TERMINATION OF ROSS GLACIER
SOUTH GEORGIA
8TH MAY, 1922
SHACKLETON-ROWETT EXPEDITION
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The average peaks in the comb ridges are about 2,000 feet, and the average level of the interior would be placed by the writer as about 600 feet above sea level. The glacial valleys run in general across the longer axis and are separated from each other by comb ridges. The majority of the glaciers show signs of withdrawal. At the N.W. end of the island many of the valleys are free of ice altogether.
One interesting investigation was carried out at Royal Bay, where the Ross Glacier comes down to the sea. The position of the foot of the glacier relative to the shore was first measured by the Gauss Expedition of 1882, then again by Nordenskjold in 1902, and then by the members of the Quest in 1922.
These measurements show this interesting fact—that there was an advance of the foot of over 4,000 feet during the period 1882 to 1902, and that now it is back in the position of 1882. It is suggested that this does not indicate any general advance or withdrawal, but rather that the glacier, which is operating, to use an hydraulic term, under a high head is being forced out to sea where the foot is afloat. It will continue to advance until the effect of the rollers on the floating mass of ice overcomes the tensile strength of the ice and it breaks away. If we assume that twenty (20) years represent this period (it may be a multiple of a smaller period), then this gives an advance per year of about two hundred and twenty (220) feet.
Geology
From Cooper Bay to Bird Island the rocks seen by the writer were of sedimentary origin. They are of the nature of grits, tuffs and phyllites. To the east of Cooper Bay the rocks are igneous. The basement is of a basic nature, with flows, at least two in number, over it. Back from Cooper Bay, and just east of the contact with the sediments, there is a small stock of a more acid rock, which has been called a syenite.
A provisional table is here drawn up to show the relative age relations, with the more recent at the top:
| AT LARSEN HARBOUR | |
| Epidosite | } |
| Spilite | } Doleritic dykes cutting these. |
| Gabbro | } |
| NORTH-WEST OF DRYGALSKI FJORD | |
| Quartz diorite stock | Complex system of dykes. |
| Gabbro | |