Theri Desert: There is a desert in Tamil Nadu and the dunes are red

What is the News?

There are a couple of theories regarding the formation of Theri Desert, the most plausible being the role of south west monsoonal winds.

What are Theri Deserts?

Theri Desert is a small desert situated in the Thoothukudi district of Tamil Nadu.

Characteristics

The desert consists of Red Sand Dunes (The red dunes are called theri in Tamil).It consists 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

The analysis of the red sand dunes in Theri desert reveals the presence of heavy and light minerals. These include Ilmenite, Magnetite, Rutile, Garnet, Zircon, Diopside, Tourmaline, Hematite, Goethite, Kyanite, Quartz, Feldspar, and 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.

Hence, it was due to these processes that the dunes are red-coloured.

How did Theri desert form?

Theory 1: Theri appears as gentle, undulating terrain. The lithology (the study of general physical characteristics of rocks) is that the area might have been a paleo (ancient) coast in the past. The presence of limestone in many places indicates marine transgression.

Based on these observations, the present-day theris might have been formed by the confinement of beach sand locally, after the regression of the sea. When high-velocity winds from the Western Ghats blew east, they induced migration of sand grains and accumulation of dunes.

Theory 2: Another theory is that Theris are geological formations that appeared in a period of a few hundred years.

For instance, there is a lot of red sand spread over Theri Desert. This red sand may have been brought from the surface of a broad belt of red loam in the plains of the Nanguneri region (about 57 kilometres from this area in Tirunelveli district) by south west monsoon winds during May-September.

Note: These processes of erosion, transport and deposit of sediments that are caused by wind at or near the surface of the earth, are called Aeolian processes. 

Source: The post is based on the article “Theri Desert: There is a desert in Tamil Nadu and the dunes are red” published in Down To Earth on 16th June 2022.