Meteorology seminars

A currently quiescent stratovolcano, Mount Shasta, California, still poses a significant hazard to nearby communities thanks to impactful non-eruptive debris flows that can occur throughout the year. In this work, we have built a more complete record of debris flow occurrence using monitoring campaigns and research into historical newspaper records; analyze debris flow frequency and triggering in the context of regional weather and climate patterns; and forecast the future of debris flow hazards at Mount Shasta. This topic is timely because of its relevance to the ongoing efforts to create up-to-date, usable, and relevant hazards assessments at United States Volcanoes, as well as a need expressed by local land managers for debris flow data. Ultimately, this work will not only enhance our understanding of debris flow occurrence at Mount Shasta, but will also aid stakeholders in land planning, hazard mitigation, and preparedness.

We investigated meteorological controls on seasonal deep-seated motion of the Barry Arm landslide, a ~500 Mm³ slope instability with tsunamigenic potential in Prince William Sound, Alaska. Using ground-based synthetic aperture radar, we identified periods of deep-seated displacement, and combined airborne ice-penetrating radar with a glacier melt model driven by local meteorological data to evaluate the role of Cascade Glacier, which covers much of the area contributing groundwater to the landslide. We show that an over-deepened section of Cascade Glacier adjacent to the most active part of the landslide likely acts as a transient reservoir that routes meltwater to the landslide and that deep-seated landslide motion initiated only when modeled glacier discharge exceeded a distinct threshold.

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.

Hélène Brogniez examines atmospheric water vapour as a major component of the climate system. The seminar explains how its relationship with temperature amplifies warming and connects this feedback to the water cycle. Observations and numerical models are considered as complementary tools for weather prediction and climate projections.

The three lectures examine how physical theory can make sense of complex systems with fluctuations and many interacting components. Syukuro Manabe describes the construction of climate models that connect atmospheric radiation, heat transport and carbon dioxide to changes in surface temperature. Klaus Hasselmann addresses the relationship between short-term weather variability and long-term climate, including methods for distinguishing human influence from natural variation. Giorgio Parisi examines disordered systems and the coexistence of multiple equilibria, with spin glasses providing a central setting for understanding apparently irregular collective behaviour. The programme preserves both parts of the prize: quantitative climate science and the statistical physics of disorder, rather than treating either as a substitute for the other.