GLOBAL, DOUBLE, YOUNGER DRYAS, GLACIAL FLUCTUATIONS IN ICE SHEETS AND ALPINE GLACIERS

The Younger Dryas (YD) glacier readvance is now generally conceded by most scientists to have been global and essentially simultaneous, although some continue to dispute this. With the many new dates now available, a close look at YD moraines in widely separated parts of the world suggests that not only was the YD global, but may have been a double, rather single climatic oscillation.

Two well-dated, YD moraines were built by the Cordilleran Ice Sheet in the Fraser Lowland in the western US., Sumas III (10,980-10,250 14C yrs B.P.) and Sumas IV (~10,250-10,000 14C yrs B.P.). In the Wind River Range of the Rocky Mts., double, 14C-and 10Be-dated, alpine, YD moraines have been documented at Titcomb Basin (11 ka mean 10Be age on inner moraine) and at Temple Lake. Similar, but not yet well dated, double moraines occur elsewhere in the Rocky Mts. and in the Cascade Range of Washington.

A similar YD moraine pattern is also found in New Zealand at Arthur’s Pass, where double YD moraines have mean 10Be ages of 11.8 ka and 11.4 ka, and at Birch Hill (mean 10Be ages 12.1 ka and 11.0 ka). The age of YD moraines at Prospect Hill, NZ is 12.7 ka 10Be yrs.

At Julier Pass, Switzerland the mean 10Be age of the outer YD moraine is 11.75 ka and 10.47for the inner moraine. Even the classic YD moraines of the Scandinavian Ice Sheet are double.

The double nature of these YD readvances in widely separated regions on several continents in both hemispheres suggests a common, global, climatic cause.