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Plate Tectonics Help (page 2)

By — McGraw-Hill Professional
Updated on Aug 31, 2011

Plates

So what is a plate anyway? Sounds like something set out on the dinner table. In the study of the Earth, the science of geomorphology is connected with the study of landforms, all the bumps and grooves on the surface of the Earth. Several continental plates make up these landforms.

Geologists know that the original supercontinent broke up into large pieces of land like the size of the North American or African landmasses. These lumps of land are called plates .

How were land and ocean plates discovered? Well, there were lots of good clues to plate locations, since collision and grinding cause a lot of pressure buildup between plates.

Volcanoes that occur along plate edges offer active and dramatic fireworks to signal plate margins. Earthquakes and eruptions are concentrated along the boundaries of rigid lithospheric plates. The plates rimming the Pacific Ocean have so many active volcanoes that the area is known as the Ring of Fire .

A geological plate is a layer of rock that drifts slowly over the supporting, upper mantle layer (asthenosphere) below it.

Continental and ocean plates are huge. They range in size between half a million to about 97 million km in area. Plates can be as much as 200 miles thick under the continents and beneath the ocean basins. Plates as much as 100 km thick fit loosely together in a mosaic of constantly pushing and shoving landforms. At active continental plate margins, land plates ram against other continental plates causing rock to pile up into towering mountains. Table 4-1 lists some of the mountain peaks found in the United States.

Table 4-1 The Western United States has most of the highest peaks in the country.

Highest point

State

Elevation (meters)

Elevation (feet)

Mount McKinley

Alaska

6194

20,320

Mount Whitney

California

4418

14,494

Mount Rainier

Washington

4392

14,410

Mount Ebert

Colorado

4399

14,433

Gannett Peak

Wyoming

4207

13,804

Mount Mauna Kea

Hawaii

4205

13,796

Kings Peak

  • tah

4123

13,528

Wheeler Peak

New Mexico

4011

13,161

Boundary Peak

Nevada

4006

13,143

Borah Peak

Idaho

3859

12,662

Mount Hood

Oregon

3426

11,239

Guadalupe Peak

Texas

2667

8749

Harney Peak

South Dakota

2207

7242

Mitchell

North Carolina

2037

6684

Clingmans Dome

Tennessee

2025

6643

Mount Rogers

Virginia

1746

5729

Mount Marcy

New York

1629

5344

Mount Katahdin

Maine

1606

5268

Black Mesa

Oklahoma

1516

4973

Brasstown Bald

Georgia

1458

4784

Mount Sessafras

South Carolina

1085

3560

Mount Greylock

Massachusetts

1064

3491

Mount Davis

Pennsylvania

979

3213

Mount Frissell

Connecticut

725

2380

Timms Hill

Wisconsin

595

1951

Charles Mound

Illinois

376

1235

Jerimoth Hill

Rhode Island

248

812

Mount Woodall

Mississippi

246

806

Mount Driskill

Louisiana

161

535

Walton county

Florida

105

345

 

The border between the Eurasian and Indian-Australian plates is a good example of where plates clash. Along this plate margin, the Himalayan range is forming with the world’s tallest mountain (Mount Everest). Where the Nazca ocean plate and South American continental plate collide, the Andes Mountains are forming. Similarly, where two ocean plates collide, one dives downward beneath the other and deep ocean trenches are formed. Like two stubborn bulls, the margin where the Pacific and Philippine plates meet created the Mariana trench (over 5 times as deep as the Grand Canyon).

All together, there are 15–20 major plates that make up the jigsaw puzzle of the Earth’s crust. Of these, geologists consider that a few are small, some are medium sized, and several are massive. The 15 medium and massive plates are the most commonly studied plates. Figure 4-2 shows a United States Geological Survey illustration of the major oceanic and continental plates. Some of these plates are divided differently depending on the latest geology information, this gives a general idea of the main plates and their size.

Plate Tectonics

 

Fig. 4-2. The Earth’s lithosphere is made of many large moving plates.

The plates found across the face of the Earth are unique to this planet. If plates were thicker, they would surround the core like a pressure cooker until the temperatures and pressures became so extreme as to melt everything. This is the kind of thing that went on in the early forming of the planet. But the Earth is unique in that the story did not end there. It continued to cool, change, regenerate, and develop with a beauty and perfection that leaves earth scientists scratching their heads and most people of the world in open-mouthed wonder.

The main evidence that continents were originally all one piece comes from the discovery of rock formations that match from one continent to another. For example, the eastern edge of South America fits like a puzzle piece into the western border of Africa. Figure 4-3 shows how these two continents could have originally fit together. Fossils found on the once connected edges of North America, Europe and northwestern Africa all match.

Plate Tectonics

 

Fig. 4-3. South America and Africa were probably one big landmass.

Practice problems of this concept can be found at: Plate Tectonics Practice Test

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