Geography Notes 1

Sunday, November 4, 2018
- What are natural hazards?
Hazards are events that threaten us or cause loss of human life and property, natural hazards
are hazards caused by the nature.
Tectonic Hazards
Earthquakes, Volcanic Eruptions, Tsunamis
Climatic Hazards
Flooding, Drought, Typhoons
Geological Hazards
Landslides, Avalanches
Biological Hazards
Pest (Locus), Disease or Bacteria
- What are tectonic hazards?
Sunday, November 4, 2018
Sunday, November 4, 2018
B. Earthquakes
The hazard consists of sudden shaking of the land which is caused by sudden release of
energy stored in the rocks beneath the earth’s surface. Earthquakes are measured by the
Richter scale. which is recorded by a seismograph.
Some Examples of Earthquakes:
Sunday, November 4, 2018
C. Volcanic Eruptions
The hazard occurs when lava, hot rocks debris, ashes and gases are ejected or emitted from
an opening in the earth’s surface.
Some Examples of Volcanic Eruptions:
C. Tsunamis
The hazard is caused by a series of big sea waves, traveling in all directions. When tsunamis
reach the shallow seas at the coast, they slow down and can tower up to over 30 meters
Some Examples of Tsunamis:
- Why should we be concerned about Tectonic Hazards?
Sunday, November 4, 2018
- What is the structure of the Earth?
The Earth is divided into three
layers, the crust, the mantle and
the core. The three layers have
different temperature, density,
thickness and composition.
(6 -70km)
(2900 km)
(3470 km)
Average Density
Less Dense
(2.7 g/cm )
(3.3 g/cm )
(11 g/cm )
(Around 22°C)
Mainly Silica
Iron and Magnesium
Iron and Nickel
In Conclusion, thickness, average density and temperature of the Earth’s layers increase from
the exterior to the interior. The more the centre of the Earth, the thicker, hotter and denser of
the layer is.
Sunday, November 4, 2018
The Structure of the Earth can be further divided into….
1. Crust
Continental Crust
- Makes up the continent and the continent shelves.
- Thick and Light
Oceanic Crust
- Found under the Oceans
- Thin and Dense
2. Mantle
Uppermost part of the mantle
- Exists in solid state
- Together with the crust, they are collectively known as the asthenosphere.
- The rocks in this layer are in plastic state.
Lower Mantle
- Exists in a solid state under high pressure.
3. Core
Outer Core
- It is very hot
- The material is in liquid form
Inner Core
- It is under the greatest pressure
- The material is in solid form
Sunday, November 4, 2018
- What are plates?
Plates are the broken pieces of the lithosphere and they can be also called as tectonic plates.
They vary in shape
Thickness and sizes
They have different thickness and sizes
The Direction of Movement
They move in different directions
The Kind of Crust they carry
Some carry both oceanic and continent crust.
Some carries oceanic crust only.
- Why do plates move?
Ridge Push (1)
1.The intense heat in the Earth’s core
causes some rocks to melt. This
molten rock is called the magma.
2. It rises towards the Earth’s surface.
3. When the rising magma reaches
the lithosphere, it creates a fissure.
4. The upwelling hot magma will fill the
fissure and form new crustal materials.
5. These materials are hot and have low densities. They rise above the existing crust, forming
an up-swelling ridge.
6. When the materials are cool off, it solidifies and becomes a new part of the oceanic
7. As the new lithosphere cools off, its density increases and slides down from the two sides
of the ridge
8. This action pushes the rest of the plates away, calling the ridge push.
Sunday, November 4, 2018
Slab Pull (2)
1. As the newly formed part of the oceanic
lithosphere continues to move away from the
ridge, it merges with some of the rock materials
in the asthenosphere and gets thicker.
2. After millions of years, they become a heavy,
dense slab plate.
3. When this plate collides with other plates, it
sinks into the asthenosphere as it is heavier.
4.This creates a suction force that pulls the rest
of the plate behind it, called the slab pull.
- What types of plate boundaries are there?
Convergent, Divergent and Transform.
Type of Plate Boundary
Divergent Plate
Convergent Plate
Transform Plate
Movement of Plates
Plates divergent or
move apart
Plates converge or
move towards each
Slides past each other
Effects on the
New Crustal Materials
are formed
The denser plate sinks
into the asthenosphere.
No crustal materials is
formed or subducts.
Sunday, November 4, 2018
Distribution of Plate Boundaries
- Three types of internal forces
Three Types of Forces: Compressional Force, Tensional Force, Shearing Force
Types of internal processes in compressional force: Folding, Faulting, Volcanism
Types of internal processes in tensional force : Faulting, Volcanism
Types of internal processes in shearing force: Faulting
These forces give rise to three internal processes: Folding, Faulting and Volcanism.
Sunday, November 4, 2018
- What is Folding?
Folding is the process by rock layers which are folded up under compressional force.
Landforms/features formed by folding: Fold and Fold Mountains, for example: The Himalayas,
The Alps, The Rockies, The Andes.
- What is Faulting?
Faulting is the process where rocks are broken and displaced relative to each other. During
the process of faulting, rocks are displaced along cracks and fractures. These cracks and
fractures along which rocks move are called faults.
Under Tensional Force, the rock block on the right moves down. The fault formed is called
the Normal Fault.
Under Compressional Force, the rock block on the right slides past each other. The fault
formed is called the Reverse Fault.
Under Shearing force, the rock block on the right slides past each other. The fault formed is
called the Strike-Slip Fault.
Sunday, November 4, 2018
Landforms/Features formed by faulting:
Block Mountains (Horst) : The upthrown block of land formed between two faults. It has a flattopped highland surrounded by steep fault scraps on two sides.
Rift Valleys (Grabens) : A downthrown block bounded by two faults. It has a flat-bottomed
valley with a steep fault scrap on each side.
What is volcanism?
Volcanism refers to all the process related to the occurrence and movement of magma.
Magma escapes from the magma chamber and reaches the earth’s surface, then magma
becomes lava. The above process is called extrusive volcanism. After that, magma cools and
solidifies before reaching the Earth’s surface, and this process is called intrusive volcanism.
Landforms/ Features formed by volcanism:
Sunday, November 4, 2018
- The major landforms found at divergent plate boundaries?
At divergent plate boundaries, Ridge Push, Tensional Force, Faulting and Volcanism is
In divergent plate boundaries, mid-oceanic ridge, rift valleys and transform fault are
also found.
1. Along the divergent plate boundaries, the South American Plate and the African
Plate split from each other and a fissure is created.
2. Hot magma rises through the lithosphere and fills the fissure. The hot lava cools and
solidifies. This creates new crustal materials.
3. Newly formed crustal materials are hot and have a low density. They rise above the
existing crust and form a mid-oceanic ridge on the seabed.
4. Ridge push causes the plates to move apart. Under Tensional force, normal
faults occurs.
5. As plates keeps on moving apart, the central block of the ridge sinks to form a ridge
6. On the other hand, the mid-oceanic ridge is not a continuous ridge, but is broken into
lots of many small segments. Each segment is connected by a fault, called a
transform fault.
In divergent plate boundaries, submarine volcanoes and volcanic islands are also
1. Cracks form in the plates under tensional force.
2. When magma rises through these cracks, volcanism occurs.
Sunday, November 4, 2018
3. Active submarine volcanoes form.
4. Repeated eruptions raise the height of the submarine volcanoes.
5. When they rise above the sea level, volcanic islands are formed.
- The major landforms found at convergent plate boundaries?
At convergent plate boundaries, slab pull, shearing force and faulting is found.
1. Ocean-Continent Collision
When the Nazca Plate and the South American Plate collide, the denser Nazca Plate
subducts under the South American Plate.
This produces a deep and elongated trough called an ocean-trench (v-shaped), which is
Peru-Chile Trench.
III. At the same time, sediment from the South American landmass is washed down
deposited in the coastal water. Later, the layers of sediments are subjected into
sedimentary rocks.
IV. When the two platers collide, the sedimentary rock is folded up under compressional
force. Fold Mountain, which is the Andes is formed.
V. During Subduction, water is released from the subjected plate and it causes the
asthenosphere to melt as a lower temperature, this forms magma. ( Heat and Water form
VI. At the same time, folding and subduction caused by compressional force produces
cracks in the rocks.
VII. When magma rises through cracks, volcanic eruption occurs, this forms volcanoes as
Mount Chimborazo on the mountain belt.
Sunday, November 4, 2018
2. Ocean-Ocean Continent.
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