Coastal Impacts of the March 11th Tohoku, Japan Tsunami in the Galapagos Islands
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On March 11, 2011 at 5:46:23 UTC (March 10 11:46:23 PM Galapagos Local Time), the Mw 9.0 Great East Japan Earthquake occurred near the Tohoku region off the east coast of Japan, spawning a Pacific-wide tsunami. Approximately 12,000 km away, the Galapagos Islands experienced moderate tsunami impacts, including flooding, structural damage, and strong currents. In this paper, we present observations and measurements of the tsunami effects in the Galapagos, focusing on the four largest islands in the archipelago; (from west to east) Isabela, Santiagio, Santa Cruz, and San Cristobal. Access to the tsunami affected areas was one of the largest challenges of the field survey. Aside from approximately ten sandy beaches open to tourists, all other shoreline locations are restricted to anyone without a research permit; open cooperation with the Galapagos National Park provided the survey team complete access to the Islands coastlines. Survey locations were guided by numerical simulations of the tsunami performed prior to the field work. This numerical guidance accurately predicted the regions of highest impact, as well as regions of relatively low impact. Tide-corrected maximum tsunami heights were generally in the range of 3–4 m with the highest runup of 6 m measured in a small pocket beach on Isla Isabela. Puerto Ayora, on Santa Cruz Island, the largest harbor in the Galapagos experienced significant flooding and damage to structures located at the shoreline. A current meter moored inside the harbor recorded relatively weak tsunami currents of less than 0.3 m/s (0.6 knot) during the event. Comparisons with detailed numerical simulations suggest that these low current speed observations are most likely the result of data averaging at 20-min intervals and that maximum instantaneous current speeds were considerably larger. Currents in the Canal de Itabaca, a natural waterway between Santa Cruz Island and a smaller island offshore, were strong enough to displace multiple 5.5-ton navigation buoys. Numerical simulations indicate that currents in the Canal de Itabaca exceeded 4 m/s (~8 knots), a very large flow speed for a navigational waterway.
KeywordsTsunami Wave Sandy Beach Acoustic Doppler Current Profiler Tsunami Height Great East Japan Earthquake
The authors wish to thank the Galapagos National Park for facilitating rapid access to typically restricted beaches. In particular, we thank the Park rangers Carlos Ortega, Jose Caizabanda, and Rene Freire for accompanying us on our surveys. Coordination through INOCAR was indispensable, and the survey would not have been possible without their help. The authors thank co-editor of this volume Jose Borrero for his extensive assistance in revising this manuscript, including the creation of the maps in Fig. 1 using the GMT plotting software (Wessel and Smith 1991). Funding for the effort was provided by a National Science Foundation RAPID grant# 1136534 to Weiss and Lynett.
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