Tsunamis have been a danger in New Zealand as long as people have lived there. Archaeological studies have shown that during the mid-15th century, many Māori moved their settlements from low-lying coastal sites to hilltops and inland sites. A number of the abandoned coastal settlements show clear evidence of tsunami inundation.
Tsunamis are also recorded in Māori oral tradition. For example, a wave that caused widespread death and damage on the western side of D’Urville Island in Tasman Bay may have been a tsunami:
Unfortunately the community at Moawhitu was eventually wiped out when a massive tidal wave called Tapu-arero-utuutu swept into the harbour and drowned almost everyone, tumbling their bodies into the sand dunes which were piled up by the force of the waves … Traditions do not record whether the tidal wave affected other communities on Rangitoto (D’Urville Island) or the mainland across Te Aumiti (French Pass), but even today kōiwi (human remains) and artefacts are frequently eroded from the dunes at Moawhitu, especially after stormy conditions or exceptionally high tides. 1
Wairarapa earthquake tsunamis, 1855
On 23 January 1855, a magnitude 8.1–8.2 earthquake, the most powerful to strike New Zealand since European settlement, shook the lower North Island. It generated not one, but several types of tsunami.
During the earthquake, the entire region west of the Wairarapa fault lurched abruptly north-east. Like soup in a bowl that is jostled, the water of Wellington Harbour slopped onto the adjacent land. The next movement of water occurred because the entire Wellington region had tilted – the eastern side of the harbour was now about 80 centimetres higher than the western side. The harbour waters ponderously moved off downhill, towards central Wellington. Houses and shops were flooded along Lambton Quay, which at that time was on the shoreline.
The greatest tsunami, however, was generated in Cook Strait. The Rimutaka Range rose as much as 6 metres, and part of the floor of the strait was probably uplifted. The tsunami destroyed sheds more than 8 metres above the sea at Te Kopi, on the southern Wairarapa coast. It moved along the strait and up the Kapiti coast – stranding fish as far north as Ōtaki – and spread across to the South Island.
Many turns of the tide
The sloop Pandora was anchored in Wellington Harbour at the time of the 1855 earthquake. Her commander, Byron Drury, reported: ‘For eight hours subsequent to the first and great shock, the tide approached and receded from the shore every 20 minutes, rising from eight to ten feet and receding four feet lower than at spring tides. One ship, I heard, was aground at her anchorage four times.’ 2
About 20 minutes after the earthquake, tsunami waves surged into Wellington Harbour through its narrow entrance, then for many hours bounced repeatedly back and forth, reflected off the harbour sides. Water also flooded into Lyall Bay from Cook Strait and Evans Bay from Wellington Harbour, putting the low isthmus between them (now Kilbirnie) under nearly a metre of water.
Peru–Chile tsunami, 1868
In August 1868, an earthquake of about magnitude 9.0 offshore from the Peru–Chile border generated a devastating tsunami. The earthquake and tsunami killed thousands of people along the South American coast. Spreading across the Pacific, it became the largest recorded distant tsunami to strike New Zealand, affecting many ports and causing substantial damage on the Chatham Islands and Banks Peninsula.
The tsunami reached the Chatham Islands around 1 a.m. on 15 August, about 15 hours after the earthquake. Māori at the village of Tupuangi were woken by water surging into their houses and fled to higher ground. Subsequently two larger waves destroyed the village and the houses of several European settlers. One Māori drowned, carried out to sea while trying to retrieve a boat that had come adrift. The tsunami also damaged buildings at Waitangi.
A tsunami reconstructed
After the devastating Peru–Chile tsunami of 1868, Ferdinand von Hochstetter, an Austrian geologist who had visited New Zealand in 1859–60, described the effects in Peru, Chile, New Zealand and other Pacific locations. He charted the progress of the tsunami across the Pacific and determined wave speeds and the ocean depth along several paths. Hochstetter’s work was the first detailed scientific analysis of a major tsunami.
Several hours later, on Banks Peninsula in the South Island, a night watchman discovered the ships at Lyttelton’s wharves sitting on the mud bottom – the water had drained from the harbour area. Around 4 a.m., a foaming wall of water surged into the harbour, and the water rose by over 7 metres. Ships’ hawsers snapped, and the ships were dashed against the wharves and each other, causing heavy damage. The sea gradually receded, but more big waves rolled in at intervals of several hours, and water levels rose and fell erratically over several days. In smaller bays around the peninsula, tsunami waves penetrated inland along valleys, damaging homes and carrying away bridges and fences.