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The Chippewa and Wisconsin Valley Lobes of the Laurentide Ice Sheet reached their maximum extent in north‐central Wisconsin about 20 000 years ago. Their terminal positions are marked by a broad area of hummocky topography, containing many ice‐walled‐lake plains, which is bounded on the up‐ice and down‐ice sides by ice‐contact ridges and outwash fans. The distribution of these ice‐disintegration landforms shows that a wide zone of stagnant, debris‐covered, debris‐rich ice separated from the active margins of both lobes as they wasted northward during deglaciation. Accumulation of thick, uncollapsed sediment in ice‐walled lakes high in the ice‐cored landscape indicates a period of stability. In contrast, hummocky disintegration topography indicates unstable conditions. Thus, we interpret two phases of late‐glacial landscape evolution. During the first phase, ice buried beneath thick supraglacial sediment was stable. Supraglacial lakes formed on the ice surface and some melted their way to solid ground and formed ice‐walled lakes. During the second phase, buried ice began to melt rapidly, hummocky topography formed by topographic inversion, and supraglacial and ice‐walled lakes drained. We suggest that ice wastage was controlled primarily by climatic conditions and supraglacial‐debris thickness. Late‐glacial permafrost in northern Wisconsin likely delayed wastage of buried ice until after about 13 000 years ago, when climate warmed and permafrost thawed.

Approximately 35 parallel, discontinuou s glacial ridges occur in an area of about 100 km 2 in north-centra l Wisconsin. The ridges are located between about 6 and 15 km north (formerly up-ice) of the maximum extent of the Wisconsin Valley Lobe of the Laurentide Ice Sheet. The ridges are between 1 and 4 m high, up to 1 km long, and spaced between 30 and 80 m apart. They are typically asymmetrical with a steep proximal (ice-contact) slope and gentle distal slope. The ridges are composed primarily of subglacia l till on their proximal sides and glacial debris-ow sediment on the distal sides. In some ridges the till and debris-ow sediment are underlain by sorted sediment that was deformed in the former direction of ice ow. We interpret the ridges to be recessiona l moraines that formed as the Wisconsin Valley Lobe wasted back from its maximum extent, with each ridge having formed by a sequence of (1) pushing of sorted ice-margina l sediment, (2) partial overriding by the glacier and deposition of subglacia l till on the proximal side of the ridge, and (3) depositio n of debrisow sediment on the distal side of the ridge after the frozen till at the crest of the ridge melted. The moraines are similar to annual recessiona l moraines describe d at several modern glaciers, especiall y the northern margin of Myrdalsjökull, Iceland. Thus, we believe the ridges probably formed as a result of minor winter advances of the ice margin during deglaciation . Based on this assumption, we calculate the net rate of ice-surfac e lowering of the Wisconsin Valley Lobe during the period when the moraines formed. Various estimates of icesurface slope and rates of ice-margin retreat yield a wide range of values for ice-surface lowering (1.7-14.5 m/yr). Given that ablation rates must exceed those of ice-surface lowering, this range of values suggests relatively high summer temperature s along the margin of the Wisconsin Valley Lobe when it began retreating from its maximum extent. In addition, the formation of annual moraines indicates that the glacier toe was thin, the ice surface was clean, and the ice margin experience d relatively cold winters.

Approximately 35 parallel, discontinuou s glacial ridges occur in an area of about 100 km 2 in north-centra l Wisconsin. The ridges are located between about 6 and 15 km north (formerly up-ice) of the maximum extent of the Wisconsin Valley Lobe of the Laurentide Ice Sheet. The ridges are between 1 and 4 m high, up to 1 km long, and spaced between 30 and 80 m apart. They are typically asymmetrical with a steep proximal (ice-contact) slope and gentle distal slope. The ridges are composed primarily of subglacia l till on their proximal sides and glacial debris-ow sediment on the distal sides. In some ridges the till and debris-ow sediment are underlain by sorted sediment that was deformed in the former direction of ice ow. We interpret the ridges to be recessiona l moraines that formed as the Wisconsin Valley Lobe wasted back from its maximum extent, with each ridge having formed by a sequence of (1) pushing of sorted ice-margina l sediment, (2) partial overriding by the glacier and deposition of subglacia l till on the proximal side of the ridge, and (3) depositio n of debrisow sediment on the distal side of the ridge after the frozen till at the crest of the ridge melted. The moraines are similar to annual recessiona l moraines describe d at several modern glaciers, especiall y the northern margin of Myrdalsjökull, Iceland. Thus, we believe the ridges probably formed as a result of minor winter advances of the ice margin during deglaciation . Based on this assumption, we calculate the net rate of ice-surfac e lowering of the Wisconsin Valley Lobe during the period when the moraines formed. Various estimates of icesurface slope and rates of ice-margin retreat yield a wide range of values for ice-surface lowering (1.7-14.5 m/yr). Given that ablation rates must exceed those of ice-surface lowering, this range of values suggests relatively high summer temperature s along the margin of the Wisconsin Valley Lobe when it began retreating from its maximum extent. In addition, the formation of annual moraines indicates that the glacier toe was thin, the ice surface was clean, and the ice margin experience d relatively cold winters.