Glacier sliding has major environmental consequences, but friction caused by debris in the basal ice of glaciers is seldom considered in sliding models. To include such friction, divergent hypotheses for clast‐bed contact forces require testing. In experiments we rotate an ice ring (outside diameter = 0.9 m), with and without isolated till clasts, over a smooth rock bed. Ice is kept at its pressure‐melting temperature, and meltwater drains along a film at the bed to atmospheric pressure at its edges. The ice pressure or bed‐normal component of ice velocity is controlled, while bed shear stress is measured. Results with debris‐free ice indicate friction coefficients < 0.01. Shear stresses caused by clasts in ice are independent of ice pressure. This independence indicates that with increases in ice pressure the water pressure in cavities observed beneath clasts increases commensurately to allow drainage of cavities into the melt film, leaving clast‐bed contact forces unaffected. Shear stresses, instead, are proportional to bed‐normal ice velocity. Cavities and the absence of regelation ice indicate that, unlike model formulations, regelation past clasts does not control contact forces. Alternatively, heat from the bed melts ice above clasts, creating pressure gradients in adjacent meltwater films that cause contact forces to depend on bed‐normal ice velocity. This model can account for observations if rock friction predicated on Hertzian clast‐bed contacts is assumed. Including debris‐bed friction in glacier sliding models will require coupling the ice velocity field near the bed to contact forces rather than imposing a pressure‐based friction rule.

中文翻译：

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冰川下岩石摩擦的控制：温带冰中碎屑的实验

冰川滑动对环境有重大影响，但在滑动模型中很少考虑由冰川基底冰中的碎屑引起的摩擦。为了包括这种摩擦力，需要对裂床接触力的不同假设进行检验。在实验中，我们在光滑的岩床上旋转一个冰环（外径= 0.9 m），有无隔离直到结块。冰被保持在其压力融化温度，融化水沿着床层的膜流到边缘的大气压力。控制冰压或冰速度的床法线分量，同时测量床剪应力。无碎冰的结果表明摩擦系数<0.01。由碎冰引起的剪切应力与冰压无关。这种独立性表明，随着冰压力的增加，在碎屑下方观察到的腔体中的水压也相应增加，从而使腔体排入熔体膜中，而使碎屑层接触力不受影响。相反，剪应力与河床法向冰速成正比。空腔和不存在胶凝冰表明，与模型配方不同，过去碎屑的胶凝无法控制接触力。另外，来自床层的热量会使碎屑上方的冰融化，在相邻的融水膜中产生压力梯度，从而导致接触力取决于床层法向冰速。如果假设岩石在赫兹的克拉斯底层接触上预测为摩擦，则该模型可以解释观察结果。