Firn—Ice Relationships, Sandy Glacier, Southern Victoria Land, Antarctica

Abstract

Sandy Glacier, occupying the head of a 3 km by 1 km cirque valley, is composed of a unique alternation of ice layers and sand layers. The sand was apparently brought by occasional very strong winds from Onyx River outwash 5 km away and 1,200 m lower. Pits dug in the accumulation zone revealed 115-210 cm of firn and sand layers directly overlying glacier ice that also contains sand layers. It is believed that not long ago there was no cover of firn on any part of this glacier. Accumulation appears to have recommenced perhaps 2-3 decades before the present. General Characteristics of Sandy Glacier The mountains of Southern Victoria Land, many of them ice-free in the area west of McMurdo Sound, contain a great variety of small glaciers and landforms of glacial origin. During the course of an investigation of cirques in 1965, Dort discovered a small glacier in the Olympus Range (Fig. 1) that was remarkably different from all others that had been observed in this area. This glacier, to which the name Sandy Glacier has formally been given, is composed, apparently throughout, of an alternation of layers of ice and layers of finely laminated sand. A discussion of the general features of this glacier and the probable origin of the sand has been presented by Dort (1967). The unique aspect of Sandy Glacier, aside from the quantity of sand present, is the fact Fig. 1. Location of Sandy Glacier in Southern Victoria Land. McMurdo Station is situated 70 km east southeast of the mouth of Taylor Valley. 104 GEOGRAFISKAANNALER ' 51 A (1969) * 3 This content downloaded from 157.55.39.215 on Wed, 31 Aug 2016 04:47:53 UTC All use subject to http://about.jstor.org/terms FIRN-ICE RELATIONSHIPS SANDY GLACIER Fig. 2. Aerial view of the northern side of Wright Valley (foreground), Bull Pass (left), and Sandy Glacier valley (cirque valley with prominent moraine top center). (U.S. Navy photo, TMA 360, F31, 156). that the sand is not present so much as an impurity or mixture within the ice as in the form of discrete and uniform layers that comprise an essential and significant part, perhaps as much as 30 % by volume, of the stratigraphic assemblage. Furthermore, the complex composition of the sand shows that it is not of local origin. It has been derived not from the mineralogically rather simple Paleozoic dolerites and quartz sandstones that crop out on the cirque headwall and upper valley slopes above Sandy Glacier, but rather it has come from a complex Precambrian gneissic terrain. The nearly horizontal unconformity that separates these two rock groups passes beneath a moraine complex close to the mouth of Sandy Glacier cirque valley and only a thin wedge of gneiss is exposed at the base of the sideslopes farther downvalley. The gneiss is, however, a major component of exposures at lower elevations in the dry (i.e., ice-free) valleys to the south and west. Sand GEOGRAFISKAANNALER * 51 A (1969) * 3 derived from break-up of this gneiss appears therefore to have been transported into the Sandy Glacier cirque from an outside source. Sandy Glacier occupies a cirque valley approximately 3 km long and 1 km wide that opens to the southwest overlooking the major lowland of Wright Valley at the point where the Olympus Range is breached by a higherlevel ice-free valley known as Bull Pass (Fig. 2). It appears that winds blowing off the ice cap to the southwest funnel into Wright Valley and, when of sufficiently high velocity, pick up quantities of sand from the Onyx River outwash and move it onto the valley sideslopes to the north. These winds are further funneled through the notch at the mouth of Bull Pass. This compression and resultant acceleration enables occasional winds to carry sand all the way up the slope. Some of it is trapped in sheltered places formed by irregular gullying at the lip of the pass. At the top of the slope, Sandy Glacier cirque is so situated that it can