October 15, 1848 Tsunami: Cook Strait, New Zealand

Reference #5324:

1848, October 16, 02:10 [local time, Oct 15, 14:10 UTC]. There are several accounts of sea level disturbances that have been interpreted as possible tsunami on three days during the 1848 earthquakes: October 16, i.e. the day of the mainshock; October 18 and October 19. According to Collinson (1848) "eight hours after the first shock [which occurred on October 16 at 0140 local solar time], it being high water but neap tides, the tide rose in Wellington one foot [0.3 m] above ordinary spring tides" i.e. the rise occurred on October 16 at about 9.40 am local solar time. Ironside's (1891) account indicating that "the vagaries of the inflow and receding of the waters ... were remarkable", although included in the transcriptions is given little credence, as there is clear confusion in his full account of the earthquakes with the effects and uplift, and almost certainly the tsunami, that occurred in the 1855 earthquake. Hence, Collinson (1848) is the only contemporary account of a tsunami on the day of the mainshock, despite there being newspapers and other journal writers that recorded day-to-day events. The date in Collinson's account is almost certainly incorrect and should be October 18.

The lack of a tsunami being recorded at any time during the sequence of earthquakes, including the mainshock, is consistent with accounts written some years after the 1848. It is not clear whether these include locations other than Wellington. However, it is unlikely that a large tsunami and/or its effects, had they occurred near the source in Marlborough or along Wellington's southern coast, were not observed despite the fact that few people lived there. Further, the lack of large or even moderate tsunami near the source is consistent with the lack of an observable tsunami within Wellington Harbour. On the other hand, it cannot be entirely ruled out that a small tsunami occurred. If a tsunami had been generated by the mainshock, it would have arrived in the Wellington City area an hour or so after the earthquake, on an ebbing tide about 2 hours after low tide. The occurrence of low tide could have masked the occurrence of a small tsunami. However, as many people lived on the beach in Lambton Harbour, and as they were disturbed by strong earthquake shaking, damage and aftershocks, they would surely have observed and commented upon any unusual repetitive ebbs and flows of the sea, had they been obvious, that is, exceeding 20-30 centimetres.

Reference #79:

1848, Oct. 16-25 possible dates of tsunami.

Reference #415:

1848, October 16, 01:40 [local time]. On October 16 at 1:40 [local time] the first of a series of shocks occurred in the region of Cook Strait. Eight hours after the earthquake, during a high water slack period, the water level in Wellington had risen 0.3 m higher than the mark of the highest flood tide. This effect, however, could have been caused not only by the earthquake but also by a strong southeast wind blowing on the 15th and 16th. Unusual changes in the sea level were noted also in Nelson and Wanganui.