Impacts of post-glacial rebound on landslide spatial distribution at a regional scale in northern Iceland ( Skagafjrdur)

In de-glaciated areas, para-glaciation (i.e. the conditioning of landscapes by prior glaciation) has often been considered a major predisposing factor in landslide occurrence; its consequences have been particularly well identified at a fine scale (especially on bedrock jointing). Hitherto, the relative impacts of para-glaciation on hillslope dynamics at a regional scale had nevertheless not been quantified statistically. We examine Skagafjorour area (northern Iceland) where landslides are widespread (at least 108 were mapped in an area of c. 3000km(2)). We compare the role of para-glaciation (debuttressing, influence of post-glacial rebound) with that of classic factors (topography, lithology, etc.) in landslide occurrence and location, using a spatial analysis based on a chi-square test. On the one hand, the results highlight that landslides are over-represented in areas where post-glacial rebound was at its maximum, with a stronger concentration of landslides in the northern part of the fjord. On the other hand, the distribution of landslides did not show any clear relationship with the pattern of glacial debuttressing. Tschuprow coefficient highlights that the influence of post-glacial rebound on landslide location is higher than the combined influence of slope gradient, curvature or geological structure. This result is supported by our initial evidence for the timing of landslides in the area: most landslides occurred during the first half of the Holocene, and a period of hillslope instability was initiated when the post-glacial uplift was at its maximum. Finally, the mechanisms that link post-glacial rebound and landsliding as well as the geomorphic impacts of landslides, are discussed. Copyright (c) 2013 John Wiley & Sons, Ltd.