A Tear in the Earth's Crust
Beneath the waters of the Andaman Sea, geological activity unfolds. This region is a back-arc basin, a depression that formed behind a volcanic island arc due to the immense forces of plate tectonics. Specifically, it is the boundary between the small Burma Plate and the Sunda Plate. These two microplates began to break away from the larger Eurasian Plate millions of years ago, a process driven by the relentless northward push of the Indian Plate colliding with Asia. This collision created the Himalayas and set in motion a chain of tectonic events, including the formation of the Andaman Sea starting around 3 to 4 million years ago.
The primary feature of this boundary is the Andaman Sea Spreading Center, an underwater rift where new oceanic crust is born. Here, the seafloor is pulling apart at a full spreading rate that has varied over time, with current estimates around 38 millimeters (3.8 cm) per year. This process began in earnest about 4 million years ago, initially at a slower rate of 16 mm per year before accelerating around 2 million years ago. The spreading center itself is a series of rift valleys and volcanic seamounts, morphologically marked by a 400–600 meter deep rift within a basin that is about 3,000 meters deep. This entire system is part of a larger tectonic puzzle that connects the Sagaing Fault in Myanmar to the Great Sumatra Fault in the south via a series of spreading segments and transform faults.