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 occurs in Fennoscandia,[1] Scotland,[2] Ireland[3] and Canada.[1][4] It is one of the three main types of . They cover large areas that have been covered by ice, and occur mostly in what is believed to have been the central areas of the ice sheets.[3] Rogen moraines are named after Lake Rogen[5] in Härjedalen, Sweden, the landform's type locality. Rogen Nature Reserve serves to protect the unusual area.
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 1970s, 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]
- Shearing of sediment under a glacier causes growth of waves with spacing characteristic of Rogen moraine (300 m to 1000 m).[9]
- 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 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]
See also[]
- Drumlin – Geological feature formed by glacial ice acting on underlying unconsolidated till or ground moraine
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
- ^ Dunlop, P.; et al. (2008). "The Bed Ribbing Instability Explanation (BRIE) - testing a numerical model of ribbed moraine formation arising from coupled flow of ice and subglacial sediment" (PDF). Journal of Geophysical Research: Earth Surface. 113: F03005. doi:10.1029/2007JF000954.
External links[]
- Glacial deposits of Sweden
- Moraines