Physical Geography seminars

Frank Paul presents early findings from the Karakoram Anomaly Cross-ECV project. The research combines satellite Earth observations with climate data to improve glacier mass-balance modelling in a region where measurements are sparse and glaciers are changing rapidly. The talk examines how these complementary records can help monitor Karakoram glacier dynamics.

Extreme heat affects rural communities, coastal regions and marine environments in different ways. This webinar presents NOAA-supported research that helps decision-makers target resilience measures to local conditions. Case studies address rural Vermont, Charleston and the Northeast Pacific. The speakers examine rural heat risk in relation to exposure and transportation infrastructure; resilience strategies that connect heat with flooding, water management and sea-level rise; and the drivers and subsurface characteristics of marine heatwaves in ecologically and economically important regions. The discussion connects research with practical decisions about location-specific resilience. The event forms part of NOAA’s Climate Program Office Heat Research Webinar Series, supported by NIHHIS and the Climate Variability and Predictability programme. Online via Vimeo with advance attendee registration. Live captions are available and the webinar will be recorded.

This presentation introduces the first range-scale Deep-Seated Gravitational Slope Deformation (DSGSD) inventory in North America, focusing on the Sawatch Range of central Colorado. Through geomorphic mapping, field campaigns, and InSAR displacement analysis, we identified and characterized 39 previously unreported DSGSD. We analyzed this inventory to reveal the governing mechanisms that condition slopes for DSGSD development and to compare it with the global DSGSD inventory. Site-specific surveys of the South Mt. Massive and Mt. Jones DSGSDs result in interpretive cross sections that relate surface morphology to subsurface geological parameters and highlight how Sawatch DSGSDs form and evolve in unique ways. Furthermore, we discuss the implications of this work to the broader context of Rocky Mountain DSGSD. Widespread Deep-Seated Gravitational Slope Deformations Across the Sawatch Range, CO, Evans (2026), USGS Landslide Hazard Seminar, 09 September 2026.

Hillslope mass wasting can have an outsized impact on both long-term landscape evolution and short-term hazards. Inputs of coarse sediment can shield river beds, alter local flow hydraulics, and impede fish passage. This talk focuses on the Fraser Canyon in British Columbia, a 375 km reach of the Fraser River where the 2018 Big Bar Landslide temporarily blocked the river and created a hydraulic barrier to salmon migration. I will examine the history of landsliding in the Fraser Canyon, evaluate hillslope morphology and valley connectivity to identify areas susceptible to future river-impacting landslides, and explore how mass wasting influences local river hydraulics within the canyon. These case studies indicate that boundary conditions at the upstream end of river networks affect downstream hillslopes, prompting questions of how drainage divide migration, incision into underlying bedrock, and valley widening impact landslide activity.

Rivers grow by moving their drainage divides. Drainage divide migration can be (1) gradual, and widely distributed, such that each stream grows headward by similar amounts, or (2) rapid, and narrowly focused, such that a single stream grows at the expense of its neighbors and carves a gorge. Do rivers share the wealth? Or is most of the water and attention grabbed by just a few? This talk describes patterns of drainage divide migration, downstream river incision, and bedrock landslide occurrence in two landscapes developed in gently-dipping sedimentary rock. First, we quantify drainage divide migration rates across a retreating escarpment within cuesta landscapes of southwestern Germany. Rates indicate that river growth is localized along mainstem rivers, which have reversed their flow direction and extended headward at rates ~10-1000 fold faster than long-term rock uplift and river incision rates. Growing mainstem rivers carve gorges into underlying stratigraphy, which includes erosionally-susceptible evaporites, marls, and swelling claystones, leading to a variety of slope failures and interesting geomorphic phenomena. Halfway across the globe, a similar story is taking shape. Rivers of northwestern Arizona are growing and connecting across a series of sedimentary basins that were previously isolated by basin and range tectonism. Rivers integrate across these basins by a combination of filling, spilling, and headward erosion. As rivers grapple across water-stressed landscapes, the winners incise deeper into diverse packages of syntectonic basin stratigraphy. Landslide inventory mapping aided by newly available aerial lidar data and 1:24000 scale geologic mapping reveals associations between landslides and incision through swelling claystones deposited in these Neogene basins. Intersections between both factors and existing infrastructure are shown. These case studies indicate that boundary conditions at the upstream end of river networks affect downstream hillslopes, prompting questions of how drainage divide migration, incision into underlying bedrock, and valley widening impact landslide activity.

The coupled hydrology and ice dynamics of the higher elevations of the Greenland Ice Sheet, where ice is beyond a kilometre thick, remains poorly understood. This lack of knowledge is a significant source of uncertainty in the models used to project the ice sheet’s sea level rise contribution, both in terms of surface mass balance and the potential for dynamic drawdown. I will discuss some of our recent and ongoing work towards (1) improving the accuracy of partitioning between refreezing and runoff processes, and (2) capturing the impact of surface meltwater on ice sliding where the ice sheet is more than a kilometre thick.

Arctic landscapes are among the most vulnerable on Earth to climate change, largely due to the rapid degradation of permafrost. In steeper bedrock-dominated terrains, warming permafrost can lead to increased sediment production via mass wasting events and amplify the delivery of sediment to channels and lakes. However, there is a fundamental lack of data on current rates of sediment production and transport in Arctic watersheds, especially those still responding to post-glacial perturbations, making it impossible to predict the responses and rates of sediment transport processes under future climate change. In this talk, I will present findings from a field-based study of the Black Mountain catchment in the Aklavik Range (Canada). This site was chosen due to the presence of an alluvial fan that post-dates the retreat of the Laurentide Ice Sheet (LIS), providing a closed system where we can consider how both paraglacial and periglacial mass flow processes have influenced physical weathering and transport rates through time.

In the past decade, several fatal landslides have impacted Southeast Alaska, highlighting the need to advance our understanding of regional geomorphic and atmospheric controls on triggering events and runout behavior. A large and long runout landslide on Wrangell Island, with area in the top 0.5% of >14,760 slides mapped in the Tongass National Forest, initiated during an atmospheric river event in November 2023 and traveled >1 km downslope, causing six fatalities. We used field observations, sequential airborne lidar, geotechnical analyses, and climate data to characterize the geomorphic, hydrologic, and atmospheric conditions contributing to the landslide. Rainfall intensities recorded at the Wrangell airport were modest (~1-yr recurrence interval), but rapid snowmelt and drainage from a ridgetop wetland may have contributed to rapid saturation of the landslide. Although strong winds were recorded, we did not observe extensive windthrow, which may downgrade its contribution to slope failure. The landslide mobilized a steep, thick (>4 m) wedge of colluvium that accumulated below a resistant bedrock ledge and entrained additional colluvial deposits as it traveled downslope across cliff-bench topography. The substantial entrainment resulted in an unusually large width, extensive runout, and low depositional slope as the landslide terminated in the coastal environment. Our results suggest that the sequencing of rain- and snow-dominated storms, geologic controls on post-glacial colluvium production and accumulation, and ridgetop hydrology contributed to landslide initiation and mobility. Advances in post-glacial landscape evolution models, frequent lidar acquisition, and additional climate data are needed to inform regional landslide hazard assessment.

Hurricane Helene devastated western North Carolina and parts of surrounding Tennessee and Virginia. A stalled front over the Blue Ridge prior to landfall of the hurricane resulted in cumulative rainfall totals of 20–30 inches from Sept. 25–27, 2024. This triggered numerous landslides and devastating flooding, and has changed the landscape of the Blue Ridge and mountain communities. This mapping and assessment of the landslides was conducted as part of the USGS Landslide Assessments, Situational Awareness and Event Response Research (LASER) and in cooperation with the North Carolina Geological Survey Landslide Hazard Program. Mapping efforts focused on the northernmost area heavily impacted from the storm: parts of Watauga, Avery, and Ashe County, NC, and parts of Johnson County, TN. Initial observational descriptions of the landslides are presented. Landslides mapped are separated into three type occurrences, hyperconcentrated earth flows, debris flows, and modified slope failures. Earth flows occurred on steep grassed slopes and consisted of soil with a mixture of vegetated clumps, saprolite, and rock. The landslide tracks were 10–338 m long, and scarp widths of 10–30 m that often cut down 1–2 m to bedrock. Earth flows often occurred in clusters, and some merged down slope. Debris flows had longer tracks, 96–1085 m, and consisted of a mixture of soil, rock, trees, vegetation, and other debris. Head scarps were 10–114 m wide and cut down through 1–3 m of colluvium to bedrock. Bedrock structures controlling the failures included joints, fractures, and foliation. Seven debris flows on Howards Creek initiated on steep slopes with aspect and slope close to the orientation of the foliation in bedrock (330/20–40° NE). Modified slope failures included landslides that initiated on road cuts, road embankments, steep cut slopes, and other slopes modified by construction (e.g., failed drainages or septic fields). Although the slope modification was important to initiate these slides, some localized along preexisting bedrock (saprolite) structures. Collectively, the impact of landslides from Hurricane Helene highlights the importance of basic geologic mapping and landslide assessment to build robust datasets to better understand and model the occurrence of landslides and strengthen our planning and rebuilding of mountain communities.

Fluvial channel steepness and hilltop curvature are commonly used as proxies for erosion rate in equilibrium landscapes, but they become less reliable in rocky steeplands dominated by debris flows. We explore an alternative metric—Adf, the drainage area at which valleys transition from slope-invariant to fluvial power-law slope-area scaling—and show that it correlates with erosion rates in several regions. Combining field data with a landform evolution model, we demonstrate that Adf provides insight into where debris-flow processes dominate, and we constrain a physically meaningful debris-flow incision law that offers new insight into how steep landscapes evolve under varying climatic and tectonic conditions.

On February 6, 2023, a Mw 7.8 and Mw 7.5 earthquake doublet struck along the East Anatolian Fault Zone in Türkiye, triggering over 3,600 coseismic landslides. Roughly a month later, a rare atmospheric river event delivered up to 183 mm of rainfall in just 20 hours to the earthquake impacted region. This extreme precipitation induced additional landslides, debris flows, and flooding. In our research, we conduct a probabilistic landslide hazard assessment using the open-source Landlab earth surface modeling library, integrating both seismic and climatic drivers. The model incorporates earthquake legacy effects, representing post-seismic slope weakening, and simulates shallow landslide susceptibility using a Monte Carlo implementation of the infinite slope stability theorem informed by remote sensing datasets. I will present three key analyses: (1) modeling hydrologic response to the AR event and mapping landslide probability with and without earthquake legacy effects; (2) examining how the sequence and combination of extreme events alter landslide hazard; and (3) demonstrating how using historic climate data can effectively replicate post-seismic landslide hazard maps that use real-time data, offering an approach for seasonal hazard forecasting in tectonically active and climate-sensitive regions.