Arctic coastal retreat through block failure

Abstract

This study investigates the mechanics of block failure in frozen bluffs underlain by permafrost along Arctic coasts. Different block failure modes with and without thermoerosional niches and ice wedges are identified. A comprehensive analytical model is developed by coupling slope stability analysis with the progressive formation of a thermoerosional niche and the existence of ice wedges in the perennially frozen backshore area. Model computations involve three steps. First, the stability of frozen cliffs is examined by calculating the factor of safety based on slope analysis using the strength of permafrost soil. Second, in the presence of thermoerosional niches at the base of frozen cliffs, the failure modes and critical niche depths are determined by applying the moving boundary of a developing thermoerosional niche to the stability analysis. Finally, the effects of ice wedges are examined by imposing a change in strength conditions related to the existence of ice wedges at different locations in the potential failure region. Different potential failure modes and the critical combination of features contributing to block failure occurrences in Arctic coastal bluffs are identified through model calculations. Nondimensional parameters, regression equations, and graphs are derived to be used for determining the block failure potential for Arctic coasts.