In the month of January, 1886, I made a hasty hydrographic survey of Taupo Lake, in connection with the topographical survey of the country. I may here give briefly the results of my observations, as they are intimately associated with some interesting questions referred to, and may contribute to forming a correct theory as to the origin of the basin. The lake covers an area of 154,680 acres, being 24 miles 70 chains in length, and 16 ½ miles wide; the mean depth is 65 fathoms or 390 feet; the greatest depth, at a point nearly in the middle, being 89 fathoms or 534 feet. Shallow water was found only at one place in the lake, that is on the Haromatangi Reef, which lies nearly half-way between Motutaiko Island and Karaka Point. Here the rock is covered by only 7 feet of water. The northern and western shores of the lake are formed of steep rugged cliffs of rhyolites and augite-andesites, with great compact masses of tuff. The height of the cliffs in the western bay varies from 100 feet to 800 feet, with deep water close alongside them, from 40 to 50 fathoms being found with our boat made fast to the cliff. At Karangahape Point the cliff is 1,500 feet in height, from its base at the bottom of the lake to the trig, station on its summit. As will be seen from the section, (Plate XIX.), it rises perpendicularly from the floor of the lake, almost overhanging the water; thus, in taking soundings, with our boat's stern touching the cliff, the lead-line showed a depth of 390 feet, and a portion of the cliff 600 feet above our heads seemed to overhang the boat. Behind these cliffs on the western side of the lake, and between the
lake and the Hauhungaroa Range, are immense beds of white pumice sands, through which the rivers and streams have worn out for themselves deep channelled courses, with frequently wide canons at the bottom. Part of the northern shore and a great deal of the eastern shore of the lake is formed by cliffs of pure pumice, in one place 300 feet above the lake, and spreading thence southerly and easterly to the slopes of the Kaimanawa Range, covering the country with a deep deposit of over 100 feet in thickness. In a north and north-east direction it extends for many miles, covering the Kaingaroa Plains, and leaving deep deposits over all the valleys from Taupo to Atiamuri and Whakamaru.
Motutaiko is an interesting feature of the lake. It is formed of a column of rhyolitic lava ascending perpendicularly from the floor of the lake to a height of 600 feet, half of it being above and half below the water. On the north side of the island are masses of coarse conglomerate, consisting of glassy varieties of rhyolite, obsidian, etc., and interbedded with tuff and pumice sands. The rhyolite on Motutaiko is a very remarkable kind of lava, and I have seen nothing like it elsewhere in the district. It has a decidedly lamellar or stratified structure; the thin sheets of stone lie one over the other, and would seem to have been of a very viscid character, cooling as the thin liquid sheets moved over one another, and assuming very ropy, twisted, and contorted forms. This is doubtless the same class of rock discovered by Dr. Hochstetter, which, he says, the Natives called taupo, and from which the lake is said to have its name. In his description, he says:—
“It consists of an extremely remarkable kind of rock, which has attracted the attention of every stranger travelling along the lake. It is a volcanic rock of very striking lamellar structure; like the leaves of a book, sometimes of microscopic fineness, the thin lamellar sheets of stone lie one above another. Greyish black layers, resembling silicious schist of various lighter and darker shades, alternate with pearl-grey, violet, flesh-coloured, sometimes even with brick-coloured layers, so that the streaky mass reminds the observer of agate. From the numerous white transparent quartz grains, and small yellowish-white felspar crystals (sanidine) enclosed, it moreover has a porphyritic structure, while in smaller or larger vesicular spaces light-brown mica appears. There can be no doubt of the genuine lava character of the rock. As by the stretching and pulling of a mass composed of mixed fusions, artificially streaked glass is produced, so this rock is likely to have originated from a volcanic magma composed of various stone fusions.”
Richthofen has, in 1860, described quite a similar kind of rock from the vicinity of Tokay, Saraspatak, etc., in Hungary,
under the name of lithaidit; while Dr. J. Ratti has named a similar lava upon the Liparian Islands, liparite.
A specimen of the lava from Motutaiko, which I brought down with me, exhibits the peculiar curved and ropy forms in which it cooled, the thin lamellar sheets conforming regularly to the curve of the stone. This island rock is possibly an old volcanic mountain, the lower materials which formed the cone being dispersed by the action of the water and the ordinary subaerial denudation, and now covering the floor of the lake. A distinctly marked terrace extends right round Taupo Lake, 100 feet higher than the present level of the water, indicating that for a long period the lake stood 100 feet higher than it now does; the fall is probably due to the lowering of its only outlet, the Waikato River, where it probably broke through a barrier, about one mile from the point where it leaves the lake. Te Heuheu points out a flat rock, on the edge of the lake at Waihi, which he says his ancestors used for a sacrificial altar shortly after their first arrival in Taupo. This shows that the lake has not altered its level within 400 years.
At Karaka Point, a promontory of the lake 4 miles from Tapuaeharuru, are some interesting caves, worn by the action of the water of the lake on the rhyolite tuff, at a time when the water was considerably above its present level. There is also an interesting natural archway, cut out of the tufaceous rock, and instructive rounded, waterworn, and conical-shaped pillars of the same formation.
It has frequently been suggested that the only one outlet of the lake—the Waikato River—does not seem to carry off as much water as the numerous tributaries supply, and that consequently there may be subterranean passages through which the water flowed to supply the volcanic foci of the district.
Whilst surveying the lake I took the opportunity to measure the volume of its rivers and streams. I append a table showing the results of the measurements, which were very carefully taken. They show that practically the same amount of water is discharged as flows into the lake, the inflow being 16,483 gallons per second, and outflow 16,230 gallons per second.
As to the origin of the lake basin, I think there can be little doubt, from the facts, that volcanic action has played a large part in its formation. It is next to incredible that the waters of the lake could have worked out such varieties of shape and contour as are seen on the great coast-like cliffs of the western shores of the lake. Their whole appearance bears evidence, I think, of violent agencies, either of eruption or subsidence. The immense pumice beds surrounding the lake, which gradually diminish in bulk and size of the particles as they recede from it, are all circumstances which point towards the present site occupied by Lake Taupo as being once the scene of great volcanic activity.
In summarising, it becomes apparent that the character of the land and the quality of the soil derived from these various rock formations must be very variable. Where the soil is derived from the marls, shales, or limestone, it is rich and fertile. Some of the soil of volcanic derivation is also good, but unfortunately a great deal of the flat land and valleys are nearly rendered useless by the surface covering of pumice sands. There is, nevertheless, a large area of good settlement land amongst plateaus and hill slopes, and extensive flats suitable for agricultural purposes in the basins of the Waipa and Mokau.