Download Forces in Earth`s Crust

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 midocean 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
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 faultblock 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