CRUMPLED FOLD

Evening Post, Volume CXI, Issue 36, 12 February 1931, Page 12

CRUMPLED FOLD

LAND FORCED UP

GEOLOGIST'S VIEWS

In a statement given to,the "Sydney Morning Herald" Professor Sir Edgeworth David, the eminent . geologist, said that in regard to the earthquake shocks at Napier, most of the severe shocks in various parts of the world were due to a progressive wrinkling of the earth's crust as the earth became older. He said the tendency was with the advancing ago of the earth for the ocean basins to become deeper and for areas of land around to be crumpled up into folds or wrinkles. I In the land areas, the material of its rocks was lighter in weight than the rock material which formed the floors of the deep oceans. There was a tondency with time for this heavy material in tho ocean floors to sink deeper towards the earth's centre, and in so doing the lighter material of the lands around the oceans was forced upwards. Thus, if one took a stretch across the Pacific from Now Zealand to Chile it might be compared to a bridge the crown of which was so heavy that the abutments were unable to sustain the weight bo that the centre of the bridge slowly subsided, and in so doing caused a heavy thrust against the abutments, which may be bent or crushed in the process. In the case of New Zealand, the North Island had been compared to a boot upside down with the toe in the direction of Auckland pointing towards Norfolk Island, New Caledonia, and thence to New Guinea. The heel pointed in the direction of the Kermadec Islands, the Tonga or Friendly Islands, and then on to Samoa. What was especially notable in the case of the recent earthquake was that whereas there wero a number of earth folds traversing the triangular area, there was only one important fold along the line just described to take up the stupendous thrust which came up against it as a result of the downward movement of the ocean floor. This great fold was continued to great depths in the sea, as, for example, the Tonga Deep, which is part of the deop ocean which extends ail the way from the east of New Zealand to near Samoa. So profound is the, depth that if Mount Everest, which is some .29,000 feet high, were cast into the deepest part it would be completely submerged. Sir Edgeworjh said that it might be some satisfaction to know that there was a part of New Zealand where the great fold or rock rampart was strongly buttressed. That was tie part /of the South Island south of Timaru, through Dunedin to Invercargill, and right across Lake Wakatipu to" Milford Sound. There the great earth, fold ben#s round so as'to. meet the thrust from the Pacific, edgeways on, and it formed an extremoly strong and resistant structure to tearthquakesj From the Bay of Plenty in the direction of Auckland and North Cape, the rock structures also formed a buttress, though;. not quite so strong as at Dunedin. :.'■ ■: ■ . .'-■ : . ,-.■■. ;,, :"' .. It was devoutly to be hoped that the result of the shocks of 1929, and' the present earthquake would havo; tho effect of relieving these vast earth pressures for some considerable time v to come. At the siame time, it was premature to predict what might happen until further data was available. These earthquake shocks were Australia's first line of defence against the tremendous pressures coming from the Pacific Ocean. / "But for this mighty bulwark," said Sir Edgeworth, "the thrusts from the Pacific would make themselves felt along our shores, and Sydney might share the same fate as Napier."