Geomorphology is a part of Earth Science that studies changes on the Earth’s surface and the forces and processes that develop them. It deals with the characteristics of the Earth’s surface and all the geological processes that try to change it over a period of time.

The earth’s crust is dynamic. It moves vertically as well as horizontally. Different types of forces are responsible for such movements:

Endogenic forces: [‘Endo’ means internal and genic means ‘generated from’] Endogenic forces are those forces that originate from within the earth itself. Such forces contribute to subsidence, land upliftment, volcanism, faulting, folding, earthquakes, etc.
Exogenic forces: [‘Exo’ means external] These are external forces that shape the earth. All the forces that act on the surface of the earth are included in this broad category of ‘Exogenic Forces’. For example, Weathering forces, Erosional forces, the sun’s energy that drives winds and the Moon’s Tidal force can also be termed as an exogenic force. They result in:
Gradation: The wearing down of sediments created by weathering (disintegration and decomposition of rocks), their mass movement and erosional activities. The material lightest goes farthest away from the winds and water waves, grading them according to their mass and size. This mechanism is also termed as level down.
Aggradation: Aggradation is the deposition of the weathered and eroded material and this mechanism is called level-up.

Geomorphic Process:

The term geomorphic process referstothe Endogenic and Exogenic forces causing physical stresses and chemical actions on earth materials and bringing about changes in the configuration of the surface.

Geomorphic agent: Any exogenic element like air, wind and ice capable of acquiring and transporting earth material is called a geomorphic agent. They deposit natural elements at lower levels transporting them over slopes.

Depending on the driving force, there can be two types of Geomorphic processes:

Endogenic Processes
Exogenic Processes

We shall study these in detail in this chapter. Geomorphic Processes

Endogenic Geomorphic Processes

The energy emanating from within the earth is the main force behind endogenic geomorphic processes. This energy is mostly generated by radioactivity, rotational, tidal friction and primordial heat from the origin of the earth. This energy due to geothermal gradients and heat flow from within induces diastrophism (the process of folding and faulting of the earth), earthquakes and volcanism.

Due to variations in geothermal gradients and heat flow from within, crustal thickness and strength, the action of endogenic forces is not uniform and hence the tectonically controlled original crustal surface is uneven.

Diastrophism:

The slow but large-scale movement of the earth’s crust is known as diastrophism. It is a process that moves, elevates or builds up portions of the earth’s crust.

In Chapter 3, we learned that convection currents inside the earth’s mantle continually cause the crust to move which further causes two types of movements:

Sudden and rapid movements like earthquakes and volcanism.

Orogenic processes:

The orogenic process (‘oros’ means mountain and ‘genic’ means creation in Greek) refers to the mountain-building process. It involves severe folding and affecting long and narrow belts of the earth’s crust. Gilbert (1890) formalized the term ‘orogeny’ as the “displacements of the earth’s crust which produce mountain ridges are called orogenic”.

Orogenic Movements are the ones, that work horizontally to the surface of the earth and therefore are also called tangential forces.

Orogenic processes:

Crustal Bending: When due to horizontal movement which is working towards each other crustal rocks are forced to bend it is called crustal bending. It can be of two kinds:
Warping: when the large area of the earth’s crust is affected by crustal bending. When the crust is bending upward it is called up warping and when the crustal part is bent downwards like a basin or depression then it is called down warping. This happens on a very large scale.
Folding: When the crust is layered and bedded with sedimentary or igneous rocks and already has a pre-existed rock structure. In such cases, a slight fold in any such structures would result in a wave-like structure. The upfolded rock strata is called anticline, and down folded strata is called a syncline.
Crustal Faults: They are formed due to fractures in the crustal block and their displacement. A Fault Plain is the plane along which the vertical or horizontal displacement takes place. Up-thrown sides and downthrown sides are the two sides representing the upper block and the lower block respectively.

Epeirogenic processes:

‘Epeiroes’ means a continent in Greek. Epeirogenic Processes are the processes that involve the uplift or warping of large parts of the earth’s crust. There is simple deformation, a continental building process. Epeirogenic movements operate vertically from the centre of the earth caused by radial forces (i.e. convection currents).

It causes regional upliftment on a large scale, spreading over the continental platform or the stable block of land. Therefore, it is not very noticeable as no obvious folding and fracturing can be seen in the rocks. These are characterized by broad, gentle and widespread warping, subsidence, upliftment, emergence, and submergence, of large land areas.

Epeirogenic Tectonic movements either be positive like upliftment or negative movement like subsidence.

Upliftment movement causes the upliftment of either the whole continent or the part of it. It can also cause upliftment of the coastal landmass. Such a type of upliftment is called emergence.
Subsidence of the continental masses again happens in two ways – one is subsidence of the land area called subsidence, alternately the land near the sea coast is moved downward or is subsided below sea level and is thus submerged under seawater. Such movements are called submergence.

Earthquakes:

It is a release of energy through the movement of crusts. It involves local relativity minor movements. It is defined simply as the shaking of the earth, caused due to release of energy, which generates waves that travel in all directions.

Basic Definitions:

Fracture: Breaksin rocks in response to stress. Fractures can be of two types:

Fault: It is a factor where the crustal plates move relative to each other over a period of time. This movement is not continuous. Plates develop stresses over a period of time due to tectonic forces; The sudden release of this energy causes earthquakes

Joint: This is the pointwhere no movement takes place.

Focus or Hypocentre: it is a point in the earth’s interior where energy is released.

Epicentre: it is a point on the surface nearest to the focus. It is the point on the earth’s surface vertically above the focus of an earthquake. It is the first to experience waves.

Seismograph: Instrument that records waves.

Seismogram: Chart on which Earthquake waves are recorded.

Types of Earthquakes:

There are five different types of earthquakes,

Tectonic earthquakes: These are generated due to the sliding of rocks along a fault plane. They are the most popular earthquakes observed all over the world;
Volcanic earthquakes: it is confined to areas of active volcanoes that cause shaking of the earth’s surface.
Collapse earthquakes: In areas of intense mining activity, sometimes the roofs of underground mines collapse generating minor tremors. These are termed collapse earthquakes. They are small earthquakes in underground caverns and mines that are caused by seismic waves produced by the explosion of rock on the surface.
Explosion earthquakes: Ground shaking may also happen due to the explosion of chemical or nuclear devices. Such tremors are called explosion earthquakes.
Reservoir-induced earthquakes: incidence of earthquake-triggered due to impoundment of water behind a dam.

Hydro-seismicity

Earthquake swarms are seismic events occurring in a local area for a short period of time. In recent times, in areas having large water reservoirs or dams large number of Earthquake swarm events have been observed; With every 10m rise in groundwater, pore pressure increases by one bar. Large changes in water level in a short period of time induce such Hydro seismicity creating Earthquake Swarms.

Earthquake waves:

Earthquake waves originate in the lithosphere. Their direction changes due to refraction and reflection when waves interact with materials of different densities. On the basis of their propagation Earthquake waves can be classified into two categories:

Body Waves: Due to the release of energy at the focus, waves move in all directions through the medium. The speed at which these waves travel depends on the properties of the material that they are passing through. For example, in a denser material seismic waves travel faster, covering large distances. There are two types of Body Waves:
P-Waves or Primary waves:
P-waves are longitudinal waves, i.e. such waves that travel through the medium in the direction of their propagation. They exert pressure on the material in the direction of movement, which creates density differences in material: Squeezing and stretching.
They travel through solid as well as fluid mediums. Sound waves and Pressure waves are a type of Primary wave.
They carry the highest amount of energy and therefore travel fastest as well as farthest, but they have the least amount of amplitude (amount of to-and-fro motion), and therefore cause less damage as compared to other waves.
S-Wave or secondary:

S waves are transverse waves, i.e. they vibrate the rock strata perpendicular to the direction of their propagation. In other words, they create troughs and crests perpendicular to the direction of propagation.
Such transverse motion can only happen in Solids, but not through fluids. These waves are important to study the structure of the earth, as they enable us to determine the regions of the earth’s interior that are molten.
S-waves are slower than P-waves and arrive at the surface with some time lag. Every second of the time lag between the S and P waves means 8 km.
1. Surface waves: Surface waves are generated when body waves intersect with surface rocks. Such waves move along the surface of the earth. It carries low energy but has a high amplitude. Thus, they are slowest and are last to be reported by seismograph, but are most destructive. They too are of two types:
Love waves: move on the surface from side to side perpendicular to the direction of propagation.
Rayleigh waves: move up and down on the surface

Measuring earthquakes:

Seismic stations are established at different locations to measure and record the earthquake waves. It is measured either according to Magnitude (strength of shaking) or intensity (impact on the environment) of shock.

Magnitude scale: It measures the strength of shaking of the ground; It does this by computing the energy released or measuring the amplitude that the earthquake carries.

Richter scale: The first widely used method, the Richter scale, was developed by Charles F. Richter in 1934. It used a formula based on the amplitude of the largest wave recorded on a specific type of seismometer and the distance between the earthquake and the seismometer. It depends on the energy released; It is expressed on a 0-10 scale in absolute whole numbers.

Richter Scale	Description
< 2	Micro Earthquakes – People cannot feel it
2 – 3.9	Minor Earthquakes – Seismographs can’t detect them
4-4.9	Light Earthquake – Causes disturbances; Noise.
5 – 5.9	Moderate Earthquakes – Buildings are damaged
6 – 6.9	Strong Earthquake – About 800 each year on earth; causes huge losses in a large area.
7 – 7.9	Major Earthquake – Takes lives on a large scale.
8 – 9.9	Great Earthquake – 1 in every 20 years; Even heavier objects are thrown into the air, and buildings are toppled.
10+	Meteoric Earthquakes – Never recorded in history.

Limitations of Richter Scale: Unfortunately, the Richter scale, does not provide accurate estimates for large magnitude earthquakes.
Moment magnitude scale (MW): It is based on the total moment release of the earthquake. The moment is a product of the distance a fault moved and the force required to move it. It is derived from modelling recordings of the earthquake at multiple stations.
- Limitations: Again, as we have seen in the case of P-waves; The waves carrying the highest amount of energy may not create the highest amount of destruction.
- The amount of destruction depends on the intensity and the direction of shaking.

Intensity scale: Intensity is a measure of the shaking and damage caused by the earthquake; this value changes from location to location.

Mercalli scale: Developed by Italian Seismologist Giuseppe Mercalli. It empirically measures the visible damage caused by the event. Its range is 1-12.

Effects of Earthquake:

The effects of earthquakes can be broadly grouped into two categories – primary and secondary hazards. Primary hazards are caused by the direct interaction of seismic wave energy with the ground.

Primary bearing upon landforms:

Ground shaking: Shaking of the ground caused by the passage of seismic waves, especially surface waves near the epicentre of the earthquake is responsible for the most damage during an earthquake.
Differential ground settlement: Due to earthquakes if only part of the foundation is affected by ground failure or part of the foundation is affected to a greater extent than other parts. This kind of effect is called differential settlement.
Land mudslides: Landslides occur when masses of rock, earth, or debris move down a slope. Debris flows, also known as mudslides, are a common type of fast-moving landslide.
Soil liquefaction: Soil liquefaction is a phenomenon in which the strength and stiffness of soil are reduced by earthquake shaking or other rapid loading.
Ground lurching: Ground lurching is the horizontal movement of soil, sediments, or fills located on relatively steep embankments or scarps as a result of seismic activity, forming irregular ground surface cracks.

Secondary hazards effects causing immediate concern to life and property:

Avalanches,
Floods from dam and levee failures,
Fires,
Structural Collapse,
Falling objects,
Tsunamis: waves generated by tremors in Ocean waters.

Volcanism

Volcanism is the eruption of molten rock (magma) from inside the Earth to the surface. It leads to the formation of many intrusive and extrusive volcanic forms (rock forms outside or inside the earth).

Volcanism indicates the derivation of material from the earth, not necessarily through abrupt volcanoes. Where volcanic material like gases, ashes and/or molten rock material (lava) escape to the ground from the interior of the earth. Volcanoes can be categorised into two parts based on the periodicity of the eruption active, dormant, or extinct.

Active volcanoes have a recent history of eruptions; they are likely to erupt again.
Dormant volcanoes have not erupted for a very long time but may erupt at a future time.
Extinct volcanoes are not expected to erupt in the future.

Material of volcanoes:

Volcanic material finds its way through the weak zone of the mantle as the Asthenosphere. The material in the upper Mantle portion is called Magma. Once it reaches the surface it is called Lava.

Thus, Volcanoes contain lava flows, Volcanic debris such as ash and dust and gases such as nitrogen compounds, sulphur compounds and minor amounts of chlorine, hydrogen and argon.

Classification of volcanoes:

Shield Volcanoes:
Barring Basalt flows, they are the largest of all volcanoes on earth. Mostly made up of Basalt (lava type) – very fluid when erupted. Thus, they are not very steep. Become explosive if water gets into the vent otherwise, low explosivity. Upcoming lava moves in the form of a fountain flows out of a cone at the top of the vent and develops into a cinder cone. Ex: Hawaiian volcanoes.
Composite volcanoes:
It is built through the eruption of cooler and more viscous lavas than basalt. Often result in explosive eruptions. Large amounts of pyroclastic material and ashes find their way to the ground. It accumulates in the vicinity of the vent forming layers that make the mouth appear as a composite.
Caldera:
It is the most explosive volcano. It tends to collapse on itself rather than building a tiny tall structure. Collapsed depressions are called calderas. It is explosive as a magma chamber not only huge but in close vicinity. Ex: Yellow Stone Volcano of the USA, Barren Island (160km east of Andaman)
Flood Basalt Provinces:
Sometimes lava flows thousands of sq. km – thick basalt lava flows. There can be a series of flows with some flows attaining a thickness of more than 50 m. Individual flows may extend for hundreds of km. Deccan Traps, covering most of the Maharashtra plateau, are much larger flood basalt provinces. It is believed that initially trap formations covered a much larger area than present.
Mid-Ocean Ridge Volcanoes: It can be more than 10,000km long that stretches through ocean basins. The central portion of this ridge experiences frequent eruptions.

Volcanic landforms:

Cooling of Magma leads to the development of igneous rocks. It may take place either upon reaching the surface or also while the lava is still in the crustal portion.

Igneous rocks are classified depending on the location of the cooling of the lava:

- - 1. Volcanic rocks (cooling at the surface) and
    2. Plutonic rocks (cooling in the crust) – They give rise to the intrusive landforms

Intrusive landforms: The lava that cools within the crustal portions assumes different intrusive forms.

- - 1. Batholiths: Large bodies of magmatic material that cool in the deeper depth of the crust and develop in the form of large domes. They appear on the surface only after the denudation processes remove the overlying materials. They cover large areas, and at times, assume depth that may be several km. These are granitic bodies. Batholiths are the cooled portion of magma chambers.
    2. Laccoliths: Large dome-shaped intrusive bodies with a level base connected by a pipe-like conduit from below. It resembles the surface volcanic domes of composite volcanoes, only these are located at deeper depths. It can be regarded as the localised source of lava that solidifies beneath the surface.

Karnataka plateau is spotted with domal hills of granite rocks. Most of these, now exfoliated, are examples of laccoliths or batholiths.

- - - Lopolith: Lava moves upwards, a portion of the same may move in a horizontal direction whenever it finds a weak plane. If it develops into a saucer shape, concave to the sky body.
    - Phacolith: A wavy mass of intrusive rocks found at the base of synclines at the top of anticlines in a folded igneous country. Such wavy material has a definite conduit source beneath in the form of Magma chambers.
    - Sheets and Sills: Near horizontal bodies of intrusive igneous rocks are called sills or sheets, depending on the thickness of materials: Sheets are thinner and Sills are Horizontal deposits.
    - Dykes: When lava flows through cracks and fissures developed in land and solidifies almost perpendicular to the ground. It gets cooled in the same position to develop wall-like structures called Dykes.

Intrusive landforms in the western Maharashtra area, which are considered feeders for eruptions led to the development of Deccan traps.

Geomorphic Processes

Geomorphic Process:

Endogenic Geomorphic Processes