Editing Mount Ruapehu (section)

===1969 and 1975 eruptions===

Ruapehu saw a period of heightened activity between 1966 and 1982, with multiple small eruptions occurring in Crater Lake and two larger eruptions in 1969 and 1975, which ejected rocks across the summit region and produced significant lahars.<ref name="Scott 2013" />

The eruption in 1969 occurred in the early hours of 22 June. It was a moderate phreatic eruption, which blasted rocks up to 1&nbsp;km northwest of the crater and sent lahars down several valleys. The Whakapapa skifield was left covered in mud. This was the largest eruption since 1945.<ref name="Healy 1978">{{cite journal |last1=Healy |first1=J. |last2=Lloyd |first2=E. F. |last3=Rishworth |first3=D. E. H. |last4=Wood |first4=C. P. |last5=Glover |first5=R. B. |last6=Dibble |first6=R. R. |title=The eruption of Ruapehu New Zealand on 22 June 1969 |journal=DSIR Bulletin |date=1978 |volume=224 |page=79}}</ref>

A larger phreatic eruption occurred at 3:59&nbsp;a.m. on 24 April 1975, blasting rocks up to 1.6&nbsp;km northwest of the crater, against the wind, and depositing ash more than 100&nbsp;km to the southeast. Nine minutes of seismic activity preceded the eruption, but crater dilation had been measured two weeks earlier. Nearly half of the water in Crater Lake was erupted into the air, which subsequently rained down onto the summit, generating lahars down several river valleys. Lahars which travelled down the [[Whakapapa River|Whakapapa]] and [[Manganui o te Ao River|Manganui o te Ao]] rivers entered the [[Whanganui River]] and poisoned it, which affected much of the aquatic life downstream.<ref name="Nairn 1979" /><ref name="Paterson 1976">{{cite journal |last1=Paterson |first1=B. R. |last2=Page |first2=C. E. |last3=Cudby |first3=E. J. |title=The effects of lahars from the 1975 April Mt. Ruapehu eruption and the threat of future eruptions on Tongariro power development |journal=New Zealand Geological Survey, Engineering Geology Section |date=1976}}</ref> Additionally, the lahars damaged ski installations on the Whakapapa ski field, several bridges and hydroelectric tunnel intakes, but no loss of life occurred.<ref name="Nairn 1979">{{cite journal |last1=Nairn |first1=I. A. |last2=Wood |first2=C. P. |last3=Hewson |first3=C. A. Y. |title=Phreatic eruptions of Ruapehu: April 1975 |journal=New Zealand Journal of Geology and Geophysics |date=March 1979 |volume=22 |issue=2 |pages=155–170 |doi=10.1080/00288306.1979.10424215|doi-access=free |bibcode=1979NZJGG..22..155N }}</ref><ref name="Montgomery 1993">{{cite book |last1=Montgomery |first1=R. |last2=Keys |first2=H. |title=Volcanic hazard management in Tongariro National Park |date=1993 |publisher=Department of Conservation |isbn=0-478-01523-2}}</ref>

Three days later, on the morning of 27 April, Ruapehu erupted again. A series of five eruptions occurred between 7:10&nbsp;a.m. and 10:18&nbsp;a.m., sending surges of mud, rocks, and ash northwards across the summit plateau and producing eruption columns up to 500&nbsp;m high.<ref name="Nairn 1979" />

The 1975 eruptions deepened Crater Lake from 55 to 60&nbsp;m to more than 90&nbsp;m.<ref name="Nairn 1979" />