Viz Lab Summer Grant 2006

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Genesis of Rogen Moraine; a quantitative spatial analysis

Margretta Meyer Graduate Student under Dr. Howard Mooers, Geology

The VDIL at UMD provided an excellent way to explore the Sigma Scan Pro software and learn about the possibilities of spatial analysis for my research. I used VDIL’s facilities to download and analyze spatial datasets. Sigma Scan Pro allowed me to trace and determine the area of transverse ribbed landforms, including string and flark topography in bogs, clouds, washboard roads, and my own research into the enigmatic Rogen moraine of northeastern Minnesota. I used aerial photography, digitized topographic maps, and satellite imagery to compare and contrast these complex and intriguing patterns in nature and civilization. Although I am still not sure I can find any connections between the genesis of Rogen moraines and other transverse patterns, I am thankful to the VDIL for helping fund my summer and MS research at UMD!

My Masters research focuses on the genesis of Rogen moraine in northeastern Minnesota. These moraines are a subglacial landform commonly found in the interior lowlands of continental ice sheets in North America and Europe, and consist of parallel ridges transverse to ice flow. These ridges seem to have an interlocking or "jigsaw" pattern and typically range in size from 300-1200m in length, 150-300m in width, and 10-30m in height. The origins of this landscape are uncertain, but recent research in Scandinavia proposed that Rogen moraine are essentially "boudinized"" till sheets that have fractured due to extensional forces at the base of the ice sheet. During retreat, the transition from a cold-based (ice frozen to bed) to warm-based (ice sliding over bed) basal thermal regime, due to the shrinking of the cold-based area, generates extensional flow. Their hypothesis thus confines Rogen moraine to the interiors of former ice sheets where cold-based conditions were present. However, there are instances where Rogen moraine do not follow this geographic distribution, such as in northern Minnesota. If Rogen moraine are the result of a boudinage of a pre-existing till sheet, there must be another mechanism to generate extensional flow. We propose that the mechanism for forming the Rogen moraine is due to a change in the ice velocity, not temperature. In northeastern Minnesota, the Rainy Lobe of the Laurentide Ice Sheet traveled over a transition from bedrock to an area of thick till deposits. Because glaciers travel more slowly over bedrock than sediment, the glacier must accelerate at the transition in bed material. This transitional zone is where the Rogen moraine are found.

We feel that the work on Rogen moraine in Scandinavia and preliminary results of our work in NE Minnesota suggest that there Rogen moraine is not confined to a particular subglacial temperature regime, but rather to a dynamic condition. It turns out that the Rogen pattern is not limited to glacial features. Similar ribbed features perpendicular to flow occur in many natural systems, including clouds perpendicular to air flow, string and flark topography in patterned peatlands perpendicular to groundwater flow, and washboard road, where these same patterns are developed perpendicular to "traffic flow."

See the following examples of naturally-occurring patterns:

Rogen moraine near Isabella, Minnesota (ice flow is NE-SW)

Satelite image of cloud cover over northern Minnesota

String and flark topography in patterned peatlands in northwest Minnesota (groundwater flow is channelized W-E in the center of the image)

Close-up of the above pattern

Washboard road