St. Mary’s Islands

A cluster of small islands fringed with dramatic columns of basalt — a frozen record of the day India split from Madagascar.

St. Mary’s Islands are famous for their columnar basalt: lava that cooled and contracted into striking polygonal columns, standing like a natural pavement of stone pillars. The Geological Survey of India has recognised them as a National Geological Monument.

The volcanic rock here has been dated to around 88 million years ago and is tied to the rifting of India away from Madagascar — one chapter in the long journey of the Indian plate across the ocean before it collided with Asia.

A short reference note: this summary draws on third-party sources such as the Geological Survey of India and Wikipedia. In time I plan to give every geological feature its own learning-oriented write-up — with custom diagrams, graphs, and study pointers — as I’ve already done for the 11 locations that have an Instagram reel.

Sources