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Rock glaciers are common geomorphic features in alpine landscapes and comprise a potentially significant but poorly quantified water resource. This project focused on three complementary questions germane to rock glacier hydrology: 1) Does the composition of rock glacier meltwater vary from year to year? 2) How dependent is the composition of rock glacier meltwater on lithology? And 3) How does the presence of rock glaciers in a catchment change stream water chemistry? To address these questions, we deployed automated samplers to collect water from late June through mid-October 2022 in two rock-glacierized mountain ranges in Utah, United States characterized by different lithologies. In the Uinta Mountains of northern Utah, where bedrock is predominantly quartzite, water was collected at springs discharging from two rock glaciers previously shown to release water in late summer sourced from internal ice. In the La Sal Mountains of southeastern Utah, where trachyte bedrock is widespread, water was collected at a rock glacier spring, along the main stream in a watershed containing multiple rock glaciers, and from a stream in a watershed where rock glaciers are absent. Precipitation was also collected, and data loggers for water temperature and electric conductivity were deployed. Water samples were analyzed for stable isotopes with cavity ring-down spectroscopy and hydrochemistry with ICP-MS. Our data show that water discharging from rock glaciers in the Uinta Mountains exhibits a shift from a snowmelt source to an internal ice source over the course of the melt season that is consistent from year to year. We also found that the chemistry of rock glacier water in the two study areas is notably different in ways that can be linked back to their contrasting bedrock types. Finally, in the La Sal Mountains, the properties of water along the main stream in a rock-glacierized basin resemble the properties of water discharging from rock glaciers, and strongly contrast with the water in a catchment lacking rock glaciers. Collectively these results underscore the role of rock glaciers as an agent influencing the hydrochemistry of water in high-elevation stream systems. 

Abstract. Water draining from rock glaciers in the Uinta Mountains of Utah(USA) was analyzed and compared with samples of groundwater and water fromthe primary stream in a representative 5000 ha drainage. Rock glacier water resembles snowmelt in the early summer but evolves to higher values of d-excess and greatly elevated Ca and Mg content as the melt season progresses. This pattern is consistent with models describing a transition from snowmelt to melting of seasonal ice to melting of perennial ice in the rock glacier interior in late summer and fall. Water derived from this internal ice appears to have been the source of ∼25 % of the streamflow in this study area during September of 2021. This result emphasizes the significant role that rock glaciers can play in the hydrology of high-elevation watersheds, particularly in summers following a winter with below-average snowpack. 

Slow-moving landslides move downslope at velocities that range from mm year⁻¹to m year⁻¹. Such deformations can be measured using satellite-based synthetic aperture radar interferometry (InSAR). We developed a new method to systematically detect and quantify accelerations and decelerations of slowly deforming areas using InSAR displacement time series. The displacement time series are filtered using an outlier detector and subsequently piecewise linear functions are fitted to identify changes in the displacement rate (i.e., accelerations or decelerations). Grouped accelerations and decelerations are inventoried as indicators of potential unstable areas. We tested and refined our new method using a high-quality dataset from the Mud Creek landslide, CA, USA. Our method detects accelerations and decelerations that coincide with those previously detected by manual examination. Second, we tested our method in the region around the Mazar dam and reservoir in Southeast Ecuador, where the time series data were of considerably lower quality. We detected accelerations and decelerations occurring during the entire study period near and upslope of the reservoir. Application of our method results in a wealth of information on the dynamics of the surface displacement of hillslopes and provides an objective way to identify changes in displacement rates. The displacement rates, their spatial variation, and the timing of accelerations and decelerations can be used to study the physical behavior of a slow-moving slope or for regional hazard assessment by linking the timing of changes in displacement rates to landslide causal and triggering factors.

 

Abstract. Rapid detection of landslides is critical for emergency response, disaster mitigation, and improving our understanding of landslide dynamics. Satellite-based synthetic aperture radar (SAR) can be used to detect landslides, often within days of a triggering event, because it penetrates clouds, operates day and night, and is regularly acquired worldwide. Here we present a SAR backscatter change approach in the cloud-based Google Earth Engine (GEE) that uses multi-temporal stacks of freely available data from the Copernicus Sentinel-1 satellites to generate landslide density heatmaps for rapid detection. We test our GEE-based approach on multiple recent rainfall- and earthquake-triggered landslide events. Our ability to detect surface change from landslides generally improves with the total number of SAR images acquired before and after a landslide event, by combining data from both ascending and descending satellite acquisition geometries and applying topographic masks to remove flat areas unlikely to experience landslides. Importantly, our GEE approach does not require downloading a large volume of data to a local system or specialized processing software, which allows the broader hazard and landslide community to utilize and advance these state-of-the-art remote sensing data for improved situational awareness of landslide hazards. 

Abstract. In steep wildfire-burned terrains, intense rainfall can produce large runoff that can trigger highly destructive debris flows. However, the abilityto accurately characterize and forecast debris flow susceptibility in burned terrains using physics-based tools remains limited. Here, we augmentthe Weather Research and Forecasting Hydrological modeling system (WRF-Hydro) to simulate both overland and channelized flows and assess postfiredebris flow susceptibility over a regional domain. We perform hindcast simulations using high-resolution weather-radar-derived precipitation andreanalysis data to drive non-burned baseline and burn scar sensitivity experiments. Our simulations focus on January 2021 when an atmospheric rivertriggered numerous debris flows within a wildfire burn scar in Big Sur – one of which destroyed California's famous Highway 1. Compared to thebaseline, our burn scar simulation yields dramatic increases in total and peak discharge and shorter lags between rainfall onset and peakdischarge, consistent with streamflow observations at nearby US Geological Survey (USGS) streamflow gage sites. For the 404 catchments located inthe simulated burn scar area, median catchment-area-normalized peak discharge increases by ∼ 450 % compared to the baseline. Catchmentswith anomalously high catchment-area-normalized peak discharge correspond well with post-event field-based and remotely sensed debris flowobservations. We suggest that our regional postfire debris flow susceptibility analysis demonstrates WRF-Hydro as a compelling new physics-basedtool whose utility could be further extended via coupling to sediment erosion and transport models and/or ensemble-based operational weatherforecasts. Given the high-fidelity performance of our augmented version of WRF-Hydro, as well as its potential usage in probabilistic hazardforecasts, we argue for its continued development and application in postfire hydrologic and natural hazard assessments. 

Abstract. Rock glaciers are a prominent component of many alpine landscapes andconstitute a significant water resource in some arid mountainenvironments. Here, we employ satellite-based interferometric syntheticaperture radar (InSAR) between 2016 and 2019 to identify and monitor activeand transitional rock glaciers in the Uinta Mountains (Utah, USA), an area of∼3000 km2. We used mean velocity maps to generate aninventory for the Uinta Mountains containing 205 active and transitional rockglaciers. These rock glaciers are 11.9 ha in area on average andlocated at a mean elevation of 3308 m, where mean annual airtemperature is −0.25 ∘C. The mean downslope velocity for theinventory is 1.94 cm yr−1, but individual rock glaciers have velocities ranging from0.35 to 6.04 cm yr−1. To search for relationships with climaticdrivers, we investigated the time-dependent motion of three rock glaciers. Wefound that rock glacier motion has a significant seasonal component, withrates that are more than 5 times faster during the late summer compared to therest of the year. Rock glacier velocities also appear to be correlated withthe snow water equivalent of the previous winter's snowpack. Our resultsdemonstrate the ability to use satellite InSAR to monitor rock glaciers overlarge areas and provide insight into the environmental factors that controltheir kinematics. 

Abstract. To explore the sensitivity of rivers to blocking from landslidedebris, we exploit two similar geomorphic settings in California'sFranciscan mélange where slow-moving landslides, often referred to asearthflows, impinge on river channels with drainage areas that differ by afactor of 30. Analysis of valley widths and river long profiles over∼19 km of Alameda Creek (185 km2 drainage area) andArroyo Hondo (200 km2 drainage area) in central California shows avery consistent picture in which earthflows that intersect these channelsforce tens of meters of gravel aggradation for kilometers upstream, leadingto apparently long-lived sediment storage and channel burial at these sites.In contrast, over a ∼30 km section of the Eel River (5547 km2 drainage area), there are no knickpoints or aggradation upstreamof locations where earthflows impinge on its channel. Hydraulic andhydrologic data from United States Geological Survey (USGS) gages on Arroyo Hondo and the Eel River, combinedwith measured size distributions of boulders input by landslides for bothlocations, suggest that landslide derived boulders are not mobile at eithersite during the largest floods (>2-year recurrence) with field-measured flow depths. We therefore argue that boulder transport capacity isan unlikely explanation for the observed difference in sensitivity tolandslide inputs. At the same time, we find that earthflow fluxes per unitchannel width are nearly identical for Oak Ridge earthflow on Arroyo Hondo,where evidence for blocking is clear, and for the Boulder Creek earthflow onthe Eel River, where evidence for blocking is absent. These observationssuggest that boulder supply is also an unlikely explanation for the observedmorphological differences along the two rivers. Instead, we argue that thedramatically different sensitivity of the two locations to landslideblocking is related to differences in channel width relative to typicalseasonal displacements of earthflows. A synthesis of seasonal earthflowdisplacements in the Franciscan mélange shows that the channel width ofthe Eel River is ∼5 times larger than the largest annualseasonal displacement. In contrast, during wet winters, earthflows arecapable of crossing the entire channel width of Arroyo Hondo and AlamedaCreek. In support of this interpretation, satellite imagery shows thatimmobile earthflow-derived boulders are generally confined to the edges ofthe channel on the Eel River. By contrast, immobile earthflow-derivedboulders jam the entire channel on Arroyo Hondo. Our results imply that lower drainage area reaches of earthflow-dominated catchments may be particularly prone to blocking. By inhibiting the upstreampropagation of base-level signals, valley-blocking earthflows may thereforepromote the formation of so-called “relict topography”.