VOLCANIC ACTIVITY IN THE ISLANDS.

Star (Christchurch), Issue 8740, 29 September 1906, Page 2

VOLCANIC ACTIVITY IN THE ISLANDS.

Continent ia tlio Mid-Pacific.

Mr H. J. Jensen, of the Geofcjgy Dd» partment of the Sydney Univerrityi aaSil Macleay Fellow of the Linnseah Society-, recently gave some interesting parttofti lam of his recent researches in -ih% Samoaa and Ton gin Islands. ' "■ /■ Referring to the lava flows f rom th» volcano on the Sanioan. island of Sa-roii^ Mr Jensen stated' in the course of an interview that the, lava was remarbably uniform in character, being all basal* tio. Abundant evidence, was to" bo found of other lava flows besides those of 1902 and 190&6. The Samoan. I*. 'ands are all volcanic, and uniftgrmfr composed of varieties of basalt, thougn the coasts are skirted with coral -reeft^ Savaii has mostly a rocky or iroto-bound coast, due to the lava which has frojji time to time come down and filled tip the space between the young coral reef and the shore. " " j -- ; "The Samoan Islands," Mr Jenseni explains, "lie on the great vblcani§ line which passes from Auctiawi through the Kermadec Group, through Falcon Jslandj Tofua, Latte, Pylstart, Keppel and Niufou to Samoa. Here w6 have represented a great, line of earth {folding and faulting. As to the causa ;ol the great volcanic activity pn v th&j i line, it is Tongaj and not Samoa, that furnishes the clue: I spent most' of my time, of course, in investigating the active volcano^ which is situated on Savaii some eight miles from the eeb, though the lava takes a' circuitoUi course, running- probably "between twelve and fifteen miles. The volcano has a height, of 2000 feet, and^n^ir stands where there was a valley before. That which broke out in 1902 is situated to the south of Aopo, and the crater is 4500 feet high. Sulphurous vapours were still rising from the crevices' the time of my visit. The new lavjk flow covers nearly thirty-fivs ■ square miles. What was originally a vallefr only a few hundred feet high is how ; -|» huge., bulging ridge about 1500 feSb high, gradually getting lower towards the* sea. The present eruption is re* markable for its absence of true tuffa and ashes, though a little tnSy material exists in the active cone itself, which is built up of interbedded messes off cinders and sooriaceous lava. „ This cone is about a third of a mile. in diameter at the base, and 330 feethigi?. The crater appears to be about 200 yards wide at the top, and the inner walls are nearly vertical. At *, deptjh, of about 200 feet in the crater is eeen the seething lake of red T hot lava, whioji flows out in two vents. The one flow is probably tihirty yafds wide, and like a river running' over, a cataract at the mouth of the tunnel. The other is sucked diagonally, downward with, 'a vortex motion. Loud rumbles are heard intermittently in the heart «f the mountain, and immense quantities of vapour rise in puffs. The lava, which, flows most rapidly 'along the reef , has built a long point or peninsula at B»-----•aenla, exceeding a- mile in. length. Large pieces of sulphur and oommou salt are said to have been ejected in the early stages. .;,-' " Speaking generally, the activity of the volcano has been gradually weaken* ing since March last. Probably so .much material has now been exuded that the pressure within is relieved, and the volcano is approaching extinction^ If it merely plugs up for a time, and should break out again, the lava may follow a y new course and destroy some beautiful villages. It wjll be remembered that the great sunspot minimum in 1902 led to widespread volcanic activity all over the earth, and several vents on the Tongan-Samcan line were active. • The Savaiiaii vent was 4500 ft above sea level, arid inasmuch as there were other vents _dn this line of activity, the pressure within did not suffice to maintain this crater in activity. The lava rose slowly, cooled in the vent, and had to ba shattered with explosive violence again and again. Probably in 1902 a great quantity of lava was secreted in a reservior under the Samoan Group, under considerable pressure, but insufficient to cause it to rise 4500 ft, and it^ consequently awaited favourable conditions to form a new vent. This occurred in the sunspot maximum year of .1905. ilov? far these disturbances, .depend on solar or lunar or other" extra-terrestrial causes, or on the actual movement of great basalt masses within the earth, is a matter of great importance, for th« solution of, which we may^ look ta Dr Lincke, director of the. Apia Observatory." . ,■..-;-. ; ;, As to the Tongan group of islands, Mr Jensen points out that they ata composed of coral; rock; but there is a line of small islands lyitfg to the west of tho main islands^— sncliidiiig Falcon Island, Tofna, Latte, Keppel and >fiur fou — which are wholly volcanio : and ■ contain craters. Falcon Island is of xc- I cent origin, and is composed of Eshef ■ and scoria. It has now been reduced ■ to sea-level, being gradually . removed ■ by the action of the sea. Tofua broke H out in Jansuary last, and remained ao- ■ tive for about two months. " It.seenWj 1 ' I 6ays Mr Jensen, "to have burst out ■ in sympathy with the. Samoan volcano, H There were two cones on the islands, H both active. _ Many other emalL craters I exist on this island, which is seven ■ miles by five, and represents th% re- H mains of a volcano which has blown to I pieces, like the Island of Krakatc*, I

liatte is a volcano, with a well-marked prater, and so a f so is Niufoij. The ftfain Tongan islands are quite different-. Tongatabu is a large raised atoll, with. a la«oon. Haapai is also -a coral island, very* narrow. The Vavau Group is the most interesting. The^e latter islands are flat-topped, and all the higher ones are terraced. I ascended the highest, till near the township of Vavau, and Examined the country, which is ootojjfrjed entirely of limestone. Beautitul marine caves exist here. , i>"The structure of Tonga casts light «h the volcanic activity in. the line I have referred to. There is in this region an earth-folding movement, having a north-north-east and south-south-jirqst direction. On the western flank 'of'Tonea there is a great fault, along which the volcanoes are situated. The western wall of this fault has subsided. S^e have a movement going on which tfc tending to build a continent m the mid-Pacific, restoring the ancient continent of Fiji." -