62 GLACIOLOGY 



These large active glaciers are the outlets for the inland snow- and ice-fields. 

 They are nourished by snows, which probably fall mostly in spring, autumn, and 

 winter. These snows are borne inland at a high level, jmrtly by the widespread 

 Antarctic cyclone, the high level constant W.N.W. to N.W. wind, partly by a 

 local intermittent N.E. wind coming off Boss Sea. The indraught of the latter 

 is due partly to the physiographic relief of the plateau giving a comparatively 

 steep down grade towards Ross Sea, partly to the difference in the specific heats of 

 ice and sea water, which leads to a much greater daily range of temperature on the 

 plateau than at sea-level, the daily range on the plateau being about 20° Fahr., 

 while that at sea-level is only about 6° Fahr. This big range of temperature en- 

 courages air currents. At night, in December-January (the time of our observa- 

 tions), the rapid chilling of the plateau surface starts air currents — the plateau wind, 

 of the nature of a land breeze. By about 9 a.m. the following moi-ning the sun, if 

 the day is fine, has so warmed the plateau that the land breeze, or fohn, is entirely 

 checked, and the withdrawal by night of cold air masses off the plateau having 

 established a high level down gradient from Ross Sea towards the plateau, snow- 

 bearing air currents stream in over the plateau from above the open water of Ross 

 Sea from the north-east. 



The Reeves Glacier fans out on reaching the sea coast to form the Nansen 

 Piedmont, stretching seawards for 20 miles. This piedmont is joined by sea ice 

 to the Drygalski Piedmont. 



The Larsen and David Glaciers together form the Drygalski Piedmont, which 

 extends seawards for 38 miles from the coast. At its sides, especially its northern 

 side, where there is a great accumulation of drift snow from the southerly blizzards, 

 and for a distance of about 10 miles west of its seaward end, the Drygalski Barrier 

 is afloat. The central part of the Drygalski Barrier is probably aground on its own 

 bottom moraine or submarine esker. This ice mass is still in forward movement, 

 perhaps a yard a day in December, as proved by the great shear planes which have 

 produced Relief Inlet and the ice barrancas and dongas. Further proof of this 

 movement is afforded by the upthrust marine muds, as described in our Chapter on 

 Raised Beaches. 



The bottom moraine and fluviatile material of the Drygalski Barrier is probably of 

 great thickness, perhaps of the order of 1500 to 1800 feet, as suggested by the only 

 three soundings available. According to this view, the piedmont is riding on a 

 species of railway embankment, which it has constructed as a support for itself when, 

 as the result of its increasing buoyancy, as deglaciation succeeded the time of 

 maximum glaciatiou, it tended to float up higher and higher above the rocky bed 

 of the Terra Nova Bay.* That during the maximum glaciation it must have com- 

 pletely filled even the deepest hollows alongside of it, such as the 668 fathom 



* That there are passages for ocean currents under the ice over the top of the embankment is 

 rendered probable through the persistent pool of open water north of the Drygalksi Tongue. 



