plate boundaries

Question 1

what are the three types of plate boundary?

Answer 1

DIVERGENT boundaries
CONVERGENT boundaries
CONSERVATIVE boundaries

Question 2

what are the three types of CONVERGENT boundaries?

Answer 2

OCEANIC- CONTINENTAL
OCEANIC- OCEANIC
CONTINENTAL- CONTINENTAL (collision margin)

Question 3

summary of what happens at DIVERGENT boundaries

Answer 3

plates MOVE APART from each other and magma plumes rise to fill the gap, cool, and create NEW CRUST.
the VOLCANIC ACTIVITY forms submarine mountain ranges (MID- OCEAN RIDGES)
the magma plumes from asthenosphere stretch crust+ lithosphere- results in parallel faults (RIFT VALLEYS)

Question 4

how do MID- OCEAN RIDGES form?

Answer 4

OCEANIC plates DIVERGE, BASALTIC lava rises through asthenosphere to fill space between plates, forming a RIDGE.

Question 5

what FEATURES occur at MID- OCEAN RIDGES?

Answer 5

• EFFUSIVE VOLCANIC ACTIVITY is present e.g. MID ATLANTIC RIDGE- eruptions at boundary between NORTH AMERICAN plate and EURASIAN plate creating world’s largest volcanic island ICELAND (shield volcanoes at basaltic lava)
• broken in segments by TRANSFORM FAULTS- can snag/ slip creating stress- pressure released as EARTHQUAKES (can lead to tsunamis)
• erupted lava cools rapidly on sea bed forming PILLOW LAVAS (rounded mounds)
• BLACK SMOKERS- water can seep into rifts and mid- ocean ridges, become SUPERHEATED, causing CHEMICAL CHANGES in the BASALTIC ROCK- contains metal sulphides- superheated water erupts on ocean floor, mixing with surrounding cold seawater and iron sulphides are released.

Question 6

how do RIFT VALLEYS form?
Example?

Answer 6

CONTINENTAL plates DIVERGE- plates STRETCH+ BULDGE, causing DOWNFAULTING between PARALLEL FAULTS, to form a valley
e.g. the EAST AFRICAN RIFT VALLEY

Question 7

what happens at OCEANIC- CONTINENTAL CONVERGENT boundaries?

Answer 7

• oceanic plate is DENSER so SUBDUCTS, creating an OCEAN TRENCH.
  as the plates CONVERGE, sediments+ rocks crumple+ are uplifted along leading edge of CONTINENTAL PLATE
  CONTINENTAL plate BUCKLES, forming MOUNTAIN CHAINS e.g. THE ANDES (pacific coast of south America)
• angle of subduction of oceanic plate: 30-70 degrees - as descends, under great pressure+ friction so FAULTING occurs in the BENIOFF ZONE- releases energy as earthquakes
• OCEANIC plate MELTS, MAGMA PLUMES rise, forming VOLCANOES

Question 8

what happens at OCEANIC- OCEANIC CONVERGENT boundaries?

Answer 8

slightly denser plate subducts, creating OCEAN TRENCH; DESCENDING plate MELTS+ magma rises and chains of VOLCANOES form (ISLAND ARCS)
e.g. MARIANA TRENCH (11,000m deep) where PACIFIC plate subducts under PHILIPPINE plate, creating MARIANA ISLANDS

Question 9

what happens at CONTINENTAL- CONTINENTAL CONVERGENT boundaries?

Answer 9

COLLISION MARGIN
little to no subduction due to similar densities
impact+ pressure forms FOLD MOUNTAINS e.g. the HIMALAYAS
NO VOLCANIC ACTIVITY- no new magma formed as so plate subducts into asthenosphere to melt
pressure can build between them- causing EARTHQUAKES

Question 10

what happens at CONSERVATIVE boundaries?

Answer 10

plates slide past each other- movement can be violent, building up pressure- released as EARTHQUAKES
NO VOLCANIC ACTIVITY
e.g. SAN ANDREAS FAULT between PACIFIC+ NORTH AMERICAN plates.