St. Mary's Islands, also known as Coconut Island and Thonsepar, are a set of four small islands in the Arabian Sea off the coast of Malpe in Udipi, Karnataka, India. They are known for their distinctive geological formation of columnar rhyolitic lava (pictured).
Scientific studies indicate that the basalt of the St. Mary's Islands was formed by sub-aerial subvolcanic activity, because at that time Madagascar was attached to India. The rifting of Madagascar took place around 88 million years ago.
Columnar rhyolite Lava here form one of the four geological monuments in Karnataka state, one of the 34 National Geological Monuments of India declared by the Geological Survey of India in 2016 for their protection, maintenance, promotion and enhancement of geotourism. The monument is considered an important site for "Geo Tourism".
History
In the year 1498, Vasco da Gama landed at St Mary's Islands on his journey from the Kingdom of Portugal, he fixed a cross and named one of these islands O Padrão de Santa Maria in Portuguese, as a dedication to St Mary, the virgin-mother of Jesus Christ, before proceeding to Calicut (Kozhikode) in the Malabar region, the present-day Kerala state.
Geography and topography
Out of the four islands, the northernmost island has a basaltic rock formation in a hexagonal form, the only one of its type in India such as Malpe and others. The island covers an area which is about in length with a width of . It has prominent coconut trees, its cover reflecting an azure south sea colour, and hence the island is also called Coconut Island. There is no habitation on the islands.
The north–south aligned islands form a non-continuous chain. The four largest islands are Coconut Island, North Island, Daryabahadurgarh Island and South Island.
The islands are generally aligned parallel to the coast line, which provide clues to the phenomenon of uplift of the west coast of India. The islands' terraces and elevated beach deposits along with the tide gauge data at the dead oyster beach in Suratkal (further south of the islands) have been deduced as proof of the reported fall in sea level of about 1 mm/per year.
The highest elevation at Coconut Island, which has generated interest among geologists and tourists, is about above msl with surrounding areas in the form of platforms in the elevation range of +, +, + and + 0 m which are stated to have been formed by wave action pointing to an "episodic sea level rise or fall of land".
Geology
The columnar basaltic lava found in these Islands, which is very well developed in the basalts of Deccan Traps, exhibit an imposing range of hexagonal shaped or multi-faced (polygonal) columns split into a horizontal mosaic. In geological terms these are called "columnar joints". The lava rocks form regular five, six or seven-sided pillars, called "laminar lava", and are found in varying heights in all the islands; the tallest of the columns is about . Considering the importance and rarity of such an occurrence, these islands were classified as a National Geological Monument in 2001 by the Geological Survey of India.