Lecture 4: The Ocean Basins

Question 1

Plate tectonics

Answer 1

Theory that describes and explains the creation and destruction of Earth’s lithospheric plates and their movements over the planets surface

Question 2

Depth sounding

Answer 2

Dropping a weight attached to sounding wire overboard and measuring the length of the wire when the weight stops falling

Question 3

Echo sounding

Answer 3

Determining the depth of the seabed or detecting objects in water by measuring the time taken for sound echoes to return to the listener

Question 4

Dredging

Answer 4

Operation of excavating materials from an aquatic environment

Question 5

Submersible

Answer 5

Small submersible boat or other craft, especially one designed for research and exploration

Question 6

Abyssal plain

Answer 6

Flat plain ~4km deep

Question 7

Oceanic trench

Answer 7

Long, narrow depression on the seafloor

Question 8

Mid-ocean ridge (MOR)

Answer 8

Undersea mountain chain at a divergent boundary, characterised by volcanism, earthquakes and rifting, all caused by the tensional forces of mantle convection that are pulling the two plates apart

Question 9

Aseismic ridge

Answer 9

Chain of (usually) underwater volcanic mountains

Question 10

Active Continental Margin

Answer 10

Convergent plate boundary between an oceanic plate and a continental one

Question 11

Passive continental margin

Answer 11

Continental lithosphere melded to oceanic lithosphere, so no relative motion between plates–formed by MORs

Question 12

Continental shelf

Answer 12

Broad, flat, submerged platform consisting of a thick layer of flat-lying shallow-water sediment that extends from the shoreline to the edge of the continental slope

Question 13

Continental slope

Answer 13

Steep slope that descends from the edge of the continental shelf to the continental rise

Question 14

Continental rise

Answer 14

Apron of muddy and sandy sediment extending from the foot of the continental slope to the abyssal plain

Question 15

Fracture zone

Answer 15

Valley that cuts across mid-ocean ridges, thus providing a passage for flow of cold bottom water from one ocean basin to another

Question 16

Scarp

Answer 16

Very steep bank or slope

Question 17

Transform fault (plate boundary)

Answer 17

Part of fracture zone between offset ridges

Question 18

Terrigenous sediment

Answer 18

Sediment transported from land to ocean by rivers

Question 19

Pelagic clay

Answer 19

Fine particles, carried in suspension, settled out in deep calm water

Question 20

Pelagic ooze

Answer 20

Remains of microscopic organisms (e.g. plankton)

Question 21

Basalt

Answer 21

Dark, fine-grained, mafic igneous rock composed largely of plagioclase feldspar and pyroxene–extrusive equivalent of gabbro

Question 22

Pillow lava

Answer 22

Blob of lava that cooled rapidly upon contact with cold seawater

Question 23

Sheeted dyke

Answer 23

Vertical volcanic layer