Marine Geology

The origin of submarine canyons is not well understood, but most likely

• is glacial, the work of glaciers depositing rock debris on the shelf.

• is erosional, started by streams during periods when the sea level was lower.

• is organic, resulting from the activities of burrowing organisms.

Mid-ocean ridges, rift valleys, and trenches are thought to

• reverse roles in the Southern Hemisphere.

• have no relationship to plate tectonics.

• mark the boundaries between tectonic plates.

• occur in the middle of tectonic plates.

Which two types of plates must collide to produce coastal mountain ranges?

• two oceanic plates.

• transform or shear boundaries.

• two continental plates.

• continental and an oceanic plate,

• no collisions will produce coastal mountain ranges.

Deep-ocean sediments tend to have proportionately more _________ sediment than continental-shelf sediment.

• biogenous

• hydrogenous

• terrigenous

According to the theory of plate tectonics, the lithosphere consists of

• several rigid plates that float on the asthenosphere.

• continents that have drifted apart to their current locations.

• hot spots that float up from the mantle.

• an unbroken solid mass that surrounds the molten interior.

According to the theory of seafloor spreading, new seafloor ____ due to ____.

• subsides at the trenches, polar reversal

• emerges from the rift valley, magma pushing up from the asthenosphere

• emerges from the mid-ocean ridge, basaltic orientation in the trenches

• all of the above may be correct at different times

The great heaps of unconsolidated sediment at the base of the continental slope are known as:

• the abyssal plains.

• the continental rise.

• the mid-ocean mountains.

• the abyssal hills.

Hydrothermal vents are located near:

• active areas of seafloor spreading.

• the edges of the deep sea trenches.

• passive continental margins.

A feature that rises out of the ocean floor and are flat-topped seamounts are called:

• guyots.

• ridges.

• island arcs.

• abyssal hills.

According to the hot spot theory, a hot spot

• always forms away from a plate boundary.

• never forms away from a plate boundary.

• is a local rising column of magma that moves with the plate above it.

• is a local rising column of magma that does not move with the plate above it.