Rogen moraine
A Rogen moraine (also called ribbed moraine) is a subglacially (i.e. under a glacier or ice sheet) formed type of moraine landform,[1] that mainly occur in Fennoscandia,[1] Scotland,[2] Ireland[3] and Canada.[1][4] They cover large areas that have been covered by ice, and occur mostly in what is believed to be the central areas of the ice sheets.[3] Rogen moraines are named after Lake Rogen[5] in Härjedalen, Sweden, the landform’s type locality.
The landform occurs in groups that are often closely and regularly spaced.[1] They consist of glacial drift, with till being the most common constituent.[1] The individual moraines are large, wavy ridges orientated transverse to ice flow.[3] Drumlins are often found in close proximity of Rogen moraines, and are often interpreted to be formed at the same time as the Rogen moraines.[1] Although Rogen moraines can span a large range of sizes,[3] the most common distribution seems to be 10-30 metres high, 150-300 metres wide and 300-1,200 metres long.[1]
The exact mechanics of Rogen moraine formation are not known, but since the 1970’s, several theories on the formation have been proposed:[2]
- Megaripples eroded in the basal ice fill during subglacial outburst floods.[6]
- Already existing landforms, such as drumlins and flutes[7] or marginal moraines[5] are reshaped due to a ~90° change in the direction of the ice flow.[5][7]
- Debris-rich basal ice or pre-existing sediments are sheared and stacked, or folded during compressive ice flow[8].
- Sediment sheets become fractured and extended during a transition of the overlying glacier from being cold based ice to warm based.[1][clarification needed]
However, it has been suggested that, due to the diversity of morphological characteristics displayed by Rogen moraine, different processes might be able to create the landform.[3] This means that all four of the processes mentioned above might be correct. The different theories that proposed a formation near or at the glacial margin have largely been abandoned.[1] Some of these theories proposed that Rogen moraines had an origin as a series of end moraines, that they formed in association with calving ice termini in glacial lakes, or that Rogen moraines formed in dead-ice, where supraglacial material fell down into crevasses in the ice.[1]
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[edit] References
- ^ a b c d e f g h i j Hättestrand, C. & Kleman, J., 1999. Ribbed moraine formation. Quaternary Science Reviews, 18:43-61
- ^ a b Finlayson, A. G. & Bradwell, T., 2008. Morphological characteristics, formation and glaciological significance of Rogen moraine in northern Scotland. Geomorphology, 101:607-617
- ^ a b c d e Dunlop, P. & Clark, C. D., 2006. The morphological characteristics of ribbed moraine. Quaternary Science Reviews, 25:1668-1691
- ^ Marich, A., Batterson, M. & Bell, T., 2005. The morphology and sedimentological analyses of Rogen moraines, central Avalon Peninsula, Newfoundland. Current Research, Newfoundland and Labrador Department of Natural Resources, Geological Survey, Report, 05-1:1-14
- ^ a b c Möller, P., 2006. Rogen moraine: an example of glacial re-shaping of pre-existing landforms. Quaternary Science Reviews, 25:362-389
- ^ Fisher, T. G. & Shaw, J., 1992. A depositional model for Rogen moraine, with examples from the Avalon Peninsula, Newfoundland. Canadian Journal of Earth Sciences, 29:669-686
- ^ a b Boulton, G. S., 1987. A theory of drumlin formation by subglacial deformation. In: Menzies, J. & Rose, J. (Eds.), Drumlin Symposium, Balkema, Rotterdam, The Netherlands, pp. 25-80
- ^ Lindén, M., Möller, P. & Adrielsson, L., 2008. Ribbed moraine formed by subglacial folding, thrust stacking and lee-side cavity infill. Boreas, 37:102-131
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