RAPID: Field Survey of the 10 August 2025, Tracy Arm, Alaska, Landslide-Generated Tsunami

The objective of this NSF Rapid Response Research (RAPID) grant is to document and quantify the impacts of an extraordinary landslide-generated mega-tsunami that occurred on August 10, 2025, when an estimated ~65 million m³ of a mountainside collapsed into Tracy Arm, a fjord in southeast Alaska. Preliminary satellite and Digital Elevation Model (DEM) analyses suggest near-field runup of ~470–500 m, potentially the second-largest tsunami ever observed, creating an urgent need for ground-truth measurements before winter snow, freeze–thaw processes, and vegetation obscure or destroy fragile high-water marks and other ephemeral evidence. A small team of 3–4 experienced tsunami researchers will conduct a rapid-response field survey in early-to-mid October 2025 (prior to winter closures) to capture perishable data in the near-source region. This project will produce the first high-precision, field-validated dataset for a mega-tsunami of this magnitude and directly address key scientific gaps in the near-field behavior of extreme, short-period landslide tsunamis, where wave heights, velocities, and forces are most intense and existing models are least validated. Field activities will integrate geotechnical, hydraulic, and remote sensing approaches, including: (1) centimeter-level surveys of runup elevations using Real-Time Kinematic (RTK) GPS and drone-derived DEMs to refine preliminary runup estimates; (2) documentation of indicators of extreme turbulence and inertia (e.g., intense scour, embedded debris, and erosional signatures) to constrain near-field hydrodynamics; and (3) mapping of boulder transport and impact signatures as proxies for the event’s high-energy flow regime. All survey points, imagery, and derived products will be archived with open access via the NHERI DesignSafe cyberinfrastructure, enabling broad community use for model validation, comparative event analysis, and education. Results will be communicated to agencies including the USGS and the National Tsunami Hazard Mitigation Program to support improved tsunami modeling and hazard planning, including implications for vessels and operations in Alaska’s glacial fjords. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.