Impact of the 29 September 2009 South Pacific tsunami on Wallis and Futuna

The 29 September 2009 South Pacific tsunami reached the islands of Futuna and Alofi, 650 km to the west of its origin, between 7 and 7:20 am on 30 September, local time. No warning was issued. We measured run-up heights and inundation distances at 41 sites around the islands. The worst impact (4.5 m run-up; 85 m inundation; 3.8 m flow depth) was observed on Alofiʹs NW beach. On Futuna, maximum run-ups of 4.4 m on the eastern tip and 4.3 m on the NW tip of the island are associated with maximum inundations of 95 and 72 m, respectively. A flow depth of 2.2 m was inferred on the NE tip. The tsunami arrived as a drawdown of water with the reef exposed well below the lowest tides. It was followed by two positive waves of similar amplitude, ca. 4 min apart. Damage was mainly limited to salt-burnt vegetation and sediments deposited at the coast. There were no casualties, but a significant disaster was avoided because the tsunami arrived in the early morning at close to low tide. This event, together with a small tsunami triggered by a local earthquake in 1993 and an oral legend about a destructive wave, indicate that the hazard is high for the 4500 inhabitants of Futuna who live on the low-lying, narrow coastal strip. The 70 min that the tsunami took to reach the island provided sufficient time for a warning to be issued, but this was not done.