INTERNAL AND EXTERNAL FORCES

ON THE EARTH’S SURFACE

SLIDE 3

FOR MILLIONS OF YEARS THE SURFACE OF THE EARTH HAS BEEN IN SLOW BUT CONSTANT MOVEMENT.

THE FORCES THAT CAUSE THIS MOVEMENT ARE INTERNAL AND EXTERNAL FORCES.

INTERNAL FORCES WORK BELOW THE EARTH’S SURFACE. VOLCANISM AND MOVEMENTS THAT BEND, FOLD OR LIFT THE CRUST

EXTERNAL FORCES WORK ON THE EARTH’S SURFACE. WEATHERING AND EROSION

IT IS ON THE OUTER LAYER OR CRUST OF THE EARTH WHERE LANDFORMS DEVELOP THAT ARE CREATED BY THESE INTERNAL OR EXTERNAL FORCES.

SLIDE 4 AT ONE TIME THE CONTINENTS WERE ALL JOINED AS ONE. THIS WAS PANGEA.

SLOWLY THEY DRIFTED TO THE POSITION THEY ARE TODAY AND ARE STILL MOVING.

THIS IS CALLED CONTINENTAL DRIFT AND WAS PROPOSED IN THE 1930S. IT WAS NOT PROVEN UNTIL THE 1970S.

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TODAY IT IS CALLED PLATE TECTONICS.

HOW DO WE KNOW PLATES ARE MOVING???

CONTINENTS MOVE DUE TO THE PLATES MOVING

INTERACTIVE WEBSITE

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THE CONTINENTS MOVE BECAUSE THEY ARE ON PLATES THAT FLOAT ON THE EARTH’S MANTLE. THERE ARE 12 OF THESE PLATES.

THERE ARE 4 TYPES OF MOVEMENT ALONG PLATE BOUNDARIES : 1. PLATES MOVING AWAY FROM EACH OTHER WHICH IS CALLED RIFTING OR DIVERGING PLATES EXAMPLES- MID-ATLANTIC RIDGE, RIFT VALLEY IN AFRICA.

2. PLATES CONVERGING OR COLLIDING( A. ONE PLATE GOING UNDER ANOTHER – SUBDUCTION. THIS IS AN OCEAN PLATE GOING UNDER A CONTINENTAL PLATE. VOLCANOES AND EARTHQUAKES FORM ALONG THE BOUNDARIES. EXAMPLES: ANDES, CASCADE RANGE TWO OCEAN PLATES COLLIDING ( SUBDUCTION) ISLAND ARCS ARE FORMED – PHILIPPINES 3. TWO CONTINENTAL PLATES CONVERGING. THIS IS THE SAME AS #2 BUT INVOLVES 2 CONTINENTAL PLATES RATHER THAN OCEAN AND COMNTINENTAL. EXAMPLES: ROCKIES AND ALPS-FOLDED MTS APPALACHIANS 4. PLATES SLIDING PAST EACH OTHER- FAULTING CALLED TRANSFORM PLATES.

1.RIFTING OR SPREADING orDIVERGING

PLATES MOVING AWAY FROM EACH OTHER WHICH IS CALLED SPREADING OR RIFTING OR DIVERGING.

EXAMPLES- MID ATLANTIC RIDGE, RIFT VALLEY IN AFRICA.

MID-ATLANTIC RIDGE

2. COLLIDING OR CONVERGING PLATES

A. SUBDUCTION ONE PLATE GOES UNDER ANOTHER

Example: ONE OCEAN AND ONE CONTINENTAL VOLCANIC MOUNTAINS ARE FORMED

B. SUBDUCTION ONE PLATE GOES UNDER ANOTHER

EXAMPLE : TWO OCEAN PLATES VOLCANIC ISLAND ARCS ARE FORMED

3. CONVERGING OF TWO CONTINENTAL PLATES TWO CONTINENTAL PLATES COLLIDING. EXAMPLE: ROCKIE MTS, ALPS, HIMALAYAS APPALACHIANS

4. FAULTING PLATES SLIDING PAST EACH OTHER THESE ARE CALLED TRANSFORM PLATES.

SLIDE 21

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SLIDE 24

INTERACTIVE WEBSITE

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THEN GO TOP THE TOPIC EARTHQUAKES, TECTONIC PLATES AND VOLCANOES.

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EXTERNAL FORCES

THESE FORCES WORK ON THE LANDFORMS THAT ARE CREATED BY INTERNAL FORCES.

NEW LANDFORMS CAN ALSO BE CREATED BY THESE EXTERNAL FORCES.

THERE ARE TWO TYPES OF EXTERNAL FORCES WEATHERIN G AND EROSION THAT CAN ALTER THE

SIZE AND SHAPE OF LANDFORMS.

1.WEATHERING BREAKDOWN OF ROCKS AT OR NEAR THE EARTH’S SURFACE

2 TYPES: PHYSICAL AND CHEMICAL PHYSICAL-

1. TREE ROOTS

2. FREEZE AND THAW CYCLE

EXAMPLES OF PHYSICAL WEATHERINGCHECKERBOARD MESA – UTAH

ZION CANYON

LONE CYPRESS –CALIFORNIA 17 MILE DRIVEBRYCE CANYON

B. CHEMICAL WEATHERING

1. CHEMICALS IN WATER DISSOLVE ROCKS.

( CARBONATION)

2. CHEMICALS IN AIR AFFECT ROCKS.

( OXIDATION)

WITH CHEMICAL WEATHERING ROCKS CHANGE THEIR COMPOSITION!!

EXAMPLES OF CHEMICAL WEATHERING

CARBONATION

OXIDATION

WEEPING ROCK - ZIONBRYCE CANYON -UTAH

2. EROSIONTHE MOVEMENT OF WEATHERED MATERIAL SUCH AS GRAVEL,

SAND AND SOIL.

THERE ARE 3 TYPES OF EROSION :

A. WATER

B. WIND

C. GLACIERS

1. WATER - WEARS AWAY CREATING CANYONS

ERODES AWAY CANYONS AND VALLEYSGRAND CANYON ZION CANYON

WATER 2.TRANSPORTS PARTICLES AND CREATES DELTAS

AND BEACHES NIGER DELTA BEACH

WIND 1. WEARS SURFACE DOWN

ARCHES BRYCE CANYON

WIND 2. CREATES NEW LANDFORMS LIKE

SAND DUNES

EGYPT LAKE MICHIGAN

GLACIERS 1. SHEET 2. MOUNTAIN