The Moving PlatesThe Moving Plates

Boundary Interactions and the Origin of Earth Features

Unit Five: Natural DisastersPart C

Layers of the Earth:Layers of the Earth:

Inner Core Outer Core Mantle Asthenosphere Lithosphere The lithosphere is

made of the crust and rigid upper mantle. It is broken into about 14 large plates.

Mass:Mass:

Percentages From Inside to Outside:

Core 32% Mantle 66% Crust 2%

The CoreThe Core

Composed of Iron and Nickel Inner Core – solid Outer Core – liquid High heat originates from gravitational pressure

and radioactivity of heavy, unstable atoms. Heat source for convection in the mantle.

Radioactive DecayRadioactive Decay Some atoms are unstable and decay or breakdown on

their own.They release small particles.

Certain heavy elements in the core, like Uranium, decay in such a way that they actually give off radiation.

Gamma rays given off by decaying heavy elements in the core heat it up, like a flame heats a pot of soup.

Magnetosphere (or E-M Field)Magnetosphere (or E-M Field)

The iron in the Earth’s core creates a magnetic blanket around our planet.

It protects us from deadly radiation from the sun, deflecting it like a shield.

Heat TransferHeat Transfer Heat moves through different materials in different

ways. Conduction = moves through solids by contact.

An example of conduction is burning your forehead with a curling iron.

Convection = moves through fluids as density changeshotter = less dense, risescooler = more dense, sinks

Radiation = Decay of radioactive materialsGamma rays, alpha particles, etc.

Heat Transfer cont.Heat Transfer cont. Heat is generated in the core via radiation. The heat in the core moves up through the lower

solid mantle through conduction (or direct contact.)

The upper mantle is partially molten and plastic, meaning it is able to flow. Heat moves through it by convection.

It is made of fluid rock, known as magma.

Heat Transfer cont.Heat Transfer cont. The heat from the lower mantle moves into the

upper mantle through convection.Magma is heated and becomes less dense so it rises. When it nears the crust, it cools, becomes more dense, and begins to sink.

The rising and falling current is like a conveyor belt, moving in a circular pattern forever. This current moves the plates.

Convection in the Upper Mantle (Asthenosphere):Convection in the Upper Mantle (Asthenosphere):

The AsthenosphereThe Asthenosphere The mantle is the

thickest layer of the Earth. It is mostly solid and very dense.

The mid to upper layer -- the asthenosphere -- is fluid and supports the rigid, solid layer above it.

The LithosphereThe Lithosphere The “lithosphere”

contains continental crust & oceanic crust & the rigid portion of the upper mantle

The lithosphere is the “plate” in plate tectonics

The Major PlatesThe Major Plates

Location of Earthquakes and VolcanoesLocation of Earthquakes and Volcanoes

Plate Interactions:Plate Interactions:

Types of Plate Boundaries:Types of Plate Boundaries: Divergent (tensional force = ) Transform (shearing force = ) Convergent (compressional force = )

Continental to continental collisionContinental to oceanic collisionOceanic to oceanic collision

Subduction (compressional force = )Continental to oceanic collision

Hot Spots

Divergent Plate Boundary:Divergent Plate Boundary:

Plates move away from each other.

New crust is formed at the boundary between the plates in a central rift valley --> Lava flows out and is added to both plates.

Features: mid-ocean ridge, rift, fissure, rift valley, lava flows, shallow earthquakes

Ocean Ridges & Rises:Ocean Ridges & Rises: Ridges are the longest chains of

mountains found on Earth, looking like the seams on a baseball.

A rift valley runs down the center and the ridge is offset along its length.

Lava flows out from the central fissure, adding new sea floor to the edges of the plates.

Small earthquakes are frequent along the ridge’s transform faults.

Ex. = Mid-Atlantic Ridge, East Pacific Rise, Antarctic Ridge, Mid-Indian Ridge.

Magnetic Polarity:Magnetic Polarity:

Magnetic Polarity:Magnetic Polarity:

The rocks forming along the edges of the mid-ocean ridge show a banded pattern of polarity reversals in the Earth’s magnetic field.

The rocks closets to the ridge are the youngest and the rocks farthest away are the oldest.

The age of the rocks near the coasts of N. America and Europe show that they formed 200 million years ago--just like Wegener speculated!

Divergent Boundary (cont):Divergent Boundary (cont):

Divergent boundaries form over time:Step 1. Continental Bulge -- magma pushes up.Step 2. Rift Valley -- land rifts apart and new crust is created. Ex. = East African Rift Valley.Step 3. Linear Sea -- rift valley floods with ocean water and becomes a long, thin sea. Ex. = Red Sea.Step 4. Ocean -- millions of years later, the sea widens to oceanic proportions. A mid-ocean ridge with a rift valley is found in the middle. Ex. = Atlantic Ocean.*

*When one ocean opens, another has to close!

Transform Boundary:Transform Boundary: At a transform boundary,

plates slide past each other

The San Andreas Fault is an example of a transform boundary

The North American Plate is sliding past the Pacific Plate.

Transform Boundary:Transform Boundary:

2 or more plates slide past each other slowly at a fault.

Stress builds up in the rocks over time and slippage occurs abruptly. The energy released causes an earthquake.

Features: fault, shallow hypocenter earthquakes

Ex. = San Andreas Fault, California (N. Am plate + Pacific plate)

C-C Convergent Boundary:C-C Convergent Boundary: Continental to continental

convergence creates folded, non-volcanic mountains.

A period of mountain building is called an orogeny.

The densities of the two continental plates are equal, so they bend upwards. The heat and pressure created by the slow, unstoppable plate motion folds the rock layers.

AnticlineSyncline

Non-Volcanic Mountain RangesNon-Volcanic Mountain Ranges

Mountains form when the two plates collide and get shorter and thicker. The tops are eroded by wind, water, and ice. Ex. = Appalachians, Atlas, Alps, Caucusus, Himalayas, & Urals

C-O Convergent Boundary:C-O Convergent Boundary: Continental to oceanic convergence

exhibits the collision of different types of crust. Ocean crust is most dense & sinks beneath the continental crust into the asthenosphere and melts.

Features: subduction zone, oceanic trench (deepest parts of the Earth’s surface), deep hypocenter earthquakes, volcanic coastal mountains, and volcanic island arcs.

Ex. = Andes (S. America), Cascades (N. America), Japanese Is., Philippine Is., Java & Sumatra, Caribbean Is.

C-O Convergent Boundary:C-O Convergent Boundary: Most trenches are named for the country or islands they parallel; i.e. Peru-Chile, Japan, Filipino, Java, Aleutian, Caribbean, etc.

Deep Earthquakes!

O-O Convergent BoundaryO-O Convergent Boundary Older plate subducts

beneath younger plate Very deep trench Part of subducted plate

melts and forms volcanoes on ocean floor

“Island Arcs” if volcanoes rise above ocean

Aleutian Islands, Alaska

The Rocky Mtns Are Weird:The Rocky Mtns Are Weird:

The Rockies formed when the N. American plate over-ran the Pacific Plate and the East Pacific Rise (the Kula & Farallon Plates).

The heat from the mid-ocean rift valley created a range of mountains.

Plutons (bubbles of magma) pushed up the land, then were eroded by moving ice into the jagged peaks visible today.

Hot Spots:Hot Spots: Hot Spots are volcanic

regions in the middle of plates, away from edges.

They feature single shield volcanoes (continental or island), hot springs and geysers.

They form as a column of magma punches through a plate as it passes over.

Ex. = Hawaii, Bermuda, & Yellowstone Natl. Park.

Hot Spots of the World:Hot Spots of the World:

Earth Features:Earth Features:

Plate Tectonics Cannot Yet Explain:Plate Tectonics Cannot Yet Explain:

-Tectonics of Earliest Earth -Location of Many Small Plate Fragments -Future Plate Motions -Global Pattern of Plates (Is there a geometrical

pattern?) -How and Where Plates Will Fragment -Details of Driving Mechanism