Thar Desert
The Thar Desert also known as the Great Indian Desert encompasses 77,000 square miles of rolling sand dunes in the northwestern Indian state of Rajasthan. Small portions of the desert also extend into the Indian states of Haryana, Punjab and Gujarat, but these states do not exercise extensive control over the region.
The Thar Desert’s name derives from the word t’hul, the general term for the region’s sand ridges. It is defined by a series of natural borders, including the Aravalli Mountain Range to the southeast and the Punjab plain in the north and northeast. To the west, lies the Indus plain and to the south, the Rann of Kutch.
The geographic isolation of the Thar desert by mountain ranges and plains contributes significantly to the weather patterns that shape its distinctive, hot, dry environment. The environment around the Thar effectively absorbs all the rain that is carried in the monsoon clouds before the clouds can reach the desert. The resulting monsoon winds in the desert are hot and dry and the desert does not share in the wet season experienced in surrounding terrains.
Origin of the Thar Desert
The origin of the Thar Desert is a controversial subject. Some experts consider it to be 4,000 to 10,000 years old, while others maintain that aridity started in this region much earlier.
Another theory states that the area turned to desert relatively recently: Perhaps around 2,000-1,500 B.C.E. Around this time, the Ghaggar river ceased to be a major river and the river now has terminated in the desert.
It has been observed through remote sensing techniques that Late Quaternary climatic changes and neo-tectonics have played a significant role in modifying the drainage courses and a large number of palaeochannels exist.
Most of the studies share the opinion that the palaeochannels of the Sarasvati coincide with the bed of present day Ghaggar and believe that the Sutlej along with the Yamuna once flowed into the present Ghaggar riverbed. It has been postulated that the Sutlej was the main tributary of the Ghaggar and that subsequently the tectonic movements might have forced the Sutlej westward and the Yamuna eastward, causing the Ghaggar to dry up.
Natural features-
There are three principal landforms in the desert region:
- The predominantly sand covered Thar
- Plains with hills including the central dune free country
- Hills
- The Thar Desert is distinguished by a series of rolling sand dunes that vary in height across the desert. While sand dunes are a common occurrence in deserts across the world, the dunes of the Thar are remarkable for their continual motion. In sharp contrast to the mountain ranges that ring the desert, the sandy desert floor is always in motion.
- The perpetual movement of the desert, while contributing the desert’s beauty has had a prohibitive effect for permanent human settlement as the sands can easily be blown over structures.
- The sands are particularly mobile due to severe winds in the region, which sweep the sands over areas of fertile soil.
- The layer of sand over much of the available farming land hinders agricultural development in the region.
- Some of the sand dunes of the Thar have become semi stabilized over time and while not completely sedentary, these older dunes move only very small degrees. Older sand dunes can reach a height of 500 feet.
Dotted among the sands of the Thar, several salt water lakes provide a unique and welcome environment for desert dwelling creatures. While the water of the lakes cannot be consumed by humans, they support much needed shelter and viable farmland. The abundance of salt water, however also serves to highlight the extreme lack of drinkable water in the Thar desert. Annual rainfall in the region is particularly low measuring from 4-20 inches, most of which falls during the monsoon season. It is difficult to estimate annual precipitation for the Thar desert however as rainfall often varies widely from year to year.
Vegetation
- The harsh natural environment and extreme temperature variations found in the Thar desert have combined to severely inhibit the growth of vegetation.
- Most of the native plants grow in small clumps, without a system of order regulating where the clumps grow or any standard number of plants in a vegetation grouping.
- The plants which have been most successful in the difficult environment have adapted to the conditions of the desert.
- It is important, in particular for plants, to have developed water storage systems to be able to provide much needed water to themselves during the dry season.
- Significant plants of the desert include gum, Arabic acacia and euphorbia. However, these plants are only found on the rocky slopes of the hills.
Wildlife
- Stretches of sand in the desert are interspersed by hillocks and sandy and gravel plains.
- Due to the diversity of ecosystems that exist within the Thar, a varied and thriving wildlife population calls the desert their home.
- Both vegetation and animal life in this arid region are very rich. About 23 species of lizard and 25 species of snakes are found here; several of them are endemic to the region.
The most notable example of a preserved ecosystem is the Desert National Park, Jaisalmer which provides an excellent example of the natural wildlife of the region. In this park, Great Indian Bustards, Blackbucks, Chinkaras, the Indian Gazelle, the Indian Wild Ass and Desert Foxes are common. These are species which are fast vanishing in other parts of India. Despite the apparent difficulty of life in the desert, the animals in the Desert National Park have found ways to adapt and thrive. The park supports these wild and naturally occurring populations of species that are threatened with existence elsewhere. It is also noted for rich seashell and petrified wood deposits.
The animals which are found in the Desert National Park exhibits many of the adaptations that are necessary for survival in the desert. These animals, along with those animals found outside the reserve, often exhibit a smaller body size, one example of biological adaptation to the region. In addition, many of the desert animals are nocturnal, a trait which allows them to avoid the sweltering heat of the day.
There are certain other factors responsible for the survival of these animals in the desert. Due to the lack of water in this region, transformation of the grasslands into cropland has been very slow. The protection provided to them by a local community the Bishnois, is also a factor.
Conservation
The Thar Desert faces a distinct environmental threat from the loss of land through wind erosion. The harsh winds of the Thar sweep the sands across the plains and into its awe–inspiring sand dune formations. However, the winds also erode valuable farming land and threaten livestock grazing areas. In an attempt to hinder the wind erosion, plants species and trees have been planted in many areas to help keep the sands attached to the ground. The new windbreaks also provide much needed shelter.
In order to plant the necessary windbreaks, it has become necessary to import exotic plants into the region. The native plants are noted for their slow growth patterns and windbreaks must mature quickly to be fully effective. The Acacia tortillis has proven most adaptable to the Thar. While the induction of foreign plants is helping the wind erosion issues, the introduction of exotic plants into any environment threatens to overthrow the preexisting environmental balance.
Why most of the world’s tropical deserts located on the Western margins of continents?
A desert is a barren area of landscape where little precipitation occurs and consequently living conditions are hostile to plant and animal life. In other words, it is extremely dry area of land with sparse vegetation.
The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation (the wearing away of the Earth’s surface by moving water, by ice, by wind and by waves, leading to a reduction in elevation and in relief of landforms and of landscapes).
There are four types of desert found in the world: sub-tropical desert, Coastal deserts, Cold desert and Polar Desert. The fifth part of the Earth’s surface is desert. They are found in Asia, Australia, Africa, North America and South America. Sahara is the world’s largest tropical desert.
There are four major factors responsible for the location of the world’s tropical desert on the western margins of continents:
1. Offshore areas of trade wind and falling under the rain shadow area: When the moisture laden trade wind flows from east to west shed their moisture on the eastern part and by the time they reach the western margin, they become dry. These dry winds make the soil more and this led to the formation of the desert.
2. Anti-cyclonic conditions: The areas between 20 °- 30 ° latitude on western margins of continents are the regions of descending air. Because of this, the air gets compressed and warm as it descends and thus the moisture keeps decreasing.
3. Formation of Rain-shadow Zone:
A region in the lee of mountains that receives less rainfall than the region windward of the mountains is called rain-shadow zone. For example: Thar Desert in India is formed due to the formation of rain-shadow zone because Aravallis mountains are situated parallel to the region. Therefore the moisture holding winds pass away from the region because there is absence of mountain barriers.
4. Presence of cold ocean currents along the western coast of continents tends to stabilise the air over the coast. This prevents cloud formation and rainfall. Hence, it leads to arid conditions or the formation of marine deserts on the adjacent coastal lands.