We derived a high‐resolution, spatially continuous map of erosion and deposition associated with the debris‐laden flows triggered by the 2011 Las Conchas wildfire and subsequent rainstorms over a 197 km2 area in New Mexico, USA. This map was produced using airborne‐LiDAR‐derived bare‐earth digital elevation models (DEMs) acquired approximately one year before and one year after the wildfire. Differencing of the pre‐wildfire and post‐wildfire‐and‐rainstorm bare‐earth DEMs yielded a DEM‐of‐difference (DoD) map that quantifies the magnitude of ground‐surface elevation changes due to erosion/deposition within each 1 m2 pixel. We applied a 0.3 m threshold filter to our DoD to remove changes that could have been due to artifacts and/or imperfect georeferencing. The 0.3 m value for the threshold filter was chosen based on the stated accuracy of the LiDAR as well as a comparison of areas of significant topographic change mapped in aerial photographs with those predicted using a range of candidate threshold values for the DoD filter. We developed an automated procedure that accepts the DoD map as input and computes, for every pixel in the DEM, the net sediment volume exported through each pixel by colluvial and/or fluvial processes using a digital routing algorithm. An analysis of the resulting sediment volume map for the Las Conchas fire demonstrates that sediment volume is proportional to upstream contributing area. After normalized by contributing area, the average sediment yield (defined as the sediment volume divided by the contributing area) increases as a power‐law functions of the average terrain slope and soil burn severity class (SBSC) with exponents equal to approximately 1.5. Our analysis quantifies the relationships among sediment yield, average terrain slope, and average soil burn severity class at the watershed scale and should prove useful for predicting the geomorphic response of wildfire‐affected drainage basins. Copyright © 2014 John Wiley & Sons, Ltd.

[1] In this study we tested upland hillslope evolution models and constrained the rates of regolith production, colluvial transport, and eolian deposition over geologic time scales in a dated volcanic landscape in northern New Mexico using field measurements of regolith thickness; geochemical analyses of regolith, bedrock, and regional dust; numerical modeling of regolith production and transport; and quantitative analyses of airborne light detection and ranging (lidar) digital elevation models (DEMs). Within this volcanic landscape, many topographically closed basins exist as a result of compressional folding and explosion pitting during eruption. The landscape has evolved from an initial state of no regolith cover at 40 ± 5 ka to its modern state, which has highly weathered regolith ranging from 0 to 3+ m, with local thickness values controlled primarily by topographic position. Our models constrain the maximum rate of regolith production in the study area to be in the range of 0.02 to 0.12 m kyr −1 and the rate of colluvial transport per unit slope gradient to be in the range of 0.2 to 2.7 m 2 kyr −1, with higher values in areas with more aboveground biomass. We conclude that a depth-dependent colluvial transport model better predicts the observed spatial distribution of regolith thickness compared to a model that has no depth dependence. This study adds to the database of estimates for rates of regolith production and transport in the western United States and shows how dated landscapes can be used to improve our understanding of the coevolution of landscapes and regolith cover.

Wildfires can dramatically increase erosion rates over time scales on the order of several years, yet few data firmly constrain the relative importance of post-wildfire erosion in the long-term denudation of landscapes. We tested the hypothesis that wildfire-affected erosion is responsible for a large majority of long-term denudation in the uplands of the Valles Caldera, New Mexico, by quantifying erosion rates in wildfire-affected and non-wildfire-affected watersheds over short (~10 0 -10 1 years) time scales using suspended sediment loads, multitemporal terrestrial laser scanning, and airborne laser scanning and over long (~10 3 -10 6 years) time scales using 10 Be inventories and incision into a dated paleosurface. We found that following the Las Conchas fire in 2011, mean watershed-averaged erosion rates were more than 1000 μm yr À1 , i.e.,~10 3 -10 5 times higher than nearby unburned watersheds of similar area, relief, and lithology. Long-term denudation rates are on the order of 10-100 μm yr À1 . Combining data for wildfire-affected and non-wildfire-affected erosion rates into a long-term denudation rate budget, we found that wildfire-affected erosion is responsible for at least 90% of denudation over geologic time scales in our study area despite the fact that such conditions occur only at a small fraction of the time. Monte Carlo analyses demonstrate that this conclusion is robust with respect to uncertainties in the rates and time scales used in the calculations.

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