Andaman Sea

This part of the eastern Andaman Sea shows how uneven sediment accumulation can shape a shelf. Although the Ayeyarwady and Salween deliver more than 600 million tonnes of sediment annually, little later material settles directly on the shelf immediately off the Ayeyarwady mouths. Instead, currents transport much of it toward the Gulf of Martaban, where a great mud wedge forms in the Martaban Depression. The deposit can reach sixty metres in thickness and extends into water about 130 metres deep.

Studies find no clear finds that later sediment moves onward into Martaban Canyon. Along the narrow western Myanmar shelf, a separate mud drape wraps the coast and thins toward the slope near 300 metres depth. About 1,290 billion tonnes of Holocene sediment are estimated to lie offshore. The result is a varied sea floor rather than a simple fan at each river mouth.

Muddy shallows and deeper water sit side by side, with islands and channels altering currents. Monsoon winds and tides determine how sediment shifts and when fishing can take place. Coastal settlements depend on both the fertile catchment outflow and the sheltered passages of the archipelago. The balance between river supply, waves and currents continues to transform the seabed.