Ground surface temperatures indicate the presence of permafrost in North Africa (Djebel Toubkal, High Atlas, Morocco)

Abstract

Abstract. Relict and present-day periglacial activity have been reported in the literature for the upper reaches of the High Atlas mountains, the highest range in North Africa (Djebel Toubkal – 4,167 m a.s.l.). Lobate features in the Irhzer Ikbi South at 3,800 m a.s.l. have been previously interpreted as an active rock glacier, but no measurements of ground or air temperatures are known to exist for the area. In order to assess on the possible presence of permafrost, analyse data from June 2015 to June 2016 from two air temperature sites at 2,370 and 3,200 m a.s.l., and from four ground surface temperature (GST) sites at 3,200, 3,815, 3,980 and 4,160 m a.s.l. allowing to characterize conditions along an altitudinal gradient along the Oued Ihghyghaye valley to the summit of the Djebel Toubkal. GST were collected at 1-hour intervals and the presence of snow cover at the monitoring sites was validated using Landsat-8 and Sentinel-2 imagery. Two field visits allowed for logger installation and collection and for assessing the geomorphological features in the area. The results show that snow plays a major role on the thermal regime of the shallow ground, inducing important spatial variability. The lowest site at 3,210 m showed a regime characterized by frequent freeze-thaw cycles during the cold season but with a small number of days of snow. When snow sets, the ground remains isothermal at 0 °C and the thermal regime indicates the absence of permafrost. The highest sites at 3,980 and 4,160 m a.s.l. showed very frequent freeze-thaw cycles and a small influence of the snow cover on GST, reflecting the lack of snow accumulation due to the their wind-exposed settings in a ridge and in the summit plateau. The site located at 3,815 m in the Irhzer Ikbi South valley showed a stable thermal regime from December to March with GST varying from −4.5 to −6 °C, under a continuous snow cover. The site's location in a concave setting favours snow accumulation and lower incoming solar radiation due to the effect of a southwards ridge, favouring the maintenance of a thick snow pack. The stable and low GST are interpreted as a strong indicator of the probable presence of permafrost at this site, an interpretation which is supported by the presence of lobate and arcuate forms in the talus deposits. These results are still a first approach and observations through geophysics and boreholes are foreseen. This is the first time that probable permafrost is reported from temperature observations in the mountains of North Africa.

Late Pleistocene glaciers to present-day snowpatches: a review and research recommendations for the Marrakech High Atlas

“…Ground surface temperatures varied from − 4.5 to − 6 °C from December to March, under a continuous snow cover and are interpreted as a strong indicator of the probable presence of permafrost in the highest parts of the Toubkal Massif. Chardon and Riser (1981) suggested that an active rock glacier occurs close to this site, although Vieira et al (2017) did not support this interpretation because there is no steep front and no clearly defined debris body. However, Vieira et al (2017) did identify small lobate forms and arcuate ramparts in the talus, possibly indicating active periglacial dynamics, either by solifluction or permafrost creep.…”

“…However, no snow was observed in the Irhzher Ikhibi Nord (Fig. 11), Vieira et al (2017) found that over the period 2015-2016 ground surface temperatures were below 0 °C for the 6 months of the year from October to March, inclusive. Ground surface temperatures varied from − 4.5 to − 6 °C from December to March, under a continuous snow cover and are interpreted as a strong indicator of the probable presence of permafrost in the highest parts of the Toubkal Massif.…”

“…Thus, any shift in climate towards increased precipitation and cooler air temperatures recorded in continuous Holocene lake and marsh sediment records will provide important insights into the viability of the High Atlas for late-lying snow and glaciers. It is also now known that the highest cirques are also likely to support sporadic permafrost (Vieira et al 2017) and any changes in climate through the Holocene will have implications for understanding periglacial processes over this period in the High Atlas. This is especially important for testing for the possibility of active Holocene rock glaciers (Hughes 2018), which are likely to have been closely associated with former niche glaciers and ice/snowpatches.…”

Timing of Pleistocene glaciations in the High Atlas, Morocco: New 10Be and 36Cl exposure ages

“…It is possible that at one stage during glacial evolution, that they were debris-covered, but there is no residual morphological evidence to support this. Small rock glaciers are evident in the very highest cirques (Hughes 2018), although these are likely to be recent Holocene features (Vieira et al, 2017). Dresch (1941) also questioned the presence of moraines in the high cirques, including the highest boulder pile in the Irhzer Tamda (Dresch 1941, p. 599, Figure 197) and instead suggested that these are deposits formed by water torrents.…”