Lahars are fast-flowing mixtures of water and volcanic rock fragments which have been responsible for some of the worst historical volcanic disasters. There is a wide spectrum of lahar types and processes, mostly linked to the relative volumes of water and rock particles. Existing models, needed for hazard forecasting deal well with the extremes of lahar behavior (floods and avalanches) but new models are needed to cover the wide middle ground for these complex phenomena, and to include the downstream evolution of a lahar and the implications for hazards to communities and infrastructure located in potential lahar pathways. Lahars can be triggered by heavy rainfall on loose volcanic deposits, by mixing of explosively erupted materials with water or ice, or by breakout of a summit crater lake. Most lahars have few warning signs and are thus essentially unpredictable. This study takes advantage of an almost unique situation where a breakout flood is predicted for the newly filled crater lake of Mount Ruapehu in New Zealand and will look to draw comparisons with Mount St Helens. The study, co-funded by the Petrology and Geochemistry and EPSCoR programs, will involve American and New Zealand scientists, students, and emergency managers in the production of a user-friendly hazard forecasting tool.
The scientific approach involves integration of field data with computational modeling of lahar flow processes. The team will develop methods of describing mathematically the complex physical processes of lahars, and the manner in which their characteristics evolve as they flow away from source. This new model will be the first to tackle in detail additions and losses of sediment and water during the emplacement of a lahar, thus occupying a niche not well treated by existing mass flow models. Sediment entrainment processes have been found to be responsible for many-fold increases in flow volume, and thus are clearly important for understanding the magnitude of downstream hazard. Field studies at the two volcanoes will provide validation of the model, before application to a wider variety of volcanoes and lahar-triggering mechanisms. By packaging the end product as a user-friendly hazards forecasting tool, it is aimed to bridge the gap between lahar researchers and the communities that may directly benefit from this project.
