Stratigraphic evaluation of a Holocene clay-slide in Northern Norway

Abstract

An almost 6,000 years old slide in marine clay at Fossmoen, Northern Norway is studied to: characterize the scar, the slide deposits and the slide event; evaluate the role that stratigraphic variations played for failure; and view the slide event within long-term landscape development. A geological model for the area is based on drilling, outcrops and ground-penetrating radar with emphasis on the stratigraphic variations of fjord deposits. The slide's age implies that the deposits were sensitive already shortly after emergence above sea level, and layers are still sensitive. River incision was probably responsible for the initial slide, whereas stratigraphy and groundwater movement controlled the location and shape of the scar. Laminated, inclined and discontinuous bedding are suggested as playing different roles for ground-water flow and pore pressures, adding to existing models on the development of soft and sensitive layers prone to sliding.

Slope stability and landslides in proglacial varved clays of western Estonia

“…In the first group small-scale failure at the river bank leads to the instability of the higher sections and, thereafter, to the formation of a retrogressive slide complex. A retrogressive development mechanism has been found in glaciomarine sediments (Geertsema et al, 2006;Hansen et al, 2007), glaciolacustrine sediments (Van Asch et al, 1984;Froese and Cruden, 1999;Geertsema et al, 2006), and also in chalk and clay (Fang, 1990;Brundsen, 1999). Brundsen (1999) explained the development of the retrogressive slides as slip surfaces adopting common shear surface by utilising the low strength of the ruptured zone, as once sheared soil has fully softened or even residual strength.…”

Clay slides in the Målselv valley, northern Norway: Characteristics, occurrence, and triggering mechanisms

“…Although vertical groundwater drainage tends to be impeded, horizontal drainage may be efficient. Also, the stratigraphic dip of the sediments could focus groundwater flow, thus increasing pore pressures where these aquifers are thin and pinch out (Hansen et al, 2007). The 1990 slide at Storleirfallet (Fig.…”

“…(Corner, 2006). Most of the slides are prehistoric, as evidenced by the elevated position of the slide scars in comparison with present-day rivers, as well as radiocarbon dates (Hansen et al, 2007). Although quite a few slides have occurred in historic times, only a few have proved fatal.…”

“…The sediments were deposited in a fjord basin of variable depth, under relative sea-level fall, during and after the final retreat of the Fennoscandian ice sheet. Detailed investigation of a single, well-defined prehistoric landslide in the Målselv valley (Hansen et al, 2007) suggests that local stratigraphy had an important impact on the dimensions and style of the slide. The distribution of permeable and impermeable layers in clay was linked to groundwater movement, leading to the development of soft sensitive layers and the subsequent clay slide.…”

Large, prehistoric clay slides revealed in road excavations in Buvika, mid-Norway

“…Land-based slides including clay slides are, on the other hand, often only described from their morphologies combined with drilling and/or geophysics (e.g. Bjerrum 1955;Hutchinson 1961Hutchinson , 1965Mollard 1977;Løfaldli et al 1981;Calvert and Hyde 2002;Bichler et al 2004;Hansen et al 2007a). However, unless an extensive drilling and geophysical survey is conducted, internal structures of slides are difficult to outline.…”