Chapter 2

Question 1

Seafloor spreading is ____.

Answer 1

the lateral movement of the oceanic lithosphere near spreading centers

Question 2

A lithospheric plate is composed of ____.

Answer 2

the upper rigid mantle (80 to 100 km) capped by either oceanic or continental crust

Question 3

____ plate boundaries are where tectonic plates move toward one another; ____ plate boundaries are where the plates slide past each other; divergent plate boundaries are where plates move away from each other.

Answer 3

convergent

transform

Question 4

The characteristics listed below apply either to active or passive margins. Select all the characteristics of active margins.

1. ocean trenches possible
2. modified by tectonic movement and volcanoes
3. broad and shallow with thick sedimentary deposits
4. known as a trailing margin
5. represents a plate boundary

Answer 4

1. ocean trenches possible
2. modified by tectonic movement and volcanoes
3. represents a plate boundary

Question 5

____ result in volcanic activity that may operate independently of plate boundaries. These volcanoes can form anywhere on a tectonic plate.

Answer 5

Hotspots

Question 6

The lateral movement of the oceanic lithosphere near ocean ridges is called seafloor ____.

Answer 6

spreading

Question 7

The Hawaiian Islands to the west of the main island have inactive volcanoes because they have moved off of the ____.

Answer 7

hotspot

Question 8

Each lithospheric ____ consists of the upper 80 to 100 km of rigid mantle rock and is topped by either oceanic or continental crust.

Answer 8

plate

Question 9

Guyots (flat-topped seamounts) are the result of ____.

Answer 9

volcanic islands being eroded after moving off the hotspot that formed them

Question 10

Plates are moving apart.

Answer 10

divergent

Question 11

Plates are moving toward one another.

Answer 11

convergent

Question 12

Plates are sliding past each other.

Answer 12

transform

Question 13

If you know the age of the rocks on a particular seamount and the distance it is from its associated hotspot, you can determine the rate of ____ motion.

Answer 13

plate

Question 14

The relatively calm trailing edge of continents are called ____ margins, while the leading edge of continents are called ____ margins.

Answer 14

passive; active

Reason: Active margins may also be called Pacific-style and passive margins may be called Atlantic-style.

Question 15

A hot spot located near a diverging plate boundary can produce a ____ ridge, which is a continuous series of seamounts very close together.

Answer 15

transverse or aseismic

Question 16

Hotspot volcanoes are likely the result of ____.

Answer 16

rising magma from the mantle

Reason: The chemistry of hotspot magma suggests a possible start at the core-mantle boundary.

Question 17

The Hawaiian Island chain is the result of a ____.

Answer 17

volcanic hotspot

Question 18

Volcanic islands in the ocean that move off of the hotspots that formed them will ____.

Answer 18

be worn down by water and wave erosion to form flat-topped seamounts (guyots)

Reason: Erosion will reduce the top of the island until it is below the wave base of erosion.

Question 19

True or false: Since hotspots operate independently of the plate tectonic system, they are not useful for studying plate motion.

Answer 19

False
Reason: The rates and direction of plate motion can be determined by how fast and in what direction the plate moves away from a hotspot since the rocks farther away from the hotspot are older than the closer rocks.

Question 20

A continuous series of seamounts very close together formed from a hotspot near a spreading center is called a ____ ridge.

Answer 20

transverse

Reason: Transverse ridges are also called aseismic ridges.