Edexcel A-Level Geography: Tectonic
Processes and Hazards
Define slab-pull.
The pull of gravity on a plate during subduction. It occurs at destructive plate
boundaries.
Describe mantle plume.
Magma rises from the Earth's core and occasionally breaks through the crust, forming
volcanoes. However, the plate is constantly moving, so a line of volcanoes is formed
over time, with the most active ones being nearest the mantle plume.
Describe composite volcanoes.
Composite volcanoes are formed on destructive plate margins. They have the following
characteristics:
- Acidic lava, which is very viscous (sticky)
- Steep sides as the lava doesn't flow very far before it solidifies.
- Alternate layers of ash and lava.
- Violent eruptions.
- Larger periods between eruptions.
Describe shield volcanoes.
Shield volcanoes are found on constructive plate margins. They have the following
characteristics:
- Basic lava is non-acidic and very runny.
- Gentle sides as the lava flows for long distances before it solidifies.
- No layers, as the volcano just consists of lava.
- Less violent eruptions.
- Shorter periods between eruptions.
Name 4 key primary hazards of a volcano.
- Lava flow
- Volcanic bombs
- Pyroclastic flows
- Ash fall
Name 2 key secondary hazards of a volcano.
- Lahars
- Jökulhlaup
Describe lava flow.
Streams of molten rock flow down a volcano and will burn and destroy everything in its
path.
Describe volcanic bombs.
A pyroclast which was semi-molten (viscous) while ejected from the volcano.
Describe pyroclastic flows.
, A mixture of dense hot rock, lava ash and gases ejected from a volcano, which move at
very high speeds.
Describe ash fall.
A thick cloud of ash falls over a city and blocks the sun whilst also poisoning the air.
Describe lahars.
Masses of rock, mud and water that travel quickly down the volcano.
Describe Jökulhlaup.
The heat of the volcano melts glaciers rapidly causing very sudden floods.
Name the 3 types of volcanic eruption.
- Plinian
- Strombolian
- Lava domes
Describe the Plinian eruption.
The Plinian eruption is the most violent eruption. Fragmentation of gassy magma and
very viscous lava. The more viscous the more explosive the eruption is.
Describe Strombolian eruptions.
Short bursts of lava every few minutes. Small lava lakes are in the conduit of the
volcano.
Describe lava domes.
A hole site, dacite or rhyolite lava is squeezed from a vent without exploding.
Describe subduction zones.
The denser and heavier oceanic plate subducts the continental plate. This process
results in geohazards such as volcanoes and earthquakes.
Define natural hazard.
A naturally occurring process or event that has the potential to affect people.
Define natural disaster.
A major natural hazard event that causes significant social, economic or environmental
damage (10 or more deaths).
Define mega-disaster.
A natural disaster that reaches catastrophic proportions (2000 or more deaths).
Define vulnerability
The ability to anticipate, cope with, resist and recover from a natural hazard.
Define resilience.
The ability to protect lives, livelihoods and infrastructure from destruction, and to restore
areas.
Why are there fewer volcanic mega-disasters?
Temporal (time) and spatial predictability.
What is the risk equation?
Risk = Hazard x Vulnerability/Capacity to cope
Describe the Pressure and Release Model (PAR).
Root causes, dynamic pressures and unsafe conditions are all part of the progression of
vulnerability on the left side of the diagram. On the other side are the natural hazards
and in the middle is the disaster.
Processes and Hazards
Define slab-pull.
The pull of gravity on a plate during subduction. It occurs at destructive plate
boundaries.
Describe mantle plume.
Magma rises from the Earth's core and occasionally breaks through the crust, forming
volcanoes. However, the plate is constantly moving, so a line of volcanoes is formed
over time, with the most active ones being nearest the mantle plume.
Describe composite volcanoes.
Composite volcanoes are formed on destructive plate margins. They have the following
characteristics:
- Acidic lava, which is very viscous (sticky)
- Steep sides as the lava doesn't flow very far before it solidifies.
- Alternate layers of ash and lava.
- Violent eruptions.
- Larger periods between eruptions.
Describe shield volcanoes.
Shield volcanoes are found on constructive plate margins. They have the following
characteristics:
- Basic lava is non-acidic and very runny.
- Gentle sides as the lava flows for long distances before it solidifies.
- No layers, as the volcano just consists of lava.
- Less violent eruptions.
- Shorter periods between eruptions.
Name 4 key primary hazards of a volcano.
- Lava flow
- Volcanic bombs
- Pyroclastic flows
- Ash fall
Name 2 key secondary hazards of a volcano.
- Lahars
- Jökulhlaup
Describe lava flow.
Streams of molten rock flow down a volcano and will burn and destroy everything in its
path.
Describe volcanic bombs.
A pyroclast which was semi-molten (viscous) while ejected from the volcano.
Describe pyroclastic flows.
, A mixture of dense hot rock, lava ash and gases ejected from a volcano, which move at
very high speeds.
Describe ash fall.
A thick cloud of ash falls over a city and blocks the sun whilst also poisoning the air.
Describe lahars.
Masses of rock, mud and water that travel quickly down the volcano.
Describe Jökulhlaup.
The heat of the volcano melts glaciers rapidly causing very sudden floods.
Name the 3 types of volcanic eruption.
- Plinian
- Strombolian
- Lava domes
Describe the Plinian eruption.
The Plinian eruption is the most violent eruption. Fragmentation of gassy magma and
very viscous lava. The more viscous the more explosive the eruption is.
Describe Strombolian eruptions.
Short bursts of lava every few minutes. Small lava lakes are in the conduit of the
volcano.
Describe lava domes.
A hole site, dacite or rhyolite lava is squeezed from a vent without exploding.
Describe subduction zones.
The denser and heavier oceanic plate subducts the continental plate. This process
results in geohazards such as volcanoes and earthquakes.
Define natural hazard.
A naturally occurring process or event that has the potential to affect people.
Define natural disaster.
A major natural hazard event that causes significant social, economic or environmental
damage (10 or more deaths).
Define mega-disaster.
A natural disaster that reaches catastrophic proportions (2000 or more deaths).
Define vulnerability
The ability to anticipate, cope with, resist and recover from a natural hazard.
Define resilience.
The ability to protect lives, livelihoods and infrastructure from destruction, and to restore
areas.
Why are there fewer volcanic mega-disasters?
Temporal (time) and spatial predictability.
What is the risk equation?
Risk = Hazard x Vulnerability/Capacity to cope
Describe the Pressure and Release Model (PAR).
Root causes, dynamic pressures and unsafe conditions are all part of the progression of
vulnerability on the left side of the diagram. On the other side are the natural hazards
and in the middle is the disaster.
