12.2 features of plate tectonics - mrvscienceandmath.com · 12.2 features of plate tectonics the...
TRANSCRIPT
12.2 Features of Plate Tectonics
The Crust
The Mantle
Outer Core
Inner Core
VOCABULARY
Word to Know
epicentre
mantle convection
asthenosphere
lithosphere
plate boundary
ridge push and slab pull
subduction zone
volcanic belt
rift valley
What lies below Earth’s surface?
• Earth is made of four layers with distinct characteristics
What lies below Earth’s surface?
• Earth is made of four layers with distinct characteristics
CRUST
• Is Earth’s outermost layer made from solid, brittle rock and is 5–70
km thick.
CRUST
• CONTINENTAL CRUST – made from a lighter type of rock
called granite (can be 70 km thick)
CRUST
• OCEANIC CRUST – made from a dense, dark rock called basalt
(can be 10 km thick)
MANTLE
• Earth’s thickest layer (≈ 3000 km)
MANTLE
• Earth’s thickest layer (≈ 3000 km)
• Mostly solid, but a portion of the upper part is molten
MANTLE
• The upper mantle (660 km thick) is composed of partly molten rock
containing iron, magnesium, and radioactive elements
MANTLE
• Transition zone separates it from the lower mantle
MANTLE
• The lower mantle is made of solid, dense material that contains the
elements magnesium and iron
MANTLE
• The lower mantle is made of solid, dense material that contains the
elements magnesium and iron
OUTER CORE
• The layer below the mantle the outer core is liquid
• It is about 2300 km thick and is composed mainly of a mixture of
iron and nickel.
INNER CORE
• with a radius of 1200 km lies at Earth’s centre
• Composed of solid iron and nickel
• large, rigid, but mobile plates of rock
• Made up of the crust and upper portion of the upper mantle, they
form the lithosphere
• Lithosphere floats on the asthenosphere.
• The asthenosphere is a partly molten layer in the upper mantle.
• The asthenosphere is a partly molten layer in the upper mantle.
• Asthenosphere is kept molten by radioactive decay of radioactive
elements
• This molten mantle is moved by convection currents = mantle
convection
• The mantle convection is one of the driving forces behind plate
movement.
More about SPREADING RIDGES
• Magma (melted rock) rises to the Earth’s surface
• It cools down and hardens when it breaks through Earth’s surface
forming new sea floor = SPREADING RIDGE
More about SPREADING RIDGES
SPREADING RIDGE
(or OCEANIC RIDGE)
RIFT VALLEY
RIDGE PUSH
• The magma cools when it reaches the surface, solidifies, and is
pushed aside as new magma pushes from below
• As new material at a ridge or rift pushes older material aside, the
tectonic plates move away from the ridge
• This is called ridge push
SUBDUCTION
• when tectonic plates are pushed apart, eventually one or both will
bump into another plate
• If a dense oceanic plate collides with a continental plate, the heavy
oceanic plate will dive deep under the lighter continental plate
SUBDUCTION
• Subduction is the action of one plate pushing below another
• As the plate pushing below, the rest of the plate follows = slab pull
SUBDUCTION ZONES
• Theses areas of subduction, called subduction zones, typically
experience large earthquakes and volcanic eruptions
A PLATE BOUNDARY
• A region where two tectonic plates are in contact
• The way the plates interact is based on the type of plate and the
direction the plates are moving relative to each other
spreading apart colliding sliding by
More about SPREADING RIDGES
SPREADING RIDGE
(or OCEANIC RIDGE)
RIFT VALLEY
DIVERGENT PLATE BOUNDARIES
• mark the areas where tectonic plates are spreading apart (i.e.
RIDGE PUSH occurs)
DIVERGENT PLATE BOUNDARIES
• Examples: The Mid – Atlantic Ridge (in the ocean) and the East
African Rift (on the land)
DIVERGENT PLATE BOUNDARIES
• Divergent Plate Boundaries are areas where SPRADING RIDGES
and RIFT VALLEYS are formed
A PLATE BOUNDARY
• A region where two tectonic plates are in contact
• The way the plates interact is based on the type of plate and the
direction the plates are moving relative to each other
spreading apart colliding sliding by
CONVERGENT PLATE BOUNDARIES
• mark the areas where tectonic plates collide (i.e. SUBDUCTION
may occur)
• Because there are 2 types of tectonic plates (Oceanic and
Continental) 3 different interactions are possible
OCEANIC – CONTINENTAL PLATE CONVERGENCE
• EXAMPLE: the Juan de Fuca Plate (an oceanic plate) and the North
American Plate (a continental plate).
OCEANIC – CONTINENTAL PLATE CONVERGENCE
• When the oceanic plate subducts under the continental plate, a deep
underwater valley called a trench forms
OCEANIC – CONTINENTAL PLATE CONVERGENCE
• When the oceanic plate subducts under the continental plate, a deep
underwater valley called a trench forms
OCEANIC – CONTINENTAL PLATE CONVERGENCE
• As subduction (and slab pull) occurs, magma can break through to
the surface, forming volcanoes
• A volcanic belt: a long chain of cone – shaped volcanoes may form
as a result
OCEANIC – CONTINENTAL PLATE CONVERGENCE
• Mountain ranges like the Coast Mountain range and Cascade
Mountain Range also form from the collision
OCEANIC – CONTINENTAL PLATE CONVERGENCE
• Many times, colliding plates resist the force of convection currents,
ridge push, and slab pull the plates get stuck in place and energy
in released in the form of an earthquake
• Most of the largest earthquakes are produced this way
OCEANIC – OCEANIC PLATE CONVERGENCE
• EXAMPLE: Aleutian Islands of Alaska and the islands of Japan and
Indonesia
• When the oceanic plate subducts under another oceanic plate
• Cooling will cause one plate to be denser than the other, and the
denser plate will slide deep into the mantle.
• A long chain of volcanic islands known as a volcanic island arc may
be produced
OCEANIC – OCEANIC PLATE CONVERGENCE
CONTINENTAL – CONTINENTAL PLATE CONVERGENCE
• EXAMPLE: the Himalayas
• When two continental plates collide
• NO SUBDUCTION - Since their densities are similar
A PLATE BOUNDARY
• A region where two tectonic plates are in contact
• The way the plates interact is based on the type of plate and the
direction the plates are moving relative to each other
spreading apart colliding sliding by
TRANSFORM PLATE BOUNDRIES
• EXAMPLE: The San Andreas Fault
• Convection currents in the mantle often cause tectonic plates to slide
past each other
• Usually are found near ocean ridges
TRANSFORM PLATE BOUNDRIES
• Since rock slides past rock, no mountains or volcanoes form
• However, earthquakes and faults (breaks in rock layers due to
movement on either side) may result
HOW ARE TECTONIC PLATES LINKED TO
EARTHQUAKES?
• a massive release of energy build up by stress of friction bewteen
tectonic plates that shakes the crust
• the location inside Earth where an earthquake starts is called the
focus
HOW ARE TECTONIC PLATES LINKED TO
EARTHQUAKES?
• The epicentre is the point on Earth’s surface directly above the focus
HOW ARE TECTONIC PLATES LINKED TO
EARTHQUAKES?
• Energy released by an earthquake produces vibrations known as
seismic waves
• There are 3 types of waves that are created during an earthquake and
each of them have different properties
MEASURING EARTHQUAKES
VOLCANOES
• The movement of tectonic plates produces three distinct types of
volcanoes: composite volcanoes, shield volcanoes, and rift eruptions
Very explosive or violent
NOT Very explosive or violent
NOT Very explosive or violent
COMPOSITE VOLCANOES
• found along plate boundaries
• Layers of ash and thick lava form a tall cone.
• As magma reaches the surface, it cools, hardens, and traps gases
below.
• Pressure builds; eventually, there is an eruption.
SHIELD VOLCANOES
• these are not found at plate boundaries but instead form over hot
spots.
• Thin magma/lava flows out from a hot spot and forms a low, wide
cone.
• The Hawaiian Islands are an example of a chain of shield volcanoes.
RIFT ERUPTIONS
• occur along long cracks in the lithosphere
• These are not explosive, but they release massive amounts of lava