Southern Ruapehu escapes massive volcanic ashfalls

Ruapehu Bulletin, Volume 14, Issue 641, 18 June 1996, Page 1

Southern Ruapehu escapes massive volcanic ashfalls

Asignificant lo cal eruption of Ruapehu volcano is in progress. So said the press release from the Institute of Geological and Nuclear Sciences at 1 1 .00am Monday morning, confirming what was patently obvious to Ruapehu area residents who awoke to clouds of ash and steam glowing orange in the sun' s first rays. However, the southern Ruapehu area remained ashfree up until the time of going to press and looked likely to stay that way as long as the south-westerly winds continued to prevail, as had been forecast. The Alert Level was raisedfromLevel 1 to Level 3. "Volcanic tremor at Ruapehu began to increase at around 6.00am and has continued to increase since

that time," statedlGNS vulcanology programme leader CJN Wilson. 'The tremor level recorded by the Dome seismometer now stands at the maximum our instruments are capable of recording." "The tremor signal recorded further down the mountain by our seismometer near the Chateau is at a level similar to that seen during the eruptive episodes of 7 and 1 1 . October. Numerous discrete eruption- style earthquakes were recorded between 01 00 and 0825 hours, the last of which coincided with the commencement of the ongoing continuous ash emission," he said. Large blocks rising to heights of 400 to 500 metres fell up to 600 and 700 metres from the vent. Observors near the mountain reported loud

detonations and windows shaking. At about 3pm the volcano started erupting every 10-15 minutes. The activity followed increased volcanic tremor on Saturday afternoon to Sunday morning, leading toscientists predicting the eruption. Scientists flying around

the volcano spent 40 minutes observing the eruption. Ash was erupting in more-or-less continuous pulses from three vents, believed to be the same vents last seen in action in October 1995. Jets of ash and steam rushed upwards for 3-5 minutes alternating with quieter periods of about the

same length, The ash jets reached 1km in height above the vents, rising to form a 5km plume close to the volcano, and higher still as the plume was blown downwind to the north. A small lahar was produced in the Whangaehu Valley which was confined to the ri ver channel and went

no further than Tukino. Staff from Whakapapa Turn to Page 2

Southern Ruapehu escapes ashfalls

FROM PAGE 1 and Turoa ski fields were evacuated and the Bruce and Ohakune Mountain Roads closed. State Highway 48 from the Chateau turn-off to Whakapapa Village was closed to all but residents and essential services. Whakapapa residents reported regular 'thudding' shakes every 3-4 minutes coinciding with eruptions

of ash. The shaking was quite unlike any usual earthquake, they said. Taupo Civil Defence officers said yesterday that the ashfall was of a nuisance value as in the October eruption, rather than a hazard. As at 1.30pm the ash plume had moved away from Taupo but continued to drop ash out as far as Rotorua.

Civil Defence controller Alan Johnson said at 1 .30pm Monday that at that stage there was no need to declare a civil defence emergency. People were advised to stay indoors, especially asthmatics or those with respiratory conditions. If people had to venture out they should wear a mask or wet handkerchief or towel. Taupo area residents were advised to conserve water because if ashfalls led • to pumps shu.tting down, there would only be 24hours' supplyinreservoirs. Those with roof-fed tanks were advised to disconnect pipes from their tanks. "Motorists using roads around the mountain and where ashfall has occurred should exercise care when driving," said Mr Johnson. Ian Wright of McCarthy's Transport reported driving through Turangi at 9.30am yesterday was like midnight, with traffic bumper-to-bumper travelling at around lOkph. The plume carried ash over the southern Bay of Plenty, and it was expected to pass over towns in the northern Bay of Plenty. such as Rotorua, Te Puke and

Tauranga. Ash that fell on theGNS Wairakei Research Centre was up to 0.5mm size and consisted of mixed new magmatic material and fine detritus that has been accumulating in the Crater Lake and vent area since last November. Large amounts of ash blanket the northern slopes of Mt Ruapehu and the Tongariro - Ngauruhoe massif, leading to advice from Department of Conservation advisory scientist Dr Harry Keys that people should keep away from walking tracks. "We don't recommend that anyone walk the Tongariro Crossing or the Round the Mountain track because the ground-hug-

ging nature of the ash plumes will make breathing difficult," said Dr Keys. He said while the ash and gas are not life threatening they can cause considerable discomfort. A meeting was held at Whakapapa yesterday to determine any local civil defence action. IGNS said the volume of ash emission and seismic activity indicate the eruption is similar in scale and type to the events on 1 1 and 12 October 1995. DoC senior conservation officer Dave Wakelin advised people to hose ash off cars and buildings if necessary. He said ash should not be rubbed off as it is very abrasive.