HOW THE GORGE WAS FORMED.

New Zealand Herald, Volume LXV, Issue 20136, 22 December 1928, Page 5 (Supplement)

HOW THE GORGE WAS FORMED.

Tim criticism of the Arapuni scheme by Mr. Holmes is based almost wholly on deductions from his belief that the Arapuni Gorge was originally duo to earthquake action. There iSj however, no authoritative support for this theory. Geological evidence, in fact, makes it quite certain that this -.vas not the origin. The various diversions of the river, which have taken place in past ages, were probably due to enormous quantities jof pumice having been carried down the river, probably from eruptions in the Taupo district. These masses of pumice were beyond the transporting power of the river when it' came to the flatter parts of its course, consequently the old channel, which now forms the headrace, was fdled up—in some cases the whole valley filled up—so that the river ran on a level very considerably above its present level and consequently wandered over land which had acted as watersheds with the river at a lower leveL

Later on, owing to the ceasing of tWo; supply of travelling material, the river!; was able to cut down again. In some cases it cut down into its old course, but ; in others it found an entirely new course.Geologists estimate that the river lias been.; flowing in its present channel for not.' less than 10,000 years. The geological ; structure of the gorge after such a period indicates its stability" Not only was nothing discovered during the exploration or the construction of j the headworks to support Mr. Holmes' ! theory, but, in fact, the whole course of the works afforded definite proof that no " earthquake crack " existed. An entirely impartial opinion on this: question is embodied in the 1917 report of ] the Geological Survey. There Dr. J. Henderson, describing the geology of the Waikato Valley, observed that the Waikato had formed the Arapuni Gorge " by cutting through the relatively hard rocks of its old valley-sides."