Acute sensitivity of landslide rates to initial soil porosity

Some landslides move imperceptibly downslope, whereas others accelerate cat astrophically. Experimental Landslides triggered by rising pore water press ure moved at sharply contrasting rates due to small differences in initial porosity. Wet sandy soil with porosity of about 0.5 contracted during slope failure, partially liquefied, and accelerated within 1 second to speeds ov er 1 meter per second. The same soil with porosity of about 0.4 dilated dur ing failure and slipped episodically at rates averaging 0.002 meter per sec ond. Repeated slip episodes were induced by gradually rising pore water pre ssure and were arrested by pore dilation and attendant pore pressure declin e.