S51D-2731
Bridging Surface and Subsurface Observations of the Pulsating Behavior of Lusi: a New-born Sedimentary Hosted Hydrothermal System in East Java.

Friday, 18 December 2015
Poster Hall (Moscone South)
Alwi Husein1, Adriano Mazzini1, Karyono Karyono1, Matteo Lupi2, Anne Obermann3 and Soffian Hadi4, (1)University of Oslo, CEED, Oslo, Norway, (2)University of Geneva, Geneva, Switzerland, (3)ETH, SED, Zurich, Switzerland, (4)BPLS, Surabaya, Indonesia
Abstract:
The Lusi eruption started the 29th of May 2006 in Eastern Java, Indonesia. Since its birth Lusi presented a pulsating behaviour with geyser-like activity. To date Lusi is still active and never stopped erupting enormous amounts of mud, clasts, water and gas with peaks of activity reaching 180.000 km3/day.

The erupting activity is characterized by[ML1] three main behaviours:

1) regular activity, which consists in the constant emission of mud breccia (i.e. viscous mud containing clay, silt, sand and clasts up to 10 cm in diameter) associated with the expulsion of water both in a liquid and vapour state as well as other gasses (i.e. mostly CO2 and CH4). Occasional powerful bursts of mud may reach up ten meters in height.

2) geysering activity consisting in more powerful eruptive events that do not seem to have a regular pattern. These typically lasts up to five minutes and comprise an initial phase marked by an elevated bubbling in the crater zone followed by an increasing amount of vapour released throughout the geysering phase.

3) quasi-absence of degassing from the main crater(s). This phase follows the geysering activity and is generally short-lived

In order to investigate the mechanisms controlling Lusi pulsating behaviour, we deployed a network of five seismometers around the crater. The seismic records highlight that the seismic signal of Lusi is characterised by tremor and volcano-tectonic events. Tremor events occur in 1 Hz and 3 Hz frequency bands while volcano tectonic events are rich in high frequencies (i.e. 2-15 Hz). We also identify an emerging signal lasting from approximately one to ten minutes. This signal appears throughout the dataset and it is characterized by a frequency content between 5 Hz and 10 Hz. To verify whether such long-lasting signal could be associated to the geysering phase we coupled the seismic monitoring with a HD camera to record the crater activity. Results reveal that the onset of such signal precedes the visual evidence of geysering activity at the surface. This implies that the signal is not originated in the immediate subsurface. We argue that such signal is generated by the geysering activity and it is caused by the discrete collapse of gas pockets rising through a super-heated fluid column filled with hot mud.