A geological engine
The Thanlwin River, also known as the Salween or Nu, begins high on the Tibetan Plateau. From there, it flows for approximately 3,289 kilometers south to the Andaman Sea, making it the longest free-flowing river in Southeast Asia. For much of its course, it carves through a series of deep, rugged canyons. One section in China's Yunnan province, where the river runs parallel to the Mekong and Yangtze, is part of the Three Parallel Rivers UNESCO World Heritage Site and features canyons up to 4,500 meters deep. This part of the river is sometimes called the "Grand Canyon of the East."
The river's immense erosive power comes from its steep gradient. Before leaving China, the river drops an astounding 4,000 meters in altitude. This dramatic descent, combined with its significant water volume, allows it to cut through the hard granitic and limestone bedrock of the Shan Plateau and Kayin State. The river's path often follows major geological fault lines, which are zones of weakness in the Earth's crust that provide a path of least resistance for the water to exploit. The geology of the region is complex, defined by the collision of tectonic plates which has lifted the highlands and created these fractures. The river's average annual discharge at Hpa-An, near the end of its journey, is around 169 cubic kilometers of water, a volume that shows its hydrological force.