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Plate Boundary Study Tool

Joan T and Naomi K
by

Mylo Xyloto

on 15 March 2012

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Transcript of Plate Boundary Study Tool

def: a series of mountain ranges on the ocean floor
curve like the seam of a baseball along the sea floor
extended into all of Earth's oceans
Plate Boundary Study Tool Divergent Boundaries def: A plate boundary where two plates move away from each other. most occur along mid-ocean ridges, where sea-floor spreading occurs.
also occur on land, in which two of earth's plates slide apart.
rift valleys (deep valleys) form along divergent boundaries (ex: the Great Rift Valley in East Africa) Convergent Boundaries def: the place where two plates come together/converge. The result is a collision where density of the plate determines which one comes on top. Three types:
ocean-continental
continental-continental
ocean-ocean Ocean-Continental Oceanic crust is more dense than continental crust, so subduction occurs as the oceanic plate sinks beneath the continental plate. Continental-Continental Subduction does not take place since neither piece of crust is dense enough to sink very far into the mantle. Instead, the collision squeezes the crust into mighty mountain ranges. Ocean-Ocean Ocean crust becomes cooler and denser as it spreads away from the mid-ocean ridge. When two oceanic plates meet at a trench, the plate that is more dense sinks under the other plate. Transform Boundaries def: a place where two plates slip past each other, moving in opposite directions. Earthquakes often occur along transform boundaries, but crust is neither created nor destroyed. Other Definitions faults- breaks in Earth's crusts where rocks have slipped past each other

plates- seperate sections the lithosphere is broken into

scientific theory- a well-tested concept that explains a wide range of observations

plate tectonics- states that pieces of Earth's litosphere are in slow, constant motion, driven by convection currents in the mantle. Earth's Center def: the layer of rock that forms Earth's outer skin. It is a layer of solid rock that includes both dry land and the ocean floor. Oceanic crust mainly consists of basalt. Continental crust mainly consists of granite. The Crust The Mantle def: a layer of hot rock.
It is made up of rock that is very hot, but solid.
The Lithosphere- the uppermost part of the mantle, similar to the crust.
The Asthenosphere- somewhat soft, solid layer below the lithosphere.
The Lower Mantle- below the lithosphere, solid material that extends all the way to Earth's core.
The Core The core is mainly made up of the metals iron and nickel.

Outer Core- a layer of molten metal that surrounds the inner core. The outer core is liquid due to the enormous pressure.

Inner Core- a dense ball of solid material. The extreme pressure squeezes the atoms of iron & nickel so much they cannot spread out and become liquid.

Scientists think that movements in the liquid outer core create Earth's magnetic field. Plate Boundaries Volcanoes Convection Volcanic belts form along the boundaries of Earth's plates. (exp: Mt. Etna between Eurasian and African).
Diverging Boundaries- Mid-Ocean Ridges underwater, and along diverging plate boundaries on land. (exp: several large volcanoes along Great Rift Valley in East Africa)
Converging- def: a heat transfer by the movement of currents within a fluid.

Convection currents- the flow that transfers within a fluid

Heat from the core and the mantle itself causes convection currents. Joan Tao
and
Naomi Kodama Continental Drift Theory In 1910, a German scientist named Alfred Wegener hypothesized that all the continents were once joined together in a single landmass and have since drifted apart. The idea became known as continental drift.
His hypothesis was rejected because he could not identify the cause of continental drift. Pangaea def: a supercontinent that contained all the continents about 260 million years ago, and started to break apart 225 million years ago.
Evidence Land features- the mountains & other features provided evidence. For example, he noticed mountain ranges and coal fields matched up.
Fossils- he noticed that many fossils were found on seperated land masses, and animals could not have swam over.
Climate- he noticed that many of the animals found could not have survived in the current climates. Volcanoes (cont. 2- Islands) Resulting volcanoes creates a string of islands called island arc.
Curve of an island arc echoes the curve of its deep-ocean trench.
Exp: Japan, New Zealand, Indonesia, Philippines, the Aleutians, and the Caribbean Islands.
Oceanic Plate subduction- Andes Mountains, in NW US (St. Helen's) Sea Floor Spreading Mid-Ocean Ridges Sea-Floor Spreading
def: a proccess that continually adds new material to the ocean floor.
In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyer belts, carrying the continents along with them.
Sea-floor spreading begins at a mid-ocrean ridge, which forms along a crack in the oceanic crust. Molten material rises and erupts. As it cools, it forms a strip of solid rock in the center of the ridge. When more molten material flows into the crack, it forms a new strip of rock. Evidence
Volcanoes (cont.) Molten Material:
Strange rocks shaped like pillows/toothpaste were discovered. Such rocks only form when molten material hardens quickly after erupting under water.
Magnetic Stripes:
Scientists discovered that the rock that makes up the ocean floor lies in a pattern of magnetized "stripes".
Drilling Samples:
Scientists found that the farther away from a ridge the samples were taken, the older the rocks were. Subduction at Trenches Volcanoes may form when 2 oceanic plates collide or when 1 oceanic and 1 continental plate collide (convergent boundaries).
Oceanic-Oceanic
-older/denser plate sinks beneath deep-ocean trench into mantle. Some of the rock above the subducting plate melts and forms magma. B/c the magma is less dense than surrounding rock, it rises towards surface. Eventually, the magma breaks through the ocean floor, creating volcanoes.
Volcanoes may also form at divergent boundaries. Volcanoes form along mid-ocean ridges the lava eventually builds up to form new mountains. They also form on divergent land boundaries. (ex: Great Rift Valley in East Africa). Deep-Ocean Trenches
def: deep underwater canyons where the ocean floor plunges into to sink back into the mantle.
Subduction
def: the process by which ocean floor sinks beneath a deep-ocean trench and back into the mantle.
New oceanic crust is hot. But as it moves away from the mid-ocean ridge, it cools and becomes more dense. Eventually, gravity pulls this older, denser oceanic crust down beneath the trench.
Subduction & Earth's
Oceans The processes of subduction & sea-floor spreading can change the size & shape of the oceans.
The ocean floor is renewed about every 200 million years.
The Pacific Ocean is shrinking while the Atlantic Ocean is expanding. Volcanic Belts Ring of Fire
def: a major volcanic belt that formed by the many volcanoes that rim the Pacific Ocean.
Volcanic belts form along the boundaries of Earth's plates, where huge pieces of crust diverge or converge. As a result, the crust often fractures, allowing magma to reach the surface. Hot-Spot Volcanoes Some volcanoes result from "hot spots in Earth's mantle.
def: an area where material from deep within the mantle rises and then melts, forming magma.
A volcano forms above a hot spot when magma erupts through the crust and reaches the surface. A hot spot can gradually form a series of volcanic mountains. (ex: Hawaiian Islands & Yellowstone National Park in Wyoming) Volcanoes Convection Continental Drift VOLCANO VOCAB! magma chamber- a pocket magma collects in
pipe- a long tube in the ground that connects the magma chamber to Earth's surface
vent- an opening
lava flow- the area covered by lava as it pours out of a vent
crater- a bowl-shaped area that may form at the top of a volcano quiet eruptions- low silica magma, in which the gases in the magma bubble out gently.
explosive eruptions- high silica magma that builds up in the volcano's pipe, and explode.
pyroclastic flow- occurs when an explosive eruption hurls out a mixture of hot gases, ash, cinders, and bombs. calderas- a huge hole left by the collaspe of a volcanic mountain
volcanic neck- forms when magma hardens in a volcano's pipe
dike- magma that forces itself across rock layers
sill- when magma squeezes between horizontal layers of rock Types of Volcanoes batholiths- a mass of rock formed when a large body of magma cools inside the crust
hot springs- when groundwater is heated by a nearby body of magma/hot rock deep underground
geysers- a fountain of water and steam that erupts from the ground Shield Wide, gently sloping
Created Hawaiian Islands
Easy flowing, non-explosive
Basaltic lava
Lava is runny and flows over a large area Cinder Cone Steep, cone-shaped
High viscosity, ash, cinders, and bombs
Exp: Paricutín
Most explosive
Simplest type of volcano
Usually the smallest Composite Tall, come-shaped
Layers of lava alternate with layers of ash
Exp: Mount Fuji, Mount St. Helens
Both violent eruptions & lava flow
Most unpredictable
Most common
Found inland from colliding boundaries Lava Plateaus Instead of forming mountains, some eruptions of lava form high level areas
1st- Lava flows out of several long cracks in an area
2nd- Thin, runny lava travels far before cooling and solidifying
Again and again floods of lava flow on top of earlier floods
After millions of years, these layers of lava can form high plateaus
Exp: Columbia Plateau (covers part of Washington, Oregon, and Idaho.) Ocean-Continental Sea-Floor Spreading
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