Shear resistance and continuity of subglacial till: hydrology rules
Shear resistance and continuity of subglacial till: hydrology rules
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DOI：
10.3189/002214311796406220
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发表时间：
2010-01-01
影响因子：
3.4
通讯作者：
Iverson, Neal R.
中科院分区：
文献类型：
--
作者：
Iverson, Neal R.
G.S.博尔顿激发了人们对可变形岩层的广泛兴趣。在临界状态下，冰碛土的抗剪强度对应变率不敏感，随有效压力线性增加。在非稳定变形过程中，拟粘性剪切阻力可由固结土的膨胀和由此产生的孔隙压力下降引起。然而，这种影响可能是不常见的，因为低水力扩散系数的敏感冰碛物也是那些在有效压力瞬变期间最不可能显著固结的冰碛物。南极洲Whillans冰流的粘滑运动表明，其基底冰碛物在快速滑动期间必须减弱，在较长时间的缓慢滑动期间必须加强。快速滑动事件的复发间隔（6-18小时）表明，耕作强度的变化，如果驱动的孔隙压力的变化相关或无关的基础冻结，集中在最上面的几厘米的床。犁的颗粒在床面和相关的过剩孔隙压力在相邻的直到可以占率减弱在快速滑动，孔隙压力衰减导致加强之间的滑动插曲。通过促进浅，缓慢的冰下水流和低有效压力，软床可能有助于维持自己减缓自己的运输。软床的抗剪性、运动学和连续性是冰下水文学中的问题。
The field observations of G.S. Boulton stimulated widespread interest in deformable beds. Shear resistance of till in its critical state is insensitive to strain rate and increases linearly with effective pressure. During unsteady deformation, pseudo-viscous shear resistance can be caused by dilation of consolidated tills and resultant pore-pressure decline. This effect is probably uncommon, however, because susceptible tills of low hydraulic diffusivity are also those least likely to consolidate significantly during effective-pressure transients. Stick slip motion at Whillans Ice Stream, Antarctica, indicates that its basal till must weaken during rapid slip and strengthen during longer periods of slower slip. Recurrence intervals for rapid-slip episodes there (6-18 hours) indicate that till-strength variations, if driven by changes in pore pressure either related or unrelated to basal freezing, are focused in the uppermost several centimeters of the bed. Ploughing of grains at the bed surface and associated excess pore pressures in adjacent till can account for rate-weakening during rapid slip, with pore-pressure decay causing strengthening between slip episodes. By promoting shallow, sluggish subglacial water flow and low effective pressure, soft beds may help sustain themselves by slowing their own transport. Soft-bed shear resistance, kinematics and continuity are problems rooted in subglacial hydrology.