Source: GNS Science
The tsunami was caused by a large seafloor earthquake off the coast of Peru on 14 August 1868 and it travelled across the Pacific and hit the Chatham Islands causing fatalities and widespread destruction.
Scientists estimate the quake was between magnitude 8.5 and 9.0 and its rupture on the seafloor was believed to be 600km long.
Known as the Arica earthquake, it caused an estimated 25,000 deaths in Chile and Peru. The tsunami it generated took 15 hours to cross the Pacific and it arrived at the Chathams in the early hours of 15 August 1868. The official death toll is unclear, but it is believed up to 20 people may have perished.
At 1am on August 15, people in the village of Tupuangi on the northwest coast of Chatham Island awoke to a loud roar as a massive wave surged inland. There were three destructive waves within an hour with the largest being 6m high.
Three families were washed away and survivors scrambled to higher ground and were left with nothing. The tsunami stripped the land of vegetation including large trees, leaving only sand and boulders.
The entire Chatham Island coastline was affected. Abnormal waves and strong currents continued for at least 24 hours after the initial waves hit.
The tsunami travelled on another 800km to New Zealand where Banks Peninsula, Lyttelton, Oamaru, Timaru, and Port Chalmers in Dunedin took the brunt of the impact. Again there were three large waves within an hour, with the last being the largest and most violent. Severely disturbed currents occurred at many coastal areas around the New Zealand coast for the following 24 hours.
The tsunami was also recorded in Samoa, Hawaii, Japan, Australia, California, and Oregon.
One of the scientists heading to the Chathams, Hamish Campbell of GNS Science, said the event was significant because it was believed to be the only recorded instance of a tsunami causing deaths in New Zealand in historic times. It was also the first tsunami in New Zealand to be documented in detail.
On 15 August the scientists will join local residents in a memorial event at Waitangi West Beach on Chatham Island. The commemoration will include a formal blessing in recognition of the event.
“In 1868 there was quite a large community living in this part of Chatham Island [Waitangi West and Tupuangi] and it was very badly affected,” Dr Campbell said.
“The purpose of the memorial event is to raise public awareness and promote educational opportunities about the major natural hazards – earthquakes, tsunami, volcanism, landslides, and extreme weather – and how society can become more resilient and co-exist with them.”
The 1868 tsunami hit without warning, Dr Campbell said. But today the Pacific Tsunami Warning Center in Hawaii monitors earthquakes and sea levels around the Pacific so that prompt alerts can be issued for any abnormal activity.
“Tsunami warnings are broadcast by electronic media and on social media. But there may not be time for official warnings if a tsunami is generated close to New Zealand.”
Dr Campbell said the golden rule was that if people feel earthquake shaking that lasts for a minute or longer or if they feel strong shaking that makes it hard to stand up, they should evacuate immediately inland or to higher ground. There is more information at: https://www.civildefence.govt.nz/get-tsunami-ready
Please see this link on our GeoNet website for a more detailed story and tsunami animations: https://www.geonet.org.nz/news/6QkxQCLs0E4A0QQqgKMQiC