Crossing the Andaman Sea

May 14, 2015 - National Geographic Orion

Crossing the Andaman Sea
Monsoon weather over the Andaman Sea.

We’re living on the edge. As we make our way south from the Andaman Islands toward Sumatra, we are traversing the far eastern margin of the Indian Ocean, cruising international waters between the shores of five nations, crossing lines both political and geographic, real and imaginary. We have left India, the fabled nation that gave its name to the great sea where the National Geographic Orion has spent the past two months. Soon we will enter Indonesia, leaving the Indian Ocean behind us as we enter the Straits of Malacca. This famous passage between Sumatra and the Malay Peninsula has been used for centuries by explorers and merchants bound east toward the Spice Islands and beyond. For us it is the threshold of the next phase of our expedition, the cultures and wildlife of the Greater Sunda Islands.

Our course today is through the Andaman Sea, one of the many peripheral seas of the Indian Ocean. Running between the Andaman and Nicobar Islands to the west and Myanmar, Thailand and Malaysia to the east, we are in shallow waters over the edge of the Asian Plate. The great subduction zone known as the Sunda Mega-Thrust, where the Indo-Australian Plate dips beneath the Asian Plate, is now to our west on the far side of the islands. The collision of these two great puzzle pieces of the Earth’s crust beneath us has created the very different landscapes in the places we have just left and those we will soon visit. It began over one hundred million years ago, as the Indian Ocean was born, and it still mediates the struggle between the ocean and mainland of Southeast Asia.

The long narrow chains of the Andaman and Nicobar islands are formed of an amazing mix of different rocks, limestone, and sandstones from the floor of the Indian Ocean, serpentine from the very bottom of the crustal plate below. These rocks were scraped and chipped off the plate as it slid beneath Asia, then churned and folded up to form the islands. Not far to the south the interaction of the two plates becomes dominated by volcanic action raising the huge mountains of Sumatra, Java, and the islands beyond. As we cruise down the Andaman Sea we are moving from a region of sediments to one of igneous rocks, part of the great Ring of Fire that follows the rim of the entire Pacific Ocean. It is another boundary, leading us to another edge.

Politically the Andaman and Nicobar Islands are the eastern extreme of India, and in a very real way they are the edge of the world. They are remote and restricted, among the most difficult of all places to visit in this world of easy jet travel, and home to some of the most isolated and least contacted groups of people on the planet. Similarly, Sumatra is the western extremity of Indonesia. From here it is 3,300 miles across the greatest archipelago on Earth to the far corner of the country in the Asmat region of New Guinea. We move from one extreme to another. We are exploring edges, crossing borders, leaving one world and entering another. Farewell to the Indian Ocean.

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About the Author

David Cothran

Naturalist/Certified Photo Instructor

David has worked for Lindblad Expeditions-National Geographic since 1993 on six continents and in over 65 countries. David is interested in many of the natural sciences, particularly ornithology, geology and marine biology; he most enjoys contrasting the broad perspectives provided by world travel with detailed investigations of local ecosystems on land and in the sea.

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