TEMPERATURE AND PLATEAU SNOW 19 



up by a warming of the ice surface by the sun's rays. Snow crystals, however, are 

 separated by non-conducting air gaps from the cold snow crystals below, and thus the 

 heat rays of the sun are free to deal with each snow-flake, as a separate unit, and 

 may melt it, and allow it to re-crystallise in the form which Dr. Mawson likened to 

 anthracene. On January 6, 1909, the surface of the snow seemed softened as we 

 sledged over it on the plateau at an altitude of over 7000 feet, when the 

 temperature at its highest was only about 5° Fahr. On January 14, 1909, when the 

 sun's rays made themselves strongly felt, the snow surface was carpeted with 

 a dazzling sheet, about half an inch in thickness, of these " anthracene " ice crystals. 

 They were each about half an inch in width, and about ^ of an inch in thickness.* 



In the ablation of the snoAv surface of the plateau the snow may thus disappear 

 partly as water vapour, partly as ice vapour, if, as seems possible, the snow surface 

 for the depth of half an inch or so can actually thaw while the shade temperature of 

 the air, except where actually in contact with the snow, is below freezing-point. 



Another interesting result from the diiference in specific heat between rock and 

 ice is that blocks of rock in the Antarctic, where the amount of insolation, during the 

 months of the midnight sun, is veiy great, have a much more marked tendency 

 to countersink themselves into the glacier ice than is the case with morainic blocks 

 on the glaciers of the Swiss Alps. In fact, soon after leaving the last source of rock 

 supply, these Antarctic moraines have so far sunk themselves below the surface of the 

 glacier that they completely disappear, becoming englacial moraine. 



Very low temperatures Avere experienced by Shackle ton's party on the King 

 Edward VII. Plateau, during a great blizzard which commenced on January 6, 1909. 

 The wind at first was S.S.W., the temperature at noon being — 25° F. at latitude 

 88° 7' S., longitude 162° E., altitude about 9837 feet. The next day the wind was 

 blowing very hard from the S.S.E., with squalls of terrific force. The temperature 

 at noon was — 33° F. On January 8, the wind hauled to the S.E., and blew harder 

 than ever, with hurricane force. The noon temperature was — 40° F. This blizzard 

 gradually slackened in the early morning of January 9. 



It is interesting to note that in the case of this blizzard there was no Fohn efiect. 

 In fact the temperature fell a good deal below what appears to have been normal at 

 that time of year for that locality, the normal temperature at noon being assumed to 

 be about - 20° F. ( - 28-8° 0.). 



In regard to rise of temperature with blizzard winds we experienced rises of 

 temperature towards the end of a blizzard of as much as, in extreme cases, 42° to 



* That snow may melt when the general air temperature is probably considerably below thaw point 

 is suggested by Amundsen's observation of icicles at Christmas 1911, hanging fiom his snow beacons at 

 The Butchery " Dog Depot," at an altitude of 10,000 feet above the sea and near lat. 8fi° S. It is highly 

 improbable in view of the temperatures registered there by Amundsen, that there is ever a true thaw 

 due to air temperature rising above freezing-point. An alternative explanation of the anthracene-like ice 

 crystals, so common on the plateau after days of strong sunlight, is that they were formed during the 

 succeeding night as the result of the condensation of ice vapour due to sublimation. 



