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Plate Tectonics and Mountain Building

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by

Michelle John

on 8 December 2014

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Transcript of Plate Tectonics and Mountain Building

Plate Tectonics

REVIEW

The
lithosphere
is divided into pieces called
tectonic plates.

Plate tectonics is the theory that describes the
large-scale movement of Earth's lithosphere.

What causes tectonic plates to move???
convection
Review

About 250 million year ago, the continents were joined in a single large landmass called
Pangaea.

Alfred Wegener proposed a hypothesis of
continental drift
, saying that the continents once formed a single landmass, broke up, and drifted.

Evidence of continental drift: mountain ranges, rock formations, fossils, ancient climatic conditions
Mid-Ocean Ridges

Underwater mountain ranges that form along cracks in the oceanic crust

Sea-floor spreading

The process by which new oceanic lithosphere
sea floor
forms when magma rises to Earth's surface at mid-ocean ridges and solidifies as older, existing sea floor moves away from the ridge
Ocean Trenches

If the sea floor has been spreading for millions of years, why is Earth not getting larger?

Scientists discovered the answer when they found huge trenches, like deep
canyons
, in the sea floor.

At these sites, dense oceanic crust is sinking into the asthenosphere.

Older crust is being
destroyed
at the same rate new crust is
forming
.
The major tectonic plates include the Pacific, North
American, Nazca, South American, African, Australian
Eurasian, Indian, and Antarctic plates.

The

Nazca
plate has only oceanic crust.
Types of Plate Boundaries

1. Convergent boundaries
2. Divergent boundaries
3. Transform boundaries
Convergent Boundaries
-form when 2 plates
collide
Continent-Continent collision

When 2 plates of continental
plates collide, they buckle and
thicken. This causes
mountains
to form.
Continent-Ocean Collision

When a plate of oceanic lithosphere
collides with a plate of continental
lithosphere, the oceanic lithosphere
subducts, because it is denser.

Subduction
zone- Boundaries where
one plate sinks beneath another plate
Ocean-Ocean Collision

When 2 plates of oceanic lithosphere
collide, the older, denser plate subducts
under the other plate.
Divergent boundaries
-where 2 plates move
away
from each other
-most are located on the
ocean
floor

-The separation of plates allows
the asthenosphere to rise toward
the surface and partially melt. This melting creates magma, which erupts as lava. The lava cools and
hardens to form new rock on the
ocean floor.
Transform boundary
-a boundary at which 2 plates
move past each other horizontally
-this friction causes
earthquakes
How can tectonic plate motion cause deformation?

The movement of tectonic plates places

stress

on rocks.

Stress is the amount of
force

per unit area that is placed
on an object.

Deformation
is the process by which rock changes shape
under stress.
When rocks bend,
folds
form.

When rocks break,
faults
form.
2 Types of Folds

1. Synclines- the youngest layers
are found at the core of a fold, usually look like
rock layers are arched upward, like a bowl

2. Anticlines- the youngest layers are found
on the outside of the fold
What are the 3 kinds of faults?

1. Strike-slip fault
2. Normal fault
3. Reverse fault
Strike Slip Fault
-In a strike slip fault, fault blocks move
past each other
horizontally
.
-Form when rock is under shear stress
-
Shear stress
is stress that pushes rock
in parallel but opposite directions.
-Common along
transform
boundaries
-Ex. San Andreas fault in California
Normal Faults
-In a normal fault, the hanging wall moves down relative to the
footwall
.
-Form when rock is under tension
-
Tension
is stress that stretches or pulls rock apart
-Common along
divergent
boundaries
Reverse Faults
-In reverse faults, the hanging wall moves
up
relative to the footwall.
-Form when rocks undergo compression
-
Compression
is stress that squeezes or pushes
rock together.
-Common along
convergent
boundaries
Faults
-The crack that forms when large blocks of rock
break and move past each other is called a
fault
.
-The blocks of rock on either side of the fault are called
fault blocks
.
-The location where 2 fault blocks meet are called the
fault plane
.
-The block above the fault plane is called the
hanging
wall.
-The block below the fault plane is the
footwall
.
What are the 3 kinds of mountains?

1. Folded mountains
2. Volcanic mountains
3. Fault-block mountains
Folded Mountains
-Form when rock layers are squeezed together
and pushed upward
-Usually form at
convergent
boundaries
-Ex. Appalachian Mountains
Volcanic Mountains
-Form when melted rock erupts onto
Earth's surface
-Can form on
land
or on the ocean floor
-Most of Earth's active volcanoes are concentrated
around the edge of the Pacific Ocean- this area
is known as the
Ring of Fire
Fault-Block Mountains
-Form when tension makes the lithosphere
break into many
faults
. Some pieces
drop down; the pieces left standing form
mountains.
-Ex. Sierra Nevada Mountains
Full transcript