Post on 22-Dec-2015
transcript
Plate Tectonics
Earth’s Interior
Earth is made of layersCrustUpper Mantle (asthenosphere)MantleOuter CoreInner Core
Scientists discovered theselayers using seismic waves from Earthquakes.
Lithosphere- Crust
Lithosphere is the outermost layer of the Earth
The Lithosphere (crust) is broken into sections called Tectonic Plates, these are sections (plates) of lithosphere that move around on the upper mantle (asthenosphere)
Types of Crust:1. Oceanic Crust- Basaltic Materials, Heavy and Dense2. Continental Crust- Granitic Materials, light and less
dense than oceanic crust
The thickness of the crust ranges from 5-60km thick depending on what type of crust. http://www.youtube.com/watch?NR=1&feature=fvwp&v=uGcDed4xVD4
Mantle and Asthenosphere
Has an upper layer called the Asthenosphere which is responsible for the movement of plates
Composed of mostly silicon, oxygen, magnesium and iron
Texture is plastic like which has the characteristic of a solid but flows like a liquid when under pressure
Approx 2885 km thickHas large convection currentsthat drive the movement of the plates
Inner and Outer Core
Outer Core:Liquid rock composed of Iron, Sulfur and
NickelApprox 2270 km thick
Inner Core:Solid dense rock composed of Iron and NickelPressure from the upper layers cause it to be
solid
Types of Plate Boundaries
1. Divergent- new crust is generated and the plates pull AWAY from each other
2. Convergent- Crust is being destroyed or uplifted and the plates move TOWARDS each other
3. Transform- where crust is neither created or destroyed and the plates that slide horizontally past each other
Divergent Boundaries
There are two types of Divergent Boundaries where the crustal plates are pulling away from each other
1. Oceanic-Oceanic- Mid Ocean Ridgeso This is responsible for Sea floor spreading
where new crust is being made as magma rises and cools in the mid ocean ridges
Divergent Boundaries Continued
2. Continental- Continental Divergent When a divergent boundary cuts through a piece of
land, the feature called a Rift Valley is formed. Example is Iceland where the North American and
Eurasian Plates are pulling apart and the African Rift Valley
Volcanoes are created in Rift Valleys as magma plumes up from the separation of the plates
http://www.youtube.com/watch?v=w7Y2R4KBwvo
Iceland
Convergent Boundaries
Convergent Boundaries-Two plates move toward each other pushing
together
Subduction Zone- zone where one plate subsides (goes underneath) another plate Responsible for active volcanism and deep subduction
earthquakes
There are 3 types of Convergent plate boundaries1. Oceanic-Continental convergence- subduction2. Oceanic-Oceanic convergence- subduction3. Continental-Continental convergence- minimal or
ancient subduction and uplifting of large mountains
Oceanic to Continental Convergence
When an oceanic plate collides with a continental plate, there is a Subduction Zone A volcanic arc is created inland 100-300km from the
coast Trenches are formed off the coast of a subduction
zone Oceanic Crust subducts under continental crust
because it is more dense http://www.youtube.com/watch?v=NbDqJy28hBw
Oceanic-Oceanic Convergence
When two oceanic plates converge there is a battle between basaltic crusts until one subducts Volcanic Island arcs are created 100-300km away
from the plate boundary – Example: Japan, Aleutian Islands
Trenches are created off the plate boundaryCleveland Volcano Aleutian Islands, Alaska
Continental-Continental Convergence
When two continental plates collide both are very buoyant and want to stay above each other. They battle towards each other but neither one subducts under the other Builds large mountain
chains with very tall mountains
No volcanoes because there is not any
subduction causing melting of the plates and rising magma
INDIA ASIA
INDIA ASIA
The ancient Himalayas were
volcanoes because as India was pushing
towards Asia, there was an ocean
between them. This caused a subduction
of ocean crust resulting in volcanoes.
Transform Boundary
Transform boundaries are where two plates slide past each other Usually a part of a system of
divergent or convergent boundaries
Example is the San Andreas Fault in California
Responsible for frequent shallow earthquakes
Hot Spots
There are several other volcanoes that are not created near a plate boundary but instead in the middle of a plate
They are created when a mantle plume is super heated by the core and burns through the crust building a volcano
In the case of an oceanic hotspot, the plate continues to move and the volcano moves off the hotspot, and becomes inactive and just an island. A new volcano will begin to form on the ocean floor and as it peaks above the ocean surface it will become the new active volcanic island in the chain
In the case of a continental hotspot, the caldera moves off the hotspot and when there is a new volcanic explosion, a new caldera forms in the chain
Examples of Hot Spots
1. Hawaiian Islands- The active and newest island is the big island of Hawaii, and the oldest inactive island is Kauai. Since the inactive volcanoes are no longer adding to the size of the island, the island will erode away over millions of years until it becomes a seamount where is no longer above the ocean surface.
2. Yellowstone- this is in the middle of a continent causing large scale eruptions that form calderas or collapsed volcanoes. The continental crust is too thick to produce tall standing volcanoes from a hotspot.
Pangaea
Present