MORPHOLOGIC MEASUREMENTS ON AN INTERMEDIATE COMPOSITION BLOCKY LAVA FLOW FIELD IN CENTRAL OREGON USING HIGH RESOLUTION (~1m) LIDAR DEMs

Lava flows of intermediate composition have morphologic characteristics (steep levees, irregular blocky surfaces) that have severely limited morphometric analyses. Accurate measurements of lava flow dimensions, morphologies and underlying topography can provide estimates of emplacement conditions, such as effusion rates and emplacement times, for prehistoric lava flows. Surface morphologies, such as compression ridges and extensional cracks provide information on flow behavior and rheology. Compression ridges form on lavas where the cool, more viscous surfaces are moving more slowly than the warm, less viscous interiors, creating surface folding. Measuring surface folding can provide estimates on strain rates and the thickness of the surface crust, which corresponds to the thermal boundary.

LiDAR allows high resolution mapping and morphometric analysis, along with analyses using signal processing techniques, such as two dimensional discrete Fourier Transform and wavelet transform, providing quantitative data such as amplitude, orientation and shapes of periodic features. This study uses LiDAR collected in June 2007 (by NCALM) of the Collier Cone lava flows, located on the NW flank of North Sister, OR. The flows show characteristic morphologic features of intermediate composition lava, such as prominent levees, well developed channels, and compression ridges. Compression ridges along the flows have maximum wavelengths of 30–60m and amplitudes of ~5-13m. Flow and channel widths range from ~300-700 m (flow) and ~125-400 m (channel) over a section of the flow that traverses slopes of 2-8˚. When these data are combined with an assumed density of 2000kg m^-3 and viscosity of 3 x 10⁵ Pa s, they suggest a flux of 10-50 m³s^-1 (using Kerr et al., 2006). This estimated flux appears reasonable when compared to the well documented 1988-1990 eruption of an andesitic lava flow at Lonquimay, Chile with a volumetric flux that decreased over time from ~100m³ s^-1 to 10m³ s^-1 (Naranjo et al., 1992) and produced a flow of similar dimensions to that of Collier Cone. Using simple measurements from high resolution LiDAR DEMs, analog and empirical models of lava flows, and historical accounts of similar flows, allows us to reconstruct flow conditions of prehistoric lava flows in a way that was previously impossible.