The Wairarapa earthquake

The lower North Island lies close to where the Pacific and Australian plates meet, and Wellington's settlers learned early that the ground moved. Small tremors were common from 1840. Then on 16 October 1848 a magnitude 7.5 earthquake centred in Marlborough's Awatere valley damaged almost every brick and stone building in Wellington and killed three people, and many settlers rebuilt in timber. Māori remembered still older upheavals. In the early 1900s the ethnologist Elsdon Best was told that Wellington's harbour had once had a second entrance, through the low ground where Rongotai and the airport now lie, and that Miramar had been an island. At Turakirae Head, on the south coast, a series of raised storm-beach ridges records earlier uplifts of the Remutaka Range in major earthquakes: inland of the ridge raised in 1855 is one dated at about 2,300 years ago, and a fainter one near the hills at about 5,000 years.

The evening of 23 January 1855 was the end of a two-day holiday for the 15th anniversary of Wellington's founding. Shortly after 9 p.m. a violent earthquake began, and in Wellington the main shock lasted at least 50 seconds. Its magnitude is now estimated at 8.2, the most powerful recorded in New Zealand. People fled outdoors and spent the night in tents and makeshift beds while aftershocks kept coming; one person counted 250 in the first 11 hours. For a day afterwards an almost continuous vibration could be felt as far away as New Plymouth. In Wellington, brick buildings put up since 1848, including the jail and the bank, were damaged, and the two-storey wooden council chambers and government offices collapsed. Most single-storey timber houses stayed up, though many lost their chimneys or shifted on their foundations. In the Hutt Valley slips blocked roads and fissures opened, and landslides scarred the Remutaka Range.

Few people died. Te Ara estimates between five and nine deaths: Baron von Alzdorf in Wellington, killed when a brick chimney fell in his hotel; two people in a fissure in Manawatū; and several Māori in Wairarapa, between two and six by different reports, when a whare (house) collapsed. The quake also set off a tsunami. Waves up to 10 metres high ran through Cook Strait, and in Wellington Harbour the commander of the Pandora reported that for eight hours 'the tide approached and receded from the shore every 20 minutes'. Buildings on Lambton Quay were flooded. The cause was a rupture along at least 140 kilometres of the Wairarapa Fault, on the eastern edge of the Remutaka Range. Land along the fault moved more than 18 metres sideways and up to 6.4 metres vertically, which Te Ara calls 'the greatest deformation and rupture of land that geologists had ever known'.

About 5,000 square kilometres of land west of the fault was lifted and tilted. The southern end of the Remutaka Range rose more than 6 metres, the uplift fading to almost nothing on the west coast of the Wellington peninsula, while across Cook Strait the lower Wairau valley sank more than a metre. Wellington's jetties were left high and dry, but a new strip of shore between the town and the Hutt Valley gave a safe road and railway route where the old track had been impassable at high tide. The lower Hutt drained, and the Basin Reserve, meant to become a shipping basin, became a cricket ground instead. Parts of today's central city stand on land that was under the sea before 1855. For a generation Wellington built in wood, but within 25–30 years the lesson had faded, and from 1913 to 1926 the official yearbook said earthquakes were 'rather a matter of scientific interest than a subject for alarm'. Using information from the surveyor Edward Roberts, the British geologist Charles Lyell described the earthquake in a new edition of his Principles of Geology, the first time the link between faulting and earthquakes was recognised.