3.1 plate tectonics

Question 1

theory of continental drift

Answer 1

Earth’s continents have moved over geological time

Question 2

lithosphere

Answer 2

hard outer shell (crust + upper mantle), oceanic/continental

Question 3

asthenosphere

Answer 3

ductile, viscous region of upper mantle

Question 4

convection current theory

Answer 4

due to radioactive decay in core, hot magma rises to surface (spreads out mid latitudes), cold, solidifies, sinks back

Question 5

dragging theory

Answer 5

• plates are subducted/dragged by oldest edges
• plates hot at ridges, cool as they move away

Question 6

hotspot

Answer 6

plume of lava that rises vertically through the mantle

Question 7

global pattern of plate tectonics

Answer 7

• seven large plates and a few smaller ones
• The Ring of Fire is a string of volcanoes and sites of seismic activity around the edges of the Pacific Ocean
• 90% of all earthquakes occur along the Ring of Fire
• 75% of all active volcanoes on Earth on ring

Question 8

divergent (constructive) plate boundary

Answer 8

-plates pulled apart by convection currents
- magma rises through the rift valley (fissures), cools, forms new crust
- accumulates form ridges
- range of submarine mountains and volcanoes (usually strato)
- mid ocean ridge
- Fernandina volcano on the Galapagos islands which formed at the Galapagos rise divergent plate boundary

Question 9

convergent (destructive) plate boundary

Answer 9

• plates are moved towards each other
• denser subducts: subduction zone
• subducted plate leaves a trench, is heated and releases volatiles: trench forms
• magma becomes mantle or leads to volcanism
• friction causes pressure build up: shockwave
• pressurised magma forces through weak areas and cracks

Question 10

convergent (collision) plate boundary

Answer 10

• two similarly dense plates moved towards each other: less subduction
• collide and fold together
• thicken crust, create fold mountains

Question 11

transform (conservative) plate boundary

Answer 11

-two plates move side by side past each other/faults
- in different speed/direction
- friction builds up pressure, plates lock, release shockwave as slide apart
- no landforms are created of destroyed
- frictional activity/earthquakes

Question 12

sea floor spreading

Answer 12

• tectonic plates move apart: magma rises through rift valley: cools : pushed away
• new ocean floor of basaltic magma is formed through volcanic activity then gradually moves away from ridge:ocean ridges
• paleomagnetism

Question 13

subduction zones

Answer 13

• plates collide: more dense pushed under less dense plate
• ocean trenches

Question 14

ocean trench

Answer 14

• long, narrow depressions in ocean floor
• adjacent to island arcs
• asymmetric, steeper towards land mass

Question 15

Benioff zone

Answer 15

• area of increased earthquake activity
• plate bends and stretches as it subducts
• differences in shape cause interlocking: friction:pressure

Question 16

ocean ridges

Answer 16

• underwater mountain range
• oceanic - oceanic divergent plates

Question 17

volcanic island arcs

Answer 17

• a chain/type of archipelago of volcanic islands parallel to the trench of two converging tectonic plates
• ocean - ocean subduction zones form island arc system when one is subducted
• Pacific, Western Atlantic
• trench outer rise: plate bends, low bulge as sediment is folded and deformed
• outer slope: gentle, broken by faults
• inner slope: steep, fragments scraped off
• accretionary prisms:slice of descending slab may form significant landforms
• Mariana Islands in Pacific Ocean

Question 18

fold mountains

Answer 18

• folded, crumbled layers of rock
• along continental margins
• length increases as width decreases
• concave/convex slopes
• no subduction of continental crust: pile up on lithosphere due to pressure between plates
• two plates collide (destructive/collision) causing folding and buckling of sedimentary rocks
• destructive: accretionary wedge uplifted
• collision: similar density: one is thrust under the other: uplift, material between plates gets compressed
• syncline, anticline, monocline