The island of Gaua, with an area of 328 km², corresponds to the upper part of a volcanic edifice 40 km wide and about 3000 m high from the ocean floor. It is a basaltic andesitic-type stratovolcano.
The summit caldera (6 x 8 km) is occupied by Lake Letas, in the middle of which rises the recent cone of Mount Garet (797 m). This lake has a depth of about 100 m and an area of 19,7 km². The water is often tinged yellow to brown and is heated by degassing at the edge of the active crater.
The large volume of this lake poses a great danger for the population by risk of shoreline breakage. The lake water flows through the Mbe Solomul River, which flows down the edge of the caldera into a 120-meter waterfall.
No eruption of Mount Garet had been reported until 1962. This volcanic, then very wooded, was probably in solfataric phase for a long time. This long period of rest ended in 1962 with the opening of a new crater on the SE flank of the cone, followed by frequent explosions with ash plumes from 1962 to 1977.
The eruptions are usually brief, one to two days, and are fairly small except the 1965 with an IEV of 3.
At present, since April 1991, degassing is carried out on the SE crater.
(Ph. Bani et al., (2012) A. Beaumais et al. (2013).)