bellwork

BELLWORKBELLWORK• Name the 3 types of plate

boundaries and an example of each.

Deforming the Deforming the Earth’s CrustEarth’s Crust

Moving ContinentsMoving Continents

• http://www.suu.edu/faculty/colberg/hazards/platetectonics/18_Pangaea.html

Tracking Tectonic PlatesTracking Tectonic Plates

Scientists use GPS to track plate

movement.Radio waves are

beamed from satellites to GPS ground stations

which record their position.

3 Possible Driving Forces3 Possible Driving Forces• Convection Currents• Ridge Push and Slab Pull

– Ridge Push – At mid-ocean ridges, the oceanic lithosphere is higher than it is where it sinks into the asthenosphere. Because of ridge push, the oceanic lithosphere slides downhill under the force of gravity.

– Slab Pull – Because oceanic lithosphere is denser than the asthenosphere, the edge of the tectonic plate that contains oceanic lithosphere sinks and pulls the rest of the tectonic plate with it in a process called slab pull.

• Plate movement causes geological events such as mountain formation, volcanic eruptions, and earthquakes.

DeformationDeformation

• The process by which the shape of a rock changes because of stress.– Stress is the amount of force per unit area on a given

material.

• Different things happen to rock when different types of stress are applied.– Rock layers bend when stress is placed on them.– When enough stress is placed on rocks, they can

reach their elastic limit and break.

CompressionCompression• The type of stress that occurs when an

object is squeezed, such as when two tectonic plates collide.

• When compression occurs at a convergent boundary, large mountain ranges can form.

TensionTension• Stress that occurs when forces act to

stretch an object

• Tension occurs at divergent plate boundaries, such as mid-ocean ridges, when two tectonic plates pull away from each other.

FoldingFolding

• The bending of rock layers because of stress in the Earth’s crust.

• Types of Folds – depends on how the rock layers deform:– Anticlines– Synclines– Monoclines

AnticlineAnticline

• Upward-arching folds.

• Caused by horizontal stress.

SynclineSyncline

• Downward, troughlike folds.

• Caused by horizontal stress.

MonoclineMonocline

• Fold where both ends are horizontal.

• Cause by vertical stress.

FaultingFaulting

• The surface along which rocks break and slide past each other.– Some rock layers break when stress is

applied– The blocks of crust on each side of the fault

are called fault blocks.

Footwall & Hanging WallFootwall & Hanging Wall• When a fault is not vertical, its two sides are

either a hanging wall or a footwall.

Normal FaultNormal Fault• When a normal

fault moves, it causes the hanging wall to move down relative to the footwall.

• Caused by rocks being pulled apart (tension).

Normal FaultNormal Fault

Reverse FaultReverse Fault• When a reverse

fault moves, it causes the hanging wall to move up relative to the footwall.

• Caused when rocks are pushed together (compression).

Reverse FaultReverse Fault

Strike-Slip FaultStrike-Slip Fault

• When opposing forces cause rock to break and move horizontally.

Mountain BuildingMountain Building

• When tectonic plates undergo compression or tension, they can form mountain ranges in several ways.

Folded MountainsFolded Mountains• The highest mountains in the world are

formed when rock layers are squeezed together and pushed upwards to form folds.– This occurs at convergent

boundaries where plates collide.– The plates buckle and thicken.– The continental crust is pushed

upward, forming mountains.

Examples of Folded MountainsExamples of Folded Mountains

• Himalayas

• AlpsIn central

Europe

• Ural Mountainsin Russia

• Great Smoky Mountains

Fault-Block MountainsFault-Block Mountains• Form when large blocks of the Earth’s crust drop

down relative to other blocks.• Tension produces mountains that have sharp,

jagged peaks.

Examples of Fault-Block MountainsExamples of Fault-Block Mountains

• Teton Range in Wyoming.

• Sierra Nevada mountain range in California

• Harz Mountains in Germany

Volcanic MountainsVolcanic Mountains

• Form when magma rises to the Earth’s surface and erupts.

Examples of Volcanic MountainsExamples of Volcanic Mountains

• Mount St. Helens in Washington

• Mount Pinatubo in the Phillipines

Uplift and SubsidenceUplift and Subsidence• Uplift is the rising of regions of the Earth’s

crust to higher elevations.– Rebound – When the crust slowing springs

back to its previous elevation, as when a glacier melts.

• Subsidence is the sinking of regions of the Earth’s crust to lower elevations.– Rocks that are hot take up more space than

cooler rocks.

Tectonic LetdownTectonic Letdown• Subsidence can also occur when the

lithosphere becomes stretched in rift zones.

QuizQuiz1. Name the 3 types of faults.

2. Name the 3 types of folds.

3. What is compression?

4. What is tension?

5. Would you find a folded mountain at a

mid-ocean ridge? Why or why not?