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The Laurentide Ice Sheet flowed southeast across the northern White Mountains during the Wisconsinan Stage. In late Wisconsinan time, the regional snowline was probably elevated above the highest peaks. Downwasting ice masses progressively ceased to flow (stagnated) as they became cut off from regional sources to the northwest. Indirect lines of geomorphic evidence and a short radiocarbon chronology indicate that deglaciation proceeded very rapidly once major elements of the regional terrain were exhumed from beneath the ice; there is a distinct downward and locally north-westward progression of deglacial events. North of the city of Berlin, regional ice flow was sustained in the Androscoggin and Dead River valleys. Ice eventually retreated in these valleys and left sequences of stratified drift graded to bedrock at the head of the 70-m knickpoint in the Androscoggin Valley at Berlin Falls. Stratified moraines record temporary positions of these retreating ice fronts. Outwash began to accumulate in the deepest part of the Androscoggin Valley downstream from Berlin after the ice in this area was beheaded at the falls. The local deglaciation was probably complete between 12,100 and 12,600 yr B.P. There is evidence for two separate phases of activity in the relict rock glacier in King Ravine in the Presidential Range. The earliest rock glacier may have formed from a stranded remnant of Laurentide ice. Later activity may have occurred during a period of significant climatic cooling.

Abstract Paraglacial coastal systems are formed on or proximal to formerly ice-covered terrain from sediments with direct or indirect glacial origin. This review addresses the roles of tectonic controls, glacial advances and retreats, sea-level changes, and coastal processes in sediment production, delivery and redistribution along the paraglacial Gulf of Maine coast (USA and Canada). Coastal accumulation forms are compositionally heterogeneous and found primarily at the seaward edge of the Gulf's largest estuaries; their existence is directly attributable to the availability of glacial sediments derived from erosion of weathered plutons within coastal river basins. Multiple post-glacial sea-level fluctuations drove the redistribution of these sediments across the modern lowland and inner shelf. Central to the formation of barrier systems was the paraglacial sand maximum, a time-transgressive phase of relative sea-level fall and enhanced fluvial sand export c. 2000–4000 years following deglaciation. Vast quantities of sand and gravel were reworked landward during the subsequent transgression and combined with additional riverine sediments to form the modern barrier systems. Today, reduced fluvial sediment loads, anthropogenic modifications of barrier and river systems, and sea-level rise have combined to exacerbate long-term coastal erosion and may eventually force these barriers toward a state of rapid landward migration.

ABSTRACT The northward retreat history of the Laurentide ice sheet through the lowlands of the northeastern United States during the last deglaciation is well constrained, but its vertical thinning history is less well known because of the lack of direct constraints on ice thickness through time and space. In addition, the highest elevations in New England are characterized by gently sloping upland surfaces and weathered block fields, features with an uncertain history. To better constrain ice-sheet history in this area and its relationship to alpine geomorphology, we present 20 new 10 Be and seven in situ 14 C cosmogenic nuclide measurements along an elevation transect at Mount Washington, New Hampshire, the highest mountain in the northeastern United States (1917 m above sea level [a.s.l.]). Our results suggest substantially different exposure and erosion histories on the upper and lower parts of the mountain. Above 1600 m a.s.l., 10 Be and in situ 14 C measurements are consistent with upper reaches of the mountain deglaciating by 18 ka. However, some 10 Be ages are up to several times greater than the age of the last deglaciation, consistent with weakly erosive, cold-based ice that did not deeply erode preglacial surfaces. Below 1600 m a.s.l., 10 Be ages are indistinguishable over a nearly 900 m range in elevation and imply rapid ice-surface lowering ca. 14.1 ± 1.1 ka (1 standard deviation; n = 9). This shift from slow thinning early in the deglaciation on the upper part of the mountain to abrupt thinning across the lower elevations coincided with accelerated ice-margin retreat through the region recorded by Connecticut River valley varve records during the Bølling interstadial. The Mount Washington cosmogenic nuclide vertical transect and the Connecticut River valley varve record, along with other New England cosmogenic nuclide records, suggest rapid ice-volume loss in the interior northeastern United States in response to Bølling warming.