Litho: Extrusive Volcanism

Question 1

What materials are ejected from volcanoes?

Answer 1

1) lava flows
2) pyroclastic material
3) gases

Question 2

When does extrusive volcanism occur?

Answer 2

When magma reaches the earth’s surface and causes volcanic eruptions.

Question 3

What are the different types of magma?

Answer 3

• basaltic
• andesitic
• rhyolitic

(With increasing silica content, more silica = more explosive)

Question 4

What is a characteristic of lava flow?

Answer 4

It flows very slowly from high to low elevation, allowing people to be easily evacuated because determining the path of a flow is easy.

Question 5

What are the 3 types of runny lava? (Low viscosity)

Answer 5

1) pahoehoe flow (tauhuey)
- twisted and ropy structure. Relatively smooth skin that wrinkles and congeals. Basaltic
2) Aa flow
- has a surface of rough jagged blocks with sharp edges and spiny projections. Basaltic.
3) pillow lava
- formed underwater when basaltic lavas are extruded underwater.

Question 6

Describe pasty lava (high viscosity)

Answer 6

Most pasty lava is erupted explosively and large volume eruptions can produce very thick lava flows which move very slowly. Lava can pile up over and around the vent as lava dome.

Question 7

Define pyroclasts and name the 3 types of pyroclasts

Answer 7

Pyroclasts are solidified fragments of rock and lava ejected from the vent.

• ash
• bomb (twisted and streamlined erupted globs of fluid solidified midair)
• blocks (angular pieces of rock)

Question 8

How are lahars/mudflows formed?

Answer 8

When volcanic ash and debris left on the slopes after explosive eruptions become saturated with water and slow down steep volcanic deposits.

Question 9

Distinguish between primary and secondary lahars and give one eg. Of each type.

Answer 9

Primary: occurs at time of eruption, can be generated by eruption of crater lake [eg. Mt. St. Helens 1980 (water from Toutle river); Nevado del Ruiz, Columbia 1985 (snow and ice) killed 2000 ppl]
Secondary: occurs years afterwards caused by rain falling on slopes with uncompacted tephra. Mudflows entrains all loose debris in its path. [eg. Mt. Pinatubo, Philippines 1991: monsoon rains repeatedly generated lahars that buried towns]

Question 10

What is a characteristic of mudflows and lahars?

Answer 10

They can attain a speed of 100km/h when it accelerates downslope. The path is restricted to topographic lows, enabling them to be predicted in advance. The buildup of tephra on a volcano slope can be easily measured and thus steps can be taken to evacuate ppl. (Eg. USU eruption in 1977 Japan)

Question 11

How are pyroclastic flows formed?

Answer 11

Pyroclastic flows are formed when hot, incandescent gases are combined with pyroclasts to form a cloud of ash and gas. Pyroclasts are carried upwards as a billowing eruption column which then collapses around the vent, and spreads out as hot avalanches. The presence of hot, buoyant gases emitted from the volcanic debris enables the ash to travel downslope in a nearly frictionless environment at high speeds. (200km/h)

Question 12

Why are pyroclastic flows so dangerous?

Answer 12

Anything that is not knocked over by the fast moving avalanche of pumice and ash usually burns after contacting fragments and gases at temps >300degrees. Most human deaths result from rapid asphyxiation that occurs in the choking cloud of ash and gas.

Question 13

What factors affect the viscosity of magma?

Answer 13

1) silica content (numerous networks of silica tetrahedral will retard flow because the strong bonds of the networks must be ruptured for flow to occur)
2) temperature (higher temp, less viscous)
2) gas content (more dissolved gas, less viscous)

Question 14

Describe shield volcanoes.

Answer 14

1) broad domed shape
2) formed when basaltic lava solidifies
3) wide base of over 100km in diameter
4) gentle convex slopes
5) thin sheets of nearly uniform thickness

Eg. Kilauea and Mauna Loa in Hawaiian islands

Question 15

Describe strato (composite) volcanoes.

Answer 15

1) formed when relatively viscous lava of andesitic composition are extruded
2) alternate layers of lava and pyroclasts (lava is viscous)
3) large and nearly symmetrical
4) steep slopes (thousands of metres high) concave in shape (steep summits and gentle towards base)
Eg. Subduction zones at the ring of fire of the Pacific (mt Fuji, Japan)

Question 16

What are cinder cones?

Answer 16

Cinder cones are volcanic peaks

Question 17

Describe basalt plateaus and how they are formed.

Answer 17

Basaltic lava bury the old landscape as they build a lava plain, creating plateau basalts. Basalts are relatively resistant to erosion and the rocks surrounding it may not be so resistant. Hence when the level of land around the flows is reduced by erosion, the basalt may act as a cap rock and the area protected by the basaltic flow may be left upstanding as a plateau. Eg. Deccan Plateau, west India where enough lava was erupted to cover the US to a depth of nearly one km.

Question 18

What are calderas?

Answer 18

Calderas are nearly circular depressions at the summit of some volcanoes that exceed one km in diameter. Formed when summit of volcanic structure collapses into a partially empties magma chamber below. Eg. Crater lake, Oregon

Question 19

Describe basalt plateaus and how they are formed.

Answer 19

Basaltic lava bury the old landscape as they build a lava plain, creating plateau basalts. Basalts are relatively resistant to erosion and the rocks surrounding it may not be so resistant. Hence when the level of land around the flows is reduced by erosion, the basalt may act as a cap rock and the area protected by the basaltic flow may be left upstanding as a plateau. Eg. Deccan Plateau, west India where enough lava was erupted to cover the US to a depth of nearly one km.

Question 20

What are calderas?

Answer 20

Calderas are nearly circular depressions at the summit of some volcanoes that exceed one km in diameter. Formed when summit of volcanic structure collapses into a partially empties magma chamber below. Eg. Crater lake, Oregon

Question 21

What are the 3 effects of lava flows on the physical environment?

Answer 21

1) dramatic change to the landscape and flattening of topography since it blankets the landscapes (eg. Mount Etna where valleys were filled by 20m thick lava flow)
2) immediate devastation to ecosystem
3) creation of new land at hotspots or volcanic island arcs (mount Kilauea is constantly growing due to high rate of lava flow)

Question 22

What are 4 effects of pyroclastic flow on the physical landscape?

Answer 22

1) complete alteration of the landscape since everything will be buried or burnt by the hot glowing gases (eg. Forested slopes of Mount St. Helens completely burnt by the 1985 eruption)
2) loss of biodiversity destruction of flora and fauna (eg. Mount Pelée animals suffocated by poisonous gases and smothering plant life as ash coats their leaves)
3) may cause lahars if debris block streams (eg. mt. Pinatubo secondary lahars formed when typhoon came ashore)
4) creation of fertile soil by ash deposits and weathered lava that are rich in phosphorous, making good agricultural land for crops to be grown, enabling good harvests.

Question 23

What are 2 effects of ash fall on the physical environment?

Answer 23

1) Contamination of water sources

2) creates haze due to fine ash particles

Question 24

What are 3 effects of lahars and mudflows on the physical environment?

Answer 24

1) destruction of landscape as everything is swept away
2) change in drainage pattern due to creation of temporary lakes if mud flows down a tributary, but lead to flooding in the long term.
3) increase agricultural productivity in the long term as ask allows a new layer of sedimentation to build on the valley floor

Question 25

What are the 2 effects of lava flow on the human environment?

Answer 25

1) destruction of property, infrastructure, crops and land. Difficult to repair as infrastructure is buried in solid lava
2) negative impacts on the economy

Question 26

What are the 3 effects of pyroclastic flows on the human environment?

Answer 26

1) complete destruction of any town in the path of the flow
2) loss of human lives due to unpredictability and fast speeds (200km/h) increasing fatality rates (eg. Mount Pelée 1902 eruption killed 28,000 ppl due to high temperatures and death by asphyxiation from poisonous gases and hot ash)
3) severe damage to economy

Question 27

What are the 4 effects of ash cloud and tephra on the human environment?

Answer 27

1) engine failure in air craft flying through clouds (eg. British Airlines in 1982, crash landing)
2) health and respiratory problems
3) disruption of travel plans and businesses due to poor visibility
4) grazing animals poisoned by ash consumption (eg. New Zealand 1995 Ruapehu eruption)

Question 28

What are the 2 effects of lahars and mudflows on the environment?

Answer 28

1) extensive property damage as buildings and land may be buried under thick layers of rock debris (eg. Mt. Pinatubo heavy rainfall triggered fresh lahars despite last eruption in 1991)
2) human deaths due to drowning in the mud, difficult to rescue since they cannot be pulled out from the viscous mud (eg. Lahars caused by Nevado del Ruiz in Columbia in 1984 swept through the town of Armero and killed 23,000 ppl)

Question 29

State the 3 prediction methods in volcanic hazard management

Answer 29

1) tiltmeters
2) seismic activity monitoring
3) gases analysis

Question 30

Explain tiltmeters as a prediction method of volcanic hazards. Include limitation and example.

Answer 30

Movements of molten magma causes ground deformations, tilting the earth’s surface, which can be measured by tiltmeters.
Limitation: most active volcanoes undergo non eruptive minor cycles of inflation and deflation. Therefore, unreliable unless backed up by seismic or other evidence.
Example: Mt. St. Helens 1980 where tiltmeters measured inflation of 0.5-1.5m per day before eruption

Question 31

Explain seismic activity monitoring as a prediction method of volcanic hazards. Include limitation and example.

Answer 31

As mamas flow through subterranean channels, they apply stresses to rocks, which can fracture and set off seismic activity which are low in magnitude.
Limitations: some eruptions are not preceded by earthquakes. Presence of tremors can also represent collapse of rock into emptying magma channels, which indicates cessation of volcanic activity.
Example: Prediction 24h in advance eruption of Mt. Redoubt in Alaska (1990)

Question 32

Explain gases analysis as a prediction method of volcanic hazards. Include limitation and example.

Answer 32

This method assumes that the composition of volcanic gases will change when an eruption is imminent. (ie. Water vapour, co2, sulfur)
Limitation: this technique is restricted by the need to chemically analyse the gas constituents immediately after they are vented from the volcano.
Example: success - mt. Pinatubo 1991
Failure- Galeras (Columbia) 1991 which killed volcanologists who thought it was safe to go to the volcano summit when the composition of gases didn’t change

Question 33

Describe 2 ways to mitigate lava flows.

Answer 33

1) spray water into its edge to cool it and create an artificial levee. (Eg. Icelandic island of Helmay in 1973 when sea water was sprayed onto the front of an aa flow that threatened to overwhelm the islands main town. This diverted the flow into the sea)
2) redirect/divert flow by blocking their path
(Eg. Divert lava flow from mt. Etna in 1992 when it reached within 1km of the town of Zafferana. Containment wall built which delayed the advancement of the flow for a few weeks. Eventually overtopped the wall and came to a halt on the outskirts.)

Question 34

Describe 1 way to mitigate pyroclastic flows.

Answer 34

Build a ‘ski-jump’ like barrier/ramp designed to channel the energy of a flow upwards to encourage it to form a buoyant like plume, cooling the gases to reduce damage.
Limitations: need a lot of knowledge and money

Question 35

Describe 2 ways to mitigate lahars.

Answer 35

1) drain crater lake when source is from lake. Eg. Kelut, Indonesia, a system of tunnels completed to drain a crater lake to reduce the possibility of secondary lahars.
2) dig channels in slopes covered with ash, such that in the event of a lahar, it would be held back by dams and retention basins, reducing the volume and energy of flow

Question 36

Describe hazard maps as a mitigation measure for volcanic hazards.

Answer 36

Making planning authorities and locals aware if the hazards and the appropriate responses to each. Hazard maps indicate possible areas that can possibly be affected by an eruptions. Authorities can build necessary infrastructure such as modifications to roofs to make them stronger and able to shed ash, protecting crops by plastic sheeting etc. (Eg. Nevado del Ruiz - hazard maps and evacuation plans drawn but largely ignored by local authorities)

Question 37

What are the 2 effects of lava flow on the human environment?

Answer 37

1) destruction of property, infrastructure, crops and land. Difficult to repair as infrastructure is buried in solid lava
2) negative impacts on the economy

Question 38

What are the 3 effects of pyroclastic flows on the human environment?

Answer 38

1) complete destruction of any town in the path of the flow
2) loss of human lives due to unpredictability and fast speeds (200km/h) increasing fatality rates (eg. Mount Pelée 1902 eruption killed 28,000 ppl due to high temperatures and death by asphyxiation from poisonous gases and hot ash)
3) severe damage to economy

Question 39

What are the 4 effects of ash cloud and tephra on the human environment?

Answer 39

1) engine failure in air craft flying through clouds (eg. British Airlines in 1982, crash landing)
2) health and respiratory problems
3) disruption of travel plans and businesses due to poor visibility
4) grazing animals poisoned by ash consumption (eg. New Zealand 1995 Ruapehu eruption)

Question 40

What are the 2 effects of lahars and mudflows on the environment?

Answer 40

1) extensive property damage as buildings and land may be buried under thick layers of rock debris (eg. Mt. Pinatubo heavy rainfall triggered fresh lahars despite last eruption in 1991)
2) human deaths due to drowning in the mud, difficult to rescue since they cannot be pulled out from the viscous mud (eg. Lahars caused by Nevado del Ruiz in Columbia in 1984 swept through the town of Armero and killed 23,000 ppl)

Question 41

State the 3 prediction methods in volcanic hazard management

Answer 41

1) tiltmeters
2) seismic activity monitoring
3) gases analysis

Question 42

Explain tiltmeters as a prediction method of volcanic hazards. Include limitation and example.

Answer 42

Movements of molten magma causes ground deformations, tilting the earth’s surface, which can be measured by tiltmeters.
Limitation: most active volcanoes undergo non eruptive minor cycles of inflation and deflation. Therefore, unreliable unless backed up by seismic or other evidence.
Example: Mt. St. Helens 1980 where tiltmeters measured inflation of 0.5-1.5m per day before eruption

Question 43

Explain seismic activity monitoring as a prediction method of volcanic hazards. Include limitation and example.

Answer 43

As mamas flow through subterranean channels, they apply stresses to rocks, which can fracture and set off seismic activity which are low in magnitude.
Limitations: some eruptions are not preceded by earthquakes. Presence of tremors can also represent collapse of rock into emptying magma channels, which indicates cessation of volcanic activity.
Example: Prediction 24h in advance eruption of Mt. Redoubt in Alaska (1990)

Question 44

Explain gases analysis as a prediction method of volcanic hazards. Include limitation and example.

Answer 44

This method assumes that the composition of volcanic gases will change when an eruption is imminent. (ie. Water vapour, co2, sulfur)
Limitation: this technique is restricted by the need to chemically analyse the gas constituents immediately after they are vented from the volcano.
Example: success - mt. Pinatubo 1991
Failure- Galeras (Columbia) 1991 which killed volcanologists who thought it was safe to go to the volcano summit when the composition of gases didn’t change

Question 45

Describe 2 ways to mitigate lava flows.

Answer 45

1) spray water into its edge to cool it and create an artificial levee. (Eg. Icelandic island of Helmay in 1973 when sea water was sprayed onto the front of an aa flow that threatened to overwhelm the islands main town. This diverted the flow into the sea)
2) redirect/divert flow by blocking their path
(Eg. Divert lava flow from mt. Etna in 1992 when it reached within 1km of the town of Zafferana. Containment wall built which delayed the advancement of the flow for a few weeks. Eventually overtopped the wall and came to a halt on the outskirts.)

Question 46

Describe 1 way to mitigate pyroclastic flows.

Answer 46

Build a ‘ski-jump’ like barrier/ramp designed to channel the energy of a flow upwards to encourage it to form a buoyant like plume, cooling the gases to reduce damage.
Limitations: need a lot of knowledge and money

Question 47

Describe 2 ways to mitigate lahars.

Answer 47

1) drain crater lake when source is from lake. Eg. Kelut, Indonesia, a system of tunnels completed to drain a crater lake to reduce the possibility of secondary lahars.
2) dig channels in slopes covered with ash, such that in the event of a lahar, it would be held back by dams and retention basins, reducing the volume and energy of flow

Question 48

Describe hazard maps as a mitigation measure for volcanic hazards.

Answer 48

Making planning authorities and locals aware if the hazards and the appropriate responses to each. Hazard maps indicate possible areas that can possibly be affected by an eruptions. Authorities can build necessary infrastructure such as modifications to roofs to make them stronger and able to shed ash, protecting crops by plastic sheeting etc. (Eg. Nevado del Ruiz - hazard maps and evacuation plans drawn but largely ignored by local authorities)

Question 49

What are the 2 effects of lava flow on the human environment?

Answer 49

1) destruction of property, infrastructure, crops and land. Difficult to repair as infrastructure is buried in solid lava
2) negative impacts on the economy

Question 50

What are the 3 effects of pyroclastic flows on the human environment?

Answer 50

1) complete destruction of any town in the path of the flow
2) loss of human lives due to unpredictability and fast speeds (200km/h) increasing fatality rates (eg. Mount Pelée 1902 eruption killed 28,000 ppl due to high temperatures and death by asphyxiation from poisonous gases and hot ash)
3) severe damage to economy

Question 51

What are the 4 effects of ash cloud and tephra on the human environment?

Answer 51

1) engine failure in air craft flying through clouds (eg. British Airlines in 1982, crash landing)
2) health and respiratory problems
3) disruption of travel plans and businesses due to poor visibility
4) grazing animals poisoned by ash consumption (eg. New Zealand 1995 Ruapehu eruption)

Question 52

What are the 2 effects of lahars and mudflows on the environment?

Answer 52

1) extensive property damage as buildings and land may be buried under thick layers of rock debris (eg. Mt. Pinatubo heavy rainfall triggered fresh lahars despite last eruption in 1991)
2) human deaths due to drowning in the mud, difficult to rescue since they cannot be pulled out from the viscous mud (eg. Lahars caused by Nevado del Ruiz in Columbia in 1984 swept through the town of Armero and killed 23,000 ppl)

Question 53

State the 3 prediction methods in volcanic hazard management

Answer 53

1) tiltmeters
2) seismic activity monitoring
3) gases analysis

Question 54

Explain tiltmeters as a prediction method of volcanic hazards. Include limitation and example.

Answer 54

Movements of molten magma causes ground deformations, tilting the earth’s surface, which can be measured by tiltmeters.
Limitation: most active volcanoes undergo non eruptive minor cycles of inflation and deflation. Therefore, unreliable unless backed up by seismic or other evidence.
Example: Mt. St. Helens 1980 where tiltmeters measured inflation of 0.5-1.5m per day before eruption

Question 55

Explain seismic activity monitoring as a prediction method of volcanic hazards. Include limitation and example.

Answer 55

As mamas flow through subterranean channels, they apply stresses to rocks, which can fracture and set off seismic activity which are low in magnitude.
Limitations: some eruptions are not preceded by earthquakes. Presence of tremors can also represent collapse of rock into emptying magma channels, which indicates cessation of volcanic activity.
Example: Prediction 24h in advance eruption of Mt. Redoubt in Alaska (1990)

Question 56

Explain gases analysis as a prediction method of volcanic hazards. Include limitation and example.

Answer 56

This method assumes that the composition of volcanic gases will change when an eruption is imminent. (ie. Water vapour, co2, sulfur)
Limitation: this technique is restricted by the need to chemically analyse the gas constituents immediately after they are vented from the volcano.
Example: success - mt. Pinatubo 1991
Failure- Galeras (Columbia) 1991 which killed volcanologists who thought it was safe to go to the volcano summit when the composition of gases didn’t change

Question 57

Describe 2 ways to mitigate lava flows.

Answer 57

1) spray water into its edge to cool it and create an artificial levee. (Eg. Icelandic island of Helmay in 1973 when sea water was sprayed onto the front of an aa flow that threatened to overwhelm the islands main town. This diverted the flow into the sea)
2) redirect/divert flow by blocking their path
(Eg. Divert lava flow from mt. Etna in 1992 when it reached within 1km of the town of Zafferana. Containment wall built which delayed the advancement of the flow for a few weeks. Eventually overtopped the wall and came to a halt on the outskirts.)

Question 58

Describe 1 way to mitigate pyroclastic flows.

Answer 58

Build a ‘ski-jump’ like barrier/ramp designed to channel the energy of a flow upwards to encourage it to form a buoyant like plume, cooling the gases to reduce damage.
Limitations: need a lot of knowledge and money

Question 59

Describe 2 ways to mitigate lahars.

Answer 59

1) drain crater lake when source is from lake. Eg. Kelut, Indonesia, a system of tunnels completed to drain a crater lake to reduce the possibility of secondary lahars.
2) dig channels in slopes covered with ash, such that in the event of a lahar, it would be held back by dams and retention basins, reducing the volume and energy of flow

Question 60

Describe hazard maps as a mitigation measure for volcanic hazards.

Answer 60

Making planning authorities and locals aware if the hazards and the appropriate responses to each. Hazard maps indicate possible areas that can possibly be affected by an eruptions. Authorities can build necessary infrastructure such as modifications to roofs to make them stronger and able to shed ash, protecting crops by plastic sheeting etc. (Eg. Nevado del Ruiz - hazard maps and evacuation plans drawn but largely ignored by local authorities)

Question 61

What are the 2 effects of lava flow on the human environment?

Answer 61

1) destruction of property, infrastructure, crops and land. Difficult to repair as infrastructure is buried in solid lava
2) negative impacts on the economy

Question 62

What are the 3 effects of pyroclastic flows on the human environment?

Answer 62

1) complete destruction of any town in the path of the flow
2) loss of human lives due to unpredictability and fast speeds (200km/h) increasing fatality rates (eg. Mount Pelée 1902 eruption killed 28,000 ppl due to high temperatures and death by asphyxiation from poisonous gases and hot ash)
3) severe damage to economy

Question 63

What are the 4 effects of ash cloud and tephra on the human environment?

Answer 63

1) engine failure in air craft flying through clouds (eg. British Airlines in 1982, crash landing)
2) health and respiratory problems
3) disruption of travel plans and businesses due to poor visibility
4) grazing animals poisoned by ash consumption (eg. New Zealand 1995 Ruapehu eruption)

Question 64

What are the 2 effects of lahars and mudflows on the environment?

Answer 64

1) extensive property damage as buildings and land may be buried under thick layers of rock debris (eg. Mt. Pinatubo heavy rainfall triggered fresh lahars despite last eruption in 1991)
2) human deaths due to drowning in the mud, difficult to rescue since they cannot be pulled out from the viscous mud (eg. Lahars caused by Nevado del Ruiz in Columbia in 1984 swept through the town of Armero and killed 23,000 ppl)

Question 65

State the 3 prediction methods in volcanic hazard management

Answer 65

1) tiltmeters
2) seismic activity monitoring
3) gases analysis

Question 66

Explain tiltmeters as a prediction method of volcanic hazards. Include limitation and example.

Answer 66

Movements of molten magma causes ground deformations, tilting the earth’s surface, which can be measured by tiltmeters.
Limitation: most active volcanoes undergo non eruptive minor cycles of inflation and deflation. Therefore, unreliable unless backed up by seismic or other evidence.
Example: Mt. St. Helens 1980 where tiltmeters measured inflation of 0.5-1.5m per day before eruption

Question 67

Explain seismic activity monitoring as a prediction method of volcanic hazards. Include limitation and example.

Answer 67

As mamas flow through subterranean channels, they apply stresses to rocks, which can fracture and set off seismic activity which are low in magnitude.
Limitations: some eruptions are not preceded by earthquakes. Presence of tremors can also represent collapse of rock into emptying magma channels, which indicates cessation of volcanic activity.
Example: Prediction 24h in advance eruption of Mt. Redoubt in Alaska (1990)

Question 68

Explain gases analysis as a prediction method of volcanic hazards. Include limitation and example.

Answer 68

This method assumes that the composition of volcanic gases will change when an eruption is imminent. (ie. Water vapour, co2, sulfur)
Limitation: this technique is restricted by the need to chemically analyse the gas constituents immediately after they are vented from the volcano.
Example: success - mt. Pinatubo 1991
Failure- Galeras (Columbia) 1991 which killed volcanologists who thought it was safe to go to the volcano summit when the composition of gases didn’t change

Question 69

Describe 2 ways to mitigate lava flows.

Answer 69

1) spray water into its edge to cool it and create an artificial levee. (Eg. Icelandic island of Helmay in 1973 when sea water was sprayed onto the front of an aa flow that threatened to overwhelm the islands main town. This diverted the flow into the sea)
2) redirect/divert flow by blocking their path
(Eg. Divert lava flow from mt. Etna in 1992 when it reached within 1km of the town of Zafferana. Containment wall built which delayed the advancement of the flow for a few weeks. Eventually overtopped the wall and came to a halt on the outskirts.)

Question 70

Describe 1 way to mitigate pyroclastic flows.

Answer 70

Build a ‘ski-jump’ like barrier/ramp designed to channel the energy of a flow upwards to encourage it to form a buoyant like plume, cooling the gases to reduce damage.
Limitations: need a lot of knowledge and money

Question 71

Describe 2 ways to mitigate lahars.

Answer 71

1) drain crater lake when source is from lake. Eg. Kelut, Indonesia, a system of tunnels completed to drain a crater lake to reduce the possibility of secondary lahars.
2) dig channels in slopes covered with ash, such that in the event of a lahar, it would be held back by dams and retention basins, reducing the volume and energy of flow

Question 72

Describe hazard maps as a mitigation measure for volcanic hazards.

Answer 72

Making planning authorities and locals aware if the hazards and the appropriate responses to each. Hazard maps indicate possible areas that can possibly be affected by an eruptions. Authorities can build necessary infrastructure such as modifications to roofs to make them stronger and able to shed ash, protecting crops by plastic sheeting etc. (Eg. Nevado del Ruiz - hazard maps and evacuation plans drawn but largely ignored by local authorities)