October 17, 1848 Tsunami: Cook Strait, New Zealand

Reference #5324:

1848, October 17, 16:10 [local time, Oct 17 04:10 UTC]. This morning [Oct 18] the tide rose to an unusual height, overflowing part of Lambton Quay and all those sections at the head of the Bay fronting the water and immediately adjoining the swamp. On Wednesday there was an unusually high tide. Although the tides are at the neap, the tide rose over the beach-road, and flooded the lower parts of some houses. The continuance of S. E. gales would, in the absence of earthquakes, be enough to account for this, yet it seems to have produced a good deal of alarm.

On Wednesday [Oct 18] we had one of the heaviest gales of wind ever experienced here from the N.,W., accompanied by much rain and a remarkably high tide...

Given the fact that the flooding of the foreshore in Wellington occurred over 17 hours after the large 17 October aftershock, none of the descriptive accounts suggest several rises and falls as would be expected in a tsunami, and most significantly, can be explained by a combination of storm surge and high tide levels, a tsunami is highly unlikely and given a validity of 0. The lack of tsunami is consistent with Fitzherbert's (1848) statement that: while "one extraordinary high tide occurred during the period of the earthquakes; it was not, however, contemporaneous with any particular shock, and may be rationally accounted for otherwise [i.e. by wind and rain]." Given the lack of tsunami in Cook Strait, the high water levels in Taranaki on October 18 are most easily explained by swell and wind waves set-up by the strong north-west gales, and possibly storm surge, as the tides were not exceptionally high.

Reference #415:

1848, October 17, 15:40 [local time]. On the 17th at 15:40, a new earthquake occurred which was more severe than the previous one... The source of the earthquake was apparently located in the valley of the Awatere River where, possibly, movements along surface fractures occurred for a distance of about 110 km. On the 18th there was a very strong flood tide. At the slack, the sea covered a road along the shore and flooded the ground floor of several houses. This flooding caused great alarm amongst the inhabitants although the flood may have resulted solely from the continuous, strong south-easterly winds.