A canyon, gorge or chasm, is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic time scales. Rivers have a natural tendency to cut through underlying surfaces, eventually wearing away rock layers as sediments are removed downstream. A river bed will gradually reach a baseline elevation, which is the same elevation as the body of water into which the river drains. The processes of weathering and erosion will form canyons when the river's headwaters and estuary are at significantly different elevations, particularly through regions where softer rock layers are intermingled with harder layers more resistant to weathering.

The Yarlung Tsangpo Grand Canyon, also known as the Yarlung Zangbo Grand Canyon, the Tsangpo Canyon, the Brahmaputra Canyon or the Tsangpo Gorge, is a canyon along the Yarlung Tsangpo River in Tibet Autonomous Region, China. It is the deepest canyon in the world, and at 504.6 kilometres (313.5 mi) is slightly longer than the Grand Canyon in the United States, making it one of the world's largest. The Yarlung Tsangpo originates near Mount Kailash and runs east for about 1,700 kilometres (1,100 mi), draining a northern section of the Himalayas before it enters the gorge just downstream of Pei, Tibet, near the settlement of Zhibe. The canyon has a length of about 240 kilometres (150 mi) as the gorge bends around Mount Namcha Barwa and cuts its way through the eastern Himalayas. Its waters drop from about 2,900 metres (9,500 ft) near Pei to about 1,500 metres (4,900 ft) at the end of the Upper Gorge where the Po Tsangpo River enters. The river continues through the Lower Gorge to the Indian border at an elevation of 660 metres (2,170 ft). The river then enters Arunachal Pradesh and eventually becomes the Brahmaputra.