ch18 flashcards

Question 1

ocean basin

Answer 1

A large, deep depression in the Earth’s surface located between continental margins and mid-ocean ridges, floored primarily by oceanic crust

Question 2

abyssal plains

Answer 2

Extremely flat and deep regions of the ocean floor, formed by the accumulation of fine sediments that cover underlying irregular topography

Question 3

trenches (oceanic trenches)

Answer 3

Deep, narrow depressions in the ocean floor formed at convergent plate boundaries where one tectonic plate subducts beneath another

Question 4

island arcs

Answer 4

Curving chains of volcanic islands that form above subduction zones, typically parallel to oceanic trenches

Question 5

mid-ocean ridge

Answer 5

A continuous submarine mountain chain where new oceanic crust is created by upwelling magma at divergent plate boundaries

Question 6

mid-ocean rift (rift valley)

Answer 6

A valley running along the crest of a mid-ocean ridge, formed by the divergence of tectonic plates and the stretching and breaking of the lithosphere

Question 7

continental shelf

Answer 7

The gently sloping submerged extension of a continent, composed of continental crust, extending from the shoreline to the continental slope

Question 8

continental slope

Answer 8

The steep descent of the seafloor from the edge of the continental shelf down to the continental rise or abyssal plains

Question 9

continental rise

Answer 9

A gentle incline at the base of the continental slope formed by the accumulation of thick sediment layers, transitioning into the abyssal plains

Question 10

submarine canyons

Answer 10

Deep, V-shaped valleys carved into the continental slope and shelf, often formed by turbidity currents and river erosion during lower sea levels

Question 11

guyots

Answer 11

Flat-topped, submerged volcanic mountains (seamounts) that were once above sea level but have been eroded and then submerged

Question 12

seamount

Answer 12

A volcanic mountain rising from the ocean floor that does not reach the ocean surface; often conical with a peak or crater

Question 13

coral atolls

Answer 13

Ring-shaped coral reefs that form around a subsiding volcanic island, eventually enclosing a lagoon as the island sinks below sea level

Question 14

terrigenous sediments

Answer 14

Sediments derived from the erosion of continents or volcanic islands, typically transported to the ocean by rivers, wind, and glaciers

Question 15

biogenous (pelagic) sediments

Answer 15

Deep-sea sediments composed primarily of the shells and skeletal remains of marine organisms, such as plankton and coral

Question 16

hydrogenous sediments

Answer 16

Sediments that form directly from seawater through chemical precipitation, such as manganese nodules and evaporites

Question 17

ophiolite sequence

Answer 17

A slice of oceanic crust and upper mantle thrust onto continental crust, typically showing layers of oceanic lithosphere including basaltic lavas, sheeted dikes, and gabbros

Question 18

pillow basalts

Answer 18

Volcanic rocks that form when lava erupts underwater, cooling quickly into bulbous, pillow-like shapes characteristic of mid-ocean ridges

Question 19

sheet dikes

Answer 19

Vertical or near-vertical, sheet-like intrusions of basaltic magma that feed pillow basalts at mid-ocean ridges

Question 20

gabbro plutons

Answer 20

Large, coarse-grained bodies of mafic igneous rock (gabbro) found at the base of the oceanic crust, representing the crystallized magma chambers beneath mid-ocean ridges

Question 21

abyssal fan

Answer 21

Large, fan-shaped deposits of sediment at the base of submarine canyons, formed by turbidity currents spreading out over the abyssal plains

Question 22

aseismic ridge

Answer 22

A long, linear feature on the ocean floor that does not display significant seismic activity, often formed by hotspot volcanism without ongoing plate boundary activity

Question 23

atoll

Answer 23

A specific type of coral reef structure that forms a ring around a lagoon, commonly forming when an island subsides and the reef growth keeps pace with sinking land

Question 24

barrier reef

Answer 24

A coral reef running roughly parallel to a shoreline but separated from it by a lagoon or channel, often formed as sea levels rise and reefs grow upward

Question 25

oceanic trench

Answer 25

Another term for a trench, a deep, elongate trough at the ocean floor, typically found at convergent plate boundaries and associated with subduction zones

Question 26

pelagic sediment

Answer 26

Fine-grained material that settles through the water column and accumulates on the deep seafloor, often composed of biogenous and sometimes hydrogenous components

Question 27

reef

Answer 27

A structure formed in shallow ocean waters by the growth and deposition of calcareous organisms like coral and algae, often hosting abundant marine life

Question 28

rift valley

Answer 28

A deep valley formed by extensional tectonics along mid-ocean ridges or on continents where the lithosphere is being pulled apart

Question 29

submarine canyon

Answer 29

A steep, narrow valley carved into the continental shelf and slope, often aligned with river mouths and formed by erosion from turbidity currents