The Trou de Fer ("Iron Hole") is a canyon on Reunion Island, off the coast of Madagascar in the Indian Ocean. The primary river flowing through the gorge, which is up to 1,000 feet (300 m) deep, is the Bras de Caverne River, which is a tributary of the Rivière du Mât. The canyon has two distinct parts; a large crater, which is fed by six prominent waterfalls, and a narrow slot canyon at its outlet, which constitutes most of the canyon's length. The Bras de Caverne River's headwaters are in a cirque high on the mountainside abutting the canyon wall, and directly after that, it drops over a waterfall about 700 feet (210 m) high. This drop is usually dry or has very little water,[1] but between that and the next, 600-foot (180 m) drop, springs feed the river, which drops over this then drops over a final 1,000-foot (300 m) undercut cliff into the Trou de Fer in a narrow plume of water.[2]
Directly to the left of this waterfall, another stream drops over the cliff, which is undercut to an extent that its lip has over 700 feet (210 m) of empty space between it and the canyon floor, of approximately the same height in two channels, and slams onto a ledge before emptying into the same pool as the Bras de Caverne waterfall. This waterfall is not as high, and has a smaller water flow. It is fed by several other falls streaming off the cliffs above it. Further to the left, at about twice the distance as from the first falls to the second, another large stream plunges into the canyon.[3] In total, there are at least six waterfalls feeding the canyon. At the base of the canyon, a separate slot canyon, or "The Narrows", begins. The water from the Bras de Caverne waterfall and the waterfall to its left drain to the slot canyon at a 90-degree angle, through a waterfall known informally as the "Washing Machine".[4] The name stems from the mist it generates, which drenches people who near the base of the falls.[5]
The slot canyon, or "The Corridor", extends for about 2 miles (3.2 km), and is said to be commonly dammed up by debris jams to form lakes, including "Lake of the Eel".[5] The porous volcanic rock composing the walls create many springs, which create countless waterfalls.[6]