Download Mid-Ocean Ridges

Earth is made of three layers
The earth is layered similar to a hardboiled egg
Earth
HardBoiled Egg
Shell is thin and hard
Crust—thin and rigid
Mantle—hot
Core—made of iron
Egg white is thick and
softer
Yolk is small and at the
center
•Lithosphere—upper
mantle and crust
•Asthenosphere—
hot upper part of
mantle
•Ocean crust—
thinnest crust, very
dense
•Continental crust—
thickest crust, not
as dense
Plate Tectonics
The theory that states:
The plates are
moving
•Earth’s lithosphere is
broken into separate
sections called plates.
•Edges of plates meets at lines
called plate boundaries.
•The theory that explains the
formation, movement and
subduction of the earth’s
plates.
Present Day Tectonic Plates
Fault
Plate Boundary
Evidence for Plate Tectonics
• Mid-Ocean Ridges
• Age of the ocean crust
• Ocean Trenches
• Magnetic stripes on the sea
floor
SEA FLOOR
•Scientists started mapping the ocean floor in the 1950’s,
•At the center of the ocean, They found huge underwater
mountain ranges, This was a surprise because they expected
the ocean to be flat in the middle of the ocean
•Scientists called the huge underwater mountain ranges MidOcean Ridges.
•Scientists collected rock samples and determined the shape of
the sea floor using a ship named the Glomar Challenger.
•Ages of rocks
•youngest rocks were closest to the ridge,
•oldest rocks were farthest away,
next to the continents.
Mid Atlantic
Ocean Ridge
Youngest
rocks
Oldest
rocks
A
B
C
Which rocks are older?
A or
B
C or
D
D
•Ocean Trenches are DEEP canyons in the sea floor that are
parallel to the continent.
•Ocean Trenches are located close to a plate boundary.
•Deepest trench on Earth is the Mariana’s Trench next to the
Philippine Islands
SEA FLOOR MAGNETIC STRIPES
1.
Earth is like a giant Bar
Magnetic
a)
b)
2.
Magnetic north pole is near
the geographic north pole
Magnetic field formed by the
motion of the hot molten metal
in the outer core
Occasionally magnetic
poles flip flop: though a
process called magnetic
reversals.
a)
b)
c)
Normal polarity: Magnetic
north pole points to south Pole
Reverse polarity: Magnetic
south pole point to the north
pole
The cause of reversal s
unknown
Divergent Boundary: occurs where plates move apart
Convergent Boundary: Occurs where plates push together
Transform Fault Boundary: Occurs where plates scrape past each other.
Transform
divergent
convergent
Divergent Boundaries
ON LAND
•Two plates move away from
each other leaving a gap between
the plates
IN THE
OCEAN
•A rift valley is a deep valley
that forms in the gap
between the moving plates
Ocean Crust
Rift valley
Ocean Crust
Divergent Boundaries
•New ocean crust is created at
Divergent Boundaries as the plates pull
away from each other.
Krafla Volcano in Iceland
Aerial view of the area around
Thingvellir, Iceland, showing a
fissure zone (in shadow) that is
an on-land exposure of the MidAtlantic Ridge.
Map showing the Mid-Atlantic
Ridge splitting Iceland and
separating the North American
and Eurasian Plates.
Features of Divergent Boundaries
•In the Ocean
•Mid-ocean Ridges (Also called spreading centers)
•Rift Valleys
Krafla Volcano in Iceland
Aerial view of the area around
Thingvellir, Iceland, showing a
fissure zone (in shadow) that is
an on-land exposure of the MidAtlantic Ridge.
Map showing the Mid-Atlantic
Ridge splitting Iceland and
separating the North American
and Eurasian Plates.
Features of Divergent Boundaries
•On Land
•Rift Valleys form when continents split
•If the continents spread far enough apart, new
ocean crust will form
Rift
valley
Newest rock A
Older
rock
B
Mid-ocean ridge
•When new crust forms at mid-ocean ridge, the magnetic minerals
line up with the earth’s magnetic field.
•When the magnetic field reverses, the rocks record the new
polarity
HOT SPOTS are relatively small, long-lasting hot regions where
magma rises in plumes.
Magma plumes develop into volcanoes that can build up and
eventually become a volcanic island or mountain.
Hot spots occur far from plate boundaries, yet tell us how fast
and in what directions plates are moving.
The Hawaiian Islands and Yellowstone are examples of hot spot
volcanoes.
CONVERGENT BOUNDARIES
1. Ocean crust is destroyed at convergent boundaries
at the same rate it is created at Mid-Ocean Ridges .
2. The location where this happens is called the
SUBDUCTION ZONE
3. Subduction is when one plate sinks beneath
another at a convergent boundary
4. Oceanic crust will subduct under the continental
crust
1.Oceanic crust is more dense than continental
crust
CONVERGENT BOUNDARIES
• Three types of convergent boundaries
– Continental-Continental Convergent
– Oceanic-Oceanic Convergent
– Oceanic-continental convergent
• The name tells you the type of crust
involved.
1. Continental-Continental Convergence: Creates mountains
a) Happens when two continental plates
crash together
b) Neither plate wants to subduct so the
edges crumples forming mountains
c) Example:
a) India crashed into Asia 50 million
years ago
b) This caused the Eurasian Plate to
crumple up and form the Himalayas
c) The collision is still happening.
Scientist now know how some types of
mountains form.
3. Oceanic-Oceanic Convergence:
Creates deep ocean trenches at subduction zones, and
island arcs.
Deep OceanTrenches occur where two oceanic plates meet; the
denser of the two plates will subduct and melt. The magma from the
melted palte will rise back to the surface and form an Island Arc
Island arc’s are chains of volcanic islands that form on the top plate,
parallel to a deep ocean trench.
EXAMPLES
Mariana trench is the
deepest at 36,000 ft
below the sea floor.
Subduction zone
Japan and the Aleutian
islands of Alaska are
island arc volcanic chain
Oceanic-continental convergence:
Creates ocean trenches, and coastal mountain ranges
1. Oceanic -continental subduction occurs where an oceanic plate sinks
beneath a less dense continental plate.
2. Deep ocean trenches form where the ocean plate subducts.
3. Coastal mountains from where the less dense continental crust is
folded upward. Some of these mountains may form volcanoes.
Subduction Zone
Subduction Zone
The Cascade mountains, home
of Mt. St. Helen, are coastal
mountains.
Transform Boundaries
1. The location where plates scrape by each other is called a
transform boundary.
2. Crust is neither created nor destroyed, it is just relocated.
3. Most transform faults are found on the ocean floor.
4. They commonly offset the active spreading centers,
The San Andreas fault is a transform boundary between the
North American plate and Pacific plate.
The San Andréa's Fault is the reason why California ha sso
many Earthquakes
Zig-zag pattern on
ocean floor
Convection is the movement of a material due to rising and
sinking of hot and cool materials. Convection Currents create
motion of hot molten rock upward and as it cools it sinks down
where it is heated again and rises.
Convection Currents move the lithosphere only a few
centimeters per year, but over a million years plates are carried
thousands of kilometers.