Mountain Glaciers of the Presidential Range in New Hampshire

Nine steep-walled cirques nearly 1,000 ft (300 m) deep and U-shaped valleys more than ¼ mile (400 m) wide were formed at one time in the White Mountains, and at least three other incipient basins were ice-deepened. These were fully formed before an overriding continental glaciation, because 20 to 60% of the coarse drift flooring the north-facing cirques was derived from rock sources down valley to the north, and there are no clear lateral or looped end moraines left. The headwalls and floors bear grooves and roche mountonnées in the same direction as regional glacial overriding.This last overriding took place in late-Wisconsin stage as based upon the nearest 14C deglaciation dates, the shallow alpine soils, or the weathering of mountaintop erratics and freshness of valley deposits. But the sharpness of the cirque rims indicates mountain glacier action no older than early Wisconsin time and the volume of removal suggests Illinoian-stage cutting as well.From forms eroded in rock it is deduced that the former local glaciers were 1 to 8 miles long (1.5 to 13 km), supported by a firn limit near 3,000 to 4,000 ft altitude (900 to 1,200 m). The summer climate may have been 17°F (9.3 °C) cooler or, if precipitation increased markedly, only 10°F (5.5 °C) cooler. No cirque or terminus faced toward the southwest quadrant, so at that time southwesterly winds drifted the snows (today, west-northwest). That the lowest cirques face north and the highest ones south indicate insolation sensitivity and fair skies during the mountain glacier ablation season.