What was left of the Hall family’s Pouawa Beach cottage after the ‘stealth tsunami’ of 1947. Photo/Alexander Turnbull Library
Monstrous 12-metre waves, an entire settlement swept out to sea and a bridge lifted and thrown a mile upstream are just a few examples of the power of the tsunami that has hit New Zealand over the past two centuries.
Toka Tū Ake EQC and GNS Science have combed through hundreds of years of historical tsunami data to create a new public resource, detailing all recorded tsunamis since 1835.
Hope is the Resource, a modern database, will increase awareness of tsunami risk in New Zealand and help inform better land use planning.
The database brings together information from monitoring equipment, newspaper articles, ship’s records, personal journal entries and Maori oral records to tell the New Zealand tsunami story.
Although the country has not experienced any tsunamis in the period that would qualify as “devastating” or worse, there have been several incidents described as “very destructive”.
Among these were the two “stealth tsunamis” at Gisborne in 1947, so named because the earthquakes that generated them were not widely felt.
According to the database, the Hall family of Pouawa Beach were at home with visitors when their cottage was “submerged” by the first wave.
“The water reached the eaves and the room the three people were in was completely overturned. The other four rooms and three sheds were demolished,” the database said.
Most of the house was swept away by the sea, but miraculously no one was killed in this terrifying event.
The same tsunami, described by some witnesses as being about 40 feet [12m] high, swept the Pouawa bridge 800m upstream.
Another of New Zealand’s largest tsunamis occurred on the Chatham Islands in 1868, sweeping a colony of 60 to 70 people offshore.
Triggered by an earthquake in Peru, the waves destroyed an entire Maori pā and the homes of two or three Pākeha settlers.
“Sand and kelp were the only remnants of the pah [sic]the drays were broken, and a 7-8 cwt [50kg] millstone erected at the pah was thrown a ‘considerable distance,'” the historical record of the incident reads.
Residents were described as being left “destitute”.
“Everything they owned was swept away when the water receded, with the loss of everything aided by an offshore wind.”
There was also a huge wave in 1855 at Palliser Bay, Wairarapa which destroyed a shed perched 8m above sea level.
“The waves from the earthquake were about 30 feet high [9m], and showed a white crest although the night was cloudy; they managed the shocks,” said an anonymous witness.
“A family would certainly have been drowned if a sailor, who had been on the South American coast, had not recognized the character of the approaching wave the moment it became visible.”
Another memory noted that the tsunami washed many balls of wool out to sea.
“It’s strange to say that the return wave brought the wool ashore, and none were lost.”
The fascinating database will be a “key tool for decision-making” and help guide New Zealand’s science and risk management sector, said Sarah-Jayne McCurrach, head of risk reduction and resilience in Toka Tū Ake.
The database shows 939 tsunami records, of which 866 are classified as “certain”.
It is hosted by the GNS and will allow open access to the scientific community as well as the public.
The database announcement coincides with the 75th anniversary of the second of two major historic earthquakes that occurred near Gisborne in 1947.
The information can help scientists understand other places in New Zealand where this type of event could occur and spark research leading to further investment in New Zealand.
Zeeland Tsunami Monitoring and Detection Network.
“Extensive research into these types of events has allowed us to better understand and model what might happen and where,” McCurrach said.
“While we may not have experienced large or devastating tsunamis like other countries have in recent years, this database shows that we have experienced very large tsunamis in the past.
That’s why it’s important to know as much as possible about what we might face in New Zealand.”