Tectonic Plate Boundaries
Plate Boundaries - where the edge of two plates meet. 3 Plate Boundaries and 1 other 1. Divergent - occurs where plates move apart (mostly in oceans) 2. Convergent - occurs where plates push together 3. Transform - occurs where plates scrape past each other 4. Hot Spots
Occurs where two plates split apart Divergent Boundaries Occurs where two plates split apart
How, you ask? Divergent boundaries form when hot material rises Heat causes crust to buldge upward Crust cracks and a rift valley forms
Magma rises through cracked, thinned crust, forming volcanoes Continued… Magma rises through cracked, thinned crust, forming volcanoes If rift valley continues widening it will sink below sea level and water from near by oceans will fill in ex.) Red Sea
http://www. lincoln. smmusd http://www.lincoln.smmusd.org/staff/Vanderveen_Web/geology/Images%20for%20notes/riftsplitscont.gif
Divergent Boundaries Mid-Ocean Ridges and Rift Valleys A. Mid-Ocean Ridges Longest chain of mountains Most contain a rift valley along their center EX.) Mid-Atlantic Ridge - reaches from Iceland to Antarctica in Atlantic Ocean
Rift Valley Gap at center of Mid-ocean ridge Molten material rises from asthenosphere, water cools the rock until it becomes solid
http://www. harcourtschool. com/scienceglossary/images/gr6/midocean_r6 http://www.harcourtschool.com/scienceglossary/images/gr6/midocean_r6.jpg
Convergent Boundaries Occurs where plates push together Crust is either folded or destroyed
Subduction Zone When one plate sinks below another crust melts in the asthenosphere and is destroyed
http://discoverourearth.org/instructor/tectonics/subduction.html
Oceanic Crust – crust that is thin but very dense (tightly packed) Continental Crust – crust that is thick but less dense (not tightly packed)
A. Continental-Continental Collision Occurs where two continental plates push together Neither plate sinks because both plates have the same density Plate edges will crumple and fold, often forming mountains ex.) Himalayas (still forming today)
http://www.extremescience.com/graphics/Deform.gif
B. Oceanic-Oceanic Subduction Occurs where one plate with oceanic crust sinks, or subducts, under another plate with oceanic crust Older plate sinks because it is colder and more dense When it reaches the asthenosphere it melts in the intense heat
2 features form at oceanic-oceanic subductions Deep-Ocean Trenches deep canyons that form in ocean floor (most found in Pacific Ocean) EX.) Pacific Plate under Philippine Plate, deepest spot is 11,000 meters into sea floor Island Arcs chains of volcanic islands that form on the top of plates Form parallel to deep-ocean trenches EX.) Japan, Philippine Islands
http://pubs.usgs.gov/publications/graphics/Fig21oceanocean.gif
C. Oceanic-Continental Subduction Occurs when ocean crust sinks under continental crust Oceanic sinks because it is colder and denser than continental crust
2 features form at oceanic-continental subductions Deep-Ocean Trenches Ex.) Pacific Plate under North American Plate (underwater earthquakes) 2. Coastal Mountains continental crust buckles to form a range of mountains Mts. Parallel to deep-ocean trenches (some form volcanoes) Ex.) Cascade Mts. In Oregon and Washington (Mt. St. Helen’s)
http://www.rcmurphy.net/Medina%202005/images/convergent.jpg
http://earth.geol.ksu.edu/sgao/g100/plots/0829_10_convergent.jpg
Occurs where two plates move past each other in opposite directions Transform Boundaries Occurs where two plates move past each other in opposite directions
As plates move, their edges scrape and grind against each other Occurs mostly near mid-ocean ridges EX.) San Andreas Fault At its present rate, LA will be a suburb of San Fran in 10 million years.
http://www.lincoln.smmusd.org
Hot Spots Can be used to track plate movement Hot spots - heated rock rises in plumes, or thin columns, from the mantle Volcanoes often develop above plumes Hot spot stays in one place as tectonic plate moves above it EX.) Hawaiian Islands
http://earth.leeds.ac.uk/dynamicearth/plates_move/hoticon.gif