VOLCANOES AND EARTHQUAKES

Southland Times, Issue 14188, 10 August 1909, Page 6

VOLCANOES AND EARTHQUAKES

Lecturing at Canterbury College last wee!;. Dr. P. Marshall, of Otago University, dealt with "Karth movements and volcanoes in the South Tactile.” Dr. Marshall showed a great many very Interesting lantern slides, some of which had evidently been secured at great risk, and gave a very Instructive address on Uie vast difference between the occurrence of volcanoes and earthquakes, lie .-■aid that tltcre was a very popular and prevalent fallacy that earthquakes and volcanoes were Inseparably connected, but his experience showed that there was no connection between them. He described the main features of the land and the soa-floor of the south-west Pacific, making special reference to coral atolls and their growth. The slides showed various islands and portions of the coiou of the dominion, and the lecturer said that the undulations of the .surface of the earth were In many eases caused by such simple things as rainfall and not by the earthquakes or volcanoes as was often supposed. Thai was borne out by the fact that the sea-lioor, which was comparatively regular, could not he affected by the InUuenees which operated on dry land. The portions of the country which were worn by Ihe sea were frequently visible, and their appearance mast be accounted for either liy the rising of the land or by the failing of the ocean. There was great divergence of opinion on that point, but to him the best explanation was that the land became elevated. There were numerous instances of that elevation which had occurred within geological periods, and he showed a section of the island of Mangala demonstrating clearly the results of rising. Tlwre were also instances of the earth’s surface having been lowered, and (he deeply Indented coast of Now Zealand was u ease in point. The indentations iiad not been caused by the erosion of the sea, but by valleys formed by streams when the land was higher. Milford Sound was caused by the depression of u glacial valley. Professor I 'avid’s borings on coral atolls had shown clearly that Darwin's theory of their origin through subsidence was correct. Wellington was ihe most classic example known of the raising of the surface, for the great earthquake of ISf» g Itad raised the shore line live feet vertically. The ieclurer went on to describe the formation of volcanoes from the simple cones mad'' by steam explosion, and showed seme remarkable pictures of lluapehu and Ngaurulioe. (hose of the interior of the crater of Urn latter and Ihe showers of falling mud helna particularly effective. Knapehn's ire-crowned crater. with ;i boiling lake in its midst, was also very i iaarly depleted. Dr. Mar-dial! said Unit Hie earthquakes of the Tarawa ra erupt nm wen- fell only in th" immediate vicinity, while Wellington, which was a creat earthquake centre, was far removed from the principal volcanic regions of New Zealand. Fart hquakes were can-ed by Ii"" earth having to adjust its coo! surface tn th" portions that were eon tract ing as th*qv cooled, while volcanoes were caused by (he water that had been absorb"'! 'Uiding a vent in it weak part of tin- crust and rushing out again as slcare.