HR: 10:20h
AN: V42B-01 INVITED     [Abstracts]
TI: Using Digital Elevation Models and LAHARZ to Forecast Inundation by Lahars
AU: * Schilling, S P
EM: sschilli@usgs.gov
AF: US Geological Survey Cascades Volcano Observatory, 1300 SE Cardinal Court Bldg 10 Ste 100, Vancouver, WA 98683 United States
AU: Iverson, R M
EM: riverson@usgs.gov
AF: US Geological Survey Cascades Volcano Observatory, 1300 SE Cardinal Court Bldg 10 Ste 100, Vancouver, WA 98683 United States
AB: LAHARZ is a statistically based method for evaluating the effects of three-dimensional topography on lahar inundation patterns. The method applies the average behavior of past lahars to forecast inundation areas and portray them on maps. LAHARZ software runs on a Geographic Information System (GIS) and requires inputs consisting of prospective lahar volumes appropriate for the size and geologic history of a given volcano, identification of lahar source areas, and a digital elevation model (DEM) of topography. When using LAHARZ, the attributes of the input DEM have a significant impact on delineation of hazard zones. During a volcano crisis, there may be no option other than to select any available DEM to construct hazard zones. Ideally, users should obtain and evaluate existing or construct new DEMs before a crisis situation. Considerations before using a DEM are its extent, resolution, projection, datum, construction method, and quality. DEMs should include the volcano edifice and its drainages, which may reach hundreds of kilometers away from the volcano. The DEM should have sufficient resolution to depict drainage shapes accurately. For example, a DEM with 1-km resolution will not portray a 500-m wide drainage accurately. Projection, datum, and algoritm used for DEM generation ensure the constructed hazard zones can be displayed accurately with other data used in hazard map preparation. Methods for checking horizontal and vertical accuracy can range from inspecting the DEM visually and comparing it with published topographic maps to visiting locations in the field visible in the DEM (e.g., road intersections or mountain peaks) and comparing coordinates with a global positioning system (GPS) at an accuracy equal to or higher than the DEM for comparison. The DEM should be hydrologically correct. It should route a hypothetical flow of water along drainage thalwegs downstream effectively. Hydrologic functions called by LAHARZ can be used to ensure continuity of flow between DEM cells representing each drainage thalwag. LAHARZ produces output that is most useful when generated for a range of prospective lahar volumes and portrayed on a base map as a set of nested hazard zones showing decreasing probability of potential inundation downstream. The completed set of potential inundation areas can be combined in GIS with other data such as elevation, hydrology, and infrastructure to create images, hardcopy maps, and perspective views for further interpretation, validation, and planning.
DE: 1810 Debris flow and landslides
DE: 1819 Geographic Information Systems (GIS)
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005