CONTROLS ON LANDSLIDES SIZE-DISTRIBUTION; RELATION BETWEEN AREA AND VOLUME OF LANDSLIDES

We studied landslides area and volume relations using 2D numerical simulations (GEO-Slope/W) and analyzed the landslides length in sliding direction (L) versus the slope-normal landslides depth (h). The geometry of the studied slope is a right-angle triangle with slope dip of 27 degrees. Cohesion (C) assigned for the entire slope material ranged 0-25 kPa and angle of internal friction (phi) ranged 0-50 degrees. Size-scales were 1m, 10m and 100m. This setting simulates sliding in homogeneous natural slopes.

We found that where C = 0 and phi >0, h/L is very small, i.e. shallow slides; where C >0 and phi = 0, h/L is large (h is maximal possible in the system). Where C >0, phi is 25 degrees and size scale is 100m, h/L is 0.05-0.1; similar to field observations (e.g. Hovius et al., 1997). Under these mechanical conditions L tends to be maximal possible and covers the entire slope. h/L increases to more than 0.2 when size scale decreases to 1m.

Following the above simulations we conclude the following: (a) landslides area and volume are mutually dependent and are constrained by the slope geometry; (b) size of shallow landslides (occur in the rather homogenous unconsolidated sediments consisting the upper few meters close to the surface) will be maximal possible and constrained by either the unconsolidated material depth or slope length. Similar observations were found in shaking-sandbox experiments (Katz and Aharonov, 2006).