南极长城站区寒冻风化特征

The Characteristics of Frost Weathering at the King George Island, Antarctica

通过对南极长城站区寒冻风化速率的观测和分析 ,结合气温等因素的变化 ,讨论了该区寒冻风化与影响因素之间的关系 .研究表明 ,该区夏季风化速率为冬季的 3.6～ 7.5倍 ;海拔较高的地方风化速率比海拔低的高 1.2 8～ 3.35倍 ;岩壁朝向东、东南的风化强度比朝向北、北西的大 2 .6～ 16倍 .低温年份的风化速率仅有高温年份的 7.2 %～ 16 .6 % .与世界其它冰缘区的风化速率对比 。

Freeze-thaw action is a factor of frost weathering in Antarctica. The weathering rate of rock is dependent on frequency, intensity and times of freeze-thaw action. In order to understanding the characteristics of frost weathering in Antarctica, some observation sites have been set up at different heights and slope-faces around the Great Wall Station in King George Island since 1988. Basedon the observation from March 1988 to March 1990, the relationship between frost weathering of rock and season, slope-faces and elevation are discussedin this paper. (1) Temperature effect A necessary condition for freeze-thaw action is a temperature fluctuation around 0℃; thus, temperature governs the weathering rate. The weathering rate of rock markedly changes seasonally and annually. It is 0.012～ 2.042 mm·a -1 in summer and 0.0314～ 0.5606 mm·a -1in winter. In low temperature year,it is only about7.2～16.6 per cent of that in high temperature year.In summer, there is more chance for temperature fluctuating around 0 ℃and higher frequency of freeze-thaw action.While in winter, the temperature is below 0 ℃, so the freeze-thaw action ceases. So do in the year with higher temperature. (2) Exposure effect The weathering rate in the slopes of the east and southeast is 2.6～16 times of that of the west and northwest.In winter, snow mainly deposits in the west slopes because of the northwest wind. In summer, snow in the east slopes melts earlier than that in the west slopes because of the southeast wind.So the times and frequency of freeze-thaw action in the west slopes is less than the east slopes. (3) Elevation effect In the seacoast at5 ma.s.l., the weathering rate of rock is very low, but in the slope with an elevation of 43～47 ma.s.l., only several hundred metersfar from the seacoast, the rateis high. The latter is several times larger thanthe former, althoughtheir rock typeis similar. Thisreflectsthat temperature changesquicklyin high elevation and the phase-change of water occurs repeatedly, so the rate of freeze-thaw action is high and the weathering is strong. The King George Island of Antarctica is located in a high latitudearea. There are 6～8 monthsin a year with temperature below 0℃, thusthe freeze-thaw action is restricted. Compared with other periglacial areasin the world, the weathering rate of rockis moderate inthe island.