Dynamics of active-layer detachment failures, Fosheim Peninsula, Ellesmere Island, Nunavut, Canada

Dozens of fresh active-layer detachments were observed on the Fosheim Peninsula in late-summer 2005 following one week of high air temperatures and nearly continuous bright sunshine. One of these shallow translational landslides started as a minor movement on an upper, steeper slope segment but over several days its front propagated 250 m downslope at velocities of 2-9 m h(-1). A second, smaller active-layer detachment developed within less than 2 hours and subsequent movement was limited. Effective stress analyses can explain the initiation of these landslides on moderate gradients. Movements across extremely low-angled slope segments, however, likely require both dynamic loading from the moving mass and very low basal undrained shear strengths produced by high porewater pressures. The lengthy development of the large active-layer detachment helps explain stratigraphic and morphologic features previously observed in these slope failures. Copyright (C) 2007 John Wiley & Sons, Ltd.