ABSTRACT Extensive glaciers covered the High Atlas mountains in Morocco during the late Pleistocene. On the northern escarpments of the Marrakech High Atlas, a series of cirques perched at ~3000–3500 m above sea level (asl) fed their valley glaciers that, in some cases, extended to as low as 2000 m asl. Cosmogenic exposure dating with 10 Be and 36 Cl has shown that at least three phases of glaciation are preserved in glacial deposits over the last glacial cycle at 50, 22, and 12 ka, which appear to correlate with marine isotope stage (MIS) 3, the global Last Glacial Maximum (LGM), and the Younger Dryas chronozone. This geochronological framework is sufficiently robust to allow for time-constrained glacier-climate reconstructions. The glaciers associated with these three phases of advance had equilibrium line altitudes (ELAs) of 2761 m asl (ca. 50 ka), 2919 m asl (ca. 22 ka), and 3213 m asl (ca. 12 ka). Glacier-climate modeling suggests that all of these phases were driven by both colder temperatures and wetter conditions than today. The dominant moisture supply to these glaciers in all phases would have been sourced from Atlantic depressions. The influence of an extended and enhanced West African monsoon on glacier development during African Humid Periods is unlikely to have been a significant influence on glacier dynamics. The climate conditions associated with the three glacier phases indicate sustained moisture supply to the highest mountain areas when records from other areas, such as the Middle Atlas lakes and marine sediment cores offshore, indicate marked aridity.

Abstract Large ice fields (>25 km 2 ) formed over the Tazaghart and Iouzagner plateaus of the High Atlas, Morocco during the Late Pleistocene. The plateau ice fields were drained by large valley glaciers forming a series of moraine assemblages. Four moraine units have been mapped and subdivided on the basis of their morphostratigraphy and the degree of soil weathering. Soil profile development index values indicate that the moraine units are widely separated in time; the oldest moraines are deeply weathered and degraded, whereas soils are absent on the youngest moraines. The highest moraine unit was formed by a small niche glacier that was present as recently as the mid-twentieth century. The Pleistocene glaciers are likely to have been associated with wetter conditions than today and colder air temperatures. Combined with ice in neighbouring areas, such as the Toubkal massif, the SW High Atlas supported some of the largest glaciers in Africa during the Pleistocene. The extent of glaciation, with ice exploiting and breaching drainage divides, has major implications for landscape development. The evolution of the High Atlas has been strongly shaped by glaciation that was closely intertwined with tectonic, fluvial and slope processes.