Some Aspects Of N.Z. Geology

Hawera Star, Volume LIII, 19 August 1933, Page 14

Some Aspects Of N.Z. Geology

Volcanic Action With Reference To Contemporary Earth Movements

G\ EOLOGICALLY, New Zealand is one of k- the most interesting countries in the _l| world, small, but with a wide range of

representative formations, ranging from Arehaen, the most ancient (known in New Zealand as the Manapouri system), to the most recent. In few parts of the world is there so great an opportunity of studying phenomena caused by part of the dense atmosphere that surrounded our planet in its earliest stages, i.e., steam- evidence of which phenomena is seen in our hot springs, geysers, fumeroles, solfataras, and volcanoes. Even Iceland, and the Yellowstone Park, TJ.S.A., show no such varietv.

It is considei-ed that this steam was “occluded” in the earth’s crust, and as the interior molten rock cools steam is released, and'rising to the surface through faults, or lines of weakness, is condensed and issues as a hot spring. The theory of occluded steam is supported by the fact t-liat these hot springs are more or less impregnated with dissolved mineral matter. The alternative theory is that surface water soaks to great depths, becomes heated, then rises again through lines of weakness. Both theories should be considered. Tlot springs are often very numerous in volcanic districts and the theory of “occluded” steam would no doubt be true in such districts; on the other hand hot springs are often found far removed from volcanic action. This is so in the South Island, while the hot springs in England, at- Bath 120 deg. Fahr. and Buxton 82 deg. Fahr., are 1000 miles from volcanoes. Enormous quantities of water, we know, do soak into the earth’s crust, and this is remarkably demonstrated by the Triassie rocks of England, i.e., the Bunter strata, the underground waters of ■which once furnished the chief source of supply for the cities Manchester, Liverpool, Nottingham, Birmingham, etc.

Fumeroles.—When steam rises and issues as a jet (a fumerole) acid gases escape and decompose the rock bordering the circle through which the steam passes and mixes, forming a thick mud, through which the steam passes with a Hopping noise as in the Porridge Pot at Rotorua. If the mud is ejected quite a cone is formed; this is the socalled mud volcano. A solfatara is a volcano in its last stages, emit-

ting steam and other gasses. White Island is a good specimen. Geysers are periodic hot springs and are also evidence of dying volcanic activity; the geyser tube is fed by springs at the lower end; the water in the tube is gradually heated' from below and is therefore at different temperatures at different levels. Part of the water thus becomes superheated, changes into steam and ejects the column of water. The Iceland geyser tube is SO feet deep. In volcanic activity the chief gaseous material is steam, but other gases are given off in relatively insignificant quantities. Where risingsteam cannot escape or is prevented from expanding by strata it explodes with terrific force, as for example, Tarawera, where a chasm 10 miles long and about half a mile wide resulted. It is estimated that a cubic mile of material was ejected and the area covered by volcanic ash was about 4000 square miles. Fragmental matters arc dust, ash, lapilli, scoria, and bombs. There is no combustion, the names indicating the various sizes of fragments. Dust, ash and lapilli, when cemented, form tuff. The outer cones of Three Kings and Rangitoto are good examples. Particles of ex-, ploded lava, i.e., dust, are often so fine that they will float for miles, c.g., at Tarawera. The dust thrown out by Coseqnina, Central America, hid the snn for an area of 70 miles and dust was borne to Jamaica, 700 miles distant. Particles from Krakatoa East Indies were collected in Europe. Bombs are large pieces of lava rotated in the air and become circular in shape. Tarawera shot up bombs of hyporsthene andesite —-the lava of Ruapehu. Action of steam is again shown in the vesicular scoriaceous structure of certain lavas, particularly noticeable in pumice, in which the steam pores are so numerous that the specific gravity of the rock is reduced and it will float. Lava flows when it rises to the vent and Hie molten rock is of intense heat—lsoo deg. C. The lowest layer of a lava flow cools rapidly and forms volcanic glass (obsidian). The upper portion, which gives off clouds of steam, becomes ropy, vesicular and eindery. Interiorly, the lava flow consolidates into more or less compact rock, which usually shows abundant crystals.

In the geological history of the planet more species have lived, failed and gone out of existence than there are species now living. There were water plants before land plants; non-flowering before flowering plants; air-breathing animals first in Silurian times; greatest extinction of life in Permian times; reptiles appear in Triassie period. In the Jurassic period we get. our first bird—a toothed bird —the oldest species detected being Archeopterix Macrura. This creature, about the size of a pigeon, was furnished with a long narrow tail of 20 vertebrae, each of which carried a pair of: strong feathers; it’s jaws were provided with conical teeth and in many of its structural, characters it approached the reptiles. Grasses appeared in the Eocene period. Any effort to measure geological periods by time is to he deprecated, though attempts have been made, and scientists differ very widely. An example might he cited in the development of the horse,, which appeared as a four-toed animal about the size of a hare in Eocene times (the Ilyracotherium). Then the Miohippus, three-toed; the Hipparian, three-toes, hut two lateral and useless, and lastly the single-toed Equus, Pliocene and recent.

Authorities have stated the “time” position thus: “If the geological history of the globe occupied 24 hours, written history would be but two seconds of the whole.”

Lrtva flows are of great extent. The lower Waikato was covered by a basaltic rock similar

[Summary of an address delivered to members of the Kawera Astronomical Society by Mr. Thomas Taylor.]

to that forming the volcanic cone.s of Auckland. Lava streams from lire Auckland volcanoes have filled up valleys eroded in the miocene rock. Shaptar Jokull, Iceland, in historic times, poured out a flood of lava 50 miles long, 15 miles broad and filled ravines 600 feet deep. The fissure-flows of India were enormous and form that solid block of igneous rock against which the Himalayas were folded.

The size of the cones varies—Egmont covers an area equal to Auckland’s 60 cones. Etna is 87 miles in circumference; Aconcagua in the Andes 23,000 feet high.

When, from any cause, an earlier vent becomes closed or the height of the pile becomes too great to allow the lava being forced to the crater, volcanic agencies fracture the mountain from beneath, giving origin to parasitic volcanoes; Fantham’s Peak is an example. In some instances a ring f>l‘ parasitic cones is formed; indeed most volcanoes of any size are composite.

The formations of the Taranaki-Wanganui district are Tertiary, which is divided into the Eocene, Oligocenc, Miocene and Pliocene periods; a wonderfully interesting- and fascinating period in the history ot the planet. It was a period of intense volcanic activity and crust movements in all parts of the world. In Eocene times, sheet after sheet of basalt was poured out in the Hebrides and Antrim. The Giant’s Causeway and Staffa belong to this period. The crust of the earth was ridged up into what later became the Atlas, Carpathians, Alps and Himalayas. In Oligocenc times a chain of volcanoes, now ext inct, hurst out from the Auvergne to the Carpathians. In Miocene times we have volcanic activity in Auckland district and England raised to its highest Tertiary elevation. There are no Miocene rocks in England.

The Pliocene, represented in New Zealand by the Wanganui system, witnessed a fresh outburst of volcanic activity. To this period belong Etna, Vesuvius and Santorin in Europe and our own Egmont and Ruapehu. The Alps, Rocky Mountains, Sierra Nevadas, were raised to their present elevation in this period. A point of great interest is that during Miocene times (i.e., when the rocks of this district were being deposited) is that there was a remarkably genial climate in the Northern Hemisphere. For example, in Greenland, 70 deg. north, fossil miocene plants are found—magnolia planes and limes. In 81 deg. north, Spitsbergen-, are fossils of firs, spruces, hazel and waterlilies.

Miocene deposits are of very great economic importance everywhere. They form one of the great coal and oil-hearing systems as in New Zealand and -North America. It gives New Zealand that excellent- building stone, Oamaru limestone.

Other interesting matters were dealt with, e.g., the comparison between the most recent deposits (Pleistocene) of Europe and New Zealand. These can he hut briefly summarised. Pleistocene deposits, not being consolidated, it is difficult to. unravel the sequences, especially so in New Zealand, owing to the absence of mammalian remains, hut in Europe it is the period of the ice age, of early man, of Palaeolithic and Neolethie man and of many extinct animals.