This 6 x 8.5 km and 800-meter deep caldera is resulted from Samalas volcanic eruption in 1257. According to Lavigne and friends’ research in 2013 the eruption procuded 40 km3 material with an eruption column stretched 43 km to the atmosphere. The Samalas eruption is predicted to be the biggest volcanic eruption during the last 7000 years, with about 2 times bigger than Tambora in 1815 and 8 times bigger than Krakatoa in 1883. Before the eruption the height of Samalasa Volcano was predicted to be 4200 meter above mean sea level. In the caldera there is SegaraAnak and the cone of active Barujari Mountain. The caldera is the highest one among active volcanoes in Indonesia.
Caldera wall is consisted of rock coating from lava and pyroclastic added with many kind of breakthroughs from dike and sill. The view of the caldera, lake and this active volcano can be seen from the peak of Rinjani and crate rim or “Pelawangan” in Sasak language. There are four crater rims which serve as a transit for 5 trekking route which are PelawanganSembalun, Senaru, Santong, Pemotoh/AikBerik and Timbanuh. Trekking route from Torean goes straight to SegaraAnak Lake.