EROSION.

Hauraki Plains Gazette, Volume XXXIV, Issue 4591, 22 August 1923, Page 3

EROSION.

ACTION IN NEW ZEALAND. (By Observer.) Evidence of erosion is to be found in every country, and during this season of the year it is particularly noticeable. Erosion is the wearing away of soil and subsoil by the elements. The two perhaps most predominating factors so far as New Zealand is concerned are frost and rain, both of which are responsible for a great deal of damage throughout the country. After the world passed through the “ball of fire” stage, and subsequent, cooling processes brought about some form of crust round the exterior of the globe, water made its appearance on the solidified crust—how, need not be discussed. With water came a defining of land and sea areas. Erosion by the sea, assisted, of course, by sub-, terranean shrinkage, has occasioned vast changes in the shape and area of the land masses. The North Sea affords a striking example, for at one time the British Isles were joined to the Continent of Europe, Famous Helgoland was some few centuries ago of quite a moderate size, having a sea frontage of some 120 miles. Today its area is about a square mile, more or less, and of late years the Germans have made strenuous efforts to preserve the coastline against erosion by the sea, by constructing huge concrete walls. This method is used in England, t,oo, where coastal inhabitants in various places point out to the visitor the spots where villages have been submerged. Sea erosion is done, firstly, by the waves, which, ceaselessly beating on the cliffs, gradually wear away the land; secondly, by the currents, which carry the dislodged clay to the unknown depths. In some parts of the coastr line of New Zealand erosion has carried away material and deposited 't at some other part of the coast, but the wearing away process far exceeds any building up. Erosion by rain and frost is of more vital interest at the present juncture, for the recent ' railway accident at Orgarue may well be cited as an effect. The rate of erosion depends on climate, topography or physical character of the country, and on the nature of the soil. New Zealand enjoys a comparatively moist climate, and. in addition, the interior suffers from severe frosts. Physically, the country is mountainous and steep. A great deal of the soil is of a most erosive type. The country, therefore, possesses all qualifications for erosion. The rain washes away a certain amount of soil. Moisture and the sun cause cracks, and the water in the cracks becomes’ frozen. In this state it increases its volume, and the consequent pressure opens the fissures and causes landslides. The bar at-the mouth of the Wairoa River in Hawke’s Bay is almost unnavigable, as that river drains some of the most erosive country in New Zealand. The general difficulties arising in the maintenance pf the Main Trunk and other railways can all be ascribed to erosion, which is one of the most irresistible forces in Nature against which man is continuously struggling.