Summary Notes
What are tectonic or lithospheric plates?
The upper part of the earth or lithosphere is broken into the number of plates known as lithospheric plates; these plates move very slowly in a particular direction.
These plates move because of molten magma inside the earth move in a circular manner, it is also called convection cell.
As a result, the movement of these plates causes changes on the earth's surface.
For example, fold mountains are created in the boundary of two convergence plates.
There are two forces work on the earth.
- Endogenetic forces
- Exogenetic forces
Landform development is the result of endogenetic and exogenetic force.
What is Endogenetic force?
Endogenetic force comes from inside earth and it is a constructive force. Temperature and density variations inside the earth are the main drivers of the endogenetic force. Vertical and horizontal movement happen due to endogenetic force. Mountain building process happens due to vertical movement of the earth and fault happen due to horizontal movement of the earth.
The following types of endogenetic force are:
Sudden Movement:
As the name suggests, the sudden movement caused rapid events and happens more quickly and can be seen within the second. Examples
Earthquake:
When the lithospheric plates move, the surface of the earth vibrates. This vibration can be travel around the earth, this vibration is called an earthquake.
Focus: The place in the crust where the movement starts or cracks happen; this point is called the focus of the earthquake.
Epicenter: The place on the surface above the focus is called the epicenter.
Greatest damage usually happens closest to the epicenter and strength of earthquake decrease away from the epicenter.
The earthquake can not be predicted, but the impact can be minimized through strong resilient infrastructure.
Common earthquake prediction:
- Studying animal behaviors
- Fish in the ponds get agitated
- Snakes come out to the surface
Earthquake preparation:
- Preventive measure:
- Should have strong resilience infrastructure
- During earthquakes:
- Stay in safe spots such as under kitchen counter, tables or desk.
- Stay away from fireplaces, mirror areas around chimney, electric poles, etc
Due to Earthquake lake formation, fracture, rupture, fault, etc, may be seen.
Volcanos
It is the vent(opening) in the earth's crust through which molten materials erupt suddenly and release a large amount of dust, gases, and molten lava. The following minor landform may be formed by volcanos:
- Volcanic mountain
- Volcanic cones
- caldera
- lava dome
- Volcanic Plug
These are continent building forces and act from the center of the earth to the earth's surface. It acts very slowly, generally can not be observed in normal human life. Two types of movements:
- Upward movement: Large scale upliftment of masses.
- Downward Movement: Submergence of land areas.
Orogenetic Movement:
This force is also called as mountain building forces. Based on the direction of the force, it can be classified into two parts.
- Tensional force: Due to divergent force, it caused cracking and faulting on the earth's surface.
- Compression force: Due to the convergence nature of force, it causes folding in the earth's crust.
What is Exogenetic Force?
Exogenetic forces are destructive forces that come from the outside earth, the primary source of exogenetic force is Sun.
The following types of Exogenetic forces are:
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| Exogenetic forces |
Weathering?
Weathering happens due to the Exogenetic process. Weathering is a breakdown of rock, minerals, soil, wood, human-made structure. In simple terms, weathering is changed form or breaking of the object due to weather conditions.
There are three main types of weathering:
- Biological Weathering: Weakening and breaking of an object into the smaller object by plants, animals, and microbes. Example: breaking of rock by growing roots.
- Physical Weathering: Over time, due to earth movement and environment changes that alternate hot and cold environment causes expansion & shrinking of rock, at the result faulting and breaking down of rock happen.
- Chemical Weathering: After the physical weathering process, biological and chemical weathering starts. It chemical weathering, rainwater react with the mineral of rock and form new rock (clay) and soluble salt. Acidity and salty nature of rainwater react differently to different minerals and at a result breaking down of rock happened.
Erosion:
Wearing away of the landscape by different agents such as water, air, ice.
Deposition
The eroded material is carried away by water, winds, ice, etc and eventually deposited in low area land
The eroded material is carried away by water, winds, ice, etc and eventually deposited in low area land
By the process of erosion and deposition, different landforms are created on the earth's surface.
Landform created by river agents
Running water of the river erodes the landform and creates other landforms.
The following landforms are created by running water or river:
- Waterfall
- Meanders
- Oxbow lake
- Flood plains
- Leaves
- Delta
Waterfall landform:
When the river falls from soft rock to hard rocks, it forms a waterfall.
Highest waterfall?
Angel falls of Venezuela
Other waterfalls:
- Niagara fall; on the border between the USA and Canada.
- Victoria falls; the border between Zambia and Zimbabwe.
Meanders:
When the Rivers enter the plains areas, it twists and turns; forming of this large bends is known as meanders.
Oxbow lake:
Due to continuous erosion and deposition along the sides of meanders; over time end of meanders loops come closer to closer; loops cut off from the river and form a cutoff lake, this cutoff lake is called oxbow lake.
Flood Plains:
Along the river, over time floods deposit layers of fine soils and other material such as sediments; this flat fertile land is called Flood Plain.
Leaves:
Raised banks are called leaves.
Delta:
In the river mouth, the river begins to break up into the number of streams called distributaries. The river becomes slow and begins to deposit its loads such as silt, sediments. Each distributary forms its own mouth; the collection of sediments from all the mouth forms a delta.
Coastal Landform created by sea waves:
The erosion and deposition of the sea waves give rise to coastal landforms.
- Beach
- Sea Caves
- Sea Arches
- Stacks
- Sea Cliff
Beaches:
The sea waves deposit sediments along the shore; formed beaches.
Sea Caves:
When sea waves continuously strike at the rocks; cracks develop; over time they become larger and wider. By this cave formed on the rocks called sea caves.
Sea Arches:
As the cave becomes bigger and bigger; only the roof of caves remain; thus forming sea arches
Stacks:
Further erosion breaks the roof of sea arches. Only walls like structure are left; these wall-like features are called stacks.
Over time, Sea cave to Sea Arches to Stacks
Sea Cliff:
The steep rocky coast rising almost vertically above the seawater is called sea cliff.
Landform created by Ice:
The following are the landforms:
- Glaciers
- Glacial Moraines
Glaciers
Glaciers are the "river of ice" that too erode the landscape by bulldozing soils & stones to expose the solid rocks from below.
A beautiful lake in the mountains is created when the ice melts.
Glacial Moraines:
The materials carried by the glacier such as big rocks, small rocks, sand, and silt gets deposited; these deposits form Glacial Moraines.
Landform created by Winds
The following landforms:
- Mushroom rocks
- Sand Dunes
- Loess
Mushroom rocks:
The wind is the active agent of erosion and deposition in the desert ecosystem. When the winds erode lower section of rocks more than the upper part of rocks; rocks left with mushroom-like structure with a narrow base and wider top; is called mushroom rock.
Sand Dunes:
When winds blow in the desert ecosystem, it takes sand with them and transport from one place to another places. When winds stop blowing, the sand fall and get deposited in low hill like structure called sand dunes.
Loess
When sands are deposited in large areas; it is called loess
Exercises
Q1. Why do the plates move?
Answer.
Inside the earth, molten Magma moves in a cyclic manner and form a convection cell. Because of this convection cell Plate moves.
Q2. What are exogenic and endogenic forces?
Answer.
Exogenic forces:
Exogenetic forces are destructive forces that come from the outside earth, the primary source of exogenetic force is Sun. Exogenetic forces are:
1.Weathering
2Erosion
3.Depositional
Endogenetic force:
Endogenetic force comes from inside earth and it is a constructive force. Temperature & density variations inside the earth are the main drivers of the endogenetic force. Vertical and horizontal movement happen due to endogenetic force. Mountain building process happens due to vertical movement of the earth and fault happen due to horizontal movement of the earth.
Q3. What is erosion?
Answer:
Erosion is one type of exogenic force. The function of erosion is wearing down the landform by various erosional agents such as water, wind, and ice.
Q4. How are flood plains formed?
Answer.
Flood plains are formed along with river courses by floods deposit of fine silt and sediments. These fertile lands are called flood plains.
The upper part of floodplains, the old flood deposit of the river is called Bangar.
The lower part of floodplains, river renew its silts every year by floods is called Khadar. Khadar is the very fertile land of flood plains and very suitable for intensive agriculture.
The upper part of floodplains, the old flood deposit of the river is called Bangar.
The lower part of floodplains, river renew its silts every year by floods is called Khadar. Khadar is the very fertile land of flood plains and very suitable for intensive agriculture.
Q5. What are sand dunes?
Answer.
Sand dunes are the one type of landform created by winds in the desert ecosystem. When winds blow in the desert ecosystem it takes sand with them and transported to other places. When winds stop blowing, the sand fall and get deposited in low hill like structure called sand dunes.
Answer.
Sand dunes are the one type of landform created by winds in the desert ecosystem. When winds blow in the desert ecosystem it takes sand with them and transported to other places. When winds stop blowing, the sand fall and get deposited in low hill like structure called sand dunes.
Q6. How are the beaches formed?
Answer.
Beach is one type of landform created by sea waves. The sea waves deposit sediments along the shore forming beaches.
Q7. What are oxbow lakes?
Answer.
Oxbow lake is like a horseshoe or U shaped structure created by running water. Due to continuous erosion and deposition along the side od meanders; the end of meander loops comes closer to closer. Over time, loops cut off from river and form cut off the lake or oxbow lakes.
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