Rapidly applied loading can cause a sudden collapse of the granular structure, suddenly increasing in the water pressure in a soil; in extreme cases this can separate the soil grains from each other.  
Features called "sand volcanoes" are often found in areas that have experienced this, created by high pressure water percolating upwards.  Alluvial and aeolian deposits are particularly susceptible to this phenomenon in low-lying areas where the ground is saturated.  Rapidly applied loading can cause a sudden collapse of the granular structure, suddenly increasing in the water pressure in a soil; in extreme cases this can separate the soil grains from each other.  For 10 points - name this phenomenon, frequently seen in earthquakes, in which a soil loses its ability to support structures and behaves like a liquid.
Features called "sand volcanoes" are often found in areas that have experienced this, created by high pressure water percolating upwards.  
liquefaction