Patterns of Multiannual Aggradation of Permafrost in Rock Walls with and Without Hydraulic Interconnectivity (Steintälli, Valley of Zermatt, Swiss Alps)

Abstract

This article shows monthly, annual and multiannual response of two rock permafrost systems with and without hydraulic interconnectivity. It is hypothesized, that interconnective systems with cleft water percolation from glacierets close to 0°C are high-entropy systems that balance rock masses at 0°C and prevent cooling but are not effective in excessive melting, as thermal conduction away from water pathways into compact rock is a function of sensitive temperature gradients. This was tested using static (permafrost distribution in 2005) and dynamic (permafrost aggradation 2005–2007) performance of two adjacent north-exposed transects with similar geometries, geology and discontinuity patterns. Transect NW is only affected by heat transfer from the rock surface. Transect NE conducts hydraulic heat transfer with glacierets by meltwater seepage. Electrical resistivity tomography (ERT) time-sections and mean apparent resistivity – median depth of investigation (AR/DOI) gradients of steep sections (> 60°) were analysed from 2005–2007. (i) In 2005, a body in a transitory (0°C) resistivity range (< 20 kΩm) was developed in Transect NE. Transect NW indicated a deeply frozen body (> 40 kΩm) of several meters diameter. (ii) Negative AR/DOI surface gradients indicate a pronounced short-term response of surface resistivities in Transect NW to surface chilling (August 13, 2007: –3.3 kΩm/m) and cool pulse propagation whereas Transect NE is well buffered (August 13, 2007: –0.1 kΩm/m). (iii) Cool mid-summer conditions in 2005 and 2006 initiated permafrost aggradation in both transects. In Transect NW, ERT displays resistivity increases by more than 70%, a spatially aggrading permafrost body and the formation of a new perennially frozen rock body. Resistivity in Transect NE increases 10–30% in the transitory body. (iv) In Transect NW, the AR/DOI gradient increased from 5 kΩm/m in August 2005 to 11 kΩm/m in August 2007, indicating significant permafrost aggradation and cooling. In Transect NE, AR/DOI increased from 0.6 kΩm/m in August 2005 to 1.0 kΩm/m in August 2007 but resistivities still do not exceed the initial freezing range significantly at any depth of investigation. Data reliability of both transects is assessed in terms of uncertainty and relative sensitivity plots.