IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

1W_3J-P9Date/Time: July 21 Poster

Periodic gas release from the LUSI mud volcano (East Java, Indonesia)
Loyc Vanderkluysen1 , Michael R. Burton2 , Amanda B. Clarke1 , Hilairy E. Hartnett1 , Jean-Francois
Smekens1
1Arizona State University, U.S.A., 2 Istituto Nazionale di Geofisica e Vulcanologia, Italy
E-mail: loyc@asu.edu

The LUSI mud volcano has been erupting since May 2006 in a densely populated district of the Sidoarjo regency(East Java, Indonesia), forcing the evacuation of 40,000 people and destroying 10,000 homes. Peak mud extrusion
rates of 180,000 m3 /d were measured in the first few months of the eruption, which had decreased to <20,000 m3 /din 2012. Mud volcanoes often release fluids in a pulsating fashion, with periodic timescales ranging from minutes todays, and LUSI is no exception. These oscillations, common in natural systems of multi-phase fluid flow, are thought
to result from complex feedback mechanisms between conduit and source geometry, fluid compressibility, viscosityand density, changes in reservoir pressure, fluid phases or vent conditions. Crisis management workers reported
observations of pulsating eruptive cycles lasting a few hours during the first two years of the eruption, and possiblybeyond. Since that time, activity has shifted to individual transient eruptions recurring at intervals of a few minutes.
In May and October, 2011, we documented the periodic explosive release of fluids at LUSI using a combinationof high-resolution time-lapse photography, open path FTIR, and thermal infrared imagery. The mud, consistingof approximately 70% water, is erupted at temperatures close to boiling. Gases are periodically released by thebursting of bubbles approximately 3 m in diameter, triggering mud fountains ~20 m in height. No appreciable gas
seepage was detected in the quiescent intervals between bubble bursts. Infrared absorption spectrometry reveals
that the gas released during explosions consists of 98.5% water vapor, 1% carbon dioxide, and 0.3% methane.
On rare occasions, minor amounts of ammonia were also detected. Using simplified plume geometries based on
observations, we estimate that LUSI releases approximately 2,300 t/yr of methane, equivalent to 0.5% of the yearlymethane production from the 4.7 million heads of cattle in East Java. We observed explosion periods from 1 to 3
minutes with a mean period of 55 s and 114 s in May and October, respectively. Two conceptual models for theperiodic behavior are assessed: 1) decompressional boiling of water as fluids ascend a pathway to the surface
suggests that bubbles form 10s of meters below the surface and continue to expand as they rise; periodicity resultsfrom the time to reheat and/or replace the fluid in the vicinity of bubble formation; and 2) slug flow in which carbon
dioxide bubbles are seeded at much greater depths and coalesce to form evenly spaced gas slugs which rise to thesurface. Our estimates of gas and mass flux, along with well-constrained fluid and mud densities, are consistent
with the development of slug flow, but high measured H2 O/CO2 ratios in the gas plume suggests that bubbles form
by decompressional boiling of water, rather than by carbon dioxide bubbles exsolved at great depths.

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