The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that eruptive activity at Lewotobi Laki-laki continued during 12-20 May, with a larger eruption on 18 May. White steam-and-gas plumes rose 50-800 m above the crater rim and drifted in various directions during 14 and 16-17 May. White-and-gray plumes rose as high as 300 m above the summit and drifted SW and W on 15 May. At 0120 on 18 May a gray ash plume rose 900 m above the summit and drifted SW and S.

A period of continuous ash, steam, and gas emissions began at around 1149 on 18 May with a dense gray ash plume that rose 800 m above the summit and drifted N. Dense ash emissions continued through the day and rumbling and banging was heard at the nearest observation post. The ash plume rose to 2 km by 1209 and 3 km by 1218, drifting N and NE. During 1246-1323 the ash plume was as high as 3.5 km above the summit and began drifting also NW. By 1405 the plume had risen to 6 km above the summit and expanded NE, N, NW, W, and SW. The plume was lower at 1430, rising to 4 km and drifting N, NW, and W. Hazy conditions due to ash in the air, possibly mixed with weather clouds based on webcam views prevented visual observations at 1527 and 1614. A dense ash plume rose to 2 km above the summit and drifted NW at 1637. At 2000 PVMBG raised the Alert Level to 4 (on a scale of 1-4). The public was warned to stay 6 km away from the center of Laki-laki and 7 km in a semicircle clockwise from the W to the NE.

At 0008 on 19 May a dense gray ash plume rose 1.2 km above the summit and drifted N and NE. Eruptive events were recorded at 0936, at 1248, at 1342, and at 1406, though conditions prevented visual observations. Ash emissions were ongoing during 1437-2149 with ash plumes rising as high as 5 km above the summit and fanning out from the E counterclockwise to the W. Webcam images at 2145 and 2150 showed incandescent material on the upper flanks and at the summit. Ash plumes rose 4 km above the summit at 2152, 1 km above the summit at 2217, and 500 m above the summit at 2315 and drifted W and NW. Incandescence at the summit was visible in corresponding webcam images. Ash plumes rose 500 m and 300 m above the summit at 0209 and 0224, respectively, on 20 May. Incandescence was again visible at the summit in corresponding webcam images.

Geological Summary. The Lewotobi edifice in eastern Flores Island is composed of the two adjacent Lewotobi Laki-laki and Lewotobi Perempuan stratovolcanoes (the "husband and wife"). Their summits are less than 2 km apart along a NW-SE line. The conical Laki-laki to the NW has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has had observed eruptions in 1921 and 1935. Small lava domes have grown during the 20th century in both of the summit craters, which are open to the north. A prominent cone, Iliwokar, occurs on the E flank of Perampuan.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)