VOLCANIC ZONE

Evening Post, Volume CIII, Issue 141, 17 June 1922, Page 9

VOLCANIC ZONE

AUCKLAND'S EXTINCT CONES

ONE CHANNEL WITH MANY .VENTS, .

The succession of earth tremors at Taupo may have caused some people to wonder whether the 63 volcanic cones around Auckland are extinct, or merely sleeping. Inquiries made by a representative of the Auckland Star regard-

ing Auckland's past volcanic action point to the fact, that, as there were so many small vents for a comparative restricted area, this should tend to satisfy residents- that the subterranean fires in the days of long ago had ample chance to blow themselves out. Dr., Ferdinand yon Hochstetter's work on New Zealand, published in Vienna in 1867, stated practically all that could be learned from a geological point of view on the Auckland volcanic MAORI TRADITIONS. The Maoris have traditions that Manukau Harbour was once a lake, and iif that is correct, then when tho volcanic disturbances occurred on Auckland Isthmus the result was to cause the Manukau to burst through the barrier between it and the ocean. The Maoris also ascribed the origin of Lako Taupo itself to a sudden depression of the great plain. They have also a quaint tradition of how the underworld took fire. A great tohunga chanced to be near Tongariro, and feared he would be frozen to .death. .As everything was covered with snow he could not light a fire to warm himself. He knew his sister was at White Island, t so he called to her to come to his assislvce. The sister ignited a torch at the volcano of White Island and carried it to the tohunga via the underworld passage, and s'Jlrted Tongariro as an active volcano, and set fire to the underworld nearly the whole distance, with the result that New Zealand has the Rotorua thermal regions. Whakari, or' Whits Island, is the northern terminal of the volcanic zone in that, district, and Tongariro, 100 miles distant, is tho southern terminal. The width of the zone is about 40 miles, and between the two terminals are innumerable geysers, mud volcanoes, and boiling waterholes. • THE AUCKLAND ISTHMUS. The following, extract from Dr. Hochstetter's work is of interest.: "The isthmus of Auckland is one of the most remarkable volcanic districts on earth. It is characterised by a large number.of extinct volcanic cones, with craters in a more or .less good state of preservation and ,with lava, streams forming extensive stone fields at tho foot of (lie liills, or with tuff-craters surrounding,' like an artificial wall, the cones of eruption of piled up scoria and volcanic ashes. These cones are promiscuously scattered over the isthmus and the neighbouring shores of Waitemata and Manukau. Volcanic action seems to have made itself n new way at. nearly every eruption, and this has splintered into very small cones; while, by always keeping one and the same channel, it might have formed one mighty volcanic mountain. EXTENT OF THE ZONE. "On tho geological map of tho isthmus I havo traced, upon, a Rectangle 20 miles long and 12 miles wide,' or within a radius of only 10 miles from Auckland, not less than 63 separate points of eruption. They aro volcanoes on tho smallest scale, cones of only 300 to 600 feet above the level of the sea. Rangitoto has the highest place amongst ihem, rising at the entrance to Auckland Harbour, as it were tlie Vesuvius of Waitemata'Bay. It measures 920 feet."

Dr. Hochstetter states th;i,_t the volcanic cones are resting on a basis of tertiary sandstone and shale. These strata are completely broken through by volcanic action from below, and examination points first of all that volcanic action repeatedly exhibited itself at one and the same place. The first outbursts were probably submarine, taking place at the bottom of a shallow muddy bay little exposed to waves and wind. That the eruptions occurred at intervals is shown by the ejecta being deposited in layers around the point of eruption. The hills formed by these first eruptions are designated tuff-cones, as they enclose circular craters. Lake Pupuke (Takapuna), Geddes Basin (Hopua), near Onehunga, Waimagoia Basin (near Panmure), the Kohuroa Hills (south of Otahuhu), are striking examples of tuff-craters. RANGITOTO AND LAKE PUPUKE. Dr. Hoehstettar also refers to the native legend that Rarigitoto came from the Pupuke crater, and adds : "It is very probable that the lake is connected by a submarine channel with Rangitoto, which may be the source of the water of the lake." With regard to Mount Wellington, Dr. Hochstetter states the lava streams to be comparatively recent, and that Kangitoto at its last eruption was probably the newest of all the Auckland volcanoes. Mount Wellington started in what was at that time a. shallow sea., but its first vent was above the water1 level. There were two tiny volcanic tuff-cones in the bottom of a crater, and then what is now known as Mount Wellington came into existence. One of the first lava streams from that volcano flowed into the old crater and surrounded the two little cones above referred to. The lava streams burst through the crater on the west side and flowed across a clay gully, and thus, by damming up the water, formed Lake St. John. j WILL THE FIRES RETURN? Apparently in 1867 the point was considered as to the possibility of the return of -volcanic action in the Auckland Isthmus, for Dr. Hochstetter writes :—' 'The question of how long the volcanic action might have lasted, and whether there is any probability of its returning, is* of course not to be answered, yet if we take the example of Mount Nuovo, near Naples, which in 1538 grew in two days and two nights to the size of a cone 400 ft high, we may venture to say that cones such as Mount Eden and Mount Wellington are likely to have sprung up in the course of a few days." A more recent writer points to the fact that the utter absence of any sign of thermal activity on the Auckland vol< canic zone is the best evidence that the danger of a return to activity may be considered a very remote possibility.