OCR A Level Geography Paper 3: Hazardous
Earth UPDATED EXAM QUESTIONS WITH
CORRECT ANSWERS SOLVED.
active volcanoes - CORRECT ANSWERS✔✔- some only see active if erupted in historic times; but can be
difficult due to records available
- others only see as active if evidence of unusual quake activity or gas emissions
- widely accepted active if erupted since last glacial period or within past 10,000 years
active, dormant and extinct volcanoes - CORRECT ANSWERS✔✔- described as these on basis of eruption
history; can be difficult to do this
- however, extinct seen as one that wont erupt again
advantages of living in a volcanic area - CORRECT ANSWERS✔✔- geothermal energy: magma is close to
the surface, groundwater turns to steam with drives turbines
- tourism and recreation
age of sea-floor rocks - CORRECT ANSWERS✔✔- during 1906s, ocean drilling programme investigated
ocean sediments on ocean floor
- recovered cores in water up to 7000m deep, revealing spatial pattern of sediments (sea-floor
spreading)
- thickest/ oldest sediments found nearest to continents
- however, cores also showed rock no older than 200 million years, confirming ocean crust constantly
recycled over this period
asthenosphere - CORRECT ANSWERS✔✔- layer in Earth's mantle below lithosphere
- high temps cause rocks to soften and become viscous, so easily deform
- 100km-300km deep, semi-molten and flows slowly
- convection currents caused by vast amount of heat generated in mantle
,- as a result, carries solid lithosphere and crust
- boundary with lithosphere difficult to define as melts and becomes incorporated into it
Benioff zones - CORRECT ANSWERS✔✔boundary between a subducting ocean plate and the overriding
continental plate at a destructive boundary
calderas - CORRECT ANSWERS✔✔large-scale volcanic crater formed as a result of an explosive eruption
which emptied the magma chamber causing the volcano sides to subside
calderas (explosive eruptions) - CORRECT ANSWERS✔✔- volcanic craters
- distance 2km+
- develop when explosive eruption destroys cone and underlying magma chamber largely empties
- without support of underground magma, sides of the volcano collapse to form a caldera
- e.g. Krakatoa eruption 1883 left caldera 7km wide
conservative plate boundaries - CORRECT ANSWERS✔✔where plates slide horizontally past each other
conservative: continental-continental - CORRECT ANSWERS✔✔- 2 continental plates try to slide past
each other side by side, but will only move after a long time after pressure has built up, which is
released in a sudden movement
- possible to see where plates have shifted
- cause earthquakes
- e.g. San Andreas Fault on west coast of USA
continental drift - CORRECT ANSWERS✔✔- continents mobile and have moved across the Earth's surface
through geological time
convection currents - CORRECT ANSWERS✔✔movement of heat from core to asthenosphere, which
causes movement of tectonic plates
, convergent (destructive) plate boundaries - CORRECT ANSWERS✔✔where 2 plates collide
- layer of crust 'lost'
convergent: continental-continental - CORRECT ANSWERS✔✔- when converge, little subduction takes
place - as have similar densities
- e.g. collision of African and Eurasian plates in Europe over past 40 million years created the Alps
convergent: oceanic-continental - CORRECT ANSWERS✔✔- subduction: denser oceanic plate forced
under continental plate
- creates ocean trench: marks subduction where oceanic crust ascends into asthenosphere, which is
asymmetrical with steepest side towards continent
- e.g. Andes, South America
convergent: oceanic-continental hazards - CORRECT ANSWERS✔✔- faulting and fracturing occur in
Benioff zone, causing earthquakes
- causes oceanic plate to melt, which rises to surface and uplift fold mountains - causing volcanoes
convergent: oceanic-oceanic - CORRECT ANSWERS✔✔- where they meet, the denser one subducts
under the other
- forms trenches
- forms island arches: as descending plate melts magma rises to the surface and forms chains of volcanic
islands
convergent: oceanic-oceanic case studies - CORRECT ANSWERS✔✔- in central Atlantic, North American
subducted beneath Caribbean plate, forming Antilles
- in Pacific 'Rim of Fire' contains island arcs e.g. Aleutian Islands, extending west from Alaska
- Mariana Trench: 11,000 m below ocean surface where Pacific subducted underneath Philippine plate
core - CORRECT ANSWERS✔✔- hot, dense centre of the Earth, lying between the crust and the mantle,
and is about 1,500 km thick
Earth UPDATED EXAM QUESTIONS WITH
CORRECT ANSWERS SOLVED.
active volcanoes - CORRECT ANSWERS✔✔- some only see active if erupted in historic times; but can be
difficult due to records available
- others only see as active if evidence of unusual quake activity or gas emissions
- widely accepted active if erupted since last glacial period or within past 10,000 years
active, dormant and extinct volcanoes - CORRECT ANSWERS✔✔- described as these on basis of eruption
history; can be difficult to do this
- however, extinct seen as one that wont erupt again
advantages of living in a volcanic area - CORRECT ANSWERS✔✔- geothermal energy: magma is close to
the surface, groundwater turns to steam with drives turbines
- tourism and recreation
age of sea-floor rocks - CORRECT ANSWERS✔✔- during 1906s, ocean drilling programme investigated
ocean sediments on ocean floor
- recovered cores in water up to 7000m deep, revealing spatial pattern of sediments (sea-floor
spreading)
- thickest/ oldest sediments found nearest to continents
- however, cores also showed rock no older than 200 million years, confirming ocean crust constantly
recycled over this period
asthenosphere - CORRECT ANSWERS✔✔- layer in Earth's mantle below lithosphere
- high temps cause rocks to soften and become viscous, so easily deform
- 100km-300km deep, semi-molten and flows slowly
- convection currents caused by vast amount of heat generated in mantle
,- as a result, carries solid lithosphere and crust
- boundary with lithosphere difficult to define as melts and becomes incorporated into it
Benioff zones - CORRECT ANSWERS✔✔boundary between a subducting ocean plate and the overriding
continental plate at a destructive boundary
calderas - CORRECT ANSWERS✔✔large-scale volcanic crater formed as a result of an explosive eruption
which emptied the magma chamber causing the volcano sides to subside
calderas (explosive eruptions) - CORRECT ANSWERS✔✔- volcanic craters
- distance 2km+
- develop when explosive eruption destroys cone and underlying magma chamber largely empties
- without support of underground magma, sides of the volcano collapse to form a caldera
- e.g. Krakatoa eruption 1883 left caldera 7km wide
conservative plate boundaries - CORRECT ANSWERS✔✔where plates slide horizontally past each other
conservative: continental-continental - CORRECT ANSWERS✔✔- 2 continental plates try to slide past
each other side by side, but will only move after a long time after pressure has built up, which is
released in a sudden movement
- possible to see where plates have shifted
- cause earthquakes
- e.g. San Andreas Fault on west coast of USA
continental drift - CORRECT ANSWERS✔✔- continents mobile and have moved across the Earth's surface
through geological time
convection currents - CORRECT ANSWERS✔✔movement of heat from core to asthenosphere, which
causes movement of tectonic plates
, convergent (destructive) plate boundaries - CORRECT ANSWERS✔✔where 2 plates collide
- layer of crust 'lost'
convergent: continental-continental - CORRECT ANSWERS✔✔- when converge, little subduction takes
place - as have similar densities
- e.g. collision of African and Eurasian plates in Europe over past 40 million years created the Alps
convergent: oceanic-continental - CORRECT ANSWERS✔✔- subduction: denser oceanic plate forced
under continental plate
- creates ocean trench: marks subduction where oceanic crust ascends into asthenosphere, which is
asymmetrical with steepest side towards continent
- e.g. Andes, South America
convergent: oceanic-continental hazards - CORRECT ANSWERS✔✔- faulting and fracturing occur in
Benioff zone, causing earthquakes
- causes oceanic plate to melt, which rises to surface and uplift fold mountains - causing volcanoes
convergent: oceanic-oceanic - CORRECT ANSWERS✔✔- where they meet, the denser one subducts
under the other
- forms trenches
- forms island arches: as descending plate melts magma rises to the surface and forms chains of volcanic
islands
convergent: oceanic-oceanic case studies - CORRECT ANSWERS✔✔- in central Atlantic, North American
subducted beneath Caribbean plate, forming Antilles
- in Pacific 'Rim of Fire' contains island arcs e.g. Aleutian Islands, extending west from Alaska
- Mariana Trench: 11,000 m below ocean surface where Pacific subducted underneath Philippine plate
core - CORRECT ANSWERS✔✔- hot, dense centre of the Earth, lying between the crust and the mantle,
and is about 1,500 km thick
