Category: Geography

Tropical thorn forest in India

It is a type of desert forest that has scrub-like vegetation. Their trees and plants are armed with thorns and spines. These forests are found in the region where the rainfall is less than 50cm annually. The tree and plants in these regions have long roots that penetrate deep into the soil to get water from the deep.

These forests are in South West Punjab, Haryana, Rajasthan, Gujarat, Madhya Pradesh, and Uttar Pradesh.

Trees found in the thorn forest in India

Examples include Babool, ber, wild date palm, Khair, neem, Khejri, palas, etc. Some of these plants are used as charcoal for cooking, and also, fodder from the forest acts as an important source of food for cattle.

Tussocky grass grows up to a height of 2m.

The leaves are mostly thick and small to minimise evaporation, and the stems are succulent to conserve water.

The animals found here are rats, rabbits, wolves, tigers, lions, wild ass, horses, camels, and mice

Tropical thorn forests in India are grouped into two based on their regions. The Northern Tropical Thorn forest and Southern Tropical Thorn Forest.

Northern Tropical Thorn Forest

These forests are found in semi-arid regions of UP, Madhya Pradesh, Haryana, Rajasthan, Gujarat, and Punjab.

These areas have rainfall of 20 to 70 cm annually. During the rainy days, rainfall will be 15 to 40 cm.

Northern Tropical Thorn Forests are grouped as Desert Thorn Forest, Ravine Thorn Forest, and Runn thorn forest.

Desert thorn examples are Prosopis spicigera, Salvadora spp, etc. Ravine thorn plant species are Acacia nilitica etc and the Runn thorn forest plant species examples are Salvadora, Tamarix, Calotropis, etc.

Southern Tropical Thorn Forest

These forests were found in the states of Madhya Pradesh, Maharashtra, Andhra Pradesh, Karnataka, and Tamil Nadu.

The average temperature here is 24 to 28 C. The annual rainfall ranges from 45 to 95 cm.

Plant species found in these forests are Acacia Nilotica, A.leucopholea, A.catechu, Prosopis spp, etc.

Peculier characteristics found in Tamil Nadu and Karnataka Tropical Thorn Forest are the formation of an umbrella-shaped crown example, Acacia planifrons.

Earthquake Waves

Earthquake Waves are or seismic waves are the vibrations generated by an earthquake or similar energetic sources such as explosions. These are propagated within the Earth or along its surface.

All the earthquakes take place in the Lithosphere. A seismograph device records the waves that reach the surface.

Earthquake waves are of two types they are body waves and surface waves. The body waves are the one which is generated by the release of energy at the focus and move in all direction by traveling through the body of the earth.

These body waves interact with the surface rocks and generate a new set of waves called surface waves.

The speed of the waves varies as it passes via different densities of materials. The speed of waves is faster in the case of denser material.

The wave’s direction changes when the waves get reflected or refracted when tries to pass through the material with varying densities.

There are two types of body waves: P and S-Waves.

P-Waves

P- Waves move faster as it the one which first arrives at the surface. This wave is similar to sound waves as they travel through gas, liquid, and solid materials.

S-Waves

S-Waves arrive at the surface after P-waves. This wave travels only through solid materials. This characteristic of S-waves that it travels only through solid materials is an important thing as it helped the scientist to understand the interior of the earth.

The reflection causes the waves to rebound and refraction makes the waves scatter in all directions.

This variation in the direction of waves is studied with help of a seismograph. The surface waves are last to get recorded in the Seismograph. The Surface waves are the most dangerous as displace rocks, collapse the building structure, etc.

Magnitude and intensity of earthquake

The earthquake is scaled according to its magnitude and intensity. The Richter scale is the magnitude scale. It relates to the energy released during the quake, it is expressed in absolute numbers, 0-10.

Another Scale is the Intensity scale, where the intensity scale takes the visible damage into account. Its scale ranges from 1-12. It is named after an Italian seismologist, Mercalli.

Propagation of Earthquake Wave’s

Different types of earthquake waves travel in different manners. As they move or propagate, they cause vibration in the body of the rocks through which they pass. P-waves vibrate parallel to the direction of the wave and it exerts pressure on the material in the direction of the propagation.

As a result, it creates density differences in the material leading to stretching and squeezing of the material. The other three waves vibrate perpendicular to the direction of propagation. The direction of vibrations of S-waves is perpendicular to the wave direction in the vertical plane.

Hence, they create troughs and crests in the material through which they pass. Surface waves are considered to be the most damaging waves. The emergence of Shadow Zone Earthquake waves gets recorded in seismographs located at far-off locations.

However, there exist some specific areas where the waves are not reported. Such a zone is called the ‘shadow zone’. The study of different events reveals that for each earthquake, there exists an altogether different shadow zone.

It was observed that seismographs located at any distance within 105° from the epicenter, recorded the arrival of both P and s-waves.  However, the seismographs located beyond 145° from the epicenter, record the arrival of P-waves, but not that of S-waves.

Thus, a zone between 105° and 145° from the epicenter was identified as the shadow zone for both types of waves. The entire zone beyond 105° does not receive S-waves.

The shadow zone of the S-wave is much larger than that of the P-waves. The shadow zone of P-waves appears as a band around the earth between 105° and 145° away from the epicenter.

The shadow zone of S-waves is not only larger in extent but is also a little over 40 percent of the earth’s surface.

Earthquake

It is simply the shaking of the earth. The cause of the earthquake is the release of energy, which generates waves that travel in all directions.

Causes of earthquake

The release of energy occurs along a fault. The fault is a sharp break in the crustal rocks. The rocks along the fault tend to move in opposite directions.

The overlying rock presses, the friction locks the rock together but the tendency to move overcomes the friction. Then the blocks get deformed and eventually they slide on one another abruptly and release energy, these energy waves travel in all directions.

The point where the energy is released is called the focus of the earthquake and is also called a hypocentre.

Erosion is the acquisition and transportation of rock debris. When the massive rocks break into smaller fragments due to weathering and other processes, the geomorphic agents like water, glaciers, wind, waves etc remove and transport these rock debris to other places.

Types of erosion

• Water Erosion – It is the removal of soil by water and transporting away, it is due to rain, gully, rill, and stream.
• Sheet and Rill Erosion – It occurs when a thin layer of soil is taken away by water when the water doe not infiltrates into the ground. Rill erosion occurs when runoff water forms small channels as it concentrates down a slope.
• Scalding Erosion–Scalding occurs when water or wind removes the topsoil layer. This exposes the sodic or saline soils in the subsoil layers.
• Gully Erosion-It is the process by which gullies are formed. Hillsides are more prone to gully erosion when they are cleared of vegetation, through deforestation etc.
• Stream Bank Erosion – It is wearing away of the banks of a stream or river. This is distinguished from erosion of the bed of the watercourse, which is referred to as scour.
• Wind Erosion -The wind is the cause of the removal of top layer soil. This occurs in arid and semi-arid lands.

These are the different types of erosion that are also responsible for Deposition.

Deposition

The deposition is the consequence of erosion. The erosional agents lose their velocity and thereby energy on the gentler slopes and the materials are carried by them start to settle.

The coarser materials get deposited first and finer materials deposit later. The deposition depression gets filled up and erosional agents act as aggradational or depositional agents also.

Karaiyar dam also called Papanasam Dam which is located 49 Km from Tirunelveli, Tamil Nadu. It is situated in the South of Western Ghat of India.

Karaiyar dam is one of the seven major dams in the Kalalkad-Mandantharai reserve area. This area is one of the 18 biodiversity hotspots in the world.

Karaiyar dam crocodiles are important fauna found here. The traveler needs to be careful while spending their time here. Slight carelessness can be fatal due to the presence of Crocodiles.

Karaiyar Dam

Karaiyar Dam was built for irrigation and other water requirement and also for power generation. Also known as Papanasam Dam and it is built over the Thabirabarani River.

This Dam height is 44 meters and its length is 227 meters. It is a picnic spot and has Kalakkad Mundanthurai Reserve. Also has boating facilities.

The endogenic and exogenic forces cause physical stresses and other chemical actions on the earth’s materials and bring changes to the surface of the earth. This is known as the Geomorphic process.

Endogenic and Exogenic forces

• The forces which work over the surface of the earth are called Exogenic forces and the forces that work inside the surface of the earth or which act interior of the earth are called Endogenic forces.
• The endogenic forces work is visible only after it causes sudden damage or severe damage. Still, on the other hand, exogenic forces create visible changes as these changes took hundreds or thousands of years.

The Endogenic processes are diastrophism and volcanism and the exogenic process is Weathering, mass wasting, erosion, oxidation, reduction, hydration and deposition. The exogenic process also depends on the climate, type and structure of the rocks.

Geomorphic agents are water, ice, wind etc. These agents remove materials and transport them over the slope and deposit them at a lower level.

Gravity is the directional force that activates all the downslope movement and also causes stresses on the earth’s material. Indirect gravitational stresses activate wave and tide-induced currents and winds. Without the gradients and gravity, there will be no mobility and no erosion and deposition are possible.

All the movement inside or outside the surface of the earth happens due to gradients from the higher level to the lower level, and from high-pressure to low-pressure areas etc.

The five geomorphic processes of weathering are

• Physical Weathering
• Erosion,
• Slumping,
• deposition and
• Mass Movement.

The four types of physical weathering are due to water, ice, plant and animals. Similarly, chemical weathering is due to water dissolving minerals in the rock, producing a new compound.

For example: When water reacts with granite, the Feldspar crystal inside the granite reacts chemically forming clay minerals, which weakens the rock and makes it more vulnerable to Weathering.

Geomorphic Processes Weathering due to glacial transportation, glacial deposition and glacial erosion.

FAQ

1. What are exogenic and endogenic forces?

The forces that act in the interior of the earth are called Endogenic forces. The forces that work on the surface of the earth is called Exogenic forces.

Interior of the earth

The earth’s interior can only be understood by indirect methods, as no one has gone deep inside the earth, due to high temperature and pressure.

The surface of the earth is due to a number of processes that happen deep inside the earth. The surface of the earth is due to exogenic as well the endogenic forces that happen inside the earth.

The radius of the earth is 6370 km and nobody has ever reached the centre of the earth. The information which we have got today is all based on observation and analysis of materials.

Inside the earth

The Interior of the earth consists of Crust, Mantle, and Core. The continental crust is made of Sial which is expanded as Silica and Al-alumina.

And Oceanic crust is made up of Sima which is expanded as Silicon and Magnesium.

The interior of the earth is extremely hot and reaches as high as 5000 degrees Celsius. This is probably because of two reasons. One is the heating when the earth is formed and the other is the heat from the decay of the radioactive elements.

Crust

The crust is the outermost part, and it is brittle. Its thickness varies from oceanic and continental areas. The crust in the oceanic region is thinner than the continental crust.

Its average thickness is 5km in the case of oceanic crust and its average thickness is 30 km in the case of continental crust.

The continental crust is thickest in mountainous regions. For example, the Continental crust is 70 km thick in the Himalayan region.

Mantle

The mantle is present after the crust. It extends from Moho’s discontinuity to a depth of 2900 km. The Mantle consists of a number of layers.

The upper layer of the Mantle is called Asthenospher that is extending up to 400km. The word Astheno means Weak. The lava comes through the Asthenosphere.

The crust of the uppermost part of the mantle is called Lithosphere and its thickness is about 10-200 km. The lower mantle extends beyond the asthenosphere which is in a solid-state.

Core

The Final layer of the Interior of the earth is the core. The core is located at the depth of 2900 km. The outermost core is in a liquid state and the innermost core is in a solid state.

The core is made of Nickel and Iron and due to it is also referred to as Nife Layer.

Cause of the interior of the earth to separate into layers

The earth is divided into layers because of gravity and density. The stratification of Earth into layers was the reason for the formation of the Earth’s iron core.

This Iron core is possibly formed by radioactive decay and strong gravitation. This might have caused high temperatures and made iron melt.

As the molten iron moved to the center of the Earth due to gravity and it displaced the materials that are less dense to the surface.

Study of Interior of Earth

Scientists study the interior of the earth by studying seismic waves. These are recorded by an instrument called Seismograph. As it is impossible to drill the center of the earth, scientists use indirect observation of the underlying matters below the surface.

Ocean floor configuration

It helps in the know about the distribution of continents and oceans. the ocean floor is divided into three divisions based on its depth and as well the forms of relief.

The division is known as Continental Margin, deep-sea basin and mid-ocean ridges. The Ocean floor configuration

Continental Margins

Continental Margins are the transition between the continental shores and deep-sea basins. These include a continental shelf, continental slope, continental rise and deep oceanic trenches.

The deep oceanic trenches are one which is interesting part with respect to the distribution of oceans and continents.

Abyssal Plains

Abyssal Plains are extensive plains that lie between the continental margin and mid-oceanic ridges.

These are the areas where the continental sediments are deposited.

Mid Oceanic Ridges

Mid oceanic Ridges are an interconnected chain of mountains system under the ocean. These are the longest mountain chain on the surface of the earth, which are submerged under the ocean.

It is characterized by a central rift system at the crest, a fractionated plateau and a flank zone all along its length.

The volcanic activity zone occurs in the crest of the rift system.

Fractionated plateau and Flank zone

Fractionated plateau

Flank zone

• The flanks are market by set of mountain and hills, which are elongated and parallel to the ridge trend.

Crop calendar Tamil Nadu

Planting Seasons in Tamil Nadu is classified into 8 types. They are:

1. Navarai
2. Sornavari
3. Kar
4. Kuruvai
5. Early Samba
6. Samba
7. Late Samba/Thaladi/Pishanam/Late Pishanam
8. Late Thaladi

The crop calendar in Tamil Nadu is classified into 8 based on the Month of Sowing, Duration or Day. This duration is classified into Short duration, Medium and Long duration.

Tamil Nadu basically cultivated Paddy as main crops. Based on which the seasons are named.

Navarai

The month of Sowing is December to January. The Duration of the crop is less than 120 days.

Short duration varieties are sown. Varieties sown in Navarai are ADT 36, ADT 37, ASD 16, IR 64, ASD 18, ADT 42, ADT 43 MDU 5, ASD 20, etc.

The districts of cultivation are Tiruvallur, Vellore, Tiruvannamalai, Cuddalore, Villupuram, Tiruchirapalli, Perambalur, Karur, Nagapattinam, Madurai, Theni, Salem, Namakkal, Dindigul, Dharmapuri, Coimbatore, Erode, and Pudukkottai districts.

Sornavari

The month of Sowing is April to May.

The Duration of the crop is less than 120 days.

Short duration varieties such as

The districts of cultivation are Tiruvallur, Vellore, Tiruvannamalai, Cuddalore, Villupuram, Namakkal, and Dharmapuri districts.

Varities sown during Somavari are IR 64, ADT 36, IR 50, ADT 37, ASD 16, ASD 17, ASD 18, ADT 42, MDU 5, ASD 20, ADT 43, CO 47, ADT (R) 45, ADT RH1, ADT (R) 47, etc.

Kar

The month of Sowing is May to June. The Duration of the crop is less than 120 days.

Short duration varieties such as:

The districts of cultivation are Tirunelveli, Kanyakumari, Tuticorin, Erode, Coimbatore, Madurai, Theni, Dindigul, Salem, Namakkal, and Dharmapuri districts.

Varieties of paddy sown during Kar are ADT 36, IR 50, IR 36, IR 64, ADT 37, ASD 16, ASD 18, ADT 42, MDU 5, ASD 20, ADT 43, CO 47, ADT (R) 45 (Dindigul only), TRY (R) 2*, ADTRH 1, ADT (R) 47, etc.

Kuruvai

Kuruvai is also known as ‘Short Term’ in Tamil Nadu. The crops are grown in Tamil Nadu in Cauvery Delta.

The month of Sowing is June to July. The Duration of the crop is less than 120 days.

The districts of cultivation are Tiruchirapalli, Perambalur, Karur, Thanjavur, Nagapattinam, Tiruvarur, Pudukottai and Erode districts.

Varieties of paddy sown during Kuruvai are ADT 36, IR 50, IR 64, ASD 16, ADT 37, ASD 18, ADT 42, MDU 5, ADT 43, CO 47, ADT (R) 45 (except Karur), TRY (R)2*, ADTRH 1, ADT (R) 47, etc.

Early Samba

The month of Sowing is July to August. The Duration of the crop is less than 130 to 135.

Medium and Long during varieties of Paddy are sown.

The districts of cultivation are Tiruvallur, Vellore, Tiruvannamalai, Salem, Namakkal, Cuddalore, Villupuram, Madurai, Theni, Ramanathapuram, Dharmapuri, Coimbatore, Erode, Pudukkottai, and Nilgiris districts.

The Varieties of paddy sown during Early Samba are IR 20, White Ponni, CO 43, Ponmani, PY 4, ADT 38, TRY 1, ASD 19, ADT (R) 44, CORH 2, etc.

Samba

The month of Sowing is August. The duration of the crop is 130 to 135 days and less than 150 days.

Medium and long-duration varieties are sown. All the districts cultivate it.

The Varieties of paddy sown during Samba are Ponmani, ADT 40, Bhavani, IR 20, White Ponni, CO 43, Paiyur 1, PY 4, CO 45, TRY 1, ASD 19, CORH 2, etc.

Late Samba/Thaladi/Pishanam/Late Pishanam

The month of Sowing is September to October. The duration of the crop is 130-135 days.

Medium and long-duration varieties are sown. The districts of cultivation are Tiruvallur, Madurai, Theni, Coimbatore, Erode, Dindigul, Kanyakumari, Tirunelveli, and Tuticorin districts.

The Varieties of paddy sown during late Samba are ADT 38, IR 20, CO 43, Ponmani, ADT 39, TRY 1, ASD 19, ADT (R)46, etc.

Late Thaladi

The month of Sowing is October to November.

The duration of the crop is 115-120 days.

Medium and long duration varieties are sown.

The districts of cultivation are Thanjavur, Nagapattinam, Tiruvarur, Tiruchirapalli, Perambalur and Karur districts.

The Varieties of paddy sown during late Thaladi are ADT 38, IR 20, CO 43, Ponmani, ADT 39, TRY 1, ASD 19, ADT (R)46, etc.

Conclusion

We have discussed Crop calendar tamil nadu, the season, its respective months, life time of crops and also the varieties of paddy cultivated during the various seasons across the districts of Tamil Nadu.