PVMBG reported that on 17 May the color of the crater lake water in Kelimutu’s Crater I (Tiwu Ata Polo) changed from green to dark green, water bubbles on the surface of the NE part of the lake were observed, and there was a weak sulfur odor. On 22 May the water color changed to a blackish-brown. The lake temperature dropped from 23 to 21 degrees Celsius during 17-22 May. At Crater II (Tiwu Koofai Nuwamuri) the water color was light blue on 17 May and had not changed color since the last visual observation. Golden-yellow sulfur deposits were scattered around the lake including in the central part and in areas to the NW, N, NE, E, and SE. Visual observations on 23 May revealed that the lake’s color had not changed, though sulfur deposits had shifted positions and had become more numerous. There was a swirling area of sulfur deposits on the water’s surface at the S part of the lake and a weak sulfur odor was noted. The lake temperature increased from 22 to 24 degrees Celsius during 17-23 May, indicating increased activity of the magmatic-hydrothermal system beneath it. The color of the lake water in Crater III (Tiwu Ata Bupu) was unchanged during 17-23 May. The changes in lake water color at Crater I, along with the changes in the floating sulfur deposits and increased water temperatures at Crater II, prompted PVMBG to raise the Alert Level to 2 (on a scale of 1-4) at 1300 on 24 May, and the public was warned to stay 250 m from the crater rims. According to a news article the Taman Nasional Kelimutu (Kelimutu National Park) restricted visitors from approaching the craters in accordance with the PVMBG guidelines. The last eruption was phreatic, and it occurred at Crater II during June 1968.

Geological Summary. Kelimutu is a small, but well-known, Indonesian compound volcano in central Flores Island with three summit crater lakes of varying colors. The western lake, Tiwi Ata Mbupu (Lake of Old People) is commonly blue. Tiwu Nua Muri Kooh Tai (Lake of Young Men and Maidens) and Tiwu Ata Polo (Bewitched, or Enchanted Lake), which share a common crater wall, are commonly colored green and red, respectively, although lake colors periodically vary. Active upwelling, probably fed by subaqueous fumaroles, occurs at the two eastern lakes. The scenic lakes are a popular tourist destination and have been the source of minor phreatic eruptions in historical time. The summit is elongated 2 km in a WNW-ESE direction; the older cones of Kelido (3 km N) and Kelibara (2 km S).

Sources: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Antara News