Understanding the driving forces behind recent changes in the eruptive behaviour of Merapi volcano, Java, Indonesia

In October and November 2010, Merapi volcano (Java, Indonesia) had its biggest eruption since 1872. Merapi, which literally means "Fire Mountain" in Javanese, is one of Indonesia's most active and dangerous volcanoes with a history of deadly eruptions. Before 2010, these eruptions have usually been characterised by several months of viscous lava effusion at the summit of the steep-sided volcano, forming lava domes which, when big enough, collapse gravitationally generating relatively small pyroclastic flows. These flows are mixtures of lava dome fragments, smaller volcanic particles (ash) and hot gases that travel down the flanks of the volcano at high velocities of > 100 km/hour and, in the case of Merapi, typically reach distances of a few kilometres from the volcano. With a few exceptions only, this eruptive behaviour has been so typical of Merapi for at least the last two centuries that the pyroclastic flows generated by the gravitational failure of lava domes are often referred to in the literature as Merapi-type nuées ardentes (glowing clouds).

In 2010, the eruptive behaviour of Merapi has changed. The unforeseen, large-magnitude explosive events were very different to previous episodes that followed Merapi's usual pattern of dome growth and collapse. On 26 October 2010, pyroclastic flows, generated during explosive eruption phases, swept down the flanks of the volcano, killing at least 34 people. The events were preceded by enhanced levels of seismicity and summit deformation that started in early September 2010. After days of high level activity, with glowing avalanches from a newly formed lava dome, pyroclastic flows and sporadic explosions generating a 7-km-high, sustained eruption column on 4 November, an unusually large explosive eruption on 5 November generated pyroclastic flows that extended up to 15 km from the volcano. Associated surges swept across Merapi's south flank, devastating villages and causing more fatalities. Since then, the death toll has risen to > 300 people, making this eruption the worst volcanic disaster at Merapi in 80 years.

This project seeks to exploit a "once-in-a-century" opportunity to capitalise on these unexpected events at Merapi through a detailed investigation of the rocks formed during the 2010 eruption. These rocks preserve a record of the sub-surface processes that operated inside the volcano before the eruption occurred. Through the use of modern micro-analytical techniques and measurements of different radioactive isotopes that decay quickly within months, decades or millennia in the rocks, we can unravel these processes (which are the driving forces behind the unusual explosive behaviour of Merapi in 2010) and their timescales. The shortest radionuclide, 210Po, has a half-life of only 138 days and can tell us about the degassing of the magma and other processes that occurred in the weeks and months before the eruption. Because of its short half-life, 210Po must be analysed quickly after the eruption and before it has decayed completely to its daughter isotope 206Pb. Once we have established where in the crust beneath Merapi the magma feeding the 2010 eruption has come from and the processes of pre- and syn-eruptive crystallisation and degassing during magma ascent to the surface, we will compare the results with analytical data we have already collected on rock samples from the preceding eruptive episode in 2006, which followed Merapi "normal" (i.e. less explosive) eruptive behaviour. Ultimately, we will attempt to link the results obtained by analysing the rocks from the eruptions to the surface manifestations of these processes (e.g., seismic signals, ground deformation, gas flux) recorded through continuous geophysical monitoring of the volcano by our Indonesian colleagues.

In response to the unusual large-magnitude explosive (and deadly) events at Merapi in October and November 2010, this project aims to unravel the driving forces behind this unusual eruptive behaviour of Merapi through a detailed petrological investigation of the eruptive products. An improved knowledge of these driving forces and the critical changes in the pre-eruptive magma system has important implications for the assessment of hazards and risks from future eruptive activity at Merapi.

We have identified two groups of beneficiaries (other than academic beneficiaries) from this project:

The first group of beneficiaries encompasses those local to the area in Indonesia and includes the Center of Volcanology and Geological Hazard Mitigation (CVGHM) in Yogyakarta, who will be able to utilise outputs informing and improving hazard assessment and risk mitigation strategies related to future eruptive activity of Merapi. Active engagement with the CVGHM during our field campaign and later via regular written contact and exchange on scientific conferences (e.g., IUGG), will ensure that our results will be disseminated effectively to this user group. Also via this route, the most important results obtained in this study will reach Indonesian government decision makers and local authorities around Merapi. Ultimately, it is the local population of > 1.1 million people living on the slopes of Merapi and in nearby Yogyakarta under permanent threat from one of the most active volcanoes in the world, who are the main beneficiaries of the project, as are tour operators, guides and tourists to the local area. We will specifically target this important end-user group of our research through the production and distribution of outreach and educational material in the form of handy, double-sided leaflets with user-friendly, accessible information on the volcanoes of Java and specifically on Merapi and its hazards. Both leaflets will be developed with the active involvement of our colleagues and distributors in Indonesia and produced in both English and Indonesian for maximum impact.

The second group encompasses a wider range of beneficiaries in the UK and abroad. These include government organisations, such as the BGS and USGS, which have an interest in understanding magmatic processes at hazardous dome-forming volcanoes. Because the general results from this work will be widely applicable to other similar volcanoes characterised by dome-forming eruptions, such as Soufrière Hills (Montserrat), to name just one of relevance to the UK and its economy, the outcomes from this project are of interest to the Montserrat Volcano Observatory and academics/academic institutions in the UK and elsewhere who are involved in research on Montserrat and similar volcanoes elsewhere. This group of beneficiaries will be informed via rapid dissemination of outputs at scientific meetings (incl. the NERC-funded International KE workshop on using petrological information in volcanic risk assessment on Montserrat in April 2011; no extra costs to the project), written peer reviewed papers in high profile journals and public lectures. We will utilise the general fascination with volcanoes to actively engage schools, university students and the wider public in the UK. Engagement of this user group through visits to schools, on-campus visit day activities for school groups, general interest seminars and incorporation of project results into the existing UG teaching programme will help generate interest in Earth science subjects and will be facilitated by tried and tested support structures in place at the investigators' host institutions. The efficacy of this activity will be measured via invited feedback from schools and university students via specific questionnaires. The levels of interest in Earth science subjects will be monitored through the widening participation activities at Keele and UEA.