Ocean basin relief features

Question 1

What is an abyssal plain

Answer 1

The deepest part of the ocean covering vast areas of ocean floor, submarine mountains and trenches interrupt the relatively flat plain

Question 2

What is the continental rise

Answer 2

gently sloping ocean floor between the continental slope and the abyssal plain

Question 3

What is the continental shelf

Answer 3

the gently sloping offshore extension of a continent extending into the ocean as far as the continental slope

Question 4

What is the continental slope

Answer 4

where the continental shelf becomes steeper as it descends to the deep ocean

Question 5

What is a guyot

Answer 5

a flat topped seamount with its summit well below ocean surface, many appear to have volcanic origin, having formed at mid ocean ridges

Question 6

What is a mid ocean ridge

Answer 6

The boundary between two diverging oceanic plates. It consists of two parallel chains of submarine mountains separated by a graben and offset in places by transform faults

Question 7

What is a shelf break

Answer 7

a drop off point from the continent

Question 8

Is a continental shelf exposed or submerged

Answer 8

either - depending on sea level

Question 9

How wide is a continental shelf

Answer 9

70km wide

Question 10

What is the difference between continental shelf and continental slope

Answer 10

where the angle of the slope increases and there’s about a 70m drop per km where it was previously 2m

Question 11

What is the continent edge

Answer 11

the boundary of the continent

Question 12

Where is a submarine canyon formed

Answer 12

where rivers enter the sea

Question 13

How are submarine canyons formed

Answer 13

when a river enters the sea it cuts a ravine into the continental slope

Question 14

How is an underwater delta formed

Answer 14

at the bottom of a submarine canyon sediment is deposited in fan shaped

Question 15

What is a turbidity current

Answer 15

the transport of sediment in mass flows

Question 16

How are abyssal plains formed

Answer 16

the blanketing of the ocean crust by fine grained sediments like clays and silt

Question 17

What is an abyssal hill

Answer 17

a hill in the abyssal plain usually only rising a few hundred metres

Question 18

Where on the plate will the sediment be thickest

Answer 18

The further from the ridge as more sediment accumulates over time

Question 19

Why do volcanoes on the sea floor build up over time

Answer 19

They erupt lava which cools to become basalt

Question 20

What is a seamount

Answer 20

An underwater mountain formed by volcanic activity

Question 21

What is a volcanic island

Answer 21

when the seamount grows above the ocean surface

Question 22

What is a guyot

Answer 22

a flat topped seamount with a summit below the oceans surface

Question 23

What is the process for a volcanic island to become a guyot

Answer 23

over time waves and sub aerial processes flatten the volcanic island. The cooling oceanic crust also becomes more dense sinking it down. Marine processes continue to erode the top until there is a guyot

Question 24

What can happen to guyots over time

Answer 24

they can subside and become part of the upper mantle due to the weight of the guyot on the oceanic crust

Question 25

What is an island chain

Answer 25

a group of islands clustered together in a line

Question 26

What can an island chain also be called

Answer 26

archipelago

Question 27

Where are island chains formed

Answer 27

Above hotspots

Question 28

How are island chains formed

Answer 28

as the plate moves islands are created when they are underneath the hotspot as mantle plume reaches the earths surface and creates land, as they move further away from the hotspot they can become extinct

Question 29

What is an atoll

Answer 29

a ring of coral that originally grew completely around the shoreline of an island and continued to grow upwards on top of itself as the island subsided or eroded away

Question 30

Where are atolls always found

Answer 30

in the tropics and subtropics because corals can only thrive in warm water

Question 31

Why do islands furthest from the hotspot often become atolls

Answer 31

because they have lost their source of magma and the island can now be eroded down beginning the atoll process or potentially forming a guyot

Question 32

How wide and tall can ocean ridges be

Answer 32

1,000km wide And up to 3km from abyssal plain

Question 33

What type of plate boundary are ocean ridges found at

Answer 33

divergent tectonic boundaries (where two plates are moving apart)

Question 34

What will be in the centre of a mid oceanic ridge ridge

Answer 34

It is either convex or has a rift valley

Question 35

What are the two main drivers of plate divergence

Answer 35

1. Convection currrents 2. Ridge push

Question 36

what is ridge push

Answer 36

When the elevated position of mid oceanic ridge ridges causes newly formed oceanic lithosphere to slide away under the force of gravity

Question 37

What are convection currents

Answer 37

circular flows of molten rock within the earths mantle

Question 38

What are some features of a slow spreading ridge

Answer 38

- spreads 2-4cm per year - rugged peaks - has a rift valley around 20km wide and 3km deep - steep elevation with rough abyssal hills - newly formed crust cools slowly and sinks into mantle at point of origin

Question 39

What is an example of a slow spreading ridge

Answer 39

the Mid Atlantic ridge

Question 40

What are some features of a fast spreading ridge

Answer 40

- spreads 16cm per year - dome like shape - no rift valley, just crack along the centre - gentle elevation with smooth flanks - newly formed crust slips away quickly and doesn’t sink at point of origin

Question 41

What is an example of a fast spreading ridge

Answer 41

east pacific ridge

Question 42

How can mid oceanic ridge look ridges be offset in places

Answer 42

two diverging plates can be divided horizontally by transform faults

Question 43

What is an oceanic trench

Answer 43

A long steep sided depression in the ocean bottom

Question 44

What and how deep is the deepest oceanic trench

Answer 44

The Mariana Trench at 11,000m at its deepest point

Question 45

At what plate boundary are oceanic trenches formed

Answer 45

at convergent plate boundaries (where continental meets oceanic)

Question 46

What causes a volcanic island arc

Answer 46

subduction of the oceanic plate beneath the continental where the melting of the crust creates volcanic reactions