Not a winter to remember...

Ruapehu Bulletin, Volume 14, Issue 670, 21 January 1997, Page 7

Not a winter to remember...

El Nino helped eruption to make '96 skiing dismal

The following report is by Department of Conser vation scientist Harry Keys and is printed, abridged, from the December 1996 issue of annual journal of the Tongariro Taupo Conservancy: The 1996 winter will not be remembered fondly by Ruapehu skiers or the ski industry thanks to the continued eruption of the Ruapehu crater. But it seems even without the eruption, it was in line to be a bad season. The 1 995/96 La Nina event continued on into the winter so that northerly and easterly weather was more common than usual. Snow did not persist for long periods below 1700m and a skiable snow pack did not exist there for nearly as long as in the previous six years. On the John Mazey scale 1996 was a poor year. Of course most people will remember (or perhaps try to forget) the ashfalls. The unexpected resumption of activity on the eve of the ski season was followed by an unprecedented and long succession of ash falls. The season and morale were disrupted far more than in 1995 by the 199596 eruption because of these falls. The more frequent southerlies of winter ensured Whakapapa was ashed while the La Nina northerlies and easterlies made sure Turoa didn't miss out either. In normal years Turoa might have missed most of the ash. The 1 7-2 1 June ash fall was followed by up to six more at Whakapapa and up to seven more at Turoa. Tukino was similarly affected. The number of ashfalls varied from place to place on the mountain because wind carried the ash to different places. A maximum of 12 ash layers had . been found in the 1996 winter snow pack by mid September, at a snow pit at 2300 m on the Whangaehu Glacier. Ash is a real problem on skifields because it affects machinery and vehicles, gets into ski gear including ski bindings, ski soles, clothing and other gear, reduces the skiing qualities of snow and its visual appeal, and can create instabilities in the snow pack. Thin ash layers also dramatically increase melt rates. At the lower altitudes on the skifields the ash was exposed for lengthy periods, accelerating melting and aggravating the problem caused by non-accumulation of snow. This ensured that Tukino had a short season and that the lower parts of the other two fields became unskiable earlier than would have occurred without the ash present.

The snow pack was affected by ash even at 2000m on the skifields. At this height the 1996 snow pack accumulated at similar rates to the long term average rates at both the Knoll Ridge and Giant snow stakes until late August. But repeated ashfalls kept on creating

what in some ways was a new ground layer. Every time the ash fell the skifields had to close or remain closed until new snow covered up the ash. This happened reasonably quickly above 2000m into September. But even here melting increased as the

snow surface wasted down to the ash and ash accumulated through various processes to the snow«urface. So increased melt rates at higher altitudes was probably the main reason why the snow pack thinned much more rapidly than normal there.