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.

Evidence of former equilibrium line elevations on Mount Olympus, Greece, coupled with estimates of uplift rate, point to more extensive Pleistocene glaciation and far colder climates than previous studies have indicated. These findings are supported by the record of glacial deposition both on the mountain and across the adjacent piedmont. The data not only provide evidence of significant equilibrium line altitude depression from a present-day elevation as much as 600 m above the mountain's summit (2917 m), but also show that Mount Olympus was glaciated on several occasions, and that the first episode of glaciation significantly predated the late Pleistocene. Piedmont sediments east and west of Mount Olympus record three discrete stages of deposition, each of which can be related to glacial activity on the mountain. Soils that separate these sedimentary units correspond to nonglacial intervals and can be correlated to a dated soil succession south of Olympus. This correlation suggests that the oldest soils correspond to the isotope stage 7 (Mindel/Riss) interglacial event (ca. 210,000 yr before present; U/Th disequilibrium) and that the oldest Pleistocene sediments record isotope stage 8 (Mindel) glaciation in the Olympus region. Subsequent stages of deposition are interpreted to record glaciation on the mountain during the isotope stage 6 (Riss) and isotope stages 4–2 (Würm) glacial events. Sedimentary units defined on the piedmont are also recognized on the Olympus upland and within valley-head cirques, where they correspond to three stages of cirque development. The distribution of these materials, as well as the occurrence of glacial erosional and depositional landforms, indicates that Mount Olympus supported upland ice during the first and second episodes of glaciation and that the first glaciation was sufficiently extensive to produce piedmont ice lobes that covered parts of the eastern, northern, and western piedmont of the mountain. Uplift-corrected cirque floor elevations, coupled with the distribution of glacial sediments, indicate that the Pleistocene equilibrium line altitude during each episode of glaciation was depressed at least 1400–1500 m, to elevations of 2000–2100 m above present sea level (asl). Assuming that lowering of the equilibrium line was solely a function of temperature, this would correspond to a mean annual temperature decrease of 8–9 °C. This contrasts with previous studies of the Mount Olympus region, which suggest that glaciation was restricted to small valley glaciers in upland and valley-head positions, that the regional Pleistocene equilibrium line was lowered only to elevations of 2200–2400 m asl, and that active glaciation was restricted to the latest Pleistocene (Würm). Study of the neotectonic history of Mount Olympus suggests that uplift persisted throughout the mid-Pleistocene–Holocene at a rate of ∼1.6 m/k.y.