A reconstruction of the last glacial maximum (LGM) ice-surface geometry in the western Swiss Alps and contiguous Alpine regions in Italy and France is based on detailed field mapping of glacial trimlines, ice-erosional features and periglacial forms. Field data provide evidence of LGM ice-surface elevations and ice-flow directions. The LGM ice surface is portrayed as a grid-format digital elevation model (DEM) using geographic information system (GIS) software.LGM ice-surface areas and ice volumes in selected regions are calculated using a DEM of the present land topography. The reconstruction described in this paper is presented in conjunction with a previously determined LGM ice-surface reconstruction for the central and eastern Swiss Alps.The LGM ice cap in the western Swiss Alps and contiguous Alpine regions in Italy and France was characterized by transection glaciers. Four main centers of ice accumulation that influenced the transection glaciers include the Rhône ice dome, the Aletsch icefield, the southern Valais icefield, and the Mt. Blanc region. Major ice diffluences were located north of Simplon Pass, on Gd. St. Bernard Pass and north of present-day Glacier d'Argentière. Estimates of LGM ice volumes in selected regions show that the largest input of ice into the Rhône Valley was from the southern Valais icefield. Centered in the southern Mattertal, the LGM southern Valais icefield had a surface elevation of at least 3010 m and an ice thickness of at least 1400 m. The LGM ice-surface reconstruction and calculated ice volumes for selected regions are the basis for a hypothesis as to how erratic boulders from the southern Valais and Mt. Blanc regions were transported to the northern Alpine foreland. Certain LGM centers of ice accumulation and ice-flow directions presented in this paper are also examined for possible paleo-atmospheric circulation information.ZUSAMMENFASSUNG Die Rekonstruktion der Eisoberflächengeometrie während des Letzten Glazialen Maximums (LGM) in den westlichen Schweizer Alpen und in angrenzenden Regionen in Italien und Frankreich basiert auf einer detaillierten Kartierung von Gletscherschliffgrenzen, Eiserosionserscheinungen und periglazialen Formen. Diese Geländedaten geben Hinweise auf die Höhe der Eisoberfläche und die Eisflussrichtungen. Die Eisoberfläche wird durch ein gitterbasiertes digitales Höhenmodel (DHM) unter Benutzung eines Geographischen Informations Systems (GIS) dargestellt. Die Eisoberflächenerstreckung und die Eismächtigkeiten werden auf Basis des DHM der gegenwärtigen Landestopographie berechnet. Die in dieser Veröffentlichung beschriebene Rekonstruktion wird mit früheren Eisoberflächenrekonstruktionen für das LGM der zentralen und östlichen Schweizer Alpen verglichen.Die Eiskappe während des LGM in den westlichen Schweizer Alpen und in angrenzenden Regionen in Italien und Frankreich war durch ein Eisstromnetz charakterisiert. Die vier Zentren der Eisakkumulation, welche das Eisstromnetz beeinflussten, waren der Rhône Eisdom, das Aletsch Eisfeld, das Eisfeld im süd...

Subglacial deformation is crucial to reconstructing glacier dynamics. Sediments associated with the Late Ordovician ice sheet in the Djado Basin, Niger, exhibit detailed structures of the subglacial shear zone. Three main types of subglacial shear zones (SSZ) are discriminated. The lowermost SSZ, developed on sandstones, displays Riedel macrostructures and cataclastic microstructures. These resulted from brittle deformation associated with strong glacier/bed coupling and low porewater pressure. Where they developed on a clay-rich bed, the overlying SSZ display S-C to S-C 0 fabrics, sheath folds, and dewatering structures. These features indicate high ductile shear strain and water overpressure. On finegrained sand beds, the SSZ exhibit homogenized sand units with sand stringers, interpreted as fluidized sliding beds. The succession of subglacial deformation processes depends on fluid-pressure behavior in relation to subglacial sediment permeability. Fluid overpressure allows subglacial sediment shear strength and ice/bed coupling to be lowered, leading to ice streaming.