Origins and structure of ocean basins - 3

Question 1

What is isostasy?

Answer 1

Mass balance of an object floating upon a fluid medium

Question 2

What control elevation of an object floating on a liquid medium?

Answer 2

Thickness of mass, density of mass and the density of the medium

Question 3

Why are continents higher than the ocean floor?

Answer 3

Continents are thicker and less dense so rise above the supporting mantle rocks more than the sea floor

Question 4

When was the first ever geological map of the sea floor made?

Answer 4

1977

Question 5

What is echo-sounding?

Answer 5

Type of SONAR, time between emission and return of pulse used to measure depth … (multiply half the time from the signals outgoing pulse to its return by the speed of sound in water)

Question 6

What is the approximate speed of sound in water?

Answer 6

1460 m/s

Question 7

What is multi beam?

Answer 7

Echo sounding, fan of sound waves emitted, swathe of depth readings from one pulse

Question 8

What is altimetry used for?

Answer 8

Measuring height and sea surface level and bathymetry

Question 9

What is the lithosphere?

Answer 9

Crust and uppermost mantle

Question 10

What is the asthenosphere?

Answer 10

Partially melted mantle rocks with plastic properties

Question 11

What is the mesosphere?

Answer 11

Deeper, rigid mantle zone

Question 12

Properties of the earth’s core

Answer 12

Molten outer and solid inner, dense, iron-nickle

Question 13

What are the three distinct physiographic provinces of the ocean?

Answer 13

1. Continental margin
2. Deep-sea basin
3. Mid-ocean ridge

Question 14

What are the sections of a continental margin?

Answer 14

Continental shelf, continental slope and continental rise

Question 15

Below what depth are rocks in the mantle no longer plastic?

Answer 15

350km

Question 16

Define Bathymetry

Answer 16

Submarine topography

Question 17

What % of the earths crust projects above sea level?

Answer 17

29%

Question 18

What is a Moho?

Answer 18

The sharp boundary between crust and upper mantle. It lies deeper below the ground beneath continents than it does beneath ocean.

Question 19

What is an ocean basin?

Answer 19

Large portion of ocean floor that lies deeper than 2 km

Question 20

Define tension

Answer 20

Pull apart force

Question 21

Define compression

Answer 21

Pull together force

Question 22

What is & where do you find normal faults?

Answer 22

When crustal rock is displaced vertically, occur along the edges of rift valleys

Question 23

What is a transform fault?

Answer 23

Fracture in the crust where movement of rocks is horizontal

Question 24

Where is the strongest magnetic field?

Answer 24

At the poles

Question 25

'Magnetic lines of force are vertically oriented' meaning ...

Answer 25

Out at S Pole and in at N Pole

Question 26

What is paleomagnetism

Answer 26

When minerals align themselves to the geomagnetic field, recording strength and direction of the geomagnetic field at a given point in time

Question 27

What is a continental margin?

Answer 27

Submerged edge of the continents ... they can be divided into 3 parts

Question 28

What is the continental shelf?

Answer 28

Top of the clastic wedge, slopes seaward at 0.5º from the shoreline to the shelf break, terminates in water between 130-200m deep

Question 29

What is the continental slope?

Answer 29

Extends downwards from the shelf, slopes at 4º to a dept of around 2-3km, can be cut with submarine canyons

Question 30

What is the continental rise?

Answer 30

Vast sedimentary plain, begins at the bottom of the slope, inclines at 1º and merges with the deep ocean at a depth of 4km

Question 31

What are deep ocean provinces?

Answer 31

Located between the continental margin and the mid-oceanic ridge

Question 32

What is an abyssal plain?

Answer 32

Flattest area on earth, depths of 3-5km, sediment itself can reach a depth of 1km

Question 33

Who first proposed continental drift?

Answer 33

Alfred Wegener

Question 34

What is seismicity?

Answer 34

Frequency, Magnitude and Distribution of earthquakes

Question 35

What is a Benioff Zone?

Answer 35

An area of increasingly deeper seismic activity