Ruapehu ash eruption phase spans three days

Ruapehu Bulletin, Volume 14, Issue 644, 9 July 1996, Page 2

Ruapehu ash eruption phase spans three days

Lava boulders the size of cars were thrown out of the

Ruapehu Crater during the current eruptive phase.

After three weeks of relati ve inactivity since the dramatic reawakening of Mt Ruapehu of 17 June the volcano on Saturday increased its level of activity to periods of continuous eruption of gas and ash. Over the weekend increased activity led scientists at Institute of Geological and Nuclear Science to raise the alert level back to 3. A morning flight by Department of Conservation staff yesterday, including Department of Conservation scientist Harry Keys, observed vigorous eruptions coming from the crater. Incandescent rocks were seen hurled from the crater and an explosion of rocks followed by a sonic boom observed. Senior conservation officer Dave Wakelin who was on the flight said "huge glowing red splats of lava or rock were seen being thrown into the air as we made an approach to the crater. On another pass the Crater exploded vigorously throwing rocks vertically to quite a height above the Crater. A sonic boom was heard and felt in the aircraft". Dr Keys also observed a ground wave preceding the sonic boom. "The ground wave was like a rapidly spreading white sheet across the ground, very similar to that seen in film of nuclear testing, followed by the sonic boom".

Fresh bomb craters in the snow were seen on the upper Waihianoa, Mangaturuturu and Whangaehu glaciers as well as in the Crater basin, well inside the two-kilometre high risk warning area. While Turoa and Whakapapa skifields received a blanket of ash, Tukino was free of ash at least until yesterday. Fresh ash has also fallen on Ngauruhoe and Tongariro. A large ash and gas cloud was moving in a north-east-erly direction and light ashfall has occurred in Turangi. The plume is mostly gas with some ash and little ash fall-out was expected. Following yesterday morning' s flight and after consultation with the Institute of Geological and Nuclear Scientist Dr Keys said that the current two-kilo-metre high risk warning area will stay the same. "Bombs are not being thrown as far as they were of 17-18 June," he said. Ash-induced avalanches have occurred over the last few days on the north-east slopes of Ruapehu and on the south side of Ngauruhoe. Dr Keys considers the potential for further such avalanches is still high, both before and after the next snowfalls. The eruptions observed are termed "Strombolian" with lava bombs thrown 100-500m above the vent,

some landing up to 900m from the vent. People have been observed climbing up to the Ruapehu's outer crater rim to view the activity. "We

urge them not to" said Dr Keys. "Climbers, trampers and back country skiers must treat the volcano with a lot of respect at present and exercise extreme cau-

tion. People going within two kilometres of the crater and onto the steep to moderate slopes where ash has fallen over the last few days do so at their own risk".