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Earth: Our HomeFull Geography
Chapter 3: Plate Tectonics
You will learn:- to explain the formation, characteristics and distribution of landforms - to describe types of volcanoes - to explain the formation, characteristics and distribution of earthquakes
Plate Movements Compression y Process of forcing something into a smaller structure by reducing it in volume by pressing it together. Tension y A pulling force, tending to stretch, to cause an extension of a body or to restore the shape of an extended elastic object.
Landforms Fold Mountains Block Mountains Rift Valleys Volcanoes
Fold MountainsProcess: Formed via compressional forces. 2 tectonic plates collide. Rock layers buckle and fold. Result in the uplifting and compression of Earths crust.
Fold Mountains Parts of a fold:Limbs Hinge / Axis
Fold MountainsCharacteristics: AgeYoung > 100 million years, 8000 m Old > 270-400 million years, lower in height than young fold mountains. Why? - due to weathering and erosion
Fold MountainsCharacteristics Types of folds:Anticline Syncline Symmetrical Asymmetrical Overfold Recumbent Overthrust
Anticline Fold Layers of rocks pushed upwards to form an inverted-V shape.
Syncline Fold Layers of rocks pushed downwards to sink and form a V shape.
Symmetrical Fold Layers of rocks are pushed towards each other due to equal strength of compressional forces on both sides.
Types of folds Increasing strength of compressional forces applied unevenly on both sides eventually results in the following: - Symmetrical fold - Asymmetrical fold - Overfold - Recumbent fold - Overthrust fold
Where are Fold Mountains Found?
Block MountainsProcess: 3 movements Tensional Compressional Sliding
A highland formed when the crust between 2 normal faults is raised.
Tensional and Compressional Forces
When tensional forces pull two blocks apart, a normal fault is formed.
When compressional forces push two blocks together, a reverse fault is formed.
When either tensional or compressional forces cause two blocks to slide past each other, a tear fault is formed.
Block MountainsProcess: A highland formed when the crust on both sides of 2 normal faults sink due to tensional forces.
Formation of block mountains(due to tensional forces)
Tensional forces from opposite ends of the crust pull the rock within the area away from each other.
The tensional forces cause normal faults or cracks to appear.
When the crusts on either side of the normal faults move apart, they sink and leave the central block standing higher than the rest, thus forming a block mountain.
Block MountainsProcess: A highland formed when the crust between 2 reverse faults is uplifted due to compressional forces.
Formation of block mountains(due to compressional forces)
Compressional forces from opposite ends of the crust push the rock within the area towards each other.
The compressional forces cause reverse faults or cracks to appear.
When compressional forces on either side of the reverse faults push two crusts together, the central block is raised to form a block mountain.
Rift Valley A lowland formed by the sinking of crust between normal faults as a resulting of tensional forces.
Tensional forces from opposite ends of the crust pull the rocks within the area away from each other.
The tensional forced cause normal faults or cracks to appear.
As the crusts on either side of the normal faults pull apart, the crust in between sinks to form a rift valley.
Where are Block Mountains and Rift Valleys found?
Volcanoes A conical or dome-shaped landform formed by the accumulation of lava emitted onto the Earths surface.
VolcanoesProcess: Vulcanicity Plate movements along boundaries and high temperatures increase pressure in the mantle. Magma forces its way upwards through vents to the Earths crust. Magma pours onto the Earths surface as lava. Lava cools and solidifies around the vent. Lava accumulation results in the formation of a volcano.
Nature & Composition of LavaBasic Lava 1,100 1,200 C Highly fluid with low viscosity Solidifies less quickly Acid lava 800 1,000C Thick, sticky and resistant to flow; high viscosity Solidifies more quickly
Types of Volcanoes Shield volcano Acid volcano Composite volcano
Shield Volcano A gentle sloping volcano that is flat near the top. Usually formed from basic lava, low in viscosity. E.g. Mauna Loa, Hawaii
Acid Volcano A volcano formed from acid lava. Steep slopes are a result of its viscous lava which solidifies near the vent. Typified by violent eruptions:Quick solidification blocks vents and pipes. Pressure builds up in the magma chamber. Violent eruption ensues.
Composite Volcano A highly common volcano which consists of alternating layers of ash and cinder, and lava. Process: Viscous lava forces its way up the vent. Magma is pushed up via other pipes and cracks in the Earths surface. Quick solidification of lava results in the escape of magma and gas. Results in mounting pressure in magma chamber. Violent eruption ensues.
Composite Volcano Appearance: Steeper at the top, with a gentler base. Why? Violent eruption of ash and cinder is followed by lava. Wind sorting of volcanic material by size accounts for appearance. Smaller particles are blown further away from the crater. E.g.Mt.Vesuvius, Italy
Where are Volcanoes Found?
Earthquakes A vibration or tremor of the Earths surface caused by the sudden release of energy stored in the crust.
1. As tectonic plates move, they exert friction on one another, causing pressure to build at their boundaries.
Tectonic plates exert friction on one another 2. Pressure gradually builds up in the plates and energy is stored up in the Earths crust.
Shock waves radiate
Pressure builds up as the plates push against one another
3. When the rocks can no longer contain the pressure, energy is released. This energy radiates out in shock waves through the crust and onto the Earths Pressure is released in an earthquake surface. Large faults will also occur as the rocks break up and move in a series of sudden jerks.
EarthquakesEnergy of earthquake dependent on: Focus point of release of energy within the Earths crust. Epicentre point on the Earths surface that lies directly above the focus. Energy released as shockwaves.
Shock waves Fault
Focus (point of origin)
EarthquakesWhat determines the strength of an earthquake? Shallow focus leads to a stronger earthquake as vibrations are felt more strongly. Shock waves of energy are felt more strongly at the epicentre.
Where are Earthquakes Found?
Just a thought Why are shockwaves felt more strongly near the epicentre and not the focus?