Controlling factors of microclimate in blocky surface layers of two nearby relict rock glaciers (Niedere Tauern Range, Austria)

Abstract

Coarse blocky material is known to have a ground cooling effect compared to other types of unconsolidated surface material, which may have an influence on spatial distribution and conservation of permafrost. In the light of climate warming, this effect may retard permafrost degradation or exert prolonged ground cooling in general. To contribute to a better understanding of this ground cooling effect and potential influencing factors, the thermal regime of blocky surface layers of two comparable nearby relict rock glaciers with opposing aspects was investigated. Air, surface and shallow ground temperature at 1 m depth were continuously measured over a four-year period at nine locations distributed over two rock glaciers. The blocky surface layer of the SWexposed rock glacier exhibits lower and more heterogeneous temperatures than the NE-oriented despite a higher potential solar radiation. The data suggest a thinner or more discontinuous seasonal snow cover at the SW-exposed rock glacier, causing a more efficient winter cooling. The importance of air flow driven heat transfer as a source of cooling is supported by the data. Results illustrate thermal heterogeneities within blocky layers and the importance of the seasonal snow cover pattern in addition to topography and microclimatic variability in high relief terrain is hypothesized.

Air Convection in the Active Layer of Rock Glaciers

“…We use this dimensionless number in the results and discussion sections to characterize the convection in the active layer. It has widely been used to analyze natural convection in a permafrost context (Kane et al, 2001;Herz, 2006;Guodong et al, 2007;Wagner et al, 2019).…”

“…In numerical studies on passive cooling in an engineering context the value of Ra crit = 4π 2 has become established (Goering and Kumar, 1996;Guodong et al, 2007;Pham et al, 2008;Lebeau and Konrad, 2009). Further, studies analyzing temperature data in a permafrost context adopted a critical threshold of ∼40 (Juliussen and Humlum, 2008;Wagner et al, 2019). Hence, in the following Ra crit = 4π 2 (39.42) is used.…”

“…Côté et al (2011) showed with experimental data that the Kozeny -Carman equation overestimates the permeability for bigger particle sizes (e.g., crushed rocks) by a factor of about 4.25. Published values for permeability in the context of active layer convection for rock glaciers (Table 4; Herz, 2006;Panz, 2008;Wagner et al, 2019) are based on the Kozeny-Carman equation with no further validation and seem thus to be overestimating the permeability. It is also important to note that modeling studies normally use values in the order of 10 −7 -10 −6 m 2 , whereas higher permeability values order of 10 −5 -10 −4 m 2 are only used in the analysis of field data (Table 4).…”

Long‐term monitoring of sporadic permafrost at the eastern margin of the European Alps (Hochreichart, Seckauer Tauern range, Austria)

“…Ground and air temperature have also been monitored since 2011 at the Dürr valley and the Schöneben cirque, respectively (Figure , white stars, 10 monitoring sites in the two valleys). Temperature monitoring at these two areas focuses on hydrological issues, although the cooling effect of the blocky layer is also considered . Relevant thermal results from these two areas are considered in the discussion.…”

“…20 Furthermore, data from a nearby automatic weather station (R-A2) Temperature monitoring at these two areas focuses on hydrological issues, although the cooling effect of the blocky layer is also considered. 21,22 Relevant thermal results from these two areas are considered in the discussion.…”