EARLY HOLOCENE MORAINES OF MT. BAKER AND THE NORTH CASCADE RANGE, WASHINGTON

Glaciers on Mt. Baker and elsewhere in the Cascade Range built multiple moraines during the early and late Holocene. Direct 14C dating of wood in moraines, the presence or absence of well–dated tephras on or between moraines, dates from peat and wood between moraines, and coring of trees on moraines provide a solid basis for establishing the glacial chronology. Four tephras are useful in dating the moraines: (1) Schriebers Meadow scoria (ca. 8800 14C yr BP); (2) Mazama ash (ca. 6850 14C yrs BP); (3) Rocky Cr. tephra (between 6528 and 5858 14C yrs BP); and (4) Cathedral Craig tephra (ca. 5800 14C yr BP).

Scoria on the SW flank of Mount Baker, dated at 8420–8800 14C yr BP, occurs in front of, but not on, moraines that are overlain by Mazama ash east of the Easton Glacier. Charcoal directly above till and beneath Mazama ash was dated at 7670 ± 130 14C yrs BP, bracketing the age of that moraine between 7670 and ca. 8800 14C yrs BP. Charcoal below Mazama ash inside another lateral moraine was dated at 7045 ± 65 14C yr BP, bracketing that moraine between 7045 and ca. 8800 14C yr BP.

Early Holocene moraines were also constructed in cirques adjacent to Mount Baker. At Pocket Lake, charcoal in a cirque moraine yielded an age of 8455 ± 75 14C yr BP. At nearby Park Butte, a moraine mantled by Mazama ash is associated with ice-marginal lake sediments overlain by a diamicton containing charcoal dated at 8820 ± 110 14C yr BP.

Multiple post LGM cirque moraines occur in upper Swift Cr. basin NE of Mt. Baker. The lower moraines are mantled with Mazama ash and minimum basal ages from sediment cores upvalley from the moraines range from 9220 to 9650 14C yr BP. Sediment cores from a moraine–dammed lake at nearby Heather Meadows yielded a minimum age of ca. 9400 14C yr BP.

Possible early Holocene moraines are also present in the Twin Sisters Range, Glacier Peak, Mount Rainier and in the Alpine Lakes area. This evidence taken together suggests a short-duration early Holocene moraine-building period, probably followed by mid-Holocene glacial recession, then multiple moraine-building episodes during the late Holocene. The contention by other authors who rely on low-resolution paleobotanical evidence, that climate during the early Holocene in the Cascade Range was essentially warmer and dryer is not supported by our work.