EARTHQUAKES AND VOLCANOES

Hokitika Guardian, 17 January 1931, Page 7

EARTHQUAKES AND VOLCANOES

NO CONNECTION. LECTURE BY PROMINENT GEOLOGIST. CHRISTCHURCH, January 13

An address on volcanic action am: earthquakes, with special reference to Xew Zealand, was delivered by Dr P. Marshall, M.A., D.sc., of the Department of Scientific and Industrial Research, and formerly Professor of Geology at Otago University, to the Teachers’ Summer School last evening.

Dr Marshall said that there were four types of volcanoes. On June 2, 1902, there was an extraordinary convulsion at Montpellier, in the island of Martinique. From the volcanic point of view it was of a very mild nature. Superheated steam mixed with the lava of molten rock in the crater of the volcano exploded and blew the lava into hot dust. This lapped over the side of the crater, went down the sides of the volcano at 100 miles an hour straight to the town of St. Pierre, and within three minutes 30,000 people were killed Only one man escaped, and he was a prisoner in all underground cell. The people did not die because they breathed poisonous gfiSetf, There was nothing poisonous about a volcano; it was quite straightforward, nothing like man’s beastliness. It was just hot-red-hot steam mixed with red-hot dust.

A JAVA DISASTER. A second type of eruption was that which was exemplified by the activity of a volcano in Java. During a perrocl of iuactiity the crater became filled with water. Then a certain amount of activity began and molten lava was pushed up from below. This caused a disturbance, and the water toppled over the edge and swept down at twenty miles an hour. The eruption killed 25,000 people who were living on the slopes of the volcano. Again the activity was a small thing from the volcanic point of view, but from the human point of view it was important. On .June 2, 1883, the greatest explosion in historical times took place in the straits of Sunda, between the islands df Java and Sumatra. Twenty cubic miles of rock were smashed and thrown up into the sky. “That is a very ordinary, common and vulgar type of volcanic activity,” said the professor ; “just a smash.” The last, but perhaps the most spectacular type, was that associated wife the expulsion of molten lava, which was generally regarded as the typical activity of volcanoes and was very much exaggerated. The lava was very hot, but it was easy to get out of the Way df it, iih oil the steep slopes it flowed at the rate of only about five or six miles an hour. Tile best example of that type was to be fotiiid in Hawaii ill the Sandwich Islands. 's‘iie volcano there was active at the present time. ARAPUNI FORMATION.

Connecting those four types of volcano with Now Zealand, the speaker said that the walls of the great gorge through which the Waikato River flowed at Arapuni were composed of loose particles of molten glass that had come out of a great volcano in that locality. The reason that no volcano was to he seen there now was that that kino of material stuffed up the crater oi the volcano it came from and frequently obliterated it. There must have beer thousands of eruptions of that type in the locality, and the professor did not see why there should not be thousands more. Pie had invented a name for the type of rock to be found m th 6 walls of the Arapuni gorge. It was “melero hyetite.” The common or explosive type of volcanic action vas exemplified in this country in the eruption that took place at Rotomahana in 1885 when 113 natives and a few white people were killed, and about a cubic mile of rock was thrown up into the air. THE SKY DARKENED. “These vulgar eruptions are most alarming” said the professor. “The clusj thrown up obscures the sun entirely. On that occasion there was darkness at mid-day, as far as Tauranga. When it is.dark like that at mid-day you think it will never be light again.” There was no warning about Rotomahana. It might be quiet until tomorrow or for 100 years or for 1000 years. The volcanic area in New Zaeland was very restricted. It extended from Ruapehu in the south to the Coromandel Peninsula and out through the Great Barrier.

.wealing with earthquakes, tlie professor said that no doubt many of those present had felt earthquakes and had felt sea-sick at the time. That was not sea-sickness ;it was funk. In the case of the most phenomenal and sero.e earthquakes, three inches up and clown was the extent of the earth’s movement The movement was caused by vibrations just like ordinary waves, perhaps a mile and a half from crest to crest. EARTHQUAKES NOT VOLCANIC. Earthquakes were frequently associated in the public mind with volcanic action, hut there was rarely any connection between the two. What happened was that the earth’s crust cooled and shrank, strains developed and a fracture occurred, causing an earthquake. They were very common phenomena, an earthquake sufficient to make the whole world shiver occurring once a fortnight. They were recorded on tlie seismographs. Professor Marshall stressed the absence of any connection between volcanic action and earthquakes, which he said were merely tlie vibrations caused by fracture of rock relieving strain resulting from the coming and contraction of the earth.