HR: 10:40h
AN: V42B-02    [Abstracts]
TI: Lahar Properties and Propagation: The Influence of Bulking and Debulking
AU: * Fagents, S A
EM: fagents@hawaii.edu
AF: HIGP/SOEST, University of Hawaii, 1680 East-West Road, Honolulu, HI 96822 United States
AU: Baloga, S M
EM: steve@proxemy.com
AF: Proxemy Research, 20528 Farcroft Lane, Laytonsville, MD 20882 United States
AB: Construction of physics-based models lahar flow processes is complicated by the need to account for varying topography, solid mass fractions and complex rheologic behaviors. The incorporation and loss of material (sediments or water) during the advance of a lahar can significantly influence the advance rate, mobility, rheology, and inundation limits of the flow, and therefore has consequences for destructive potential. We have developed a theoretical treatment based on the conservation of flow volume and mass to describe the effects of such processes on flow characteristics. We apply our model to a common scenario of lahar generation and evolution; the formation of an initially dilute flow by catastrophic breaching or ejection of a volcanic summit crater lake, followed by bulking due to incorporation of substrate materials, and later debulking due to sediment deposition. The key features of this model are time-dependence and the inclusion of two terms describing the influx or efflux of sediments to or from the flow, at a rate proportional to the volumetric flow rate. For lahars triggered by crater-lake water, we derive the time-evolution of flow behavior for comparison with the well-documented lahars of Mt. Ruapehu, New Zealand. Our model produces qualitatively realistic behavior with respect to flow depth and density profiles, downstream hydrograph evolution, erosional and depositional regimes, and transformations between streamflow, hyperconcentrated flow and debris flow conditions. However, there is a need for further testing with a suite of field data sets. These include detailed pre- and post-event topographic cross-sectional and longitudinal transects of potential lahar pathways, as well as observations on active lahars (i.e., discharge hydrographs at multiple downflow localities, high-water marks reflecting the passage of the peak stage, and observations of the flow erosional/depositional and rheologic/density regimes). The resulting calibration will allow refinement of the lahar physics and eventual use of the model in a predictive sense for assistance with hazard assessment.
DE: 1810 Debris flow and landslides
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005