Plate Tectonics Flashcards
Main Topics
- Internal Structure of the Earth
- Continental Drift Theory
- Theory of Plate Tectonics & Types of Plate Movement - Convergent, Divergent, Transform
- Volcanoes - Formation, Types, Impacts, Mitigation
Internal Structure of the Earth
Layers of the Earth
4
Layer
Est. Temperature
Depth / Thickness
Material
Crust
* Temperature dependent on weather & climate of the atmosphere above it
* About 70km thick
* Solid rocks & soil forming landforms
Mantle
* 800 - 3000 °C
* About 2900km thick
* Semi-molten rock called Magma
Outer Core
* 5000 °C
* About 2200km thick
* Liquid Iron
* Nickel
Inner Core
* 6000 °C
* About 1250km thick
* Solid Iron Sphere
* Radioactive Materials (e.g. Uranium)
Internal Structure of the Earth
Layers of the Earth
Crust
Est. Temperature
Depth / Thickness
Material
Crust
* Temperature dependent on weather & climate of the atmosphere above it
* About 70km thick
* Solid rocks & soil forming landforms
Internal Structure of the Earth
Layers of the Earth
Mantle
Est. Temperature
Depth / Thickness
Material
Mantle
* 800 - 3000 °C
* About 2900km thick
* Semi-molten rock called Magma
Internal Structure of the Earth
Layers of the Earth
Outer Core
Est. Temperature
Depth / Thickness
Material
Outer Core
* 5000 °C
* About 2200km thick
* Liquid Iron
* Nickel
Internal Structure of the Earth
Layers of the Earth
Inner Core
Est. Temperature
Depth / Thickness
Material
Inner Core
* 6000 °C
* About 1250km thick
* Solid Iron Sphere
* Radioactive Materials (e.g. Uranium)
The Earth’s crust & Lithosphere (5-7pts)
- The crust, which is the most outermost layer of the earth, is broken into tectonic plates that move in relation to one another.
- These tectonic plates are part of the Lithosphere, which includes the crust and the uppermost mantle.
- Tectonic plates can be made up of either oceanic crust, continental crust or a combination of both.
- Oceanic crust is found beneath deep oceans and are denser than continental crust, which are located beneath the earth’s continental land masses and under the shallow seas close to continents.
- Oceanic crusts are denser than continental crust as they consist mainly of basalt, a heavy and dense rock formed from magma which has cooled quickly.
- Continental crust consists of lighter rocks, including granite, which age range widely from very recently formed to nearly 4 billion years old.
- The asthenosphere is the denser, weaker layer beneath the lithospheric mantle.
Plate Tectonics Theory
2pt
Plate Tectonics Theory
* The Plate Tectonics theory states that the Earth is in constant motion.
* Convection currents in the mantle drives the movement of plates.
* Plate movements creates major landscape and landforms such as volcanoes, fold mountains and many more.
* Plate movements also cause earthquakes.
Movement of Tectonic Plates
2pt
- The movement of the earth’s crustal plates is believed to be due to convection currents which occur in the mantle.
- Convection currents are created by heat from the earth’s core - much of which is generated by radioactive decay in the core.
Movement of Tectonic Plates
How & Why Plates Move:
8 steps
- When radioactive materials break down in the core, heat is released.
- Convection currents are movements of heat within the mantle. Material in the mantle is heated by the core, causing the mantle material to expand, rise and spread out beneath the plates.
- This causes the plates to be dragged along and to move away from each other.
- Then, the hot mantle material cools slightly and sinks, pulling the plates along.
- The sinking mantle material heats up again as it nears the core - the whole process repeats.
- Slab-pull force occurs when a denser oceanic plate is forced beneath a less dense continental plate or oceanic plate in a process called subduction. This is thought to be the main driving mechanism for plate movement.
- As the plate subducts, it pulls the rest of the plate along. The subducting or sinking plate drives the downward moving portion of convection currents.
- The mantle material which is found away from where the plates subduct drives the rising portion of convection currents.
Movement of Tectonic Plates
What is slab-pull force?
- Slab-pull force is a geophysical mechanism whereby the cooling and subsequent densifying of a subducting tectonic plate produces a downward force along the rest of the plate. The denser plate sinks back into the mantle and pulls the rest of the plate along.
Distribution of Volcanoes, oceanic trenches and earthquakes (read through ig)
- Volcanoes (red) are found along the plate boundaries.
- Some volcanoes can be located in the middle of the plate, away from the boundaries (e.g. Hawaiian Islands)
- Oceanic trenches (yellow) are also found along the plate boundaries and near the volcanoes.
- They are also found in the Pacific Ring of Fire, along the boundary of the Pacific Plate, Indo-Australian Plate, the Philippine Plate and the Nazca Plate.
- Ocean trenches are long, narrow depressions on the seafloor. These chasms are the deepest parts of the ocean—and some of the deepest natural spots on Earth.
- Volcanoes, oceanic trenches and earthquakes are found along plate boundaries, such as at the Pacific Ring of Fire.
- Volcanoes and earthquakes can occur at locations in the middle of the plate (but not oceanic trenches).
- Plate movements that take place along these boundaries cause the formation of volcanoes and oceanic trenches, and the occurrence of earthquakes.
- There are different types of plate movements responsible for the formation of the different features.
Types of Plate Movement
3 types, 3 1 1
Types of Plate Movement
1. Convergent Plate Movement (Destructive Plate Boundary)
i. Continental – Continental Convergence (C-C Convergence)
ii. Oceanic – Oceanic Convergence (O-O Convergence)
iii. Oceanic-Continental Convergence (O-C Convergence)
- Divergent Plate Movement (Constructive Plate Boundary)
i. Oceanic - Oceanic Divergence (O-O Divergence) - Transform Plate Movement (Conservative Plate Boundary)
i. 2 plates sliding past each other
- Convergent Plate Movement
how many?
- Convergent Plate Movement
* Convergent Plate Movement (Destructive Plate Boundary) - Continental – Continental Convergence (C-C Convergence)
- Oceanic – Oceanic Convergence (O-O Convergence)
- Oceanic-Continental Convergence (O-C Convergence)
- Continental = form fold mountains, Oceanic = form volcanoes
Continental-Continental Convergence (C-C Convergence) (6pt)
- Continental-continental convergent boundaries pit large slabs of crust against each other.
- Due to lower density, both of the continental crustal plates are too light and buoyant to be subducted.
- In most cases, neither plate subducts.
- Instead, the continental crust at these convergent boundaries gets folded, faulted, and thickened, forming great mountain chains of uplifted rock. (fold mountains)
- Little volcanic activity occurs because rocks from the crust do not sink deep into the mantle.
- Earthquakes, faulting & folding are common.
- The Himalayas and the Tibetan Plateau, the result of 50 million years of collision between the Indian and Eurasian plates, are the most spectacular manifestation of this type of boundary.
Oceanic-Oceanic Convergence (O-O Convergence) (4pt)
Oceanic-Oceanic Convergence (O-O Convergence)
* Tip of the subducting oceanic plate melts due to friction with the overriding oceanic plate, and heat at great depth, producing silica-rich magma (silicon dioxide)
* Magma moves up any breaks or fractures on the overriding oceanic plate to form a magma chamber, as it is less dense than the asthenosphere and as gases in the magma expands.
* The built-up of pressure in the magma chamber forces magma to escape through the vents on the oceanic crust as lava. Lava cools and solidifies around the vent. Overtime, through repeated eruptions, it accumulates/builds up to form a submarine volcano at or near the subduction zone.
* When the volcano builds up and rise above sea level, it forms a volcanic island or a chain of volcanoes known as a volcanic island arc.
Oceanic-Continental Convergence (O-c Convergence) (7pt)
- When a thinner and denser oceanic plate converges with a thicker and lighter continental plate, the oceanic plate descends beneath the latter due to ‘slab-pull’ force into the asthenosphere.
- A long, narrow and deep oceanic trench is formed where the oceanic plate dips into the asthenosphere.
- The movement of the subducting plate is not smooth, producing vibrations called earthquakes along the subduction zone.
- Tip of the subducting oceanic plate melts due to friction with the overriding continental plate, and heat at great depth, producing silica-rich magma.
- Magma moves up any breaks or fractures on the overriding continental plate to form a magma chamber, as it is less dense than the asthenosphere and as gases in the magma expands.
- The built-up of pressure in the magma chamber forces magma to escape through the vent on the land surface as lava. Lava cools and solidifies around the vent. Overtime, through repeated eruptions, it accumulates/builds up to form a volcano.
- Edges of continental plate, and sediments near the edges of continental shelf and on the seafloor are contorted and folded to form fold mountains.
- Divergent Plate Movement
how many?
- Divergent Plate Movement
* Divergent Plate Movement (Constructive Plate Boundary) - Oceanic - Oceanic Divergence (O-O Divergence)
Oceanic-Oceanic Divergence (O-O Divergence) (5pt 2 subpt)
- When two oceanic plates move away from each other, the rising convection current below lifts the lithosphere producing a mid-ocean ridge, rows of submarine mountains.
- The ridge is a high area compared to the surrounding seafloor because of the lift from the convection current below.
- Tensional forces stretch the lithosphere and produce a deep fissure forming the spreading centre.
- A fissure is a long, narrow crack opening along the surface of Earth.
- When the fissure opens, pressure is reduced on the super-heated mantle material below. It responds by melting and the new basaltic magma flows into the fissure. The magma then cools and solidifies to form new seafloor. This process is called seafloor spreading.
- Being less dense than the surrounding older rocks, the new sea floor rises in elevation, resulting in gravitational sliding that pushes the older rocks away from the spreading center. This is known as the ‘ridge push’ force.
- Shallow earthquakes are often associated with this crustal stretching. Basaltic magma from the asthenosphere wells up along any crustal fractures to form submarine/undersea volcanoes. Some of these volcanoes rise above sea level to form volcanic islands.
- Transform Plate Movement
how many?
- Transform Plate Movement
* Transform Plate Movement (Conservative Plate Boundary) - 2 plates sliding past each other
- Transform Plate Movement (Conservative Plate Boundary)
1. 2 plates sliding past each other
2 plates sliding past one another at conservative plate boundary
* They occur when 2 plates slide past each other.
* Great amount of stress built up in these areas, but there is little volcanic activity & little crustal material is destroyed
- Eg : the San Andreas Fault in California, USA
* Plates slide past each other along transform faults (could be opposite directions / same direction but one moving faster than the other)
* Causes fault line & earthquakes
Volcanoes (3pt)
- A volcanic cone is a triangle-shaped hill formed as material from volcanic eruptions piles up around the volcanic vent, or opening in Earth’s crust.
- A landform produced by magma merging via an opening in the crust is lava flow
- Lava cools and solidifies to form a layer of volcanic material
- With each eruption, layer upon layer of cooled rock built up to form a volcano.
Craters & Calderas (5pt)
- Craters are formed by the outward explosion of rocks and other materials from a volcano.
- Calderas are formed by the inward collapse of a volcano.
- Craters are usually more circular than calderas. (Calderas may have parts of their sides missing because land collapses unevenly.)
- Craters are also usually much smaller than calderas, only extending to a maximum of one kilometer (less than a mile) in diameter
- Crater or caldera eventually filled with water → crater lake
Diff. b/w craters and calderas? (2)
- Craters are usually more circular than calderas. (Calderas may have parts of their sides missing because land collapses unevenly.)
- Craters are also usually much smaller than calderas, only extending to a maximum of one kilometer (less than a mile) in diameter
how is a crater formed
Craters are formed by the outward explosion of rocks and other materials from a volcano.
how is a caldera formed
- Calderas are formed by the inward collapse of a volcano.
