Active Layer Boundary Conditions in Steep Rockwall Permafrost

There is much debate about the presence and role of fluid water in the permafrost active layer in steep bedrock environments. This holds for water both at the macro and micro scale (pores). While initial long-term experiments e.g. by Hasler started investigations based on the hypothesis that large ice bodies progressively formed inside deep cleft structures found in rockwalls and ridges this could not be backed up by observations. As far as observations at depth in solid rockwalls are possible, compact ice lenses have only been documented at significant scale in deeper sections of rupture planes of (large) rock falls.

The boundary conditions of an active layer on an inclined plane (steep rock walls or steep sections of rock glaciers) are significantly different from low to neglectable slope angles predominantly found in arctic permafrost environments. In arctic soil or rock columns fluid water mobilized on or in the active layer sits for long periods of time on an impermeable permafrost body with runoff only happening slowly in dominantly horizontal directions. Contrary to this we argue that in steep (30 degree plus) environments fluid water runs off or escapes quickly through the active layer effectively draining the latter when observed over significant timescales. Especially with climate-induced permafrost warming at a global scale, the refreezing of fluid water on the permafrost table is minimal. This effectively leads to a “drying” of the steep mountain peaks. Our assumptions are backed up by observations that (i) fluid water availability through snowmelt dominates in periods of active layer deepening and not during refreezing, (ii) iceshields and firn flanks are reduced leaving only bare rock/soil as well as (iii) the boundary conditions found in first order physical principles, e.g. energy balance, gravity as well as fluid flow. In this presentations we approach these questions from a conceptual perspective, highlight principle boundary conditions and invite further collaborators to further the discussion.