Velocities of rock glaciers and their surface, near surface and hydrothermal regimes in the Austrian Alps: Clear signs of climate change?

The link between rock glacier velocity and climatic forcing is well established in permafrost research, especially for rock glaciers. This understanding underpins the inclusion of rock glacier velocity as an associated parameter of the Essential Climate Variable “Permafrost” within the Global Climate Observing System since October 2022. In this context, the rock glacier velocity (commonly abbreviated as RGV) is defined as a spatially averaged interannual horizontal velocity time series related to a RG unit or a part of it. However, RGV does not invariably track climatic forcing in a simple, linear manner, which can obscure the climatic signal. In this study, we combine primarily multi-decadal RGV monitoring with long-term observations of ground surface and near-surface temperatures, as well as spring water temperatures, at two sites in the Hohe Tauern, Austrian Alps: the Dösen rock glacier (DOE) and the Hinteres Langtalkar rock glacier (HLK). Both are well-developed, typical alpine rock glaciers. Each features a dominant rock glacier spring that drains runoff from the landform and its contributing hydrologal catchment. Annual in-situ geodetic surveys began in 1995 (DOE) and 1999 (HLK). Ground surface and near-surface temperatures, along with several meteorological variables, have been monitored using miniature temperature loggers and standard meteorological sensors since 2006 at both sites. Spring water temperature monitoring started in 2016 at DOE and 2017 at HLK. Our results indicate a clear relationship, in part, between RGV and temperature (air, ground, water). However, this relationship weakens or disappears where geodetic points are not, or are only partially, representative of permafrost creep. Moreover, summer spring-water temperatures can be damped by heat exchange with internal ice, such that melt of the ice component buffers water peak temperatures. These findings underscore the importance of parallel, co-located monitoring of ground, water, and air temperatures (and other climatic parameters), alongside carefully designed geodetic sampling that targets zones of active permafrost creep.