Glacial stages and post-glacial environmental evolution in the Upper Garonne valley, Central Pyrenees

Abstract

The maximum glacial extent in the Central Pyrenees during the Last Glaciation is known to have occurred before the global Last Glacial Maximum, but the succession of cold events afterwards and their impact on the landscape are still relatively unknown. This study focuses on the environmental evolution in the upper valley of the Garonne River since the Last Glaciation. Geomorphological mapping allows analysis of the spatial distribution of inherited and current processes and landforms in the study area. The distribution of glacial records (moraines, till, erratic boulders, glacial thresholds) suggests the existence of four glacial stages, from the maximum expansion to the end of the glaciation. GIS modeling allows quantification of the Equilibrium Line Altitude, extent, thickness and volume of ice in each glacial stage. During the first stage, the Garonne glacier reached 460m in the Loures-Barousse-Barbazan basin, where it formed a piedmont glacier 88km from the head and extended over 960km. At a second stage of glacier stabilization during the deglaciation process, the valley glaciers were 12-23km from the head until elevations of 1000-1850m, covering an area of 157km. Glaciers during stage three remained isolated in the upper parts of the valley, at heights of 2050-2200m and 2.6-4.5km from the head, with a glacial surface of 16km. In stage four, cirque glaciers were formed between 2260m and 2590m, with a length of 0.4-2km and a glacial area of 5.7km. Also, the wide range of periglacial, slope, nival and alluvial landforms existing in the formerly glaciated environments allows reconstruction of the post-glacial environmental dynamics in the upper Garonne basin. Today, the highest lands are organized following three elevation belts: subnival (1500-1900m), nival (1900-2300m) and periglacial/cryonival (2300-2800m).

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

“…Additional thermal data and knowledge on activity and inherited elements are necessary to subdivide the infraperiglacial belt. The middle periglacial belt is located at lower altitude than the “periglacial” and “periglacial‐type” previously proposed,, in which a dominance of frozen ground (SFG and permafrost) implies a lowering of the upper and lower altitudinal limits. The supraperiglacial belt matches the supraperiglacial belt proposed by Serrano et al and González‐García, but the lower limit has now been set 200 m lower because of the new recording at 2,900 m a.s.l.…”

“…Additional thermal data and knowledge on activity and inherited elements are necessary to subdivide the infraperiglacial belt. The middle periglacial belt is located at lower altitude than the "periglacial" and "periglacial-type" previously proposed,41,93,94 , in which a dominance of frozen ground (SFG and permafrost) implies a lowering of the upper and lower altitudinal limits.The supraperiglacial belt matches the supraperiglacial belt proposed by Serrano et al93 and González-García 41 , but the lower limit has now been set 200 m lower because of the new recording at 2,900 m a.s.l. Winter season ground temperatures at this altitude are lower than −6°C and are close to those of permafrost-related landforms.The current active periglacial environments in Iberian mountain ranges are located in the upper parts of the highest mountain ranges and are mostly related to seasonal frost dynamics 58.…”

Phylogeography and species delineation of the genusPhoxinusRafinesque, 1820 (Actinopterygii: Leuciscidae) in the Iberian Peninsula

“…such as Noguera Pallaresa are located in the Beret plateau, which is separated from the Garonne Basin by only a few kilometers (~2,500 m). The landscape of this relatively horizontal area arose as a consequence of the geomorphological footprint left by glaciers during the Last Glacial Maximum (Fernandes, Oliva, Palma, Ruiz‐Fernández, & Lopes, ). Therefore, another plausible explanation for the presence of Phoxinus sp.…”

Flood Consequences of Land-Use Changes at a Ski Resort: Overcoming a Geomorphological Threshold (Portainé, Eastern Pyrenees, Iberian Peninsula)

“…Pleistocene glaciations affected the whole Pyrenees [33]. Around Torreta de l'Orri, four cirques -including the one forming the headwaters of Portainé basin-are the southernmost glacial features in the area.…”