Risky World COPY Flashcards
What leads to volcanoes and earthquakes occurring
The movement of the plates leads to volcanoes and earthquakes occurring
What are the four different types of plate boundaries
Constructive
Conservative
Destructive
Collision
What happens at a constructive boundary
Two plates are pulling apart due to convection currents.
As they pull apart the rock in the mantle melts to form magma.
The magma then erupts At the surface as lava and forms a volcano.
Many are formed undersea
What is an example of a constructive plate boundary
Both American plate moves apart from Eurasian plate in the Atlantic Ocean. Iceland is formed by this volcanic activity
What suppers at conservative margins
Only earthquakes occur at these margins .
Two plates try to slide past each other.
Often plates stick and pressure builds up.
When this pressure is finally released it causes an earthquake
What is an example of a conservative plate boundary
The North American plate slowly moving as the Pacific plate also moves against it, in the same direction. San Francisco and Los Angeles are on this boundary
What happens at destructive margins
Occurs when oceanic crust moves towards continental crust.
As the oceanic crust is heavier, it is forced downwards at an angle.
This is subduction. As it is forced downwards the pressure increases.
This can trigger extremely violent earthquakes.
The heat produced by friction turns the descending oceanic crust back into liquid rock called magma.
Hot magma tries to rise to the surface but when it succeeds there will be violent volcanic eruptions.
Most of the Pacific Ocean is bounded by destructive margins where the oceanic crust is being destroyed
What is a plate boundary
The place where two plates meet is called e plate boundary
Give an example of a destructive margin
The Nazca plate moves towards the South American plate and is forced underneath it.
What happens at collision margins
Occur when the two plates moving together are both continental crust.
They are equally dense, so neither can sink.
Sedimentary rocks between the plates are pushed up.
Earthquakes occur and fold mountains are formed
Rocks formerly on Ocean bed are pushed together, buckled and forced up to for Himalayan mountains.
Give an example of a collision margin
The indo Australian plate moves towards the Eurasian plate which is almost stationary
What is debris
Debris is small glassy blobs which form in the air from the lava spray and fall downwind of the vent. The nearby residents are probably not in any danger.
What is plume
The eruption releases a giant plume of ash that reaches 12-15 miles above sea level. For the next several days, the ash will spread around the earth, falling over thousands of square miles.
What are Lahars
Mudflows of volcanic material due to ash and debris mixing with water. On steep slopes speeds can reach 22m/s. They may occur because ice has melted in the area
What are landslides
The eruption triggers a massive landslide of rock and soil that races down the side of the volcano, covering the surrounding areas with 1,000 cubic yards to more than 130,000 cubic yards of debris
What is lava flow
Lava flows down the sides of the volcano and may over nearby roads
A greater threat to property than human life due to opportunity for evacuation.
Basic lava flows more quickly than acidic lava. Next time the volcano erupts, it’s lava may cover nearby towns, very fluid lava can flow tens of miles from a volcano vent.
What are pyroclastic flows
These high density mixtures of hot, dry rock fragments, lava particles, ash and hot gases. They move incredibly quickly from their source, typically greater than 80km/hr. They are ,inked with composite volcanoes. They would destroy everything in their path
Ash and tephra fall
Ash is material below 2mm in diameter whilst tephra is anything above this. It is usually formed when magma is fragmented by explosions, and can stay in the atmosphere causing global variations in weather patterns. Ash falls do not cause many deaths but can lead to breathing difficulties.
Ash (alternative)
The eruption releases clouds of ash. Towns downwind of the eruption may be completely covered in a thick layer of ash and plumice.
Lava tubes
Some lava may flow through channels of bordered lava called lava tubes, which can transport the kava tens of kilometres away from the volcanic centre.
Dome
As lava pushes up like an inflated balloon, a small dome is created - typically only a few hundred feet high, domes often form on the sides of a strato volcano or in the crater of a collapsed volcano
Fire fountain
The thin lava of a shield volcano can produce spectacular displays called fire fountains. These sprays of lava can rise Hundreds of feet and last for hours
Volcanic gases
Gases emitted from volcanoes include water vapour, carbon dioxide, sulphur dioxide, hydrogen sulfide, helium and carbon monoxide. They really cause deaths but can be problematic as many are heavier than air
Primary volcanic hazards
Are immediate and come from the volcano itself Lava flows Pyroclastic flows Ash and tephra fall Volcanic gases
Secondary volcanic hazards
Can arise from the primary hazards or result from other factors
Lahars
Volcanic landslides
Tsunamis (rare)
