Transcript File

RCI Geography
A little review…
There are three main types of plate
boundaries:
1. Divergent boundaries -- where new crust is generated as
the plates pull away from each other.
2. Convergent boundaries -- where crust is destroyed as one
plate dives under another.
3. Transform boundaries -- where crust is neither produced
nor destroyed as the plates slide horizontally past each other.
Divergent Plate
Boundaries
- New crust is created as two or more plates
pull away from each other. Oceans are born
and grow wider where plates diverge or pull
apart.
Result:
Ridges are created, such as the MidAtlantic ridge and new crust is being created as
magma fills this space forming land.
• The Mid-Atlantic
Ridge, which
splits nearly the
entire Atlantic
Ocean north to
south, is probably
the best-known
and most-studied
example of a
divergent-plate
boundary.
• Aerial view of the
area around
Thingvellir,
Iceland, showing a
fissure zone (in
shadow) that is the
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 the fissure).
• East Africa may be the site of the Earth's
next major ocean. Plate interactions in the
region provide scientists an opportunity to
study first hand how the Atlantic may have
begun to form about 200 million years ago.
Geologists believe that, if spreading
continues, the three plates that meet at the
edge of the present-day African continent will
separate completely, allowing the Indian
Ocean to flood the area and making the
easternmost corner of Africa (the Horn of
Africa) a large island
Convergent Plate
Boundaries
-Occurs when one plate dives under another,
creating subduction zones (where you will find
mountains or volcanoes)
- Crust is destroyed and recycled back into the
interior of the Earth
We will look at 2 Types of Convergent
Boundaries
A) Ocean to Continent
B) Continent to Continent
A) Ocean to Continent
- When an oceanic plate pushes into a continental
plate, the oceanic plate will slide underneath because it
is more dense
-The overriding continental plate is lifted up and
mountains are created, often in the form of a volcano!
Trenches are formed at the point where the oceanic
crust dives under (Marianis Trench)
Result: Large volcanic
chains are created, along with
deep-water trenches!
• The
convergence
of the Nazca
and South
American
Plates has
deformed
and pushed
up limestone
strata to
form
towering
peaks of the
Andes
B) Continent to Continent
- When two continents meet head-on, neither is
subducted because the continental rocks are
relatively light
- The crust tends to buckle and be pushed upward
or sideways
Result: Large mountains
and mountain chains are
created, such as the
Himalayas! (Mt. Everest)
• The 6,000km-plus
journey of
the India
landmass
(Indian
Plate)
before its
collision
with Asia
(Eurasian
Plate)
about 40 to
50 million
years ago
• Sunset view of towering, snow-capped Mt. Everest,
from the village of Lobuche (Solu-khumbu), Nepal
Who know’s where
this is?
Transform Boundaries
- Transform-Fault Boundaries are where two
plates are sliding/grinding horizontally past one
another (Like the N.A and Pacific plates)
Result: Transform-Fault boundaries are
locations of recurring earthquake activity. Most
fault boundaries are found in the ocean but the
most notable one on land is the San Andreas
fault in California (1,300 km long!)
• The Blanco,
Mendocino,
Murray, and
Molokai
fracture
zones are
some of the
many
fracture
zones
(transform
faults) that
scar the
ocean floor
and offset
ridges
The San Andreas fault
zone, which is about
1,300 km long and in
places tens of
kilometers wide, slices
through two thirds of
the length of
California. Along it,
the Pacific Plate has
been grinding
horizontally past the
North American Plate
for 10 million years, at
an average rate of
about 5 cm/yr
Hotspots
Regions of earthquake and volcanic
activity which do not occur along
plate boundaries
• The vast majority of
earthquakes and volcanic
eruptions occur near plate
boundaries, but there are some
exceptions
• Map of part of the Pacific basin showing the volcanic trail
of the Hawaiian hotspot-- 6,000-km-long Hawaiian RidgeEmperor Seamounts chain
What are the consequences of the
plates moving?
• Formation of new land 
mid-ocean ridges
• Creation of mountains,
volcanoes, and trenches from
convergent boundaries
What are the consequences of the
plates moving?
• Formation of new land 
mid-ocean ridges
• Creation of mountains,
volcanoes, and trenches from
convergent boundaries
• An area where large numbers of
earthquakes and volcanic eruptions occur
around the edge of the Pacific Plate
• Continuous series of oceanic trenches,
volcanic arcs, and volcanic belts. It has
452 volcanoes and is home to over 75%
of the world's active and dormant
volcanoes, and 90% of the world’s
earthquakes