STEAM AND ASH

Evening Post, Volume CXL, Issue 54, 1 September 1945, Page 9

STEAM AND ASH

RUAPEHITS ACTION

REPORT TO GEOLOGISTS

'A report on his observations at Mount Ruapehu was given to a conference of geological experts in Wellington this week by Mr. Horace Fyfe, field geologist on the staff of the Geological Survey, who spent three weeks at the mountain. ■. "Such stories as a huge rock being hurled some miles from the mountain and being clearly visible from remote localities can be discredited," said Mr. Fyfe in his report. It was impossible, he declared, to distinguish any particular stone from a distance of miles, and if one such stone were ejected, there would be abundant evidence of others of comparable size plastering the mountain. No one who had been up the mountain had observed anything of that nature. PEOPLE NOT CONCERNED. In general, as had been noted by others, he said, the people living nearest Ruapehu were least concerned about its activity. It had given them a new interest in life, and though the ash was a considerable nuisance to those living in its trail, they accepted the situation cheerfully and hopefully, and looked for a change of wind that would carry the ash to the uninhabited eastern slopes of Ruapehu. The present activity at Ruapehu was a "vulcanian" type of eruption characterised by explosive outbursts, with the emission of considerable quantities of ash-laden steam that formed typical "cauliflower" clouds. The ash was, in reality, fine particles of rock derived from lava concealed in the vent and fragmented by rapid evolution of steam generated from the original water con- • tent of the lava. The generation and expansion of the steam, and of the small quantities of accompanying gases, exerted a- considerable cooling effect on the rather pasty or viscous andesitic lava of the volcano, so that at the present stage of the eruption there was little likelihood of the emission of lava. In any case, should lava be emitted at a later stage, it would form a rather sluggish flow that would travel ■ slowly and for no great distance, would cause no damage an the uninhabited mountainous country it would cover, and should occasion no alarm. "A lava flow is not to be dreaded, for the largest- flow, of fairly recent, though of prehistoric," origin in the Tongariro-Ruapehu zone, extends only a mile and a half from its source." . . The explosive outbursts were not due to an explosive combination ol gases in the vent, but were of the steam-boiler type—steam liberated from the magma or molten rock lower down in the crater, generated a considerable pressure in the viscous molten rock and was ultimately released with explosive force, shattering it into sand and dust fragments and so giving rise to the volcanic "ash." That type of eruption was not to be confused' with more violent outbursts that had occurred elsewhere in historic times, and there was no danger of Ruapehu "blowing its head off." THE PRESENT CRATER. During visits to the crater no lava or red-hot rocks were observed, though hot rocks were ejected on occasions, the majority falling back into the crater. In the early stages of the eruption, Mr. R. Oliver observed glowing rock through the fissures in the growing thqloid, but the numerous steam, explosions had so shattered the tholoid that the crater now consisted of a mass of fragmented rock through which a number of vents discharged huge volumes of steam, tinged on occasions with pinkish or yellowish compounds, the former giving a decided pink coloration to the ash-laden clouds for considerable distances from the crater, and giving the appearance of a feebly-glowing cloud. , Mr. Fyfe stated that the reported "glare from the mountain could not be attributed to red-hot rock in the crater. It was due- to electric discharges or,lightning generated by the. rapid movement of ash particles in the steam clouds. "These lightning discharges that accompany every outburst can be clearly seen at night, and seen and heard in the daytime when close to the crater," he said. "They occur almost unceasingly when the volcano is more active, and when the discharge takes place within the cloud it illuminates the cloud with a reddish glow that is mistaken for 'fire' from the volcano. There is nothing "unusual about these lightning displays, rsvhich accompany all eruptions in Which fragmental material is ejected." The fine ash from Ruapehu would for considerable distances in jthe upper- atmosphere, and was not jbnly likely to appear at remote localities in New Zealand, but before long Iwould probably, be reported from South America of, at least, colourful sunsets might be experienced there that could be attributed to it. The following telegram was received i today from Mr. Beck:—"Activity moderate, with frequent explosive episodes. Steam escaping, with liberal ash." Mr. A. M. Pritchard, of the Works Department, who flew over the mountain yesterday, reported today that Ruapehu was "comparatively quiescent."