Download Tectonic Plates Boundaries

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
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
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.org/staff/Vanderveen_Web/geology/Images%20for
%20notes/riftsplitscont.gif
Divergent Boundaries
1. 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
B. 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/midoc
ean_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. ContinentalContinental 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 oceanicoceanic subductions
1. 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
2. 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 oceaniccontinental subductions
1. 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
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
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