Unit 4: Earthquakes & Volcanoes AIM: How does stress in the crust change Earth’s surface?
Forces in Earth’s Crust • The movement of Earth’s plates creates enormous forces that squeeze or pull the rock in the crust. • Stress – a force that acts on a rock to change its shape or volume. • Some rocks can become brittle and snap • Some rocks can bend slowly
What are the 3 Types of Stress? • Tension, compression, and shearing work over millions of years to change the shape and volume of rock. • Tension: stretches rock so it becomes thinner • Occurs where 2 plates are moving apart.
What are the 3 Types of Stress? 2. Compression: squeezes rock until it folds or breaks. • Occurs where 2 plates are colliding.
What are the 3 Types of Stress? 3. Shearing: pushes a mass of rock in two opposite directions • Can cause rock to break and slip apart, or change its shape.
Kinds of Faults • Fault – a break in the crust where rock surfaces slip past each other. • Most faults occur along plate boundaries.
Kinds of Faults • Normal Faults: tension pulls crust apart – divergent • Fault is at an angle: • 1 block of rock lies above – hanging wall • the other lies below – footwall • Hanging wall slips downward Animation
Normal Fault at Death Valley, California http://geotripper.blogspot.com/2008_02_01_archive.html
Kinds of Faults 2. Reverse Faults: caused by compression • Same structure as normal fault, but rock moves in opposite direction • Hanging wall slides upward Animation
Kinds of Faults 3. Strike-Slip Faults: plates move past each other sideways • Caused by shearing formed at transform boundaries Animation
Changing Earth’s Surface • Folding – rock bends without breaking • Upward folds – anticline • Downward folds – syncline • Colliding plates can compress and fold crust over wide area • Produces largest mountain ranges • Ex: Himalayas in Asia “Folding” Video Clip
Anticline-syncline pair in Silurian strata, Newfoundland, New Jersey. http://www.rci.rutgers.edu/~schlisch/structureslides/rte23folds.html
Changing Earth’s Surface 2. Stretching Earth’s Crust - two normal faults cut into rock • Parallel formation creates fault-block mountains Fault-Block mountains Video Clip
Changing Earth’s Surface 3. Uplifting forces can raise plateaus • Large area of FLAT land elevated high above sea level • Forces in crust push up large, flat blocks of rock Plateau nearZion National Park, Utah