**3. Discrete Debris Accumulations and terminology**

The term Discrete Debris Accumulations (DDA) has been used to encompass a range of features that can be mapped in the field or from aerial photographs (Whalley, 2009). It is used here as a non-genetic and descriptive term, such that focus can be given to whatever is under study without any preconceived notion of origin or significance. The actual interpretation of these features is, in the British Isles, very much related to the use of analogues. This is especially significant when the presence of ice (of some origin) is considered and so the recognition of ice-debris features and their mechanisms is considered. Although DDAs *may* be paraglacial it could be that some are fossil glacial features and not at all modified by post YD activity. Hence, there needs to be some care in distinguishing between periglacial, proglacial, paraglacial and permafrost in these studies.

This paper is specifically concerned with recognising the process and mechanisms of debris accumulations rather than dating *per se*. In particular, the association of specific features can be associated with climatic conditions. For example, moraines are associated with glaciers and the size (mass balance) of the glaciers. In the British Isles there is an assumed west-east gradient in glacier net balance, such has been found in Scandinavia (Chorlton & Lister, 1971). There are also possibilities of changes in prevailing winter storm tracks that may influence the size of glaciers (Whalley, 2004) that have not yet been investigated for the palaeo-conditions for the British Isles compared with suggestions for northern Scandinavia (Bakke et al., 2005; 2008).

The traditional view of the relationship between glacier extent, mass balance and glacial record is the linear set of boxes in Figure 1. The 'geological record' is usually taken as being manifest in the simplest (or least complicated) debris accumulation associated with glaciers; a moraine. Although the basic idea may hold, interpretation is more complicated for periglacial features such as snowbanks and their rock debris remnants such as 'protalus lobes'. Is such a feature classed as periglacial, proglacial or indeed paraglacial (Slaymaker, 2007; 2009)? This problem will be considered in more detail below.

Using Discrete Debris Accumulations to Help Interpret

**5. Debris input to glacial systems** 

effects may be produced.

al., 1998) care must be taken in the temporal interpretation.

1999).

Upland Glaciation of the Younger Dryas in the British Isles 5

monsoon) and the effects of continentality as suggested above. For example, Harrison et al. (1998) suggested that a small glacier existed in the lee of the Exmoor plateau. This was based on their interpretation of a small moraine or protalus rampart at the foot of a small valley head (combe/corrie/cirque). Indeed, the use of the term 'moraine' or 'protalus lobe' may well indicate differences of interpretation. Some of these, perhaps indistinct, features, tend to be problems of interpretation rather than mapping. Certain debris accumulations in the English Lake District (Sissons, 1980) present problems of climatic interpretation, especially when it is not clear what the features represent in terms of debris and ice input. Similarly, Harrison et al. (2008) have discussed features that have generally been called 'rock glaciers' and their environmental significance. More precise matching of formation processes and mechanisms to environmental conditions will help to improve modelling of ice mass extents and volumes and associated climatic environments (Gollege & Hubbard, 2005; Hubbard,

To the basic glacial parameters of Figure 1 weathered rock debris needs to be added to the system for there to be traces in the geological record. This complication is rarely considered; not just a morainic marker but to consider where, when and from where the debris addition was made. It may well have a considerable effect on the system as a whole. The total amount may be important. Dead ice preserved at the snout of a glacier long after the debrisfree glacier has melted may give hummocky moraine or even a rock glacier form. Further, the debris flux may have an effect upon the ice extent. For example, a glacier in equilibrium that receives a debris input near the snout (as from a large rockfall) could produce a glacier advance as the ablation area is reduced. The timing of debris input (at the start or end of a glacier advance phase for example) may be significant. Some work has been done on this in the British Isles, eg. (Ballantyne & Kirkbride, 1987). Although dating such events via cosmogenic ratio methods is now becoming easier (Ballantyne & Stone, 2004; Ballantyne et

Figure 2 indicates the potential complexity here, again related to altitude, continentality and temporal input variations. Rock debris can be added to a glacial, permafrost or periglacial system. Unknowns include the relative and absolute amounts of ice/water and debris but also the flux changes in time (Nakawo et al., 2000; Whalley et al., 1996). Even 'simple' glacial systems may show this. For example a large rockslide on or near the snout of a glacier may allow the snout to advance but if away from the snout the glacier may be hardly affected. In the relatively small glacier in the British Isles however, substantial, but largely unknown,

Figure 3 illustrates possible scenarios produced by the relative additions of weathered debris quantities to snow/ice bodies. This should not be taken to show that certain features *will* form but that they are possible given the relative components at any time. For example, the time element is not considered as part of the formative process. Some features might be form 'rapidly', others take some time. For the most part process studies do not give a good indication of the time needed to produce a feature. If the debris is lacking then there may be no feature formed at all. However, the diagram does suggest that there is a continuum of

features and it does help guide interpretation of what is seen or mapped.

Fig. 1. The basic controls on glaciers and their responses in the geological record; from Whalley (2009) after Andrews (1975) and Meier (1965). The boxed sequence is embedded within domains that ultimately affect the geological record.
