EARTHQUAKES AND VOLCANOES.

Timaru Herald, Volume CXXXIV, Issue 18834, 24 March 1931, Page 5

EARTHQUAKES AND VOLCANOES.

REVIEW OP YEAR 1930. Last year has experienced a number of minor geological catastrophies, but has fortunately escaped without any of the first magnitude (writes Professor J. W. Gregory in the “Manchester Guardian”). The first four months have been described as “a period of seismic tranquillity unequalled in recent annals of seismology.” The uneventfulness of the year is the more satsfactory since Italy has been under the growing menace of a major volcanic outbreak. Vesuvius has shown signs since 1925 of increasing unrest. The most alarming symptoms are the rising temperature of its hot springs, the more abundant discharge of gas from the crater and fum&rles, and the highest proportion in it of hydrochloric acid, which is characteristic of the most intense stage of volcanic activity. Hence the minor eruptions of Vesuvius during the year were watched with anxiety as possibly the prelude to a violent explosion. The deep-seated forces which have been gathering strength under Vesuvius maj be relieved by slow discharge from hot springs and blowholes and through the crater, and by a succession of minor eruptions such as have happened in each of the last six years, but the recent developments of the volcano, judging from its history, will probably culminate in one of its periodic catastrophic eruptions, of which the last was in 1906.

Feeling the pulse of a volcano in order to foresee coming eruptions is most systematic at Vesuvius and at Hawaii in the North Central Pacific. The observatory at Hawaii carefully observes the tilting of the surface in order to detect underground changes. The methods used are of extreme delicacy. Milne found that the instruments he had erected to observe earthquake phenomena enabled him to detect m Toklo falls of rain on the other side of Japan, as the weight of the water caused the land to sink and tilt his observatory; and after the water had run off or evaporated the land slowly recovered. This claim was received with some incredulity; but the same effect is observed in Hawaii. Thus after heavy rain on August 10 to 12 the land was tilted to the south, and regained its former level on the 13th after the cessation of rain. The movement was of appreciable amount; for a vertical wand was in August tilted from N.E. to S.W. through 2.41 seconds of arc. The change of slope may be due to the shifting of material deep underground, for Kilauea was tilted away from the central crater, presumably owing to a rise of molten rock into the pipe of the volcano. This movement and a deepseated earthquake on Hawaii on September 25 may indicate that processes are in operation that may cause a new eruption. The most powerful eruption of 1930 was that of Merapi in Central Java during December. The Pegu and Pyu Earthquakes. The seismic armistice of the early part of the year was first disturbed by an earthquake which did some damage in Southern Greece and Crete on February 14; and toward the close of the year the same seismic area was affected by the more fatal shock in Anatolia reported on December 11. The long quiet was broken -in the restless East by a severe shock in Borneo on March 26. It was followed on May 5 by a disastrous earthquake on Eastern Burma. From the Gulf of Martaban a broad valley, drained by a small river, the Sittang, runs inland between the mountain range of the Pegu Yoma to the west and the steep face of the plateau of Eastern Burma. The features of the Sittang Valley and of the Upper Irrawadi, which is its continuation to the north, indicate their formation by the sinking of their floor, and their eastern margin is notorious for catastrophic earthquakes. Ava, the former capital of Burma, was devastated on March 23, 1839, by one of the most terrific earthquakes on record. Mandalay the present capital and Maymyo the seat of Government in the hot season both near the eastern edge of of this valley to the northeast of Ava, were seriously damaged by earthquakes in May, 1912, which were felt as far south as Toungoo. On May 5 this year the most southerly known earthquake on this line overwhelmed the city of Pegu, 42 miles north-west of Rangoon. Much of Pegu was haken down, most of the rest destroyed by fire, and a thousand of the residents were killed. At Rangoon there were 46 fatal casualties and many buildings damaged. Later in the year the instability of this line was further shown by an earthquake on December 4. Its centre was at Pyu, forty miles south of Toungoo and 70 miles north of Pegu. At Pyo twenty houses were shaken to pieces, the courthouse and some shops destroyed by fire, and 36 lives lost. The westward extension of the chain of disturbances that began in Borneo was marked on the day after the Pyu earthquake by a still greater calamity in North-Western Persia, with a deathroll of about 2000. The centre was at Salmas, eighty miles west of Tabriz, which suffered from severe earthquakes in 1879 and 1883. The next member of the series Was on July 3, and was felt throughout Assam and most of Bengal. Its centre was at Gauhati, the chief town of Assam, on the Brahmaputra, 50 miles from Shillong, the centre of the destructive shock in 1897. Buildings were damaged in Calcutta, over 300 miles away, and the shock was felt st#ongly through an area of 300,000 square miles. The fact that it nevertheless caused no loss of life indicates that it was deepseated. , The Italian Earthquake. An Italian earthquake of October 30 also had a range unusually widespread in proportion to its destructiveness. It disturbed an area of 120,000 square miles: it was felt throughout Central Italy and as far north at Padua, southward beyond Naples and across the Adriatic in Trieste. Its centre was fortunately under the Adriatic. The nearest town is Senigallia on the Italian coast near Ancona, and in it a third of the houses were destroyed, another third and the quay badly damaged, and ten people killed. The town had suffered from earthquakes, which apparently started near the same centre in 1672, in 1690, and on September 21, 1897. This series is probably due to re - newed movements on the fracturts bounding the sunken floor of the Adriatic Sea. The tendency of earthquakes that belong to the same regional series to occur at different sites is illustrated by that In the Izu Peninsula. The appalling catastrophe which over--whelmed Tokio and Yokohama in 1923 was due to a violent dislocation of the floor of Sagami Bay at the eastern end of the southern coast of the main island in the Japanese Archipelago. The western shore of Sagami Bay is the Izu Peninsula, which projects south from the foot of the great extinct volcano of Fujiyama. West of the peninsula is Suruga Bay, which corresponds in position and nature to Sagami Bay. The eastern coast of the Izu Peninsula was disturbed in the spring by a succession of 3684 slight shocks; they have proved to be the precursors of an earthquake which on November 26 shattered the towns of Shizuoken and Mishima, did serious damage along the western coast of the peninsula, and caused a loss of 245 lives. The disaster was the most severe in Eastern Japan since 1923, for the two most fatal of Japanese earthquakes since that date—those of Tango on March 7, 1927, and of Taaima on May

23, 1925, were both on the western side of the island. The earthquake was due to a subsidence of the peninsula which has been left upstanding between Suruga and Sagami Bays, both of which are doubtless due to the foundering of their floors beneath the Pacific. The powerful submarine earthquake that broke twelve cables off the Newfoundland Banks on November 18, 1929, belonged to the previous year; but this year’s work of the cableships has shown that the earthquake was due to the subsidence of a strip of the sea floor in continuation of Cabot Strait.