indirectly related to the volcanic event

Question 6

What is a lahar?

Answer 6

A destructive mudflow which occurs as a result of a volcanic eruption

Question 7

What is a tsunami?

Answer 7

A large wave triggered by seismic activity

Question 8

What is acid rain?

Answer 8

Volcanoes eruption suphirpus gases which can result in acidic rainwater

Question 9

How many people are estimated to be at risk of volcanic hazards worldwide?

Answer 9

500 million

Question 10

What are some primary hazards of volcanoes?

Answer 10

Lava and pyroclastic flows. Tephras. Nuee ardentes. Ash fallout and volcanic gases

Question 11

What are some secondary hazards of volcanoes?

Answer 11

Lahars. Volcanic landslides. Tsunamis and acid rain

Question 12

What is meant by intraplate?

Answer 12

In the middle of a plate, away from the margins

Question 13

What % of volcanic activity is found at plate margins?

Answer 13

95%

Question 14

What are hawaiian eruptions?

Answer 14

Effusive and produce basalt lava which relatively high temps (1100-1250°C). Lw silica content (<52%). Less viscous. Spreads over long distances (over 20km at speeds of 50km/h)

Question 15

What are plinian eruptions?

Answer 15

More explosive. Produce andesitic and rhyolitic lava. Lower temps (600-1000°C). Higher silica content (>69%). More unpredictable

Question 16

What are pyroclastic flows?

Answer 16

Dangerous mixture of hot rock, lava, ash and gases. Can move at speeds of 200m/s and are typically 350-1000°C

Question 17

What are subduction zones?

Answer 17

Zones where thin, dense oceanic crust is forced beneath thicker, less dense continental crust at a destructive plate boundary

Question 18

Why is ash an issue for humans?

Answer 18

Covers a large area, often thousands of kms. Highly abrasive so impacts breathing abilities, and disrupt machinery. Can block out sunlight, reducing visibility and temperatures

Question 19

What is a shield volcano?

Answer 19

A volcano with gentle sloping sides, characteristic of fluid basaltic lava

Question 20

What is a caldera?

Answer 20

A large volcanic crater often formed following a highly explosive eruption where the summit of the volcano is removed

Question 21

What are hotspots?

Answer 21

Sites where mantle plumes rise up through areas of thin crust, causing volcanic activity in areas away from plate boundaries

Question 22

What is ground deformation?

Answer 22

The change in shape of the ground before or after a volcanic eruption; often it is due to the movement of magma below the surface

Question 23

What are short-term responses to volcanoes?

Answer 23

Depend on the magnitude and the vulnerability of local people. Evacuations and deployment of emergency services. International aid/help

Question 24

What are long term responses to volcanoes?

Answer 24

Preparedness, mitigation, prevention and adaption. Hazard maps and monitoring. Alert systems

Question 25

What is meant by phreatic?

Answer 25

Steam driven explosions which occur when water beneath the ground is superheated by magma

Question 26

What is the Volcanic Explosivity Index?

Answer 26

Logarithmic scale
0-1 is effusive
4-6 is plinian
Yelloestone is above 8