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?