THEORY OF THE ERUPTION.

Nelson Evening Mail, Volume XX, Issue 144, 18 June 1886, Page 2

THEORY OF THE ERUPTION.

(Correspondent Evcniny Post.) The discoveries made by the expedition to Rotomahana on its south side enables us for the first time to construct a connected account of the eruption, and to form an idea of the extent and character of its influence. As to the phenomena connected with the first outbreak there is naturally some discrepancy in the various statements, owing to the excitement under which the observations were made, out a careful comparison of the descriptions given by tho most competent and careful observers shows that the first outbreak undoubtedly began in that peak of Tarawera mountain known as Ruawahia. Not improbably some shifting of the earth's crust beneath the mountain or some change within it producing the

generation of great heat caused the prolonged earthquake and rumblings which were heard between 1 and 2 o'clock in the morning, forming the first of the series of phenomena which attended the eruption. Soon after 2 o'clock Ruawahia was observed to be aflame. Above it hung a canopy o£ black smoke, producing on the mountain the appearance of a large mushroom, and the lightning played with such brilliancy round the peak that the glare from the volcanic fires was hardly distinguishable. There is no doubt, however, that the mountain did emit flames, attended with the belching forth of red-hot stones, which could be distinctly seen as they were ejected into the air and as they rolled down the mountain sides. This continued for about an hour before the vomiting of the great mud cloud out of Lake Rotomahana which fell so disastrously on the village of Wairoa. This cloud was observed by those watching the eruption of Tarawera to come up some miles south of the great mountain, and its apparent location gave rise to the belief, now proved erroneous, that Mount Kakaramea and the adjacent lake Okaro were in eruption. The disturbances in Tarawera and violent earthquakes must, it may well be believed, have produced great fissures in the tender earth crust beneath Lake Rotomahana, letting the waters of the Lake in large volumes down upon the central fires. The rapid generation of steam thus produced would be sufficient to account for the ejectment of a vast body of mud, which, driven by the force of the cyclone which the violent atmospheric disturbances had produced, travelled across the south shores of Lake Tarawera in a track that is distinctly marked. This mud was deposited with marvellous rapidity. The survivors from the Hazard family state that the first shower which fell was exclusively stones, and made an uproarious rattle on the roof. Within half an hour from the commencement of the mud shower such an enormous quantity was deposited that the roof, without any prior warning, fell straight in. A similar experience occurred with the other houses at Wairoa. The steep angle of the roof of Sophia's house, which caused the weight of mud deposited on it to rest on the ground, alone saved it. Why the dry dust and earthy matter produced by the rupture of the earth mounds at Tarawera and around Rotomahana settled in vast quantities in a direction opposite to that taken by the mud shower can only be attributed to initial impulse and local air currents. The mud cloud was born upon a current that was subject to local disturbances. This inference is fully borne out by the deposit of dust in Ohinemutu (the direction taken by the mud shower) being considerably smaller than at Tauranga, 40 miles distant. Persons who saw it from Ohinemutu speak of tho mud cloud as working up against the general direction of the prevailing wind. The heavy stones fell within the radius of about one mile from the point of eruption. We found no stone of more than half a pound weight further away, although pieces of scoria of two or three ounces are picked up beyond Wairoa, nine miles from the nearest crater, and are plentiful along the Kaitereria track. Showers of light ash are also reported as far as Galatea, 40 miles away. The largest of the craters now in activity threw no stones beyond the side of the hill, while a spectator, if the ground is not treacherous, might stand with safety on the brink of the smaller craters, the stones projected falling back almost entirely within the crater. Now with regard to the area of land permanently desolated by the eruption. If we assume that the debris is totally devoid of fertilizing properties, I estimate that the ruin by the showers of dry earth, sand, and scoria will not extend beyond the circuit of four miles, having Rotomahana as its centre. This was previously fern and tussocks land of poor quality. By referring to the map the boundary may be traced along the shore of Lake Ririwhakaitu, round to a line passing half way up Kakaramea Mountain, and embracing the whole of the shores of Lake Okaro. Beyond that the dust deposits are not heavier than might be ploughed in. The ruin by mud was extensive, and embraces the whole strip of country between the shore of Lake Rotorua nearest to Tarawera. and as far as Taheke at the one end, and about two miles beyond Wairoa road at the other end. All the bush within this area has been stripped of foliage and may die ; but the undergrowth will probably break out in leaf again, and become luxuriant as ever. The loss from the destruction of the Terraces, if as we cannot but fear they are gone, is simply incalculable. A marvel which was without a parallel on the earth has been swept away, and even if ever replaced by the same agencies working in the silicious strata, and this is improbable, a long geological period would be necessary for their reproduction. The eruptions now in progress are attended by frequent earthquakes. They were felt while we were in camp, and two during the four hours spent on the dust-hills around Rotomahana, one of such violence that the swaying of the hill we were standing on was visible to the eye. If these craters keep in activity they will form as great an attraction to tourists as the terraces, but when escape has been found for the forces recently set into motion they may subside into quiescence, or become intermittent. The Rotorua district, however, must always be a very wonderful one, such as tourists through New Zealand will never willingly leave out of their routes. The district now offers novelties which surpass everything seen here before, and it furnishes the most extraordinary example of how geological changes in the earth's strata are sometimes effected in the course of a few hours. The half-buried houses and whares at Wairoa are perfectly unique, and the village ought to be left standing just as it is, except so far as excavations are necessary to recover bodies or property. Rotomahana, as an exhibition of Nature's forces, is infinitely more marvellous than ever it was before. To see this large basin torn and lashed with a fury that baffles description ; roaring, cannonading, and screeching ; driving into the air at one spot columns of steam, such as might be generated in the boilers of a leviathan steamship ; and from another orifice in the same crater, sending out black columns of smoke and showers of stones — is a spectacle that can only lose in magnificence by any attempt to convey an impression of it in words. I feel that I dare not attempt to do it justice. Fortunately from the configuration of the ground a full view may be obtained of an area embracing at least fifteen active craters from the break or the hill immediately above the Lake. The situation enables one to look right down into several craters, and to see the whole of the surrounding country obtaining at the same time a very fine view of Ruapehu and Tongariro.