Using satellite observations and field visits, two independent researchers from France have identified eight sites around Jaisalmer in the Thar Desert, that show linear features resembling geoglyphs.

What are geoglyphs?

• Geoglyphs are large, un-explained geometrical patterns on land usually proposed to be man-made features.
• The largest concentration of geoglyphs is reported from southern Peru, covering an area of about 1,000 square km.
• A new paper published notes that the identified geoglyphs in the Thar Desert cover an area of about 6 square km.

Boha Geoglyphs in Thar

• The authors’ main area of interest was Boha, a small village 40 km to the north of Jaisalmer where they noticed a series of concentric and linear features.
• They named these features Boha geoglyphs and suggested that the features could be at least 150 years old.
• It is however conceivable that they were built at the beginning of the British colonial period, in the middle of the 19th century.

How are they patterned?

• The Boha geoglyphs are clearly manmade as the main unit is a giant spiral, but they have been eroded due to the cars running over the lines lately.
• So, they are clearly not formed by weathering or another natural phenomenon.”
• The observed features might have been formed naturally, but degraded over time due to both natural and human-related causes.

Degraded over time

• The rocky terrain is home to a typical weathering feature, especially over the iron-rich sandstone and shale beds.
• Here, extreme aridity and high temperature lead to slow geochemical translocation of minerals for centuries, such that the heavier minerals like iron and manganese move away from the lighter minerals.
• This lead to the gradual formation of alternate bands of harder and softer mineral concentrations.
• With time the areas with softer materials get slowly eroded, while the harder ones stand out, producing the typical concentric or box-like geometric features.

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