The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported increased seismic activity and deformation at Lewotobi Laki-laki during 30 August-6 September. The seismic network recorded a significant increase in the number of harmonic tremor earthquakes and deep volcanic earthquakes during 30 August-4 September and a shallow volcanic earthquake was detected on 5 September. Tiltmeter data indicated slow inflation over that same time, while GNSS (Global Navigation Satellite System) data indicated deflation; the deformation data suggested that the activity was occurring at shallow levels. On 6 September a period of continuous tremor was detected, indicating rising magma near the surface. At 1000 the Alert level was raised to 4 (the highest level on a scale of 1-4) and the exclusion zone was increased to 6 km from the center of Laki-laki and 7 km in a semicircle clockwise from the SW to the NE. At 1806 that same day a gray ash plume rose 1 km above the crater rim and drifted NW, W, and SW. White plumes rose as high as 1 km above the crater rim and drifted in multiple directions on 8 September and were not visible on 9 September.

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)