No abstract

In crystalline mountain regions, relict rock glaciers are apparent sediment accumulations that likely influence the runoff in alpine watersheds as a result of their discharge behavior. However, little is known about their impact on the streamflow further downstream. More than 560 mostly relict rock glacier-related landforms have been identified in the Styrian part of the Niedere Tauern Range (Austria). The catchment of a single relict rock glacier (Schöneben Rock Glacier, SRG), and two catchments with relict rock glaciers in their headwaters were investigated with a simple lumped-parameter rainfall-runoff model. The model parameters of the SRG catchment are in agreement with the existing conceptual understanding of the discharge dynamics and provide the parameter configuration to simulate the runoff of ungauged relict rock glacier catchments in the area. In addition, a semi-distributed approach was applied to quantify the impact of relict rock glacier-influenced headwaters on the downstream runoff. The results suggest that the contribution ranges from about a quarter to more than four times its areal share. The highest impact is observed during the late snow melt period and in the late summer. This highlights the relevance of these sediment accumulations in relation to water manage ment issues, in particular concerning altering meteorological conditions due to climate change.Reliktische Blockgletscher sind augenscheinliche Sedimentanhäufungen in kristallinen Gebirgsregionen, die aufgrund ihrer Abflussdynamik die Entwässerung alpiner Einzugsgebiete beeinflussen. Jedoch ist ihre Auswirkung auf unterstromige Gerinne weitgehend unbekannt. Mehr als 560 meist reliktische Blockgletscher sind im Steirischen Anteil der Niederen Tauern (Österreich) ausgewiesen. Ein über einen reliktischen Blockgletscher (Schöneben Blockgletscher, SRG) entwässerndes Einzugsgebiet und zwei Einzugsgebiete, die ihrerseits reliktische Blockgletscher in ihren hoch gelegenen Anteilen beinhalten, wurden mit Hilfe eines einfachen, räumlich nicht aufgelösten (lumped Parameter) Niederschlags-Abflussmodells untersucht. Die Modellparameter des SRG-Einzugsgebiets stimmen mit dem vorliegenden konzeptionellen Modell überein und dienen als Grundlage der Parameterkonfiguration zur Abflusssimulation anderer Blockgletschereinzugsgebiete in der Region, für die keine Abflussdaten zur Verfügung stehen. Zusätzlich wurde ein semi-distributiver Ansatz angewendet, um den Einfluss von Blockgletscher beeinflussten Einzugsgebieten auf die unterstromigen Gerinne zu quantifizieren. Die Ergebnisse zeigen, dass der Abflussanteil unterstromig von einem Viertel bis zu mehr als dem Vierfachen des Flächenanteils der übergeordneten Einzugsgebiete beträgt. Die höchsten Anteile können gegen Ende der Schneeschmelze und im Spätsommer beobachtet werden. Dies unterstreicht die wasserwirtschaftliche Bedeutung dieser Schuttakkumulationen in alpinen Einzugsgebieten, vor allem unter der Berücksichtigung der sich ändernden meteorologischen Bedingungen im Zuge des Klimawandels.

Relict rock glaciers are complex hydrogeological systems that might act as relevant groundwater storages; therefore, the discharge behavior of these alpine landforms needs to be better understood. Hydrogeological and geophysical investigations at a relict rock glacier in the Niedere Tauern Range (Austria) reveal a slow and fast flow component that appear to be related to the heterogeneous structure of the aquifer. A numerical groundwater flow model was used to indicate the influence of important internal structures such as layering, preferential flow paths and aquifer-base topography. Discharge dynamics can be reproduced reasonably by both introducing layers of strongly different hydraulic conductivities or by a network of highly conductive channels within a low-conductivity zone. Moreover, the topography of the aquifer base influences the discharge dynamics, which can be observed particularly in simply structured aquifers. Hydraulic conductivity differences of three orders of magnitude are required to account for the observed discharge behavior: a highly conductive layer and/or channel network controlling the fast and flashy spring responses to recharge events, as opposed to less conductive sediment accumulations sustaining the long-term base flow. The results show that the hydraulic behavior of this relict rock glacier and likely that of others can be adequately represented by two aquifer components. However, the attempt to characterize the two components by inverse modeling results in ambiguity of internal structures when solely discharge data are available.

The validity and applicability of various methods to infer hydraulic properties of sloping aquifers in alpine settings using the power law relationship between the discharge recession and its first time derivative is explored. For this purpose, a synthetic spring catchment implemented in the numerical groundwater flow model MODFLOW as well as the example of a relict rock glacier in an alpine setting is examined. The various approaches are found to differ particularly in the late time domain, whereas most of them agree fairly well in the early time domain and at the transition point between the two time domains. As the early recession may be affected by uncertainties from inappropriate initial conditions, it is proposed to use the transition point for estimating aquifer thickness and transmissivity. Using only prolonged winter recessions in the analysis of the field data from the relict rock glacier yields estimates of aquifer thickness and hydraulic conductivity consistent with results from a geophysical survey and tracer tests, respectively. In the other seasons, the recession is frequently interrupted by minor recharge events, and using the lower envelope of the entire data is found to yield estimates that are too high in the given case. It is thus recommended to focus on the winter recession in the analysis of hydrograph data from alpine settings.

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.

Kellerer-Pirklbauer, A., Pauritsch, M. and Winkler, G., 2015. Widespread occurrence of ephemeral funnel hoarfrost and related air ventilation in coarse-grained sediments of a relict rock glacier in the Seckauer Tauern Range, Austria.ABSTRACT. This paper examines the occurrence of ephemeral hoarfrost crystals at funnel openings (funnel hoarfrost) detected between large blocks at the surface of the presumably relict Schöneben Rock Glacier. Field mapping on 25 November 2011 identified 51 individual funnel openings with notable hoarfrost crystals distributed over the entire rock glacier. Hoarfrost was no longer detectable a few days after the initial mapping campaign. At least in the period 20-25 November 2011 temperature conditions at the rock glacier surface were favourable for hoarfrost formation and preservation as indicated by different types of measurements. A period of 24-48 h of hoarfrost-suitable weather conditions would have been sufficient to form the observed hoarfrost if crystal growth rates of 2-4 mm h −1 are assumed. The void systems with funnel hoarfrost seem to be rather localised and limited in horizontal (10s of metres) and vertical (some metres) extent. Presumably the observed funnel hoarfrost was caused by the so-called chimney effect, although no larger reversible air circulation systems with warm air exhalation were identified. Continuous ground temperature data from several sites at the rock glacier surface (period November 2011-December 2012 showed that hoarfrost sites are cooler and thermally buffered compared with non-hoarfrost sites at similar elevations. This seems to be related to the decoupling of the air above the rock glacier and the pore air during periods of atmospheric warming. Only the combination of specific micro-climatic (temperature/humidity), geometric (open void systems) and sedimentological (grain size/sediment structure) conditions allow the formation of the ephemeral funnel hoarfrost at this rock glacier.