TAUPO-NUI-A-TIA

Taupo Times, Volume II, Issue 68, 6 May 1953, Page 1

TAUPO-NUI-A-TIA

TALES OF THE TAUPO COUNTRY

(R.H.

W.)

The explosive outbursts from the cater of Ngauruhoe which have, during the past summer often been of a spectacular nature, indicate that Ruaimoko, the ancient Maori Vulcan, As not dead, but merely sleeping. They have been similar to ihe activity that has characterised the volcano in historic times. The earliest eye-witness account of Ngauruhoe's activity, given by John Carne Bidwill, who climbed to the summit from the Mangatepopo Valley in March, 1839, describes how "a thick column of black smoke rose up for some distance and then "spread. out like a mushroom." Bidwill was perhaps wiser than some more recent climbers, for he states that "I did not stay at the top so lon'g as I could have wished, because I heard a strange noise coming out of the crater, which I though t betokened another eruption." Recent Lava Flow Ngauruhoe is a younger subsidiary cone of the multi-cratered Tongariro volcano, though now something over a thousand feet higher, and is built up of alternating lava flows and beds of tufF and agglomerate. The lava flow which poured down the western side of the cone in 1949 was the first, however. actually seen in historic times, though it seems possible that laval flow near the head of the Mangatepopo Valley may have oecurred in the eruption of 1869. Though some of our geologists have thought it did not occur at that time, a description given to me by the late Colonel J. M, Roberts, N.Z.C., of the activity as seen from Opepe, near Taupo, indicates that this view may be mistaken. Colonel Roberts was stationed at the Armed Constahulary post at Opepe in 1869, and described the great explosive "shots" seen and the noises heard. One day, after a night when a glow could be seen on the - cone, three great columns of steam were seen rising, one from the summit, the other two from the lower slopes. This description is certainly wTiat might be expected had a lava flow taken place from the crater, and the two lower steam columns might well have been rising from the twin terminal points of the lava flow to be seen today.

Hot Avalanches An interesting feature of the 1949 eruptions, in addition to the lava flow, was the occurrence of what are known as "hot avalanches." The classic example of this type of eruption oecurred at Mont Pelee, Martinque, in 1902, and was called a "nuee ardente," or glowing cloud. These "glowing clouds" consist of flne ash and coarser rock fragments, all mcandescent, permeated by hot gases, which rush down the slopes of a volcano, the mixture behaving in many ways like a fluid. The classic exampfe at Mont Peiee in 1902, which destroyed the town of St. Pierre in a few minutes, killing some thirty thousand inhabitants, had a temperature as it passed through the town sufficiently high to melt bottle glass (650-700 degrees centigrade). These hot-sand avalanches sweep down volcanic slopes under the force of gravity, with very high velocity, mowing down everything in their path, al though beyond the Iimit of the cloud no {effects ai*e produce d. The hot avalanches which oecurred- at Ngauru- 1 hoe in the 1949 eruptions were but miniature affairs, compared with the .classic one at Mont Pelee, or compared with those that have oecurred in Java and elsewhere. but it is very obvious that anyone on the slopes of the cone who happened to be in the path of one of them would have no hrope of survival. Deposits of andesitie ash from Ngauruhoe occur as far north of the the mountain as Tauranga-Taupo, on the eastern shore of Lake Taupo, of a depth of three inches and more in thiekness, made up of small dark rock fragments and ash. In 1949, minute amounts of ash fell in Taupo, and traces were observed as far away as Tauranga. During activity in 1917, Mr W. Mead, of National Park, found small fragments of the fresh scoria on the snow slopes of Ruapehu, eight ^niies distant, In May, 1926, Mr C. P. Worley, of Auckland, saw, from

the Rift Valley, an enormous red-hot block shot clear of the crater to land more than half-way down the slope of the cone, and estimated the block to be the size of a flve-roomed house. But none of the eruptions of Ngauruhoe in historic times have been such as to cause any real danger beyond the immediate vicinity of the mountain itself.