Tectonic Plate Boundaries Types of motion and effects

Transform Tectonic plates slide past each other Results in linear fault valleys or undersea canyons Grinding plates results in a wide boundary zone for earthquakes No magma is formed, so crust is cracked and broken, not destroyed or created

i. Instead, linear valleys can mark the boundaries ii. San Andreas Fault - moving northwards as rest of California moves southwards - at a rate of about 6cm each year

Convergent Tectonic plates colliding with each other Collision causes one or both plate edges to buckle i. Results in mountain ranges forming ii. Sometimes trenches form from one plate sliding (subducting) under the other

B. Chain of volcanoes often forms parallel to the boundary, mountain range, and trench C. Earthquakes can result D. Subducting oceanic plates melt, causing magma to rise and form new continental crust made of granite

II. Himalaya Mountains 2,900km long between India and Tibet Began forming 40-50 million years ago when India and Eurasia, two separate land masses, collided Still causes disastrous earthquakes today

III. Subducting Zones When the older of two colliding oceanic plates is pushed under the younger one i. Because older crust is more dense, meaning the younger one is pushed over the top of the older one ii. Enters the asthenosphere

B. Can result in trenches as much as 70 miles wide, hundreds of miles long, and several miles deep i. Marianas Trench, where the Pacific Plate is pushed under the Eurasian Plate ii. Deepest sea floor in world - more than 36,000 feet below the surface

C. Trench-Flipping i. Occurs when descending oceanic crust also carries a continent, which is less dense ii. Continent dives into trench, following, until it becomes stuck

iii. Crust crumples into mountains, causing the leading edge of oceanic plate riding over the other plate to deposit some crust on top of the continent iv. Pressure builds up until the oceanic crust eventually is forced under the continent, flipping the trench

Divergent Tectonic plates moving away from each other Due to heat from radioactive decay in earth’s interior Over convection currents i. Lifts lithosphere

C. Stretches and breaks, sliding away D. Divergent plate boundaries created due to heat from radioactive decay in earth’s interior E. Results in creation of mid-oceanic ridges i. Atlantic Ocean - 2cm per year

Mid-Oceanic Ridges Stretching of the lithosphere creates deep fissure Pressure released upon breaking i. Melted mantle/magma flows into fissure, where it solidifies and grows, pushing original broken crust further away upon creation of new crust

B. Typically 30-50km wide when on land, whereas on the ocean floor, rifts are no wider than 1km

C. Sea-floor spreading i. Process of new crust being produced and attaching itself to trailing edge of plate as mid-ocean ridge is created ii. Older crust is further from ridge iii. Made of basalt

II. Underwater mountain range Over 35,000 miles long Over 12,000 feet high Over 1,200 miles wide

Faults Slight fractures in Earth’s crust caused by stretching and compression of plates Two main types Normal Faults: crust stretches to form a basin/range flanked by fault-block mountains i. Southern Rocky Mountains

B. Reverse Fault: compression squeezes crust together as one block slides over another, creating overthrust mountains i. Montana’s Glacier National Park

C. Lateral/Transform/Strike-Slip Faults:when fractures in the surface are vertical but result in mainly horizontal movement of the blocks and when plates grind, shear, slide past each other, causing earthquakes but not mountains i. Found where significant movement occurs along a fracture in the crust

Earthquakes A perceptible shaking of Earth’s surface Can be almost unfelt to so violent a whole city topples and people can be tossed about Results from a sudden release of tension in Earth’s crust

II. Caused by seismic activity Measured by a seismograph i. Frequency, type, size ii. Three depths: shallow-focus (less than 70km deep); mid-focus (70-300km deep); deep-focus (300-700km deep)

B. Origin called epicenter C. Micro (less than 2.0), Minor (2.0-3.9), Light (4.0-4.9), Moderate (5.0-5.9), Strong (6.0-6.9), Major (7.0-7.9), Great (8.0 and greater) i. 2004 Sri Lanka Tsunami (9.1-9.3) is third largest measured; lasted 8.3-10 mins

III. Comprised of: Hanging Wall - block above fault plane Footwall - block below fault plane IV. Shapes: Syncline - bend in the rock swooping downward Anticline - bend in the rock rising upward like a hill