1. The Earth and it’s Litosphere

2. Structure of the earth The earth has many layers: The inner core
The outer core
The mantle and
The crust
The crust is further divided into:
The continental crust which is about 35km thick and
The oceanic crust which is about 5km thick

3. The mantle is divided into two:
The Asthenosphere which is hot and weak and
The Litosphere which rigid and solid. The Litosphere is the uppermost part of the mantle and the crust.
It is the weak rock of the Asthenosphere that allows the Litosphere to move.
This movement of the Litosphere is called Plate Tectonics

4. Plate tectonics
Is a theory that land masses are not fixed but migrate slowly across the globe.
The Litosphere is broken into a dozen major segments called plates
These plates (which are rigid so each move as a distinct unit) are either:
Oceanic plates or
Continents and ocean basins
The splitting of continental blocks form:
New oceans and
Older sea floors are recycled back into the Earth’s interior
This splitting causes Earthquakes, Volcanoes and Mountains

5. 3 Types of margins or boundaries of plates
Divergent plates – move away from each other
Convergent plates – move towards each other
Transform faults – slide past each other

6. Divergent plates Have upwelling of magma to form new oceanic floors
The hot magma (molten rock) rises to the surface of the ocean floor, cools and forms part of the sea bed.

7. 3 types of Convergent plates
Oceanic and Continental plates moving towards each other – form Continental Volcanic Arc such as Mt. St. Helens in Washington. USA.
Oceanic and Oceanic plates moving towards each other – form Volcanoes on the ocean floor called Volcanic Island Arc such as Kick-em-Jenny off the coast of Grenada, Japan and in the Philippines
Continental and Continental plates moving towards each other – form mountain belts such as India and Asia moving towards each other to form the Himalayas

9. Tidal waves
Wave height depend on the wind speed, length of time the wind has blown and the distance the wind has blown across open water.
When the wave approaches shore the length of the wave decreases and the wave height increase, it becomes unstable, collapses (or breaks) and water rushes forward
Any disturbance in the water in the open ocean causes the wave length to change (increases)
So as the wave length increases in the open ocean when it reaches near the shore the height of the wave is greater than usual…tidal waves

10. Disturbances in the ocean
Volcanic Activity
Earthquakes

11. Earthquakes
As plates slide past each other (transform faults) they sometimes move back into place. The (elastic) energy released from this movement causes the litosphere to move more vigourously.
The movement of the Earth’s surface along with other objects (infrastructure) attached to it, such as buildings can collapse
It is the result of infrastructural damages that causes the death of many people

12. General Volcano structure
1. Magma chamber 2. Bedrock 3. Conduit (pipe) 4. Base 5. Sill 6. Branch pipe 7. Layers of ash emitted by the volcano 8. Flank 9. Layers of lava emitted by the volcano 10. Throat 11. Parasitic cone 12. Lava flow 13. Vent 14. Crater

13. Causes of volcanic eruptions
The buoyancy and the pressure of the gas within the earth’s crust cause the volcano to erupt. Magma is formed when the upper mantle of the earth melts. A volcano is erupted when the magma (the hot liquid) rises upwards by the pressure of gas that is dissolved in it. This is one of the three predominant theories.
According to the second theory, magma contains dissolved substances such as water, sulfur dioxide and carbon dioxide. The solubility of the gases is high as the pressure increases. The solubility of water decreases as the magma moves closer to the earth’s surface and eventually separates from the magma.When the ratio of the gases becomes more in magma it causes the magma to disintegrate into pyroclasts, a combination of partially molten and solid fragments, and the volcano erupts explosively.
The third theory says that a volcano erupts when new magma is injected into a chamber that is already brimming with magma of similar or different compositions. The eruption occurs when the magma moves upwards due to the injection of new magma.