week 2 - physiography of the ocean basins

Question 1

how can the earth be subdivided?

Answer 1

by the ocean basins and the continents

Question 2

what is the theory of isostasy?

Answer 2

suggestion that the earth consists of blocks of rigid lithosphere (about 100 km thick) which are floating in isostatic equilibrium on a plastic region of earth’s mantle called the asthenosphere

Question 3

concept of buoyancy

Answer 3

a rigid body floating on a fluid will sink into the fluid until the mass of the displaced fluid exactly equals the total mass of the rigid body

Question 4

density

Answer 4

the mass of a substance divided by its volume
- measured in grams per cubic centimeter
- held constant and volume is allowed to vary

Question 5

why do larger blocks float higher than smaller ones?

Answer 5

they displace a larger volume of water, and the bouyant force is therefore greater

Question 6

two important facts about the earth

Answer 6

1. the earths interior is not rigid (deformable)
2. the materials of the ocean basins are denser and/or thinner than the materials composing the continents

Question 7

continental crust

Answer 7

1. composition close to granite
2. 35 kilometers in thickness

Question 8

oceanic crust

Answer 8

1. 5 kilometers in thickness
2. composed of basalt with a higher density than granite

Question 9

why do the continents stand at a higher elevation than water?

Answer 9

because they are composed of thick masses of lower density materials

Question 10

why do larger mountain ranges stand higher on land?

Answer 10

because they are supported by thick roots of granitic rock (up to 70 kilometers)

Question 11

why do larger mountain chains on the ocean flood stand higher?

Answer 11

because the lithosphere is hot and therefore has a lower density than the lithosphere of the deeper ocean basins (convection)

Question 12

isostasy

Answer 12

the equilibrium that exists between parts of the earths crust
- behaves as if it consists of blocks floating on the underlying mantle
- rises if material is removed and sinks if material is deposited

1. the mass will displace its weight
2. the object will sink until the buoyancy force in the ocean is equal to the weight
3. larger objects with more volume will float higher

Question 13

geomorphic features of the ocean floor

Answer 13

1. continental margins
2. deep ocean floor
3. seamounts
4. plateaus
5. ridges and rises not from mid ocean ridge and rise system
   - fragments of continental crust or volcanic edifices

Question 14

formula for density

Answer 14

(p = m/v)
m = mass (how much space something occupies, how much is in that space)
v = volume (how much is in that space)

Question 15

relationship with earth’s interior structure and density

Answer 15

as you go further down into the earth, the density will increase

Question 16

chemical composition of earth’s layers

Answer 16

1. crust - low density rock
2. continental crust (granite) - 30 to 70 kilometers thick and 2.7 g/cm to the third power
3. oceanic crust (basalt) - 5 to 8 kilometers thick and 3 g/cm/3
4. mantle - higher density material below crust and above out core, 3.3. g/cm/3
5. core - most dense layer composed primarily of iron

Question 17

physical properties of the earth

Answer 17

1. lithosphere - cool rigid outer layer (crust and upper mantle) 100 kilometers thick
   - things do not flow because the layer is rigid
2. asthenosphere - plastic (seems like it is solid and not moving, but moves slowly overtime), part of the mantle blow lithosphere (upper mantle)
   - 600 kilometers thick
   - things can flow because it is plastic
3. mesosphere - plastic, but stronger than the asthenosphere (middle and lower mantle)
4. inner and outer core - inner is solid but the outer is liquid

Question 18

order of continent parts going into the ocean

Answer 18

1. shelf
2. slope
3. rise

Question 19

continental shelf

Answer 19

gently sloping depositional surface extending from the shoreline to the continental slope

Question 20

continental slope

Answer 20

relatively steep surface seaward of the continental shelf

Question 21

continental rise

Answer 21

gently sloping deposition surface at the base of the continental slope

Question 22

shelf break

Answer 22

at 140 meters the depth separates the shelf and the slope

Question 24

two types of continental margins

Answer 24

1. atlantic type - passive margins
2. pacific type - active margins

Question 25

atlantic type - passive margins (5 things)

Answer 25

1. wide, gently sloping continental shelf
2. steeper continental slope descending to the deep sea
3. flatter continental rise at the base of the slope - formed by accumulation of sedimentary materials
4. most common in the atlantic ocean, but also occurs in others
5. no plate boundaries and low degree of tectonic activity
   - low to no volcanoes or earthquakes along the margin

Question 26

pacific type - active margins

Answer 26

1. narrow shelf and slope descending abruptly into a deep marginal trough or trench, parallel to the continental margin
   -ex. area off chile and peru
2. continental rise is absent
3. large island arcs are typical of the western pacific
4. ocean trenches are the deepest places on the seafloor, about twice as deep as the ocean basin
   - deepest is the marianas trench
5. high degree of tectonic activity

Question 27

what comprises the continental margins?

Answer 27

sediments derived form rivers that deposit their material in the nearshore environment or by coastal erosion
- redistributed in the nearshore environment currents or by gravity processes
- because of gravity, sediments will slope, which is important for transporting sediments down the continental slope and onto continental rise or abyssal plains

Question 28

turbidity currents

Answer 28

short lived, gravity induced currents consisting of mixtures of sediment and water which flow downslope as a density current
- often triggered by earthquakes
- primary means by which terrigenous (land derived) sediment is transported from shallow water onto the deep ocean floor

Question 29

submarine canyons

Answer 29

steep walled, v shaped valleys that incise into continental shelves and slopes and open out at depth onto the continental rise
- associated with the mouths of large rivers
- conduits that funnel turbidity currents and sediments from the continental shelf onto the deep ocean floor
- smaller submarine canyons are common features on the shelf of the pacific coasts of the united states

Question 30

submarine fans

Answer 30

mouths of submarine canyons associated with large lobes of sediment

Question 31

mid ocean ridge and rise system

Answer 31

ocean floor chain of mountains that is 75,000 km long with a width of 500 to 1500 kilometers

• has a central rift valley that can be as much as 1 km deep and a rugged topography on its flanks
• 1 to 2 kilometers above the deep ocean basin and is frequently cut and mountain crests are offset by numerous fracture zones
• form at divergent plate boundaries
• linear zones of irregular topography on the sea floor, 10 to 100 km wide and up to 3500 km long

Question 32

fracture zones

Answer 32

where the ridge moves away from each other

Question 33

abyssal hills

Answer 33

deeper ocean basins where water depths are typically more than 5 km
- covered by much more sediment than the rugged flanks of the mid ocean ridge system
- rolling hills are found here

Question 34

abyssal plains

Answer 34

1. found near some atlantic type continental margins where sediments from turbidity currents have flowed off the continental rise and spread out over the ocean floor
2. flat or very gently sloping areas of the deep ocean floor
3. among the earths flattest and smoothest regoins
   - cover 40% of the ocean floor
   - produces extremely flat stretches of the ocean floor

Question 35

seamounts

Answer 35

hills that are more than 1 km above the ocean floor