EVIDENCE FOR NORTHEAST FLOWING ICE IN THE LEE OF THE SANDWICH RANGE, NEW HAMPSHIRE

There is overwhelming evidence from both striations and streamlined features to establish glacial ice flowing from NW to SE across central New Hampshire for much of the period of the last glaciation. However, recently released LiDAR data has provided evidence for changes in ice flow direction during deglaciation. Importantly, these changes in flow direction bear evidence for active ice retreat, even in the area directly downstream of mountains that would have been expected to block the flow of ice, causing stagnation in their lee.

The Sandwich Range, extends approximately 8.5km from Sandwich Mtn (1,217m) in the west to Mt Chocorua (1,060m) in the east. South of the range is the Squam Lake - Bearcamp River lowland that lies between the Sandwich Range and the Ossipee Mountains. Drumlins and till shadows in this area record the dominant SE ice flow direction (130˚) during the time when the ice was thick enough so that flow direction was not significantly affected by the mountains. In contrast, small scale flutes ranging from 1-7m high and up to 0.5km in length record the direction of flow during the last stage of active ice when flow was diverted around the mountains. In many cases, the flutes originate at surface irregularities associated with bedrock outcrops or large boulders and thus provide a unidirectional flow vector.

Flutes in the lowland indicate late stage ice flowed eastward (83˚) out of the Squam Lake basin, slowly turning NE (47˚) as the ice approached the south slope of Mt Whiteface near Wonalancet. Thick till deposits are common where the ice flowed up against the south side of the mountain. Meltwater flowing along the ice margin in this area, carved a series of over 50 lateral meltwater channels at elevations below 670m. All the channels slope eastward reflecting the general slope of the ice lobe. A potential moraine occurs at an elevation of 475m near the southern edge of the Sandwich Wilderness Area. This eastward flowing lobe was in contact with a south to southwest flowing lobe that spilled around the east side of the range from ice moving south from the Saco River Valley into the Ossipee Lake area. With continued retreat the two lobes separated opening up the Swift River Valley in Tamworth. This sequence of landforms clearly shows that active ice was able to flow around and fill the area south of the Sandwich Range.