B. Outlet of the Lake. (Plates 7, 8, 9, and 11.)
The river discharges from the present lake through a somewhat open valley cut in gravels and overlying glacial deposits (Plate 7). As the exposures of the beds involved are more clear and complete on the western bank, these will be described first. The surface rises gently from lake level for some seventy feet to an old beach, which is a very persistent feature of the lake shores. There is a narrow bench some ten feet higher, and this is succeeded after another sixty to seventy feet by a shelf formed of irregular mounds, presumably morainic, and then finally by a well-defined, narrow ridge, looking like a terminal moraine (Plates 9 and 11), and ending in a cliff at the river end. It has a fairly even summit, which at Trig. B reaches a height of 226 feet above the lake. Near the cliff-face the ridge bears W.N.W., in its middle section W. 15° N., further west the direction reverts to W.N.W., and this continues as far as the road crossing, beyond which the ridge appears as a detached section with N.W. orientation; and then, after an interval, it is resumed with northerly direction, to terminate about half a mile north-west of the outlet of the lake. At this end lies the deserted bed of an old outflow from the lateral glacier margin (Plate 11), which follows concentrically round the outside of the ridge, channels the outwash plain at first, and finally merges with it.
On the eastern bank of the river, the lake-beach is developed close to the outlet, but modified and reduced in height near the downstream end (Plate 8), while behind it, that is, to the east, stretches
View looking east across the southern end of Lake Pukaki. The middle distance is occupied by the great morainic complex (A). The extension of the ridge with silts to the east of the river is marked by (R), the whole length being shown; the doubtful extension of deposits of the same glacial phase to the north by (R?). Behind the former and to the right of the latter is the site of the old lateral stream bed, while on the extreme right of the picture the boulder-clay under the moraine shows as a white scar at the top of the river terrace. The seventy foot lake-beach in the foreground is marked (C) and lies on both sides of the road; it shows on the east side of the river near the line of the top of the trees.
View looking downstream from just below the hotel The terrace (C) on the left is part of the seventy-foot lake-beach lowered in level to about sixty feet by river erosion, while the true level of seventy feet appears on the west of the river (C). The cliff ending the ridge (R) shows in the middle distance, and the outwash plain (O), composed of gravels, is in the fan distance.
Looking upstream towards the river-cliff. The outwash plain (O) with occasional boulders is on the left; the tussock-covered slopes (B) are probably of gravels, the upper levels of which can be faintly seen a little higher than the track. The silt beds marked (R) lie above them. The older morainic complex west of the liver can be seen (D) in the distance on the right, in front of which lies the extension of the ridge (R') to the north. The flat terrace, mentioned in Section C, 4, shows on the extreme right of the picture between the letters D and R'.
a detached ridge (Plate 7) with N.–S. orientation, composed apparently of morainic blocks, but evidently a remnant of the ridge west of the river. North of this remnant lies an area of morainic hummocks perhaps dating from the same glacial phase. Behind the ridge fragment stretches an old, deserted stream channel, the counterpart of that west of the river, which joins the present river with marked discordance, and close to the junction a fragment of outwash plain persists at a level accordant with that of the plain west of the river. East of the deserted channel, the ground rises fairly steeply to the summit of the great moraine which in this locality reaches a height of 400 feet above the lake.
At the actual outlet of the lake, the cross-section of the channel of the Pukaki River is open (Plate 7), but this rapidly becomes more confined, and finally the banks are steep and almost precipitous. This is the case where the river cuts through the ridge just mentioned (Plate 8); where it enters the outwash plain, a quarter of a mile from the lake, the bed is deeply incised, 110 feet on the west and 180 feet on the east bank, into the surface of the plain.