August 6, 1858 Tsunami: New Zealand

A heavy sea, with waves breaking a long way offshore, broke over the foreshore and inundated roads near the shoreline in and about Napier over several days from the morning of 6 August 1858. From the top of the Bluff, the rock off Ahuriri Bluff was visible in the troughs of the waves. Ships were unable to leave port. It was reported that there was insufficient wind in Hawke Bay or along the coast to account for the heavy sea and it was thought to be caused by southeast winds between Napier and Wellington. After the sea becomes smooth the water level is still high.

Tide heights predicted by NIWA's Tide Forecaster (http://www.niwa.co.nz/services/free/tides) for the period 6-10 August 1858 vary from small spring in the afternoon of August 6 to just over Mean HW Perigean Spring (MHWPS) or "King" tide on the evening of August 10, accounting for high water levels reported for the later part of the period.

When considered in conjunction with high spring tides, the duration and effects of this event are more consistent with swell and possibly storm surge produced by a storm at sea rather than with tsunami. A validity of 0 is assigned.

Note that this event occurred when Napier and the surrounding area was lower than it is today, having been raised by the 1931 MS7.8 Hawke's Bay earthquake (see description in the National Earthquake Information Database, and on the GeoNet website, www.geonet.org.nz).

Note also that this event has been included in the database to forestall its being interpreted as tsunami. (reference #5324)