Late Glacial Origin of the Sandbanks, Webb Bay, Labrador

Abstract

SUMMARY The Sandbanks of Webb Bay, Labrador owe their origin to ice marginal conditions during the last stages of deglaciation of this section of the Labrador coast. Several phases in their evolution are recognized. Phase 1 was characterized by disintegration of the remnants of Webb Bay and Ado's Brook valley ice masses into separate local bodies with ice marginal runoff in an eastern direction. During Phase 2 the first and highest ice-dammed lake formed. Eastward ice marginal flow continued into Phase 3, when a large system of kame terraces (altitude 360 feet) formed beside the receding Webb Bay Ice. They led to new and lower ice marginal lakes in the eastern part of the Sandbanks. Phase 4 was dominated by the construction of a more extensive system of kame terraces almost 100 feet lower than those formed in Phase 3. Locally, minor moraines helped to direct runoff and control development of these newer kame terraces. In Phase 5, meltwater from the ice and runoff from the deglaciated highlands filled a large marginal lake (altitude 230 feet), which may have contributed to subglacial drainage down Port Manvers Run. Phase 6, the last of the glacial conditions associated with formation of the Sandbanks, was introduced by withdrawal of ice far enough so that the eustatically rising sea level was able to reach part of the Sandbanks. A terrace at 135 feet above sea level is believed to be the local upper marine limit. Stagnant ice still covered the floor of Hummock Valley at the western end of the Sandbanks at this time. Subsequently isostatic adjustment has lifted the last glacio-fluvial and some of the glacio-marine features above sea level.