Abstract Decameter-scale eolian dunes were observed following a burst of intense rainfall in the sand sea of eastern Saudi Arabia. Planar, translational collapse structures developed over large areas of the dune slipfaces and were observed in pristine condition hours after their formation. Individual slipped blocks were approximately 10 cm deep over areas up to one hundred square meters. Observed geometries indicate a sequence of deformation beginning with downslope creep progressing to propagation of updip tensile fractures, finally thrust ramps developed at the downdip limits. Movement halted in all cases after about 10% displacement. A mechanical model is developed here based in part on snow avalanches and landslides to account for the observed deformation sequence. Rainwater loading increases differential stress in the dry internal parts of the dune. Rainwater infiltration also forms an impermeable wetting front below which air increases in pressure bringing the effective stress state towards the frictional sliding criterion, triggering downslope creep of the cohesive wet slab above. The wet slab has cohesion and tensile strength via proliferation of intergranular rainwater fluid bridges. Downslope creep led to updip tensile cracks releasing the slab, promoting slip and leading to downdip compressional failure with thrust structures. Exposure of the overpressured substrate in between the opening tensile cracks enabled pressure to bleed off ensuring the mechanism is self-limiting and therefore less hazardous than snow avalanches. The preservation potential of these structures is reasonably high due to their scale and likelihood of rapid burial by dune migration, but the distribution is patchy due to pre-existing moisture content of the dunes inhibiting the process, and the footprint of intense rainstorms usually being relatively small compared with the sand seas.

中文翻译：

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风成沙丘滑面雨致平面塌陷

摘要 在沙特阿拉伯东部沙海爆发强降雨后，观测到了十米尺度的风成沙丘。在沙丘滑面的大面积上形成了平面平移倒塌结构，并在其形成后数小时内在原始条件下观察到。单个滑动块在高达 100 平方米的区域内深约 10 厘米。观察到的几何形状表明一系列变形，从下坡蠕变开始，向上倾拉伸裂缝扩展，最后在下倾极限处形成推力斜坡。在大约 10% 的位移后，所有情况下运动都停止了。这里开发的力学模型部分基于雪崩和滑坡，以解释观察到的变形序列。雨水负荷增加了沙丘内部干燥部分的压力差。雨水渗入还形成了一个不可渗透的湿锋，在该湿锋下方，空气压力增加，使有效应力状态趋向摩擦滑动准则，从而引发上方粘性湿板的下坡蠕变。湿板通过粒间雨水流体桥的扩散而具有内聚力和抗拉强度。下坡蠕变导致上倾拉伸裂缝释放板坯，促进滑动并导致止推结构下倾压缩破坏。暴露在张开的拉伸裂缝之间的超压基材能够释放压力，确保该机制是自限性的，因此比雪崩危险性小。