Plate Boundaries
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ment.action?quick=12o&att=2773
Divergent Boundary
1) Divergent boundary
• 2 plates move apart
• Most occur at mid-ocean
ridge
• New crust is created by
magma pushing up from
the mantle
Rift valleys occur when
boundary is on land
Sea Floor Spreading
Rift Valleys
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
Rift valleys occur when boundary is on land
Plates pull apart causing faults in the crust.
Magma fills in and forms new land.
Rift Valley
http://www.wwnorton.com/college/geo/egeo/
flash/2_11.swf
•
Map showing the Mid-Atlantic Ridge splitting Iceland and separating the
North American and Eurasian Plates. The map also shows Reykjavik,
the capital of Iceland, the Thingvellir area, and the locations of some of
Iceland's active volcanoes (red triangles), including Krafla.
Lava fountains (5p;10 m high) spouting from eruptive fissures during the October 1980 eruption
of Krafla Volcano. (Photograph by Gudmundur E. Sigvaldason, Nordic Volcanological Institute,
Reykjavik, Iceland.)
Aerial view of the area around Thingvellir,
Iceland, showing a fissure zone (in
shadow) that is an on-land exposure of
the Mid-Atlantic Ridge. Right of the
fissure, the North American Plate is
pulling westward away from the Eurasian
Plate (left of fissure). This photograph
encompasses the historical tourist area of
Thingvellir, the site of Iceland's first
parliament, called the Althing, founded
around the year A.D. 930. Large building
(upper center) is a hotel for visitors.
(Photograph by Oddur Sigurdsson,
National Energy Authority, Iceland.)
One young divergent plate boundary that you'll recognize is actively
forming the Red Sea. Although the Arabian peninsula and Africa were once
linked to form a single continent, they are now being ripped apart. The
white arrows show the directions the two plates are moving. You can see
that a new ocean, the Red Sea is being formed as they separate.
• http://www.absorblearning.com/media/attac
hment.action?quick=12n&att=2771
• http://esminfo.prenhall.com/science/geoanim
ations/animations/35_VolcanicAct.html
2) Convergent
boundary
– 2 plates come
together
– Collision occurs
– Density of the
plate determines
which ends up
on top
What Goes On At Ocean-Continent Convergent Plate
Boundaries?
•Earthquakes occur as the ocean plate subducts
•An ocean trench forms as the sea floor bends
•Volcanoes form as magma erupts from the subduction
zone
•Mountains form as sediments are folded and faulted
http://www.classzone.com/books/earth_scien
ce/terc/content/visualizations/es0902/es0902
page01.cfm?chapter_no=visualization
• http://education.sdsc.edu/optiputer/flash/sub
duction_5.htm
• http://esminfo.prenhall.com/science/geoanim
ations/animations/35_VolcanicAct.html
• http://www.absorblearning.com/media/attac
hment.action?quick=12s&att=2781
• http://www.classzone.com/books/earth_scien
ce/terc/content/visualizations/es0808/es0808
page01.cfm?chapter_no=visualization
Ocean-Ocean Plate Boundary
•Earthquakes occur as one ocean plate subducts
•An ocean trench forms as the sea floor bends
•A volcanic island arc forms as magma rises above the
subduction zone
•Old oceanic plate is more dense than new oceanic plate
•Old oceanic plate slides under the new oceanic plate and
returns to the mantle
• http://education.sdsc.edu/optiputer/flash/con
vergance2.htm
• http://esminfo.prenhall.com/science/geoanim
ations/animations/35_VolcanicAct.html
• http://www.absorblearning.com/media/attac
hment.action?quick=12u&att=2785
Continent-Continent Convergent Plate Boundary
oMountain building occurs as the continental crust is
folded and faulted
oEarthquakes occur as two continents collide
NO volcanic activity
India crashes into Asia
Himalayan Mountains and Tibetan Plateau
• http://www.classzone.com/books/earth_scien
ce/terc/content/visualizations/es1105/es1105
page01.cfm?chapter_no=visualization
• http://www.absorblearning.com/media/attac
hment.action?quick=12t&att=2783
3) Transform
boundary
– Crust is neither
created nor
destroyed
– 2 plates slip past
each other
– Earthquakes
frequently occur
–
http://www.wwnorton.com/college
/geo/earth/flash/4_2.swf
• http://www.learner.org/interactives/dynamice
arth/slip3.html