Preprints
https://doi.org/10.5194/egusphere-2024-789
https://doi.org/10.5194/egusphere-2024-789
12 Apr 2024
 | 12 Apr 2024

Massive mobilization of toxic elements from an intact rock glacier in the Central Eastern Alps: insights into ice melt dynamics

Hoda Moradi, Gerhard Furrer, Michael Margreth, David Mair, and Christoph Wanner

Abstract. In the Central Eastern Alps, an increasing number of high-altitude streams display high concentrations of toxic solutes such as Al, F-, Mn, and Ni that may strongly exceed drinking water limits. Previous studies have shown that these elements are mobilized from rock glaciers occurring at the origin of the streams. This is caused by the weathering of pyrite producing sulfuric acid and therefore promoting the leaching of these elements from the crystalline host rocks. After mobilization, the elements are temporally stored and enriched in the rock glacier ice. Today, the climate-change-induced accelerated melting of rock glaciers thus leads to a quick and focused export in summer when ice melt export rates are high. The temporal storage of mobilized elements in the rock glacier ice opens up the opportunity to use the strong chemical signal in the streams to track rock glacier melt dynamics and to identify the governing processes controlling the export of ice melt. To test this and to assess the consequences of accelerated rock glacier melt on streamwater quality, here we present a two-year dataset (2021, 2022) of monitoring a high-alpine stream originating from an intact rock glacier located in Eastern Switzerland. The monitoring includes monthly sampling and discharge measurements at the rock glacier outlet, as well as continuous tracking of the geogenic fluxes of toxic solutes using a pressure and conductivity probe. Our monitoring revealed high annual fluxes with strong seasonal variation, whereby the fluxes were highest during the warm summer months. In 2021, the annual fluxes were up to several tons each, which is remarkable given that the area of the rock glacier covers only about 40’000 m2. Interestingly, in 2022 the fluxes were about 30 % lower despite the record-high summer temperatures. A similar difference was observed for the annual discharge recorded for the two years. This suggests that the export of both ice melt and toxic solutes are strongly controlled by the amount of water from snowmelt and precipitation infiltrating into the rock glacier system. The dry weather and low discharge rates in 2022 thus likely lead to lower export rates compared to 2021, when snow height and precipitation rates were above average. Nevertheless, in both monitoring years the degradation of the rock glacier significantly contributed to the discharge of the downhill stream. Based on these aspects, we present conceptual models for accumulation of toxic solutes in rock glacier ice well as for their water driven mobilization during accelerated rock glacier degradation. Finally, we argue that monitoring solute fluxes exported from rock glaciers is a promising future research direction for obtaining more reliable estimates of the amount of ice melt exported from rock glaciers.

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Hoda Moradi, Gerhard Furrer, Michael Margreth, David Mair, and Christoph Wanner

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-789', Stefano Brighenti, 09 May 2024
  • RC2: 'Comment on egusphere-2024-789', Anonymous Referee #2, 09 May 2024
Hoda Moradi, Gerhard Furrer, Michael Margreth, David Mair, and Christoph Wanner

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Massive mobilization of toxic elements from an intact rock glacier in the Central Eastern Alps: insights into ice melt dynamics Hoda Moradi, Gerhard Furrer, Michael Margreth, David Mair, and Christoph Wanner https://zenodo.org/doi/10.5281/zenodo.10558549

Hoda Moradi, Gerhard Furrer, Michael Margreth, David Mair, and Christoph Wanner

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Short summary
Number of high-altitude streams with high concentrations of toxic elements (Al, F, Mn, Ni) due to pyrite weathering and sulfuric acid production is increasing in the Eastern Alps. In contact of sulfuric acid, these elements are released from rocks and stored in ice in rock glaciers. Today, climate change accelerates rock glacier ice melt which leads to a quick and focused element export in summer. Our research tries to assess consequences of accelerated rock glacier melt on streamwater quality.