Like Krakatoa, Batur was initially formed in the shape of a sharply pointed cone over 3,500 meters above sea level. A terrific explosion blew the point off the cone, atomized a large portion of the volcano, and collapsed the bulk of the mountain into the magma chamber which was emptied by the initial cataclysm.

Before the present caldera was born, Penelokan and Kintamani lay on the western slope of the “first” Gunung Batur. Now Penelokan and Kintamani are spread out along the top of the caldera’s outer crater rim. The present younger, smaller volcano—of the effusive rather than explosive type—gradually grew out of the crater floor over a period of hundreds of thousands of years.

Batur erupted in 1917, destroying 65,000 homes, 2,500 temples, and 1,372 people. Its last major eruption was in 1926, when the village below was covered in lava. In 1959 a crack in the lakebed emitted poisonous gases, coloring the water green and killing all the fish. There was further activity in 1963 during the Gunung Agung catastrophe, when lava spilled down Batur’s southeastern flank. The lava flows from those eruptions can still be seen beside the lake. In August 1994, one of Batur’s lower peaks began belching smoke and debris. In Kedisan you could hear the mountain rumble, and from any vantage point the volcano glowed red. Climbers were prohibited from ascending the peak and people all over Bali complained of throat ailments, coughing, and congestion—Batur belched NO3 and sulphuric acid up to 450 times a day.