Earthquakes & Volcanoes (Cambridge (CIE) IGCSE Geography): Flashcards
Exam code: 0460 & 0976
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Define lithosphere.
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Cards in this collection (25)
Define lithosphere.
The lithosphere is made up of the two types of crust together with the rigid upper part of the mantle; its thickness varies.
Define asthenosphere.
The asthenosphere is a partially molten, plastic-type layer of the upper mantle which moves under high pressure and lies between about 35 and 250 km deep.
What are the two metals that make up the Earth's solid inner core?
Iron and nickel.
Compare the thickness and density of oceanic and continental crust.
Oceanic crust is thinner (5–10 km) but heavier and denser; continental crust is thicker (25–100 km) but older and less dense.
Which rock mainly composes the oceanic crust, and which mainly composes the continental crust?
Oceanic crust is composed mainly of basalt; continental crust is composed mainly of granite.
Into how many large tectonic plates is the Earth's crust broken?
15 large tectonic plates, plus several smaller ones.
Which process generates the geothermal heat that drives tectonic plate movement?
Radioactive decay within the Earth.
According to slab pull theory, what drives plate movement in addition to convection currents?
The weight of the denser oceanic plates subducting and dragging the rest of the plate along.
Within the mantle there are ______, which are upwellings of superheated rock that can create divergent boundaries or hotspots.
Within the mantle there are mantle plumes, which are upwellings of superheated rock that can create divergent boundaries or hotspots.
Name the four main types of plate boundary.
Divergent (constructive), convergent (destructive), collision, and transform (conservative).
Approximately ______ of earthquakes occur around the rim of the Pacific Ocean, a zone called the 'Ring of Fire'.
Approximately 90% of earthquakes occur around the rim of the Pacific Ocean, a zone called the 'Ring of Fire'.
True or False?
Volcanoes only ever occur at plate boundaries.
False.
Most volcanoes occur at divergent and convergent boundaries, but they also occur at hotspots away from plate boundaries, where plumes of magma escape through the crust.
At which two types of plate boundary do volcanoes form?
Constructive (divergent) and destructive (convergent) plate boundaries only.
At a destructive (convergent) boundary, why does the oceanic plate subduct?
The oceanic plate is denser and heavier than the continental plate, so it subducts beneath it, causing friction and heat that melt the crust to form magma.
What landform is created at a collision boundary, and give an example.
Fold mountains, such as the Himalayas, formed as two continental plates of similar density push the land upwards.
At a conservative (transform) boundary, ______ are the only hazard, as the plates move past each other.
At a conservative (transform) boundary, earthquakes are the only hazard, as the plates move past each other.
Define the focus of an earthquake.
The focus is the point below the Earth's surface at which the earthquake starts.
What is the epicentre of an earthquake?
The point on the Earth's surface directly above the focus.
On which scale is earthquake magnitude now measured, and which scale did it replace?
The Moment Magnitude Scale, which replaced the Richter scale. Damage is measured separately on the Mercalli Scale.
True or False?
Earthquakes at divergent (constructive) boundaries tend to be stronger than those at destructive boundaries.
False.
Earthquakes tend to be weaker at divergent boundaries because the plates are moving apart; they are stronger at convergent, collision and conservative boundaries.
Describe the key features of a composite (strato-) volcano.
Steep sides, sticky (viscous) lava, more explosive eruptions and alternating layers of ash and lava; they tend to form at convergent (destructive) boundaries.
Shield volcanoes have gently sloping sides and runny lava, and tend to form at ______ plate boundaries or hot spots.
Shield volcanoes have gently sloping sides and runny lava, and tend to form at divergent (constructive) plate boundaries or hot spots.
Define a dormant volcano.
A dormant volcano has not erupted for many years, but there is evidence of a magma reservoir beneath it.
On which scale is the magnitude of a volcanic eruption measured?
The Volcanic Explosivity Index (VEI), an open-ended scale; the highest in recorded history was a 7 (Tambora, 1815).
What is a pyroclastic flow, and how fast can it move?
A fast-moving, very hot cloud of poisonous gases mixed with ash. It averages about 100 km/h but can reach up to 700 km/h, causing total destruction.
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