Sunday Island—Physical Features.
Sunday Island is roughly triangular in shape. Its greatest length is 10–5 km., and its area 29·25 sq. km. The present crater, oblong in shape, the longer diameter being about 3·3 km., occupies a large portion of the island, and contains three lakes (fig. 1 and Plate XXIII), From the craterrim there branch off three main ridges—one runs north-west from Expedition Hill to Hutchison Bluff, another south-west from Mount Junction to Smith Bluff, the third south-east from Moumoukai to the east coast. These, with their ramifications, form practically the whole of Sunday Island.
With the exception of some level ground in Denham Bay, in the crater, and on Low Flat and the adjoining Terraces, the whole of the surface of
Sunday Island consists of a series of narrow ridges and deep ravines. High cliffs are frequent both along the coast and inland. This extremely rough island, which, though small, is difficult to travel over, has by the action of sea and rain been modelled out of a volcanic cone composed mainly of pumice and other andesitic tuffs.
Green Lake appears to have been the centre from which the last outbursts of volcanic activity proceeded. The water is of a dark bottle-green colour, and has a strong alkaline taste.
At the foot of Expedition Hill is a small sheet of fresh water known as Tui Lake, hidden in the forest. It is difficult to give reasons for the presence of this lake, as, on account of the porous nature of the soil, nowhere else on Sunday Island does water lie in small hollows.
Blue Lake, which is nearly circular in outline and very shallow, lies between the small or inner crater-ridge surrounding Green Lake and the
north side of the large or, as I will refer to it later, Sunday crater ridge. The bottom is a blue volcanic mud, and the water is clear, fresh, and good drinking.
South Bay Gorge bears witness to the vast amount of material removed by subaerial denudation in Sunday Island. The ravines which intersect the hills in all directions are deep, with steep, often precipitous, sides; while the tops of the ridges are narrow, usually 2 m. or 3 m. wide, and sometimes, where not protected by vegetation, razorback edges. The boundaryridges of South Bay Gorge are pushed back by the action of rains constantly removing the tuffs; hence towards Denham Bay and Scenery Bay they present convex outlines. The largest valleys on Sunday Island—namely, those which descend to sea-level in South Bay and on the north coast, where one has pushed its way right back to the Denham Bay ridge—intersect the older tuffs of the Expedition volcano. Their basins are wide at first, but narrow to gorges at the coast. Hence the depth and shape of the valleys indicate their relative age.
The greater part of the coast-line is formed of sea-cliffs. At their bases are boulder beaches formed of fragments of lava set free by the disintegration of volcanic tuffs. There is a beach composed of coarse gravel in Denham Bay, while at the base of the Terraces and on Low Flat are some sandy beaches.