Evaluation of Geophysical Mass Flow Models Using the 2006 Block-and-ash Flows of Merapi Volcano, Indonesia
Abstract
The dynamics and depositional processes associated with block-and-ash flows (BAFs) are most commonly inferred to be a function of granular or inertial grain flow, similar to debris flows and cold rock avalanches. Existing geophysical mass flow models are either based on frictional (Mohr-Coulomb) behavior (the Titan2D model developed at the University of Buffalo, USA) or another rheological law (i.e., a constant retarding stress), eventually adding some viscous and turbulent components (the VolcFlow model developed at the Laboratoire Magmas et Volcans, Clermont-Ferrand, France). The 2006 BAFs of Merapi have been used to test the validity of these two well-established models. Our work has allowed the definition of key flow parameters that will lead to more reliable predictions of the areas and levels of hazards associated with such flows. We first show that with the incorporation of spatially varying bed friction angles, Titan2D is capable of reproducing the paths, runout distance, areas covered and deposited volumes of the 2006 Merapi flows over highly complex topography. However, some discrepancies with field data are noted and the velocity and travel time of the flows do not match entirely. Using a single free parameter (a constant retarding stress), simulations obtained with the VolcFlow model also reproduce the morphology and distribution of the natural deposits as well as the time of emplacement and velocities of the flows. The results suggest that the performance of these models in simulating actual events is critically dependent on (1) the calibration of the model by using extensive field- based data such as deposit distribution, processes of flow generation, transport and deposition, (2) the incorporation of a suitable empirical law into the model (spatially varying bed friction angles or constant retarding stress) and (3) the choice of input parameters, such as location and volume of the initial pile of material and source characteristics (single or multiple dome-collapse, dome-collapse duration and total volume of collapsed material). The model evaluations presented here provide an invaluable tool for guiding hazard assessement of BAFs during future eruptive crises at Merapi.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2009
- Bibcode:
- 2009AGUSM.V71B..02C
- Keywords:
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- 8414 Eruption mechanisms and flow emplacement;
- 8488 Volcanic hazards and risks