Observations of tsunami and runup heights in Santa Cruz Harbor and surrounding beaches from the 2022 Hunga Tonga-Hunga Ha'apai tsunami

The 14 January 2022 eruption of Tonga Hunga-Tonga Ha'apai volcano generated tsunamis that impacted the west coast of the United States on the morning of 15 January 2022. This data release presents runup heights and tsunami heights collected by the U.S. Geological Survey (USGS) and the California Geological Survey (CGS) during surveys at the Santa Cruz Harbor and beaches in Santa Cruz County, California, on January 19th and 20th, 2022 (Figure 1; USGS Field Activity 2022-607-FA). Evidence of tsunami inundation included high-water marks on buildings and harbor infrastructure (Figure 2a), wrack lines (Figure 2b), and flow-direction indicators such as bent vegetation (Figure 2c). Elevations surveyed at the maximum inland extent of tsunami inundation are classified as "runup heights." High-water mark elevations are classified as "tsunami heights." At Seabright, Beer Can, and Manresa beaches, the inferred tsunami inundation limit was identified as the highest wrack line on each beach. The wrack line coincided with a change in sand color, with the inundated side consisting of darker colored sand (Figure 2d). Based on eyewitness and video observations of the tsunami in Santa Cruz Harbor, most of the surveyed tsunami and runup heights are the result of inundation from the highest wave around 08:50 PST (16:50 GMT). Flow-depth markers on buildings and infrastructure from a later wave were measured and reported as lower tsunami heights and are noted. The final point data are provided in a comma-separated text file and are projected in cartesian coordinates using the Universal Transverse Mercator (UTM), Zone 10 North, meters coordinate system. Figure 1. Map and aerial imagery showing tsunami survey locations, including a) map of all survey locations; b) survey points at the Santa Cruz Harbor and nearby Seabright beach; c) survey points at Beer Can Beach; and d) survey points at Manresa Beach. Figure 2. Examples of post-tsunami evidence of inundation and flooding. a) High-water marks (tsunami heights) on an electrical box marked by lines of fine organics and mud (red arrows). The upper mark represents the maximum water surface elevation from the wave at approximately 08:50 PST. The lower mark represents the water surface elevation most likely from a later wave. b) A tsunami wrack line (runup height; red line) at the north end of the Santa Cruz Harbor, identified by lightweight plant fragments, woodchips, and trash. c) Bent grasses representing the direction of return flow back towards the harbor (blue arrows, orange pen for scale). d) The tsunami wrack line and darker sand representing the inundation extent of the tsunami at Beer Can Beach.