Periglacial environments and frozen ground in the central Pyrenean high mountain area: Ground thermal regime and distribution of landforms and processes

Abstract

The periglacial belt is located in the highest parts of temperate mountains. The balance between mean air and ground temperatures and the presence of water determine the effectiveness of periglacial processes related to permafrost, the active layer or seasonally frozen ground (SFG). This study combines thermal and geomorphological data obtained in four Pyrenean massifs (Infierno‐Argualas, Posets, Maladeta and Monte Perdido) to improve knowledge on the occurrence and distribution of frozen ground. The methodology used is based on the study of landforms as frozen ground indicators, mapping processes, ground temperature analysis, basal temperature of snow, thermal mapping and geomatic surveys on rock glaciers and protalus lobes. In the Pyrenean high mountain areas the lower limit of frozen ground is at ~2,650m a.s.l., possible permafrost appears above 2,650m a.s.l. on north‐ and south‐facing slopes, and probable permafrost is dominant above 2,900m a.s.l. Unfrozen ground with cold‐associated geomorphological processes reach 2,900m a.s.l. and unfrozen and frozen ground distribution points to a patchy pattern throughout the periglacial belt. The most widespread frozen grounds are SFG. The thermal data, mean annual ground temperature, cold season temperatures, bottom temperature snow measurements, freeze/thaw cycles and distribution of landforms permit the establishment of a periglacial land system divided into three main belts: infraperiglacial, middle periglacial and supraperiglacial. The large number of processes and landforms that are involved and their altitudinal and spatial organization make up a complex environment that determines the geoecological dynamics of high mountain areas.

Long‐term trends (1958–2017) in snow cover duration and depth in the Pyrenees

“…Seasonal snow is essential for most environmental, hydrological, and geomorphological processes in mountain areas. The insulation effect whereby snow cover protects the underlying substrate from atmospheric temperatures directly controls the thermal regime of soils and determines the phenological cycles of plants and animals living at high elevations (Kankaanpää et al ., 2018; Wang et al ., 2018; Serrano et al ., 2019). The snowpack also acts as a natural reservoir of water, formed during the cold season from the accumulated precipitation.…”

Mapping the potential distribution of frozen ground in Tucarroya (Monte Perdido Massif, the Pyrenees)

“…Besides, this type of mapping can be combined with information of periglacial thermal processes to define landsystems (Evans et al 2017). The altitudinal thermal classification of landforms (González-García, 2013;Serrano et al, 2019) permits us to considerate as permafrost or SFG indicators four of the mapped landforms (Table 1). Surface ground temperatures (GTS) and the ground thermal regime were monitored by means of 18 continuous data-loggers (Ibuttons DS1922L and DS1921G) placed at depths of between 2 and ~10 cm between 2014 and 2016.…”

“…Maps of permafrost distribution were made in Posets Massif, differentiating among sporadic, discontinuous and continuous permafrost Lugon et al, 2004). The spatial distribution of mountain permafrost was obtained around the Aneto peak by means of the Inverse Distance Weighting (IDW) interpolation model (Chueca and Julián, 2010), and thermal and permafrost maps have been made in the Alba-Maladeta, Infiernos Massif and La Paúl Cirque (González-Garcia, 2013;Serrano et al, 2019). The entire Pyrenees was mapped on a scale 1:500,000 also using an IDW interpolation model (Serrano et al, 2009).…”

Elevation Effects on Air Temperature in a Topographically Complex Mountain Valley in the Spanish Pyrenees

“…Air temperature data were checked by applying a quality control that ensured that the dataloggers were not buried under snow. For this, daily air temperature ranges were analyzed, discarding those days with hourly standard deviation < 0.1 • C and an average air temperature < 2 • C. The air temperature in snow-burial conditions was constant at a value close to 0 • C [74], so it was relatively easy to filter out this issue. The 10 locations passed this filter and 0 samples were discarded.…”