LIDAR APPLICATIONS TO LAVA FLOW MAPPING AND HAZARD ANALYSIS

Assessment of lava flow hazards requires fundamental knowledge of the past behavior of lava flows (vent location, eruption frequency, flow advance rates, areal flow coverage and thickness), as well as accurate models of flow emplacement dynamics. Evaluation of these components is being transformed by the growing availability of digital topography derived from Airborne Laser Swath Mapping (ALSM) of lava-dominated landscapes. In heavily forested regions, such as the western slopes of the Oregon Cascades, acquisition of bare-earth LiDAR data has transformed our ability to map individual lava flow boundaries and to distinguish among flows of different ages and compositions on the basis of geomorphic features. As a result, we can now identify at least eight different lava flows (three newly identified using LiDAR) that have entered into the upper McKenzie River (the source of drinking water for Eugene, OR) within the past 4000 years. Even in locations that lack vegetation, however, quantitative morphologic studies of lava flows have been limited by logistical challenges posed by the rough surfaces and complex flow structures that characterize lava flow fields. We are addressing this problem by using LiDAR-derived topography to (1) map complex channel networks, (2) measure channel and levee dimensions, as well as surface structures, along the length of individual flows, and (3) relate channel structures to pre-existing topography (both slope and effects of topographic confinement). By comparing these measurements to theoretical models of channel development, we can not only test the accuracy of existing models but also the resolution of DEMs required to make predictive forecasts of flow advance rates and distances. Specifically, we demonstrate that the control of local topography on flow emplacement, particularly for very low viscosity of Hawaiian lava flows, requires digital topography at sub-meter scales for accurate predictions of flow paths. Finally, lava flows resurface the landscape, thereby altering the local hydrology and vegetation patterns. We are also exploring ways in which LiDAR data can be used, in conjunction with detailed field mapping, to examine questions related to both re-vegetation of flow surfaces and the evolution of lava flow hydrology.