In addition to the usual volcanic hazards, the crater lake of Ruapehu ejects frequent lahars.

    Ruapehu network map. 

At 2797 m, Ruapehu is the highest mountain in the North Island. Three summit craters have been active during the last 10,000 years including South Crater which contains the currently active vent. The active vent is filled by Crater Lake; water from this lake is frequently ejected on to the ice and snow during eruptions causing lahars.

Most Recent Eruption

  • When: 25 September 2007
  • Effects: This was an explosive eruption, lasting about 7 minutes. During the eruption explosions spread ash, rocks and water across the summit area, producing lahars in two valleys including one in the Whakapapa ski field. In contrast with the previous eruptions in 1996, there was no high ash plume to produce ash fallout over a wide area.

Last Volcanic Alert Bulletins

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Magnesium in the Crater Lake

The concentration of magnesium in the waters of the Crater Lake increases whenever there has been an intrusion of magma. Unfortunately this is after any eruptive activity! Once that episode is finished, the concentrations are slowly diluted as the high concentration water drains away and the lake is replenished by rainfall and snow melt. The graph below shows evidence of the minor September 2007 eruption; however we cannot be certain of the cause of a rise during 2009.

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