**2. The Younger Dryas (YD) in the British Isles and the dating of events**

In the British Isles, the cold period known as the Younger Dryas Stadial (12.8 – 11.5 ka BP) (Muscheler et al*.*, 2008) but also, and more usually, considered to be 11 – 10 ka BP. It is also known as the Loch Lomond Stadial after the large inland loch to the north of Glasgow. The last stage of the Last Glacial Maximum in the British Isles is generally taken to be the Dimlington Stadial (Rose, 1985) 26 – 13 ka BP as part of the Late Devensian Glaciation. As such, the Younger Dryas saw a deterioration (increasingly cold and wet) period in which glaciers advanced (or grew) again. It followed a relatively warm period known in the British Isles as the Windermere Interstadial (= Allerød). The variability of the dating the YD may be related to when the cooling stage started and its severity. That the YD is generally agreed to be a world-wide phenomenon (Ivy Ochs et al*.*, 1999) with glacier advances being seen e.g. in the Colorado Rockies of interior USA (Menounos and Reasoner, 1997) as well as more maritime areas such as the British Isles. It is also suggestive that the timing may not be exactly coeval everywhere but may indicate that responses to climate change may differ, e.g. in latitude, altitude as well as 'continentality' across the islands. These uncertainties need to be taken into consideration when viewing the landforms and processes in this paper. For example, the date of a recessional moraine of a glacier in the Alps may be known to a year but this is highly unusual in moraine sequences as far back as the YD. Even dated trees need to be put in context. Similarly the known maximum advances of glaciers in the Little Ice Age (again variously defined in terms of chronology but generally taken to be 1600 – 1850 CE). Examples from the Alps and Pyrenees as well as elsewhere provide some near present-day analogues that help interpretation in the British Isles.

In upland areas, where the Younger Dryas glaciers may have been small and reacting to subtle variations in a rapidly changing climate, the analysis may require careful mapping and interpretation for specific areas. This is shown by Benn and Lucas in their landsystems approach in NW Scotland (Benn & Lukas, 2006). They use present-day analogues to help their interpretation much in the same way that Hauber et al. (2011) have used Svalbard to provide periglacial analogues for Martian landforms. The use of analogues is used generally for the interpretation of surface features in planetary geology (Farr, 2004). This use is appropriate as periglacial and possibly permafrost features are associated with upland regions of the British Isles in the Younger Dryas. Compilations of processes, mechanisms and chronologies can be found in Ballantyne and Harris (1994) and Gordon and Sutherland (1993) and other overviews have been provided in several other volumes (Boardman, 1987; Gillen, 2003; Gordon, 2006; Gordon & Sutherland, 1993; McKirdy et al., 2007; Wilson, 2010).

A distinction should be made be made between periglacial, that is, around a glacier and permafrost, a thermal condition where the mean annual air temperature is assumed to be <-2°C. So a snowbank is generally assumed to be a periglacial feature but is not glacial, ie with the dynamics of a glacier-ice body. Neither condition is extant in the British isles at the present day and we shall see that may produce interpretational difficulties. The term paraglacial has been used to indicate features that are postglacial and are involved with sediment movement (Ballantyne, 2002; 2007). It was instituted into the literature by Church and Ryder (1972) as, materials that were produced by 'non-glacial processes that are conditioned by glaciation'. Ballantyne (2007) defines it as 'the study of the ways in which

In the British Isles, the cold period known as the Younger Dryas Stadial (12.8 – 11.5 ka BP) (Muscheler et al*.*, 2008) but also, and more usually, considered to be 11 – 10 ka BP. It is also known as the Loch Lomond Stadial after the large inland loch to the north of Glasgow. The last stage of the Last Glacial Maximum in the British Isles is generally taken to be the Dimlington Stadial (Rose, 1985) 26 – 13 ka BP as part of the Late Devensian Glaciation. As such, the Younger Dryas saw a deterioration (increasingly cold and wet) period in which glaciers advanced (or grew) again. It followed a relatively warm period known in the British Isles as the Windermere Interstadial (= Allerød). The variability of the dating the YD may be related to when the cooling stage started and its severity. That the YD is generally agreed to be a world-wide phenomenon (Ivy Ochs et al*.*, 1999) with glacier advances being seen e.g. in the Colorado Rockies of interior USA (Menounos and Reasoner, 1997) as well as more maritime areas such as the British Isles. It is also suggestive that the timing may not be exactly coeval everywhere but may indicate that responses to climate change may differ, e.g. in latitude, altitude as well as 'continentality' across the islands. These uncertainties need to be taken into consideration when viewing the landforms and processes in this paper. For example, the date of a recessional moraine of a glacier in the Alps may be known to a year but this is highly unusual in moraine sequences as far back as the YD. Even dated trees need to be put in context. Similarly the known maximum advances of glaciers in the Little Ice Age (again variously defined in terms of chronology but generally taken to be 1600 – 1850 CE). Examples from the Alps and Pyrenees as well as elsewhere provide some near present-day

In upland areas, where the Younger Dryas glaciers may have been small and reacting to subtle variations in a rapidly changing climate, the analysis may require careful mapping and interpretation for specific areas. This is shown by Benn and Lucas in their landsystems approach in NW Scotland (Benn & Lukas, 2006). They use present-day analogues to help their interpretation much in the same way that Hauber et al. (2011) have used Svalbard to provide periglacial analogues for Martian landforms. The use of analogues is used generally for the interpretation of surface features in planetary geology (Farr, 2004). This use is appropriate as periglacial and possibly permafrost features are associated with upland regions of the British Isles in the Younger Dryas. Compilations of processes, mechanisms and chronologies can be found in Ballantyne and Harris (1994) and Gordon and Sutherland (1993) and other overviews have been provided in several other volumes (Boardman, 1987; Gillen, 2003; Gordon, 2006; Gordon & Sutherland, 1993;

A distinction should be made be made between periglacial, that is, around a glacier and permafrost, a thermal condition where the mean annual air temperature is assumed to be <-2°C. So a snowbank is generally assumed to be a periglacial feature but is not glacial, ie with the dynamics of a glacier-ice body. Neither condition is extant in the British isles at the present day and we shall see that may produce interpretational difficulties. The term paraglacial has been used to indicate features that are postglacial and are involved with sediment movement (Ballantyne, 2002; 2007). It was instituted into the literature by Church and Ryder (1972) as, materials that were produced by 'non-glacial processes that are conditioned by glaciation'. Ballantyne (2007) defines it as 'the study of the ways in which

**2. The Younger Dryas (YD) in the British Isles and the dating of events** 

analogues that help interpretation in the British Isles.

McKirdy et al., 2007; Wilson, 2010).

glaciated landscapes adjust to nonglacial conditions during and after deglaciation'. However, in many cases this does not help with the interpretation as it may not be at all clear what was glacier or snow or permafrost-related. Further discussion can be found in Slaymaker (2009).

If there are problems in interpreting the significance of moraines this is also true of landscape features where the ice-debris mix is of less certain origin and formative process unclear. For example, the ice-cored moraines investigated by Østrem in Scandinavia (Østrem, 1964) were interpreted by Barsch (1971) as being 'rock glaciers'. This dispute (Østrem, 1971) is still not resolved. There are several reasons for this uncertainty; problems of observation as well as nomenclature and understanding of the geological processes and mechanisms involved and their rates of operation. This is despite advances of glacial theory, sedimentology and dating techniques. Additionally, researchers coming from diverse backgrounds have tended to have different, often divergent, views about the processes operating and therefore the interpretations. Further discussion on this will follow below.
