Discrete debris accumulation (DDA) is a non-genetic term in mountain glacial geology to aid identification of non-lithified sediments on a valley or mountain slope or floor. It is intended that the debris accumulation is discrete such that it can be mapped, in the field and/or from aerial or satellite imagery. The origin or formative process may well not be known clearly or be changed by subsequent investigators it is advisable to have a non-genetic field reference so that discussion can then be used to ascertain, if possible, the origin. Mountain areas may currently have glaciers (glacierized) or have had glaciers (glaciated) or be subject to forms of periglacial activity. A moraine would be an easily identified DDA as would an esker. Although scree (talus) is generally easily identified and mapped, these deposits may be modified by ice, avalanches or downslope movement to create essentially new landforms. Many small slope failures and landslides can give the appearance of moraines or protalus ramparts on slopes. After mapping as a DDA, further investigation might draw light on the origin of the feature.
The term was apparently first used by Sven Lukas [1] for a very specific feature in Svalbard.
Independently, it was suggested in the literature in W. B. Whalley [2] and subsequently in Whalley, 2012[3] as relating to the basic definition and usage as above. This book chapter provides several photographic examples.
The 'cirque infills' described by Hätterstrand et al. (2008) [4] in the Khibiny Mountains, Kola Peninsula could be described as discrete debris accumulations, although their origin is postulated by these authors as being moraine remnants of an ice sheet pushing into these cirques rather than as rock glaciers formed within the cirques.
A recent term introduced by Brighenti et al. [5] is 'Cold Rocky Landforms' (CRLs) as a more general term including landforms generally identified as: protalus ramparts, valley-wall rock glaciers, talus (or scree) slopes and 'ice-embedded' moraines. 'Structurally, CRLs have a surface mantle of rocky debris and interiors composed of ice and rock'. However, it is by no means clear that any CRL necessarily contains ice in any form. Ice would not be present in areas that have long since lost any ice, whether from glaciers or snowbanks such as in upland Britain, where DDAs, as difficult to map entities, are known to exist.
References
edit- ^ Lukas, Sven Nicholson, Lindsey I, Ross, Fionna H, and Humlum, Ole. Formation, meltout processes and landscape alteration of high-Arctic ice-cored moraines—Examples from Nordenskiold Land, central Spitsbergen, Polar Geography, 29/3, 2005
- ^ Whalley, W. B. On the interpretation of discrete debris accumulations associated with glaciers with special reference to the British Isles. In: Periglacial and Paraglacial Processes and Environments, edited by J. Knight and S. Harrison, 85-102. London: Geological Society of London Special Publication 320. 2009
- ^ Whalley, W. B., Using Discrete Debris Accumulations to Help Interpret Upland Glaciation of the Younger Dryas in the British Isles, Chapter 1, In: Studies on Environmental and Applied Geomorphology. Eds, Piacentini, T. and Miccadei, E. InTech Europe, ISBN 978-953-51-0361-5, 2012.
- ^ Hättestrand, C., Kolka, V. and Johansen, N., Cirque infills in the Khibiny Mountains, Kola Peninsula, Russia-palaeoglaciological interpretations and modern analogues in East Antarctica. Journal of Quaternary Science, 23(2): 165. 2008
- ^ Brighenti, S., Hotaling, S., Finn, D.S., Fountain, A.G., Hayashi, M. Herbst, D., Saros, J.E., Tronstad, L.M. and Millar, C.I. Rock glaciers and related landforms: overlooked climate refugia for mountain biodiversity, Global Change Biology, 27, 10.1111/gcb.15510 2021
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