Story: Historic volcanic activity
Page 4 – Ruapehu, 1861–1945
Early eye-witness accounts
To New Zealand’s earliest European settlers, snow-capped Mt Ruapehu appeared benign and too remote to pose any danger. The earliest written accounts of activity are from 1861, when it was reported in the New Zealand Spectator and Cook’s Strait Guardian that, ‘dense volumes of smoke were seen issuing from the crater, and at night a lurid glare was reflected by the heavens’. 1 The settler Henry Sarjeant witnessed an outburst from Ruapehu’s Crater Lake surging down the Whangaehu River:
I suddenly saw … a huge wave of water and tumbling logs ... [the wave] appeared to be covered with what we first thought to be pumice but the intense cold which made us shiver and turn blue caused us to discover that this was no less than frozen snow. Mixed with this was a mass of logs and debris. Very soon a bridge passed us stuck in the roots of a giant tree and a few minutes later about a dozen canoes came down. 2
In the 19th century Ruapehu’s activity was low-key, limited to occasional small steam and ash eruptions from the summit Crater Lake. In 1889, 1895, 1903 and 1925, eruptions spilled water out of the lake, creating volcanic mud flows known as lahars.
Ruapehu eruptions, 1945
In March 1945 Mt Ruapehu stirred, beginning a series of eruptions that continued intermittently through the year.
On 8 March the pilot of a plane reported a plume of steam rising from the crater, and ash dusting the mountain’s eastern slopes. On 19 March a dome of lava emerged from Crater Lake, accompanied by steam explosions visible from about a hundred kilometres away. A week later, however, in another large explosion, the lava dome disappeared.
In the first two weeks of May, steam and ash rose in a continuous column. Activity then slackened. But by 19 June ash was pouring from the volcano, covering a large region as far north as Taupō. Another lava dome appeared on 7 May, and it grew through June, spilling all the water out of Crater Lake.
In July, August and early September explosive eruptions ejected rocks and columns of steam and ash. Wind carried the ash as far south as Upper Hutt, near Wellington, and as far north as Whakatāne. Noisy eruptions during the first week of August made authorities briefly consider evacuating communities around the mountain.
A lucky escape
In May and June 1945 geologist Robin Oliver observed Mt Ruapehu’s growing lava dome. During a quieter period, he and J. Witten Hannah camped overnight inside the crater. An explosion on the evening of 1 July showered them with red-hot rocks and ash. Both men received burns and Oliver was knocked unconscious. Hannah hauled him some distance from the crater, left him in a sleeping bag, and descended the mountain in the dark for help. A rescue party found Oliver the next day. The men were lucky to survive – the explosion had blasted out rocks weighing up to 8 tonnes.
On 1 September a group of sightseers barely escaped injury when they ventured up to the summit and were bombarded by small rocks. Volcanic activity continued through September at a moderate level. In late September and October ash fell on Taupō, Rotorua, Whakatāne, Napier and Hastings. Eruptions in November and early December spread ash on communities around the mountain and in Hawke’s Bay.
In 1945 Chateau Tongariro, 9 kilometres from Ruapehu’s crater, was a wartime mental hospital. Its electricity failed repeatedly when ash penetrated the hospital’s generators, and the streams supplying water eventually became too muddied to be filtered. The hospital closed in December, and 180 patients had to be relocated.
Ruapehu’s outbursts caused more wide-ranging disruption. The wind spread ash for hundreds of kilometres. In heavy ashfalls, asthmatics suffered and many people remained indoors. Hundreds of cases of ‘Ruapehu throat’ were reported to doctors and pharmacists, and eye irritations were common wherever ash fell.
Dry ash was easily stirred up by passing vehicles. Gritty clouds drifted into houses and buildings, and played havoc with machinery. Wet ash stuck like cement to roofs, windows and flat surfaces. It contaminated rainwater tanks if people did not disconnect their downpipes before the ash fell.
Cars were vulnerable, their paintwork and windscreens scratched by ash. The New Zealand Army were forced to move some 700 vehicles from Waiōuru. Crops around Ōhakune withered, and stock did not like the taste of ash-covered pastures. Farmers around Taihape found ash in the wool of the sheep they sheared.