Risk of Tectonic Hazards (Edexcel A Level Geography): Flashcards
Exam code: 9GE0
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Define plate boundary.
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Define plate boundary.
A plate boundary is where two tectonic plates meet and interact, creating earthquakes, volcanoes and other tectonic processes.
What are the three main types of plate boundary?
The three main types are divergent, convergent and transform plate boundaries.
Name the three categories of convergent boundary.
The three categories are oceanic–continental, oceanic–oceanic and continental–continental (collision boundary).
Where do about 95% of earthquakes occur?
About 95% of earthquakes occur at or near plate boundaries, especially around the Pacific Ring of Fire.
True or False?
The most powerful earthquakes are usually at convergent or conservative boundaries.
True.
The most powerful earthquakes are mainly associated with convergent and conservative plate boundaries.
Around of tsunamis occur in the .
Around 70% of tsunamis occur in the Pacific Ocean.
Many earthquakes and volcanoes cluster around the of .
Many earthquakes and volcanoes cluster around the Ring of Fire of the Pacific.
Define intra-plate earthquake.
An intra-plate earthquake occurs within a tectonic plate, away from plate boundaries, often along reactivated ancient fault lines or zones of weakness.
What is a hotspot volcano?
A hotspot volcano forms above a stationary magma plume as a tectonic plate moves over it, creating a chain of volcanic islands.
In a hotspot island chain, the island is furthest from the .
In a hotspot island chain, the oldest island is furthest from the magma plume.
Define lithosphere.
The lithosphere is the rigid outer layer of the Earth, made of the crust and the uppermost rigid mantle, broken into tectonic plates.
Define asthenosphere.
The asthenosphere is a semi-molten, plastic layer of the upper mantle that flows slowly and allows tectonic plates to move above it.
What is the Mohorovičić discontinuity (Moho)?
The Moho is the boundary between the crust and the mantle, marked by a sudden change in seismic wave velocity.
The two types of crust are and .
The two types of crust are continental and oceanic.
Explain ridge push at mid-ocean ridges.
Heated, rising mantle at mid-ocean ridges creates elevated crust that gravitationally slides away, pushing oceanic plates apart as new crust forms.
How does slab pull move tectonic plates?
As cold, dense oceanic lithosphere subducts, gravity pulls it deeper, dragging the rest of the plate into the subduction zone.
Mirror-image magnetic stripes on the ocean floor provide evidence for .
Mirror-image magnetic stripes on the ocean floor provide evidence for seafloor spreading.
What happens at a convergent (destructive) boundary between oceanic and continental plates?
The denser oceanic plate subducts beneath the less dense continental plate, forming deep ocean trenches, Benioff zone earthquakes, and volcanic arcs.
The narrow earthquake zone in a subduction area is called the .
The narrow earthquake zone in a subduction area is called the Benioff Zone.
True or False?
At collision boundaries there is no volcanic activity.
True.
At collision boundaries, similar-density continental plates crumple to form fold mountains, but with no subduction there is no magma generation and so no volcanoes.
What is a transform (conservative) plate boundary?
A transform boundary is where plates slide past each other horizontally, often sticking then slipping to produce earthquakes but no volcanoes.
How do magma properties at divergent boundaries affect eruptions?
Divergent boundaries produce hot, low-viscosity, low-gas basalt magma, causing frequent, gentle, effusive eruptions and mainly shallow, mild earthquakes.
At convergent boundaries, eruptions are often because the magma is and gas-rich.
At convergent boundaries, eruptions are often explosive because the magma is viscous and gas-rich.
Define tsunami.
A large sea wave generated by sudden water displacement, usually from submarine earthquakes, but also landslides, volcanic eruptions or rare meteor strikes.
How does a submarine earthquake generate a tsunami?
A sea-bed jolt suddenly displaces water upwards, creating waves that travel across the ocean and grow taller as they approach shallow coastal waters.
As a tsunami approaches land, its speed and its wavelength becomes .
As a tsunami approaches land, its speed decreases and its wavelength becomes compressed.
True or False?
Tsunamis are most common around the Pacific Ring of Fire.
True.
Most tsunamis occur near plate boundaries, especially around the Pacific Ring of Fire where earthquakes and volcanic activity are frequent.
Define pyroclastic flow.
A fast-moving mixture of hot gas, ash and rock fragments that flows down a volcano, causing extreme temperatures and widespread destruction.
hazards are a direct result of the eruption, whereas hazards result from the primary hazards.
Primary hazards are a direct result of the eruption, whereas secondary hazards result from the primary hazards.
What is a volcanic lahar?
A lahar is a fast-flowing mixture of mud, rocks and water that travels down volcano slopes, destroying almost everything in its path.
Define P wave.
A primary seismic wave that is the fastest, reaches the surface first, travels through solids and liquids, and causes backwards–forwards ground motion.
True or False?
L waves are the least damaging seismic waves.
False.
Love (L) waves are surface waves, move side to side, concentrate energy at the surface and are usually the most damaging type.
Earthquake include ground shaking and crustal fracturing, while secondary hazards include and liquefaction.
Earthquake primary hazards include ground shaking and crustal fracturing, while secondary hazards include landslides and liquefaction.
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