Submergence of Floating Concrete Docks at Crescent City Harbor during the 2025 Kamchatka Tsunami

On July 29, 2025, an MW 8.8 Kamchatka earthquake generated a Pacific-wide teletsunami that produced energetic, long-period surges in Crescent City, California, with dominant harbor oscillations at periods of approximately 20, 25, and 40 min. Although water levels were moderate relative to previous tsunamis, currents in the inner boat basin were sufficiently strong to test the post-2011 marina rebuild. This paper documents a rare failure mode observed in situ: temporary submergence of large concrete floating dock modules at H Dock without structural breakup. We present tide-gage records, bathymetry, as-built information, and time-lapse video collected during the tsunami. During a flood surge, visually estimated current speeds of approximately 3.0–4.3 m/s (10–14 ft/s) impinged on H Dock, after which the deck lost freeboard and sank uniformly beneath the water surface. Frame-tracked kinematics indicated an approximately steady descent rate of 2.2 cm/s (0.85 in./s) following a brief approximately 1.3 cm/s2 (0.5 in./s2) acceleration; given the dock mass per unit length, the onset of submergence was consistent with a net downward force of roughly 44 N/m length of dock (3 lb/ft), implying that the flow just exceeded a critical threshold for submergence. The dock remained submerged for approximately 2 min and reemerged with sections misaligned. A mechanism consistent with observations was a negative lift induced by accelerated, constricted underdeck flow (i.e., the Venturi effect) that reduced pressure beneath the float and overcame the residual buoyancy of the float.