Figure 6. Cross-section of the March 1997 landslide, drawn through middle of the map in Figure 5. The upland is to the left, and the outrunner blocks traveled toward the right. The ruled lines in the intact bluff represent clay layers (beds) that are tilted slightly to the north. Similar ruling in transported blocks shows that they have rotated by various amounts during the landslide movement as measured at the site. An important aspect of rotational slumps, common in high clay bluffs such as this, is that failure occurs on a curved slip surface at depth because the clay is not strong enough to support the overlying weight. Comparison of the bluff before (dashed line) and after the slump shows that the base of the bluff has moved forward and the top of the bluff has moved back, effectively reducing the slope angle to a more stable configuration.
Last updated on October 6, 2005