Volcanic Hazards

Question 1

What is a lahar?

Answer 1

A mudflow consisting of pyroclastic material and water which flows down a volcano, often along a river valley.

Question 2

What are the two types of volcano?

Answer 2

Explosive and effusive.

Question 3

What are the characteristics of effusive volcanoes?

Answer 3

Basaltic magma.
1000-1200°c.
Low viscosity.
Shield volcanoes.
Long lava flows.
Gas emissions.

Question 4

What are the characteristics of explosive volcanoes?

Answer 4

Rhyolitic magma.
650-800°c
High viscosity.
Composite volcanoes.
Violent eruptions.
Pyroclastic flow.
Short lava flows.

Question 5

How far can lava flow on effusive volcanoes?

Answer 5

Up to 50km.

Question 6

How far can lava flow on explosive volcanoes?

Answer 6

Rarely spreads more than 8km.

Question 7

What gases do volcanic eruptions emit?

Answer 7

Sulfur dioxide.
Methane.
Carbon monoxide.
Chlorine.
Carbon dioxide.

Question 8

What eruption types are associated with explosive volcanoes?

Answer 8

Strombolian.
Vulcanian.
Vesuvian.
Plinian.
Strato-volcano.

Question 9

What eruption types are associated with effusive volcanoes?

Answer 9

Icelandic.
Hawaiian.
shield volcanoes.

Question 10

What is a composite (strato) volcano?

Answer 10

A tall, cone shaped volcano built up by alternating layers of solidified lava and ash.

Question 11

Which plate boundary are composite (strato) volcanoes more commonly found at?

Answer 11

Destructive (convergent) plate margins.

Question 12

What is a shield volcano?

Answer 12

A broad, doamed volcano with gently sloped sides, built up by accumulation of numberous fluid lava flows.

Question 13

What is the most violent eruption type?

Answer 13

Plinian.

Question 14

What are the characteristics of a Plinian eruption?

Answer 14

Rhyolitic magma.
650-800°c
Exceptionally violent.
Produce large columns of ash and gas.

Question 15

What is the most gentle eruption type?

Answer 15

Icelandic.

Question 16

What are the characteristics of an Icelandic eruption?

Answer 16

Basaltic magma.
1000-1200°c
Gently flowing lava, creating lava plateaus.

Question 17

Where are volcanoes found?

Answer 17

Volcanoes are most commonly found on plate margins, but also on hot spots, forming archipeligos such as Hawaii.

Question 18

Why do hot spots occur more in the ocean than on land?

Answer 18

Oceanic crust is thinner and easier to penetrate than continental crust.

Question 19

How long is the pacific ring of fire?

Answer 19

40,000km.

Question 20

What is pyroclastic flow?

Answer 20

A mixture of hot rock fragments, lava particles, and ash in hot air.

Question 21

What eruption types are pyroclastic flows more common in?

Answer 21

Andesitic and rhyolitic.

Question 22

How fast can pyroclastic flows travel?

Answer 22

Up to 300km/h.

Question 23

How far can a pyroclastic flow travel?

Answer 23

Up to 40km from the source.

Question 24

How hot are pyroclastic flows?

Answer 24

Temperatures are often between 100-700°c.

Question 25

How fast can lahar flow downslope?

Answer 25

Up to 50km/h.

Question 26

What is used to measure seismic activity?

Answer 26

A seisometer.

Question 27

What does a seisometer indicate?

Answer 27

Microquakes, sensed through seismic acivity, can indicate rising magma fracturing and cracking the overlying rocks.

Question 28

What is used to measure Ground deformation?

Answer 28

A tiltometer.

Question 29

What does a tiltometer indicate?

Answer 29

Bulging of the ground is caused by rising magma. Slope angles and the increasing distance between set points can be measured by a tiltometer.

Question 30

What is used to measure iron-rich magma?

Answer 30

A magnometer.

Question 31

What does a magnometer indicate?

Answer 31

Changing magnetism within the volcano is a common geophysical indication of rising magma.

Question 32

What is used to measure rising groundwater?

Answer 32

Hydrological instrumentation.

Question 33

What does hydrological instrumentation indicate?

Answer 33

Rising magma will both heat groundwater and corrupt it with gas such as sulphur, making it expand, and rise.

Question 34

What is used to measure early warning signs?

Answer 34

Remote sensing equipment.

Question 35

What does remote sensing equipment indicate?

Answer 35

Remote camera surveillance records physical changes in and around the main crater. Thermal images and gas sampling can also be included.

Question 36

What is the Volcanic Explosivity Index (VEI)?

Answer 36

A scale to measure and compare the size and intensity of a volcanic eruption by recording the volume of erupted material and the height of projected gas/material.

Question 37

How does the VEI scale escalate?

Answer 37

Logarithmically, meaning each step up the scale represents a 10x increase in explosivity.

Question 38

When was the VEI developed?

Answer 38

In 1982

Question 39

What are the advantages of the VEI?

Answer 39

It enables volcanic eruptions to be compared to one another. A small, easy to understand scale. Can be used to predict future eruptions. It is versatile, made up of both quantitiative and qualitative data.

Question 40

What are the disadvantages of the VEI?

Answer 40

Doesn't capture atmospheric and climatic impact of the eruptions. Doesn't differentiate between effusive and explosive volcanoes. Doesn't account for power output of an eruption.

Question 41

Around how many eruptions have been rated a VEI-8?

Answer 41

About 50.

Question 42

When did the most recent VEI-8 eruption occur?

Answer 42

Approximately 27,000 years ago.

Question 43

Why does the VEI only go up to an 8?

Answer 43

Because it's a logarithmic scale and a VEI-9 eruption has never occurred. It can be expanded though as it is an open-ended scale.

Question 44

What are primary effects of volcanic eruptions?

Answer 44

Tephra. Pyroclastic flows. Volcanic gases.

Question 45

How many people died from carbon dioxide emissions in the crater of Lake Nyos in 1986?

Answer 45

1,700

Question 46

What are secondary effects of volcanic eruptions?

Answer 46

Lahars. Flooding. Volcanic landslides. Tsnunamis. Acid rain. Climatic change. Death/ injury (human and livestock). Destruction of property/land.

Question 47

What is pahoehoe?

Answer 47

Smooth, unbroken, basaltic lava.

Question 48

What is aa?

Answer 48

Basaltic lava, characterised by a rough, rubbly surface.

Question 49

What are jokulhlaups?

Answer 49

Melting of glacial ice due to the heat of a volcanic eruption.