Boundaries, Stresses, and Faults OH MY! How do geologic events change and shape Earth’s surface?

Remember… The Lithosphere is made of… The CRUST + The Upper Rigid Mantle Plates may be called by different names: Crustal Plates Lithospheric Plates Tectonic Plates

Plates around Earth move in different directions & cause different geologic events (things that happen on Earth).

Let’s recall what makes the plates move… Convection Currents in the mantle move the plates as the core heats the slowly-flowing asthenosphere (the elastic/plastic-like part of the mantle).

There are 3 types of Plate Boundaries There are 3 types of Plate Boundaries. Each one has a type of STRESS on the rock & a way that it breaks, called a FAULT: Divergent Boundaries Convergent Boundaries Transform Boundaries Let’s break it down…

Divergent Boundaries Place where 2 plates pull away from each other

How is the rock pulled at Divergent Boundaries How is the rock pulled at Divergent Boundaries? Rock gets THIN in the middle as it is pulled apart. This STRESS is called

What happens when the rock SNAPS from the Stress of Tension What happens when the rock SNAPS from the Stress of Tension? A Normal Fault (fault is a break in Earth’s crust) Rock drops down as it breaks

What happens next @ Divergent Boundaries? A geologic feature or event… May form RIFT VALLEYS on continents SEA-FLOOR SPREADING in the ocean

Helpful Hints… Divergent is like “dissecting” or “dividing” If you pull warm bubble gum or silly putty, it will thin in the middle until it is stressed so much that it breaks. Happens on land & under H2O

Transform Boundaries Place where 2 plates slide past each other

How is the rock broken at Transform Boundaries? Rock is pushed in two opposite directions (or sideways, but no rock is lost) This stress is called SHEARING

What happens when the rock is sheared (or “cut”) from the Stress of Shearing? A STRIKE-SLIP FAULT Rocks on each side of the fault slip past each other as they break.

What happens next at Transform Boundaries? May cause Earthquakes when the rock snaps from the pressure. A famous fault @ a Transform Boundary is the San Andreas Fault in California.

Helpful Hints… Shearing means cutting (“Shears” are like scissors) Transform boundaries run like trains going past each other in different directions & they shake the ground! San Andreas Fault, CA 

Convergent Boundaries Places where plates crash (or crunch) together or subduct (one sinks under)

How is the rock pushed at convergent boundaries? Rock is pressed or squeezed together. This stress is called COMPRESSION

What happens when the rock is squeezed from the Stress of Compression? A REVERSE FAULT Rock is forced upward as it is squeezed.

What happens next @ Convergent Boundaries? May form Mountain Ranges. These are Folded Mtns. Like the Himalayas or the Rockies.

How Do Mountains Form? The forces of plate movement can build up Earth's surface, so over millions of years, movement of faults can change a perfectly flat plain into a gigantic mountain range Sometimes, a normal fault uplifts a block of rock, so a fault-block mountain forms When a piece of rock between two normal faults slips down, a valley is created

Anticlines and Synclines Describs downward and upward folds in rock An _______is a fold in a rock that arcs upward A _______ is a fold in a rock that arcs downward These folds in rocks are found on many parts of the earths surface where compression forces have folded the crust.

What else happens @ Convergent Boundaries? May form Volcanoes @ Subduction Zones as denser oceanic plate dives under less dense continental plate.

Helpful Hints… Convergent = “Connecting” boundaries May work like a trash compactor smashing rock. Rock goes crunches up to make folded mountains. Rock goes down “under” @ subduction zone.

Plate Boundaries: Can you match the boundary name correctly with its diagram? _____________

Plate Boundaries: Correct Answers: Divergent Convergent Transform

d. Describe processes that change rocks and the surface of the earth. Standard: S6E5. Students will investigate the scientific view of how the earth’s surface is formed. d. Describe processes that change rocks and the surface of the earth. Review: (Make sure you use voc. from your notes) 1. How does the process of subduction recycle rock? 2. How can magma rise up on the ocean floor? 3. What happens to rock to form folded mountain ranges?

Standard: S6E5. Students will investigate the scientific view of how the earth’s surface is formed e. Recognize that lithospheric plates constantly move and cause major geological events on the earth’s surface. Review: 1. List the geologic event(s) that can occur at each plate boundary. (What happens or is formed here?) ____ & ____ @ Divergent Boundaries ____ & ____ @ Convergent Boundaries __________ @ Transform Boundaries

Standard: S6E5. Students will investigate the scientific view of how the earth’s surface is formed f. Explain the effects of physical processes (plate tectonics, erosion, deposition, volcanic eruption, gravity) on geological features including oceans (composition, currents, and tides). Review: (Make sure to use voc. from your notes) Explain how Earthquakes occur. How can new ocean floor be created? How do mountain ranges form? Why is density important at subduction zones?