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Plate Tectonics Table of Contents Drifting Continents Sea-Floor Spreading The Theory of Plate Tectonics Forces in Earth’s Crust Volcanoes and Plate Tectonics Volcanic Eruptions

Drifting Continents Piecing It All Together The coastlines of some continents seem to fit together like a jigsaw puzzle.

Pangaea: The History of the Continents

Drifting Continents Pangaea and Continental Drift Many types of evidence suggest that Earth’s landmasses were once joined together.

Sea-Floor Spreading Ocean Floors Mid-ocean ridges rise from the sea floor like stitches on the seams of a baseball.

Sea-Floor Spreading Mid-Ocean Ridges

Clues about Continental Drift

Sea-Floor Spreading Sea-Floor Spreading Some mid-ocean ridges have a valley that runs along their center. Evidence shows that molten material erupts through this valley and then hardens to form the ocean floor.

Sea-Floor Spreading Subduction Oceanic crust created along a mid-ocean ridge is destroyed at a deep-ocean trench. During the process of subduction, oceanic crust sinks down beneath the trench into the mantle.

Sea-Floor Spreading Deep-Ocean Trenches The deepest part of the ocean is along the Mariana Trench. Several trenches in the Pacific Ocean are shown in yellow.

The Theory of Plate Tectonics Slip-Sliding Away In 30 million years, it may take an hour longer to fly from New York to London because the cities are moving slowly apart.

Plate Tectonics

The Theory of Plate Tectonics Earth’s Plates Plate boundaries divide the lithosphere into large plates.

The Theory of Plate Tectonics Plate Motion Since the breakup of Pangaea, the continents have taken about 200 million years to move to their present location. 200 Million Years Ago Earth Today 115 Million Years Ago

Types of Boundaries

The Theory of Plate Tectonics How do the plates move? Divergent Boundaries Convergent Boundaries Transform Boundaries

The Theory of Plate Tectonics Earth's Changing Crust As plates move, they produce mountains, volcanoes, and valleys as well as mid-ocean ridges and deep-ocean trenches. Use the terms from the list to label the diagram.

Forces in Earth’s Crust Stress in Earth’s Crust Stress can push, pull, or squeeze rock in Earth’s crust. Three kinds of stress can occur in the crust.

Forces in Earth’s Crust Faults The three main types of faults are defined by the direction in which rock moves along the fault.

Forces in Earth’s Crust The low angle of a thrust fault allows rock in the hanging wall to be pushed great distances. For example, over millions of years, rock along the Lewis thrust fault in Glacier National Park has moved 80 kilometers.

Forces in Earth’s Crust Anticlines and Synclines Compression can cause folds in the crust. Two types of folding are anticlines, which arch up, and synclines, which dip down.

Forces in Earth’s Crust Forces in Earth’s Crust Tension and Normal Faults What are the hanging wall and the two footwalls in diagram A? What is the new position of the hanging wall after movement occurs in diagram B?

Forces in Earth’s Crust Tension and Normal Faults As tension forces pull the crust apart, two normal faults can form a fault-block mountain range.

Forces in Earth’s Crust The Kaibab Plateau Look at the sequence of drawings. In your own words, describe what happens in the last two diagrams.

Earthquakes

Volcanoes and Plate Tectonics The Ring of Fire The Ring of Fire is a belt of volcanoes that circles the Pacific Ocean. As with most of Earth’s volcanoes, these volcanoes form along boundaries of tectonic plates.

Earthquakes

Volcanoes and Plate Tectonics Volcanoes and Converging Boundaries Volcanoes often form where two plates collide.

Volcanoes

Volcanoes and Plate Tectonics Hot Spot The Hawaiian Islands have formed one by one as the Pacific plate drifts slowly over a hot spot. This process has taken millions of years.

When Earth Erupts

Volcanic Eruptions Inside a Volcano A volcano is made up of many different parts.

Volcanic Eruptions Magma Composition Magma varies in composition. It is classified according to the amount of silica it contains. The less silica that the magma contains, the more easily it flows.

Volcanic Eruptions Cascade Volcanoes The Cascade volcanoes have formed as the Juan de Fuca plate sinks beneath the North American plate.

Volcanic Eruptions Mt. Rainier Mount Rainier is part of the Cascade volcanoes. All past eruptions of Mount Rainier have included ash and lava.

Volcanic Eruptions Magma at Mount Rainier