Plate tectonics:
The Key to understanding mountain
formation
Plate boundaries
• ..\..\..\Documents\CLASSES\Mtn_geog\10\
Videos\ess01_int_boundaries\ess05_int_bo
undaries.html
Volcanoes, earthquakes
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Videos\ess02_int_tectonic\ess05_int_tecton
ic.html
World’s tectonic plates
Earth’s Topographic Regions
Clue #1:
Mountain ranges found only in
certain areas (edges of continents)
Marine fossils on top of Everest
•Granite core
•sedimentary
rock layer
•Limestone
(top)
Clue #2: Material composition of
mountains
N side, view from Rongbuk Monastery, Tibet
Clue #3:
Continental Shields
in interior of
continents
GEOLOGY OF THE USA
Craton (kratos;
Greek for strength)
• old and stable part of the
continental crust that has
survived the merging and
splitting of continents
•interiors of continents
•formed of a crust of
lightweight rock, e.g. granite,
attached to a section
of the upper mantle.
Clue #4:
Ocean crust oldest near continents and
youngest towards middle of oceans
oldest
youngest
Plate motion
• Plates move away from, toward, or slide
past each other.
• There are 3 types of plate boundaries:
- divergent
- convergent
- transform.
Three types of plate boundary
A. DIVERGENT PLATE
BOUNDARY
• occur along spreading
centers where plates
are moving apart
• new crust is created by
magma pushing up
from the mantle
Example:
Mid-Atlantic Ridge
•a topographically high area
near the middle of the Atlantic
Ocean
•splits nearly the entire
Atlantic Ocean north to south,
Divergent: Atlantic Ridge
LAVA FOUNTAINS
KRAFLA VOLCANO
ICELAND
B. CONVERGENT PLATE
BOUNDARY
• Plates are moving
toward each other
• destruction (recycling)
of crust takes place
along convergent
boundaries
Sometimes, pne plate sinks (is subducted) SUBDUCTION ZONE
Convergent plate boundaries
3 types depending on type of plate involved:
• Oceanic-continental convergence
• Oceanic-oceanic convergence
• Continental-continental convergence
1. Oceanic-Continental Collision
•oceanic Nazca Plate is pushing into and being subducted
under the continental part of the South American Plate
•South American Plate is being lifted up, creating the Andes
•Strong, destructive earthquakes
•rapid uplift of mountain ranges are common in this region.
Oceanic-continental:
Pacific RING OF FIRE
Example: Andes Mtns
West margin of the South
American continent
•oceanic Nazca Plate is
pushed toward and
beneath the continental
portion of the
South American Plate
•typical example of a
convergent plate
boundary
ALPAMAYO,
CORDILLERA BLANCA
2. Oceanic-oceanic Collision
Subduction processes in oceanic-oceanic
plate convergence result in the
formation of volcanic arc islands
Examples of volcanic arc islands
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•
•
•
•
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Aleutians
the Kuriles
Japan
the Ryukyus,
the Philippines
Indonesia
3. Continental-continental Collision
• neither plate subducted because
the continental rocks are relatively light
• like two colliding icebergs, plates resist
downward motion
HIMALAYAS
collision between the
Indian and Eurasian
plates has
pushed up the
Himalayas
and the Tibetan Plateau
C. TRANSFORM BOUNDARY
• At a transform plate
boundary, plates slide
past each other.
• Crust neither produced
nor destroyed
Example:
San Andreas fault in California
Pacific Plate slides past the
North American Plate.
Special case: HOTSPOTS
“Plume” = huge
column of
upwelling lava
HOTSPOTS
HAWAII VIDEO
http://www.teachersdomain.
org/resource/ess05.sci.ess.ea
rthsys.hawaii/
How fast are plates moving?
• The Arctic Ridge
– slowest rate (less than 2.5 cm/yr)
• East Pacific Rise near Easter Island, in the
South Pacific about 3,400 km west of Chile
– fastest rate (more than 15 cm/yr).
Plate Motion Summary
Mountain Maker, Earth shaker
• Interactive media