Internal Forces Internal Forces Shaping the EarthShaping the Earth

Continental DriftContinental Drift– The continental drift hypothesis proposes that The continental drift hypothesis proposes that

the earth was once a the earth was once a supercontinentsupercontinent that that divided and slowly drifted apart over millions of divided and slowly drifted apart over millions of years. years.

– A geographer from Germany named Alfred A geographer from Germany named Alfred Wegener called this supercontinent Wegener called this supercontinent PangaeaPangaea (a (a Greek word that means “all earth”). Greek word that means “all earth”).

– Pangaea split into many Pangaea split into many continental platescontinental plates that that drifted, crashed into each other, and split apart drifted, crashed into each other, and split apart several times before they came to their current several times before they came to their current positions. This took FOREVER! Millions of years!positions. This took FOREVER! Millions of years!

PangeaPangea

LandformsLandforms

– LandformsLandforms are naturally formed features on the are naturally formed features on the surface of earth. There are many different types surface of earth. There are many different types of landforms (pg. 34-35 in Textbook).of landforms (pg. 34-35 in Textbook).

– ReliefRelief is the difference in elevation of a landform is the difference in elevation of a landform from its lowest point to its highest point. from its lowest point to its highest point.

– There are four categories of relief:There are four categories of relief:– mountainsmountains– hillshills– plainsplains– plateausplateaus

TopographyTopography- TopographyTopography is the combination is the combination of the surface shape and composition of the surface shape and composition of the landforms and their distribution of the landforms and their distribution in a region.in a region.

-The seafloor also has landforms -The seafloor also has landforms similar to those above water. similar to those above water.

-The floor of the ocean has -The floor of the ocean has ridges, valleys, canyons, ridges, valleys, canyons, andand plains.plains.

-Mountain chains similar to those-Mountain chains similar to those on the continents cover parts of on the continents cover parts of the ocean floor. The longest the ocean floor. The longest continuous underwater range is continuous underwater range is the the Mid-Atlantic RidgeMid-Atlantic Ridge, which extends , which extends for thousands of miles north to south for thousands of miles north to south through the middle of the Atlantic Ocean.through the middle of the Atlantic Ocean.

Plate TectonicsPlate Tectonics

• Tectonic platesTectonic plates are enormous moving pieces of are enormous moving pieces of the earth’s lithosphere.the earth’s lithosphere.

• Tectonic plates move in one of four ways:Tectonic plates move in one of four ways:1. 1. spreading spreading or moving apartor moving apart2. 2. subductionsubduction or diving under another or diving under another

plate plate3. 3. collisioncollision or crashing into one another or crashing into one another4. 4. slidingsliding past each other in shearing past each other in shearing

motion motion

Divergent BoundaryDivergent Boundary

1. Divergent boundary1. Divergent boundary- - plates move apart, plates move apart, spreading horizontallyspreading horizontally

~~ExampleExample: Between : Between Saudi Arabia and Egypt, Saudi Arabia and Egypt, these two plates are these two plates are spreading apart makingspreading apart makingthe Red Sea even wider.the Red Sea even wider.

Convergent BoundaryConvergent Boundary

2. 2. Convergent boundaryConvergent boundary- - plates collide, causing plates collide, causing either one plate to dive either one plate to dive under the other or the under the other or the edges of both plates to edges of both plates to CrumpleCrumple

~~Example:Example: In South Asia, In South Asia, India is crashing into the India is crashing into the Asian continent and building Asian continent and building up the Himalayan Mountains.up the Himalayan Mountains.

Transform BoundaryTransform Boundary

3.3.Transform boundaryTransform boundary- - plates slide past plates slide past one anotherone another

~~Example:Example: In North In North America the San America the San Andreas Fault in Andreas Fault in California.California.

EarthquakesEarthquakes• When two plates meet each other they cause folding and When two plates meet each other they cause folding and

cracking of the rock. This is a very slow process. Only a few cracking of the rock. This is a very slow process. Only a few centimeters a year.centimeters a year.

• This fracture of the earth’s crust is called a This fracture of the earth’s crust is called a fault.fault.

• As plates grind or slip past each other at a fault, the earth As plates grind or slip past each other at a fault, the earth shakes or trembles causing an shakes or trembles causing an earthquakeearthquake. .

• A special device called a A special device called a seismographseismograph can detect earthquakes. It measures can detect earthquakes. It measures the size of the waves created by an the size of the waves created by an earthquake.earthquake.

• The The Richter ScaleRichter Scale uses information collected by seismographs uses information collected by seismographs to determine the relative strength of an earthquaketo determine the relative strength of an earthquake

TsunamiTsunami

• Sometimes an earthquake Sometimes an earthquake causes a causes a tsunamitsunami, a giant , a giant wave in the ocean that can wave in the ocean that can be higher than 100 feet tall. be higher than 100 feet tall.

• The world record for a The world record for a tsunami was set in 1971 tsunami was set in 1971 off the Ryuku Islands nearoff the Ryuku Islands nearJapan, where the wall of Japan, where the wall of water reached 238 feet- water reached 238 feet- more than 20 stories high!!!!more than 20 stories high!!!!

VolcanoesVolcanoes

• Magma, gases, and waterMagma, gases, and waterfrom the lower part of the crust from the lower part of the crust or the mantle collect in or the mantle collect in underground chambers. underground chambers. Eventually the materials Eventually the materials pour out of a crack in the pour out of a crack in the earth’s surface called a earth’s surface called a volcano.volcano.

• Most volcanoes are foundMost volcanoes are found along tectonic plate boundaries. along tectonic plate boundaries.

• When the magma flows out When the magma flows out onto the land slowly it may spread onto the land slowly it may spread across an area and cool. Magma across an area and cool. Magma that has reached the earth’s surface that has reached the earth’s surface is called is called lavalava..