January 23, 1855 Tsunami: Northern Island, New Zealand

January 23, 1855 after 21:00 [local time] there was an earthquake in Wellington and vicinity, lasting for 1.5 min. In Wellington, the ship Pandora was anchored in 11 m of water. According to the captain, the shocks that were generated during the earthquake, which lasted over a minute, felt as if the ship was hitting rough bottom. Disembarking with his mate onto the beach, the captain became aware of a rapid succession of ebbs and flows. The waves were observed for at least 50 minutes, as they rolled over the shore of South Island. A "terrible" tidal wave rushed onto the shore. (reference #415) The 1855 January 23 0932 UT 2111 Local time MW8.2-8.4 Wairarapa earthquake generated New Zealand's largest historical locally-generated tsunami. The tsunami most affected the Cook Strait region, where the Wairarapa Fault and subsidiary faults (Wharekauhau Thrust and small play fault) ruptured beneath Cook Strait causing significant uplift (up to 6.4 m) of a large region west of the fault on the northern side of the strait and a small amount of subsidence on the southern side. The effects of the tsunami were observed at least as far north as Waikawa Beach, where fish were deposited above high water mark, and as far south as the Clarence River mouth and possibly Kaikoura, although evidence for the latter is equivocal. A bore in the Avon River attributed by De Lange & Healy (1986) to tsunami and the "great sea wave" in Otago harbour (Davie, 1870) were almost certainly seismically induced seiches, not tsunami. Seiches, often confused with tsunami on the coast, were observed in coastal rivers and estuaries at Wairoa (Hawke's Bay), Motupipi in Golden Bay, Kaiapoi and at Lyttelton, as well as in many inland water bodies. The greatest known height (10-11 m) reached by the tsunami was at Te Kopi in Palliser Bay, where a shed on a cliff 9 m above the sea was swept away. Here also, on the night of the earthquake and tsunami, a sailor who had experienced a tsunami in South America, persuaded a family to leave the shore. Nearby, at Whangaimoana, a tool that had been on the shore at the time of the earthquake was found many years later in a location 10 m above high water mark. High waves were also observed along the coast south of Wellington and along the Wairau Bar on the southern shore of Cook Strait, probably reaching 6-7 m near Rarangi. In Lyall Bay the tsunami swept about 2-2.5 km inland, inundating what is now the suburb of Miramar. The sea sweeping in from Lyall Bay (est. height above sea level at time, 4-5 m) reportedly met the water sweeping in from Evans Bay, on the Wellington Harbour side of Rongotai Isthmus (est. height above sea level at time 3-4 m). Within Wellington Harbour, water levels varied considerably. At Petone and along the road to the Hutt Valley, fish were deposited (the tide was high at the time of the earthquake) but the water levels do not seem to have reached much more than a metre or so above normal. However, the shops along the beach front at Lambton Quay (now on reclaimed land 200 m from the shore) were inundated with waves about 1.4-2.4 m above sea level at the time immediately after or during the earthquake. Barnett et al. (1991) (Grapes & Downes (1997)) separated the source of the tsunami within the harbour into three different components: the horizontal movement, causing an immediate "slosh"; differential vertical movement across the harbour; and the much greater deformation in Cook Strait and extending across the whole region west of the fault. For a local source tsunami, the duration seems to have been quite long, observations consistently indicating that in Wellington harbour and in Cook Strait water levels oscillated for 8-12 hours. It was also said that the tides were irregular for a week (see entries for January 24-31, January 24 and February 3). (reference #5324)