Primary Transverse Crevasses
Primary Transverse Crevasses
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主要横向裂缝
DOI：
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发表时间：
1969
影响因子：
3.4
通讯作者：
G. Holdsworth
中科院分区：
文献类型：
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作者：
G. Holdsworth
在初始横向破裂区域的温带冰川上的应变率测量表明，临界应变率为3.5±0.5×10−5d−1，对应的区域应变率梯度为5×10−8 d−1m−1。只有一段冰川的理论纵向应变率(Nye，1959[c])与该点表面的测量值基本一致。对极地冰川(夏季10m深度温度−2 7.9℃)的相应测量表明，其临界应变率约为0.6±0.0 5×10−5d−1，对应的应变速率梯度约为3×10−9d−1 m−1。在某一断面上，理论应变率与实测值基本一致。温带冰川裂隙深度为23.5~28m，极地冰川裂隙深度为23.9±0.5m，呈楔形。利用奈伊的裂缝深度公式中的区域应变率值，只能得到与深度测量值大致一致的结果。在距离1.2公里的范围内，温带冰川横向裂缝的间距变化很大，从30米到96米不等，但最初的间距在55米到96米之间，前四种情况下S的间距在2.7d到3.3d之间变化，其中d是裂缝深度。在寒冷的冰层中，裂缝的间距要均匀得多，从57 m到66 m不等。只有一次得到了S≈2.5d的值。这种更大的间距一致性可以用流动的动力学来解释。尽管两个冰川在温度、尺寸和应变率参数上有很大的差异，但(1)裂缝深度非常相似，(2)裂缝的间距相似。有两条证据证明，断裂带上的应变可以忽略不计的假设是不正确的。在最可靠的情况下，主扩展应变率的方向在2°至7°范围内垂直于裂缝迹线。
Measurements of strain-rates on a temperate glacier in a region of initial transverse fracturing indicate a critical strain-rate of 3.5±0.5 × 10−5 d−1, associated with a regional strain-rate gradient of 5 × 10−8 d−1 m−1. At only one section of the glacier is the theoretical longitudinal strain-rate (Nye, 1959[c]) in approximate agreement with the value measured at the surface at that point. Corresponding measurements on a polar glacier (temperature −27.9°C at 10 m depth during the summer) indicate that the critical strain-rate is about 0.6±0.05 × 10−5 d−1, which is associated with a gradient of strain rate of about 3 × 10−9 d−1 m−1. At one section there is close agreement between the theoretical and measured longitudinal strain-rate. For the temperate glacier crevasse depths ranged from 23.5 to 28 m; in the polar glacier one crevasse was 23.9±0.5 m deep, assuming a wedge form. Only an approximate agreement with the measured values of depth is obtained by using the regional strain-rate values in Nye’s crevasse-depth formula. Over a distance of 1.2 km the temperate glacier transverse crevasse spacings are very variable, ranging from 30 m to 96 m, but initially the spacings range from 55 m to 96 m, and for the first four cases the spacing s varies from 2.7 d to 3.3 d, where d is the crevasse depth. In the cold ice, crevasse spacings are far more uniform, ranging from 57 m to 66 m. A value of s ≈ 2.5 d is obtained in only one case. This greater uniformity of spacing may be explained in terms of the dynamics of flow. Despite large differences in thermal, dimensional and strain-rate parameters between the two glaciers, (1) the crevasse depths are closely similar, and (2) the spacings of crevasses are similar. It has been demonstrated from two lines of evidence that the assumption that the strain on an intercrevasse block is negligible is not correct. The direction of the principal extending strain-rate is, in the most reliable cases, perpendicular to the crevasse traces within 2° to 7°.