From UPSC perspective, the following things are important :
Prelims level : Theri Desert in Tamil Nadu
Mains level : Desertification of land and preventive measures
Most of us may not know the small desert situated in the state of Tamil Nadu. It consists of red sand dunes and is confined to the Thoothukudi district.
- The red dunes are called theri in Tamil.
- They consist of sediments dating back to the Quaternary Period and are made of marine deposits.
- They have very low water and nutrient retention capacity.
- The dunes are susceptible to aerodynamic lift.
- This is the push that lets something move up. It is the force that is the opposite of weight.
Mineral composition of Theris
- The analysis of the red sand dunes reveal the presence of heavy and light minerals.
- These include Ilmenite, Magnetit, Rutile, Garnet, Zircon, Diopside, Tourmaline, Hematite, Goethite, Kyanite, Quartz, Feldspar, Biotite.
- The iron-rich heavy minerals like ilmenite, magnetite, garnet, hypersthene and rutile present in the soil had undergone leaching by surface water.
- They were then oxidised because of the favourable semi-arid climatic conditions.
How did they form?
- Theris appear as gentle, undulating terrain.
- The lithology of the area shows that the area might have been a paleo (ancient) coast in the past.
- The presence of limestone in many places indicates marine transgression.
- The present-day theris might have been formed by the confinement of beach sand locally, after regression of the sea.
- When high velocity winds from the Western Ghats blew east, they induced migration of sand grains and accumulation of dunes.
Another story of their formation
- Another view is that these are geological formations that appeared in a period of a few hundred years.
- The red sand is brought from the surface of a broad belt of red loam in the plains of the Nanguneri region (about 57 kilometres) by south west monsoon winds during May-September.
- The winds after draining the moisture behind the Mahendragiri hill and the Aralvaimozhi gap of the Western Ghats become dry and strike the plains in the foothills, where vegetation is sparse.
- Deforestation and the absence of vegetative cover in the Aralvaimozhi gap and the Nanguneri plains are considered to be the major causes of wind erosion.