Sea Floor and Plate Tectonics

How are normal polarity and reverse polarity of Earth's magnetic field different?

A compass points toward the North Pole during normal polarity and to the South Pole during reverse polarity.

In general, what is our best evidence that the orientation of Earth's magnetic field has changed over time?

A record of Earth's magnetic field is recorded in oceanic rocks, which show a clear pattern of changes in Earth's magnetic polarity.

What is a tablemount?

A seamount that grew above sea level, experienced wave erosion, and is now inactive.

What is a seamount?

An active volcano that occurs along the crest of the mid-ocean ridge.

Which of the following mountain ranges are examples of continental arcs?

Andes and Cascades

Crustal rifting is currently occurring in East Africa. Which of the following features would you expect to find there?

Normal Faults; Long, wide valley; and Lava Flows

Why are volcanic chains associated with convergent boundaries?

Partial melting occurs due to subduction.

Plate A has oceanic lithosphere on its leading edge that is 10 million years old. Plate B has oceanic lithosphere on its leading edge that is 200 million years old. Which plate will be subducted if they collide with each other, and why?

Plate B will subduct because it is older—and therefore colder—and more dense.

How do plates move at divergent plate boundaries?

Plates move apart.

How do plates move at convergent plate boundaries?

Plates move toward one another.

How do plates move at transform plate boundaries?

Plates slide past one another.

Which fault in Southern California was created by the sliding of the Pacific Plate past the North American Plate?

San Andreas Fault

Why do coral reefs at the ocean surface grow away from seamounts over time?

Seamounts subside as tectonic plates move. Coral reefs grow away from the seamount in order to stay near the sunlight.

What type of stress would be found at a transform boundary?

Shear stress

What would happen to Earth if ocean floor were created at divergent boundaries at a faster rate than it is destroyed at convergent boundaries?

The Earth would increase in volume.

The western edge of the Juan de Fuca Plate is a divergent boundary with a ragged, zigzag edge. (See the figure.) Which of the following describes the motion of the Juan de Fuca plate on its southern boundary at the Mendocino Fault?

The Juan de Fuca Plate has right-lateral motion with the Pacific Plate along the transform Mendocino Fault.

What is the relationship between the crust and lithosphere?

The crust is part of the lithosphere.

At a subduction zone where oceanic lithosphere meets continental lithosphere, which would subduct and why?

The oceanic lithosphere would subduct because it has a higher density at 3.0 grams per cubic centimeter.

Why are volcanoes NOT found at transform boundaries?

Transform boundaries do not cause changes to the pressure, temperature, or composition of the mantle.

Which of the following statements about Earth's magnetic field is most accurate?

Earth's magnetic field switches polarity at irregular time intervals.

Which is the correct order of coral reef development near seamounts?

Fringing reef, barrier reef, atoll

What do you think will happen to the location of Los Angeles with continued activity along the San Andreas Fault over a long time span?

Los Angeles will slide to the northwest.

What is a volcanic arc?

a row of volcanoes that forms on the overriding plate near a subduction zone

Where is the youngest ocean floor found?

along the crest of mid-ocean ridges

The East African rift is a divergent plate boundary that is splitting the continent of Africa into two pieces. What will eventually form around this divergent boundary?

an ocean

Which type of tectonic boundary is the result of two tectonic plates colliding with each other?

convergent boundary

In general, where do earthquakes AND volcanic eruptions occur?

convergent plate boundaries and divergent plate boundaries

Which type of plate boundary is most closely associated with the formation of new ocean floor?

divergent

Which tectonic boundary results when two tectonic plates pull apart from each other?

divergent boundaries

Plates move apart at __________ boundaries, move together at __________ boundaries, and move side-by-side at __________ boundaries.

divergent/convergent/transform

How often does the Earth's magnetic field switch polarity?

every 100,000 to several million years

Which geologic features are associated with divergent boundaries?

mid-ocean ridges and continental rift valleys

Complete this statement: Divergence is to moving away as convergence is to _______.

moving toward

What forms at divergent plate boundaries?

new oceanic lithosphere

Which geologic features are associated with convergent boundaries?

ocean trenches and volcanoes

Where would you expect to see alternating bands of rock with different magnetic polarities?

on both sides of the mid-ocean ridge

In general, where do volcanoes form in subduction zones?

on the overriding plate, away form the convergent boundary

Which type of tectonic boundary is the result of two tectonic plates sliding past each other?

transform boundary

Divergent boundaries are not one, smooth ridge of separation. Instead, they are broken into a series of segments, with different segments of fault offset from others. What features allow for the offset of divergent boundaries?

transform faults

Where do coral reefs exist with sea mounts?

tropical latitudes

Would NOT be found at a divergent boundary?

volcanoes producing andesitic lavas and thrust faults

Would be found at a divergent boundary?

volcanoes producing mafic lavas and normal faults

What is the difference between a barrier reef and an atoll?

Barrier reefs surround an inactive volcano emerging above sea level, while atolls surround the previous location of a submerged volcano.

In a collision between two continental plates, can a continental plate subduct? Why or why not?

Continental plates are too buoyant to subduct.

Which of the following statements about coral reefs and seamounts is most accurate?

Coral reefs at the ocean surface grow away from seamounts over time.