Permafrost in talus slopes: what are the main drivers of low temperatures and ice content ?

Coarse-blocky landforms are assumed to be the most resilient permafrost occurrences due to low thermal conductivity and their seasonal asymmetric internal convection processes and have been addressed in many field and modelling studies. In this contribution we will put a specific focus on the most general of these landforms, the ubiquitous talus slopes, which are understudied compared to other mountain permafrost landforms such as rock glaciers. Talus slopes exist in all mountain ranges and at different elevations, including middle mountains where they give rise to specific undercooled micro-climatic conditions. In many cases, internal convection processes are the main reason that the cool micro-climatic conditions could be preserved over long time scales. The ice content can be variable, ranging from zero at low elevations to the presence of ice cores at elevations where permafrost is widespread. However, the ice content in most talus slopes is generally unknown, as boreholes are extremely scarce and standard geophysical techniques (such as Electrical Resistivity Tomography and Seismic Refraction techniques) exhibit problems in detecting medium to small ice contents in coarse blocky substrates. In this contribution we use a compilation of data from a large number of different talus slopes in Europe, the Central Andes and Central Asia to attempt to (1) quantify the influence of slope angle, substrate and thickness of the talus on the internal air circulation and its cooling effect and (2) address the application of emerging geophysical techniques to improve the quantification of ice content in these substrates.