Study of an Ice Core to the Bedrock in the Accumulation zone of an Alpine Glacier
Study of an Ice Core to the Bedrock in the Accumulation zone of an Alpine Glacier
复制标题
高山冰川堆积带冰芯对基岩的研究
作者：
M. Vallon;J. Petit;B. Fabre
摘要 每年夏天，冰开始形成的地下水位大约为 30 m，加速了夏季冰的转化（每年形成的冰的 80% 在不到 2 个月的时间内出现）。以这种方式形成的冰含有0%至0.6%的水。由于发芽热的影响，平均含水量随着芽长的增加而逐渐增加。但是，在基岩附近，即 180 至 187 m 之间，蓝冰的渗透性使得含水量下降（0.3%，而 160 至 180 m 之间为 1.3%）。从 33 m 深度开始，沉积成因的叶状结构逐渐在冰中形成。其倾角定期增加至 145 m。在 145 m 处，它突然从 20° 跳跃到 40°，然后在 170 m 处从 40° 跳跃到 65°，这可以通过 bergschrund 中的旧修改来解释。这种叶理在基岩（180-187 m）附近消失，那里的冰中没有气泡。冰晶的平均尺寸在冰雪中缓慢增加，在30至50 m之间呈现季节性波动，然后在50至80 m之间从1或2毫米的直径跳跃到10或20毫米。在 180 至 187 m 之间，冰由大晶体组成（直径 3-10 cm；然而，由于样品的重结晶，该数字可能不准确）。冰晶光轴的非常强的近垂直方向很快消失，并且从 66 m 开始，在具有大晶体的冰中，出现了多个最大值的织物（通常是 3 或 4 个方向，形成三角形或菱形）。另一方面，在形成平行于叶状平面的带的小晶体中，只能看到一个优先取向方向，或者两个彼此接近的方向。中等尺寸（10 至 50 毫米）的晶体通常具有两个彼此成约 50° 角的优选取向方向。无论晶体有多大，最常见的 c 轴取向与垂直方向之间的角度在 60 至 170 m 长度范围内都不会发生变化。
Abstract A water table appearing every summer where the ice begins, at a gerpth of approximately 30 m, accelerates the transformation of firn into ice during the summer (80% of the ice formed every year appears in less than 2 months). The ice formed in this way contains from 0 to 0.6% water. The average water content increases gradually with the gerpth because of the heat of gerformation. But, near bedrock, between 180 and 187 m, the permeability of the blue ice is such that the water content drops (0.3% as compared to 1.3% between 160 and 180 m). From a gerpth of 33 m, a foliation of sedimentary origin gradually gervelops in the ice. Its dip increases regularly to a gerpth of 145 m. At 145 m it jumps sudgernly freom 20° to 40°, then at 170 m freom 40° to 65°, which can be explained by old modifications in the bergschrund. This foliation disappears near bedrock (180-187 m), where there are no bubbles in the ice. The average size of an ice crystal increases slowly in the firn, shows seasonal fluctuations between 30 and 50 m, then jumps freom a diameter of 1 or 2 mm to 10 or 20 mm between 50 and 80 m. Between 180 and 187 m, the ice is mager of large crystals (3-10 cm diameter; the figure, however, is probably inexact due to a recrystallization of the samples). The very strong sub-vertical orientation of the optic axes of the firn crystals disappears quickly, and freom 66 m on, in ice with large crystals, a fabric of multiple maxima appears (generally, 3 or 4 directions, forming a triangle or a rhombus). On the other hand, in the small crystals that form bands parallel to the plane of foliation, only one direction of preferential orientation can be seen, or two close to one another. Crystals of intermediate size (10 to 50 mm) generally have two directions of preferred orientation at an angle of approximately 50° to one another. No matter how big the crystals are, the angle between the most common c-axis orientation and the vertical does not change freom 60 to 170 m gerpth.