The Theri Desert, located in the state of Tamil Nadu, is a fascinating geological formation that has been a subject of study and debate. Several theories surrounding its formation have been proposed, with the most plausible ones citing the pivotal role of south-west monsoonal winds. This article presents an in-depth discussion of the desert’s characteristics, its mineral composition, and the theories regarding its formation.
The Theri Desert: An Overview
Known for its distinct red sand dunes, the Theri Desert is confined to the Thoothukudi district of Tamil Nadu. The term ‘theri’ refers to these red dunes in the local Tamil language. Of particular interest is the desert’s sediment, which dates back to the Quaternary Period that began 2.6 million years ago. Derived from marine deposits, these sediments exhibit low water and nutrient retention capacity. They are vulnerable to aerodynamic lift, which is the force that counteracts weight and enables upward mobility.
Unraveling the Mineral Composition of Theri Desert
Petrographic studies and X-ray diffraction analysis of the red sand dunes have revealed the presence of a range of heavy and light minerals. These include Ilmenite, Magnetite, Rutile, Garnet, Zircon, Diopside, Tourmaline, Hematite, Goethite, Kyanite, Quartz, Feldspar, and Biotite. The semi-arid climate of the region has facilitated the oxidation of iron-rich heavy minerals such as ilmenite, magnetite, garnet, hypersthene, and rutile in the soil. These processes give the dunes near Tiruchendur – a coastal town in the Thoothukudi district – a distinctive reddish color.
The Formation of Theri Dunes
The Theri dunes present as a gentle, undulating terrain. Lithology studies hint that the area was likely a prehistoric coast. Indications of marine transgression are evident in the widespread presence of limestone deposits. The dunes today might have been formed from the localized confinement of beach sand following the regression of the sea. High velocity winds from the Western Ghats blowing eastward led to sand grain migration and accumulation of dunes.
Yet another perspective suggests that these geological formations have developed over a few centuries. A significant amount of red sand, originating from a broad belt of red loam in the plains of the Nanguneri region (approximately 57 kilometers away), is dispersed across these dunes.
Climate Impact and Aeolian Processes
The south-west monsoonal winds during May-September play a crucial role in this distribution process. Other factors such as deforestation and lack of vegetative cover, which lead to wind erosion, also contribute to this. Dry monsoon winds of high velocity churn up the red loam, driving large columns of red sand eastward until they meet the sea breeze near Tiruchendur’s coastal tract and get deposited there. These wind-driven processes, including erosion, transport, and deposit of sediments at or near the earth’s surface, are referred to as Aeolian processes. They are responsible for the continual redistribution of sand in the region.
