- Grand Etang is the only high-altitude lake of volcanic origin in Reunion Island. Tens of thousands of years ago, a river dug a deep valley in the Piton des Neiges massif, the Bras d'Annette river. Then, 6000 years ago, eruptions of Piton de la Fournaise spawned lava flows down the slopes of the massif, penetrating the valley, crossing the Bras d'Annette and completely blocking the valley and the Bras d'Annette river. Some eruptions also took place near the trail leading to Grand Etang, and there are several cones of slag dating from the same period. A lake formed and, over the years, erosion filled in the bottom of the lake with pebbles, sand and silt, giving it a flat bottom. At an altitude of 500 metres, it filled up with slightly mineralised water and fluctuations in its level can be very sizeable. Dried out in January 1998 after a dry period, it reached a depth of 14 metres of water in February, one month after. Similarly, we saw it dry at the beginning of 2006, cyclone Diwa caused it to overflow and the ONF had to forbid access to the 'Grand Etang' route because the water had submerged the trail which allowed people to do a circuit of the lake. The water supply to this lake is provided partly by the waterfalls of Bras d'Annette, but mainly by the runoff water coming from the high ramparts that surround it. There is no visible drainage out of the lake, the water filtering into the porous volcanic rock.
- Difference in height
- 545.32 m
- Gourd, raincoat, hiking shoes, Warm clothes.
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Juste magnifique !!! Je conseil juste d'être bien réveillé car certains endroits peuvent être bien fatiguant... sinon il ne fait pas passer à côté de cet endroit !