In describing the watershed of this wide region, I may point out that the area of the lake basin may be defined by those divisions of the country which give rise to the rivers, creeks, and other waters flowing into it, and which have their origin for the most part in the extensive mountain ranges scattered over various parts of the table-lands.
Although on the most recent maps of the colony only about eight rivers, namely, the Waitahanui, Hinemaiai, Tauranga, Waimarino, Upper Waikato, Waihaha, and Waihora, are represented as flowing into the lake, I found on the western shore, in addition to other smaller streams, the Kuramanga, Kuratao, Whareroa, Mangakara, Whanganui,[40] Waikino, and Waikomiko, besides three other streams on the northern shore, the names of which I was unable to obtain.
It will therefore be seen that there are not less than seventeen rivers running into this lake, with innumerable smaller streams, while it should be remarked that the only river or stream of any kind flowing out of this immense area of water is the Waikato, at the north-east end. Most of the rivers on the eastern side of the lake receive their waters from the north-western slope of the Kaimanawa mountains, and those from the west, from the Tuhua, Hauhungaroa and Hurakia ranges. Comparatively little water flows into the lake at the northern end, since the country thereabouts dips mostly in the direction of the valley of the Waikato. It is in fact at its southern end that the lake receives its greatest volume of water from the Upper Waikato river, and its numerous tributaries. This river, rising at an altitude of 7000 feet on the eastern side of Ruapehu, is fed by the snows of that mountain, and of Tongariro, as well as by the enormous watershed of a large portion of the Kaimanawa mountains, along the western base of which it runs in its winding course to the lake, receiving likewise on its way the eastern streams of the Kakaramea ranges, and the overflowing waters of Lake Rotoaira, as they descend by the Poutu river. With but one outlet to relieve it of this tremendous watershed, it is not surprising that the waters of the lake rise rapidly during the rainy season, while with the continuance of heavy winds its waves are lashed into fury, and break upon its shores with the force and roar of a raging sea.
In considering the geological features of the region of Lake Taupo, it may be imagined here, as in other cases, that the primary volcanic eruptions were submarine, and that when first that portion of New Zealand now known as the North Island appeared above the surrounding sea, forced upwards by some volcanic freak of nature, the Taupo table-land rose perhaps rapidly, perhaps by slow degrees, to its greatest elevation. The volcanic eruptions which produced this phenomenon may, in short, have been instantaneous or slow in their action; but be that as it may, their work has been indelibly impressed upon the face of Nature in a way which has caused its wonderful results to last through vast periods of time. The volcanic agencies, however, did not rest here. The Plutonic fires, still active in the interior of the earth, burst through the elevated plane, and caused big mountains to rise up in the form of serrated ridges and truncated cones, which poured out their streams of lava and other kindred products over the surrounding country. Hence dotted along the Taupo volcanic zone are stupendous mountain ranges and graceful trachytic cones standing alone or rising from amidst a cluster of minor elevations to heights which vary from 1200 to nearly 10,000 feet above the level of the sea. Of the former class the most extensive are the Kaimanawa mountains and the kindred systems, with the Tuhua ranges and the wooded heights of Hauhungaroa and Hurakia, while the cone formation is exemplified in the grandest proportions in Ruapehu, Tongariro, Pihanga, Tauhara, Kakaramea, Kuharua, Puke kai-kiore, Karangahape, Haurungatahi, Hikurangi, Hurakia, and Titiraupenga, all of which indicate various centres of volcanic action.
The existence of a body of water of the area of Lake Taupo, and of its form and depth in the centre of this elevated region, may be accounted for in several ways. It may have originated in the terrific throes of an earthquake, or by a fracture or break in the plateau. I am, however, of opinion that the present basin of the lake was at one time an active crater, which had its existence long prior to the period when the volcanic cones surrounding it sprang into existence, and that at the time of its activity it was considerably higher than it is at the present day, its subsidence or depression having been caused by one of those sudden changes peculiar to regions subject to volcanic disturbance. Moreover, many of the leading geological phenomena, as exemplified throughout the surrounding country, would seem to point to this conclusion. Perhaps one of the most remarkable features of the Taupo volcanic zone at the present day is its vast pumice plains, which radiate, as it were, from a common centre over an extensive area of country. The largest of these plains stretches in a north-easterly direction from the lake shore, with a gradual fall or incline in the same direction. It is through the western margin of this plain that the Waikato winds through its terraced valley, and it is around this valley that may be more distinctly seen the enormous deposits of pumice, which have been distributed far and wide, as it were, by the action of rapidly rolling waters.
From every outward indication it would appear that this vast deposit of pumice rock had its origin in the once active crater forming the basin of the great lake, and that both Ruapehu and Tongariro rose above their still higher planes long after the period when the great Taupo crater now forming the cup of the lake was the principal outlet of volcanic fires in this wide field of Plutonic action. As a matter of fact the distribution of pumice drift around the enormous base of Ruapehu and Tongariro is as nothing when compared with the great pumice formation of North-Eastern Taupo, and this statement will apply equally to the plains westward and south-westward of the lake. The greatest overflow or distribution of pumice appears to have been, as before pointed out, at the north-eastern division of the lake basin, where the area of depression is greater than at any other part, and at a point over thirty miles distant from either Tongariro or Ruapehu. It was, I believe, when the fires of the great lake volcano died out that the waters rose from the subterranean springs below, and overflowing the then more elevated crater, distributed the light pumice rock over the area of country which had a gradual fall then as now in the direction in which the extensive deposits of pumice are still to be found. This enormous crater was, no doubt, at one time the highest point of the island, until its period of volcanic extinction and subsidence set in, after which stage the pent-up fires burst forth in the stupendous form of Ruapehu, and when the latter in its turn became extinct, Tongariro, with its minor system of volcanic cones, sprang into existence.
TERRACE FORMATION AND HOT SPRINGS.
(Valley of the Waikato.)
I am not aware whether this theory of the crater basin of Lake Taupo is a new or an old one, and I only endeavour to exemplify it as it presented itself to my mind, after a careful examination of the country for many miles around the lake, and from data gained during my ascent of the highest mountains of this great volcanic centre. I may, however, likewise point out that the Taupo natives still have a well authenticated tradition, which would seem to show that even during the history of the race upon the island, the lake basin was at one period considerably higher than it is at the present day. But, beyond the above fact to support this theory, it is well known that the formation of lakes in extinct craters is common throughout the volcanic regions of the island. Lake Takapuna, near Auckland, may be taken as a notable instance. The blue lake at Wairakei, near Lake Taupo, is situated in a depressed crater, and Rotokawa, a little further to the east, is of the same formation. Lake Rotoaira, south of Taupo lake, is nothing more than a depressed crater, while there are no less than four lakes on the Tongariro mountains formed in the same way. There is likewise a lake formed by a crater on the summit of Ruapehu, while the two lakes which I discovered to the south-west of that mountain, and named respectively Rangitauaiti and Rangitauanui, were nothing more than depressed craters filled with water from subterranean springs.