Geomorphology, rock, rock cycle, geography, geography notes, weathering, erosion, mass movement, earth, relief features, igneous, metamorphic, sedimenatry
Sum or aggregate of one or more minerals is termed as rock. Especially feldspar and quartz are two common minerals which are generally found in the rocks. The scientific study of rocks is called Petrology.
Feldspar: Si (silica) + O2 (oxygen) Quartz: Sand + Granite
Types of rocks
There are 3 types of rocks:
- Igneous rock
- Sedimentary rock
- Metamorphic rock
These rocks are being formed due to solidification of lava. The solidification of lava can take place either inside or outside the earth surface.
Extrusive Features – The landforms which are being formed by the lava and gets deposited outside the surface of the earth. E.g. lava plateau i.e. Deccan plateau, Arabian plateau, Canadian Shield
Intrusive Features – The features formed due to the deposition of lava that takes place inside the surface of the earth. Four different types of deposition take place:
- Lapolith – Deposition of lava in U-shape
- Lacolith – Deposition of lava in ᴒ- shape
- Dyke – Vertical deposition of lava
- Sill – Horizontal deposition of lava
Important characteristics of igneous rocks
- No fossil is being found in igneous rock. Due to high temperature organic matter gets converted to liquid form and loses all its properties.
- No concept of layer system
- Rich source of minerals
The rocks which are being formed by erosion done by air, water, biological substance and huge pressure is called sedimentary rocks. These rocks are formed due to the lithification of sediments. Due to presence of organic matter fossil fuels are found in this type of rocks. E.g. Oil and Shale gas
These rocks are formed through 3 major activities:
- Mechanical Erosion – Erosion done by air and water. E.g. Sandstone, Limestone
- Through organic mode – When the eroded sediments under high pressure gets compact with fossils. E.g. Petrol
- Through Chemical mode – The sediments formation with chemical like reactions or biological changes under sun and water. E.g. Potash
The rocks which come under heavy pressure and temperature, and change its physical as well as chemical properties are called metamorphic rocks. The changes take place in two ways:
Dynamic Changes – Only mechanical changes take place. No change in chemical properties.
Thermal Changes –In these both mechanical as well as chemical changes take place.
E.g. Marble, Quartzite
It is the process by which one type of rock gets converted into another. The three types of rocks those are igneous, sedimentary and metamorphic rocks can change into each other by a number of physical processes; cooling, melting, weathering, erosion, heat, compacting, cementing etc.
Mechanical disintegration and chemical decomposition of rocks by the action of various elements of environment is being termed as weathering. Weathering occurs on site that is at a same place and should not be confused with erosion, which involve the movement of rock and minerals by agents such as wind, water, snow, waves and animals. The material left out after breking of rocks into finer particles together with organic matter constitutes soil.
Various characteristics that affect weathering:
- Geological characteristics – Weathering of rocks depends upon its structure, its composition and relief features.
- Climatic and biotic vegetation – This weathering is based on the vegetation of a particular region
- Tropical areas – weathering will be mainly done by water and chemical mode
- Semiarid region – weathering is more mechanical in nature
Types of Weathering
- Mechanical Weathering: The disintegration of rocks in which only mechanical breakdown takes place while there is no change in chemical composition.
There are 3 types of mechanical weathering:
- Block Separation – Weathering in sedimentary rocks which lead to the disintegration of bigger rocks into smaller ones.
- Granular Disintegration – This type of disintegration generally takes place in igneous rocks. As igneous rock is coarse in nature water enter into and the rocks and expand.
- Haloclasty – Salt crystallisation otherwise known as haloclasty, causes disintegration of rocks when saline solutions seep into cracks and joints in the rocks and evaporate, leaving salt crystals behind. These salt crystals expand as they are heated up, exerting pressure on the confining rock thus causing disintegration.
- By air – Formation of Loess Plateau. The air which acts as an eroding agent generally in desert of semi arid region picks up sand from this region and moisture from any nearby water body and deposit in the form of a compact structure. This compact structure is termed as Loess plateau.
- Chemical Weathering:
- Oxidation – In this atmospheric oxygen react with iron leading to the formation of iron oxide and rust as the weathering object.
- Solution – In this process the soluble salt which gets dissolved in water gets deposited on rocks. E.g. Karst Topography.
- Carbonation – In this process atmospheric carbon dioxide reacts with the carbon rocks and result in formation of carbonates.
- Hydration – In this process water gets added in the rock due to which chemical composition changes.
- Biotic Weathering:
- Through heterotrophs – In this various animals which lives underground like rabbits, snakes dig the soil and causes biotic weathering.
- Through phototrophs – In this lichen grows on the rocks by extracting minerals thus causing weathering of the rock.
Movement of mass of rocks under the influence of gravity with two geomorphic agents, that are running water and air, which helps in the movement of rocks.
Types of movement – Slow and Rapid
Slow Mass Movement
In this mass movement the slope is generally moderate and the movement on this slope is called as ‘creep’. The material which is moved in this type of movement is salt.
Rapid Mass Movement
In this mass movement the slope is generally high. The movement takes place on clay and mud. Based on the material on which mass moves there are three types of rapid mass movement:
- Earth flows – This is the movement of material which has been saturated with water leaving a scar at the point of origin and benches at the lower end of the slope.
- Mud flows – Mudflows occur when large volumes of unconsolidated material become saturated with water to form semi liquid mud which then flows down slope.
- Avalanches – This is the gravitational fall of ice and rock material down a mountain side.