A COMPARISON OF MODERN AND ANCIENT GLACIAL LANDFORMS, SEDIMENTS, AND PROCESSES OF BREIÐAMERKURJÖKULL, ICELAND AND THE LAKE MICHIGAN LOBE IN SOUTHWESTERN MICHIGAN, USA

Glacial landforms exposed on the well-studied, deglaciated foreland of Breiðamerkurjökull, Iceland during the last two centuries provide an excellent modern analog for landforms formed by the Lake Michigan lobe in southwestern Lower Michigan during the late Wisconsin deglaciation ~19,000 to 13,000 years ago. The availability of a deglacial chronology, LiDAR DEMs, and sedimentary facies data for both Breiðamerkurjökull, Iceland and the Lake Michigan lobe, Michigan provide a basis for comparison.

Breiðamerkurjökull advanced to its Little Ice Age maximum by about ~1890 CE and experienced retreat punctuated by several minor readvances during the 20^th century. The Lake Michigan lobe reached its maximum position sometime between 26,000 and 21,000 years ago. After ~21,000 years ago, the Lake Michigan lobe experienced overall recession punctuated by significant readvances. While both glaciers experienced overall recession, a major difference is that the recession of Breiðamerkurjökull has been relatively steady compared to the more complex recession and readvance history of the Lake Michigan lobe during deglaciation.

Both Breiðamerkurjökull and the Lake Michigan lobe are or were active temperate glaciers retreating into an eroded glacial over-deepening. This trapped glacial silt in proglacial lakes and resulted in incorporation of this silt into basal till and in glaciolacustrine sediment. LiDAR DEMs document that in both settings streamlined landforms formed during advance and are superimposed on pre-existing landforms such as moraines and glaciofluvial fans. These over-ridden moraines/ice-contact fans appear to be a common landform both in the glacial forefield of Breiðamerkurjökull and in uplands of the classic Valparaiso uplands of western Michigan. Both settings also suggest the formation of moraines at multiple scales superimposed on subglacial landforms during overall recession. Both settings indicate the former presence of buried ice in hummocky moraine topography, and pitted fans and outwash plains. Understanding past glaciers requires a knowledge of modern analogs; although spatial and temporal scales vary significantly between modern and past glaciers, processes are likely analogous in many cases.