Lahars (debris flows and related floods) : in situ measurements, rheometry and flow modelling, damage assessment, mitigation and financial protection – LAHARISK

The problem of lahars (volcanic debris flows, hyperconcentrated flows and associated floods) is twofold: they are 2-phase flows, with poorly known laws and are extremely damaging. Two types of investigation are required to tackle the problem: 1) in situ measurements of rheology in active flows and deposits, and 2) research into the physical and organisational vulnerability (detection of building response and preparedness of governmental organisations). These two aspects are poorly developed, leading to great lahar risk, because of uncontrolled urban development. A multidisciplinary effort is required using quantitative methods. The first step is in situ measurements of physical parameters of active lahars to determine hydrodynamic and rheological properties, both of active flows and their deposits. This data can be combined with knowledge of building and infrastructure to reduce the associated risk. This is especially true for assessing the effect of physical impact, erosion and land coverage by rapidly emplaced sediment. Presently, we are making in situ observations at Semeru (Java); an active volcano persistently producing lahars. This work is complemented by numerical and analogue simulations of lahars in which input parameters are calibrated to field observations. Reduction of hazardous consequences may be achieved through micro-zoning of valleys and towns exposed to risk, partially through numerical codes, and integrated with field data. The effect on solid infrastructure is assessed by quantitative impact assessment procedures. Quantitative evaluation is supported in GIS analysis through damage matrices, incorporated into the risk zonation, to give damage maps valid of each type of building or infrastructure. Each flow type (concentrated, hyperconcentrated, flood) is treated. The data is used with an evaluation of network breakdown for local and regional systems in times of crisis Lahar risk requires a multidisciplinary approach including material and construction stability and resistance analysis, insurance and governmental preparation. The feedback into research, by way of the formulation of questions for monitoring and alert methodologies is developed. This is done using GeoProMT (Geospatial Project Management Tool), a collaborative platform to document and communicate the fundamental steps in transforming information for extreme events at various scales for analysis and management. GeoProMT has been established by our partners at the Center for GeoHazard Studies at the University of Buffalo (NY, USA). The sites for our detailed measurements and risk analysis are: 1) Arequipa (Peru), a city of 1,000,000 people which is repeatedly affected by lahars, and 2) the installed station at Semeru, near the city of Lumajang, Indonesia. Analogue and numerical modelling is undertaken by the Laboratoire Magmas et Volcans (Université Blaise Pascal), Clermont-Ferrand), and rheological and hydraulic investigations carried out at ETNA (Cemagref, Grenoble). CNAM (Paris) and LaMI-Polytech’ Clermont- Ferrand specialize in construction and risk. LAMETA (Theoretical and Applied Economy, Montpellier) provides expertise in assessing damage to monetary risks and insurance policies in hazard-zones. Strong international collaboration is provided with 1. Massey University (New Zealand) in geophysical measurements on Semeru, and 3. SUNY University at Buffalo (USA) with GeoProMT. The entire project is well networked to attain a synergy of local operators; IRD Peru for example working with local Civil Defence and the Javanese local administrations working with the research partners (DVGHM in Bandung) to attain a comprehensive approach to lahar risk.