Thermomechanical erosion modelling of Baydaratskaya Bay, Russia with COSMOS

Rapid coastal erosion threatens Arctic coastal infrastructure, including communities and industrial installations. Erosion of permafrost depends on numerous processes, including thermal and mechanical behaviour of frozen and unfrozen soil, nearshore hydrodynamics, atmospheric forcing, and the presence of sea ice. The quantification and numerical modelling of these processes is essential to predicting Arctic coastal erosion. This paper presents a case study of Baydaratskaya Bay, Russia, using the COSMOS numerical model to predict thermal-mechanical erosion. In particular, this study focuses on thermoabrasional rather than thermodenudational processes. A field dataset of onshore thermal and mechanical soil characteristics was supplemented by sources from the literature to serve as input for the model. A detailed sensitivity analysis has been conducted to determine the influence of key parameters on coastal erosion rates at the study site. This case study highlights the need for expanded data collection on Arctic coastlines and provides direction for future investigations

Postwildfire Soil-Hydraulic Recovery and the Persistence of Debris Flow Hazards

Deadly and destructive debris flows often follow wildfire, but understanding of changes in the hazard potential with time since fire is poor. We develop a simulation-based framework to quantify changes in the hydrologic triggering conditions for debris flows as postwildfire infiltration properties evolve through time. Our approach produces time-varying rainfall intensity-duration thresholds for runoff- and infiltration-generated debris flows with physics-based hydrologic simulations that are parameterized with widely available hydroclimatic, vegetation reflectance, and soil texture data. When we apply our thresholding protocol to a test case in the San Gabriel Mountains (California, USA), the results are consistent with existing regional empirical thresholds and rainstorms that caused runoff- and infiltration-generated debris flows soon after and three years following a wildfire, respectively. We find that the hydrologic triggering mechanisms for the two observed debris flow types are coupled with the effects of fire on the soil saturated hydraulic conductivity. Specifically, the rainfall intensity needed to generate debris flows via runoff increases with time following wildfire while the rainfall duration needed to produce debris flows via subsurface pore-water pressures decreases. We also find that variations in soil moisture, rainfall climatology, median grain size, and root reinforcement could impact the median annual probability of postwildfire debris flows. We conclude that a simulation-based method for calculating rainfall thresholds is a tractable approach to improve situational awareness of debris flow hazard in the years following wildfire. Further development of our framework will be important to quantify postwildfire hazard levels in variable climates, vegetation types, and fire regimes. © 2021. The Authors. Journal of Geophysical Research: Earth Surface published by Wiley Periodicals LLC on behalf of American Geophysical Union. This article has been contributed to by US Government employees and their work is in the public domain in the USA.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Terrestrial processes affecting unlithified coastal erosion disparities in central fjords of Svalbard

Terrestrial influences of coastal cliff morphology and hydrological impact on coastal erosion in unlithified cliff sediments in the inner fjords of Svalbard are assessed. Differential global positioning system measurements have been taken annually over the past two to four years at four field sites in central Svalbard. Measurements were combined with aerial imagery using ArcGIS and the Digital Shoreline Analysis System to calculate rates of erosion in varying geomorphological cliff types. A total of 750 m of coast was divided into two main cliff types: ice-poor and ice-rich tundra cliffs and further divided based on their sediment depositional character and processes currently acting upon sediments. The results show that the most consistent erosion rates occur in the ice-poor cliffs (0.34 m/yr), whereas the most irregular and highest rates occur in ice-rich cliffs (0.47 m/yr). Throughout the study, no waves were observed to reach cliff toes, and therefore erosion rates are considered to reflect an effect of terrestrial processes, rather than wave action. Terrestrial hydrological processes are the driving factors for cliff erosion through winter precipitation for ice-poor cliffs and summer precipitation for ice-rich cliffs. Sediment removal from the base of the cliffs appears to be mainly conducted by sea ice and the ice foot during break up as waves did not reach the base of the studied cliffs during the observed period