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Periglacial and paraglacial environments: a view from the past into the future

JASPER KNIGHT* & STEPHAN HARRISON Department of Geography, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9EZ, UK *Corresponding author (e-mail: [email protected])

Periglacial and paraglacial (cold-climate) environ- These views of land surface response to ments, located outside the margins of past and deglaciation are based on the premise that the pro- present ice sheets but responding to similar climate cesses and climates associated with glaciation are forcings, are key to identifying climate change related to an increase in sediment generation (by effects upon the Earth system (Warburton 2007). glacial processes themselves, and by enhanced These environments are relicts of cold Earth weathering) (Kirkby 1995). In reality, landscape processes and thus are most sensitive to climate responses are more subtle and strongly conditioned change that took place during the last glacial–inter- by local-scale geological and topographical factors glacial transition, and at the present time under that lie outside of these models. enhanced global climate warming. These effects include changes in humidity/aridity and radiation balance, which are most significant in the higher The limitations of uniformitarianism and at high elevations where periglacial and paraglacial environments are most common Our view of the processes and products of present- and where these environments occur near their day and paraglaciation is set within climatic limits (Harris 1994; Matsuoka 2001). Vari- the context of evidence preserved in the geological ations in humidity and radiation balance have impli- record, in particular glacial–interglacial cycles cations for heat budgets, water balance, land surface duing the late (Raymo 1997; Tziperman stability, downslope sediment supply, biodiversity et al. 2006). In turn, these have given rise to repeated and biogeochemical cycling (e.g. Schneider et al. cycles of sediment generation and delivery down- 1999; Scott et al. 2008). The dynamics of cold- slope into lowland basins and coastal margins climate environments are, therefore, strongly con- (Bridgland 2002; Van der Zwan 2002; Warburton trolled by external climatic forcing; and hence 2007). These are manifested stratigraphically as periglacial and paraglacial processes (and the land- stacked sequences of periglacial and paraglacial forms and sediments that result from them) can be sediments and structures, which are observed in considered as a transient response to the landscape many locations worldwide (e.g. Blikra & Nemec disturbance and land surface instability that accom- 1998; van Vliet-Lano¨e et al. 2000; Matsuoka panies climatic change (Hewitt et al. 2002). 2001). These climate-driven sediment cycles can This view of a transient landscape responding to be used to help interpret temporal patterns and pro- environmental disturbance is significant because it cesses of sediment accumulation in local-scale underpins influential deterministic and steady-state depocentres, and can, therefore, help distinguish models in cold-climate science (Church & between climatic and non-climatic (such as local Slaymaker 1989; Andre´ 2003; Warburton 2007). geological, topographical, etc.) controls on sedi- These models predict a rapid increase in sediment ment fluxes (van Vliet-Lano¨e et al. 2000). This uni- yield (which results from land surface disturbance) formitarian approach can be used effectively in associated with initial climate forcing, followed by order to evaluate climate-driven sediment patterns exponential decay of sediment yield towards back- over centennial–millennial timescales. ground rates which are achieved as land surfaces Much of our understanding of past periglacial are stabilized (Church & Ryder 1972; Ballantyne and paraglacial processes and environments comes 2002). Such a view of climatic causality is useful from a synthesis of observations drawn from con- because it can be used to consider the magnitude temporary environments and from preserved geo- and longevity of landscape impacts of past and logical evidence from the last glacial–interglacial future climate changes, respectively. transition (and into the early Holocene). Very little

From:KNIGHT,J.&HARRISON, S. (eds) Periglacial and Paraglacial Processes and Environments. The Geological Society, London, Special Publications, 320,1–4. DOI: 10.1144/SP320.1 0305-8719/09/$15.00 # The Geological Society Publishing House 2009. Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021

2 J. KNIGHT & S. HARRISON is known about the extent, dynamics and evolution activity has helped shift the focus of highest sedi- of periglacial and paraglacial environments associ- ment fluxes from upland (river headwater) to ated with older glacial cycles. This is probably lowland parts of catchments, which has implications owing to low preservation potential in areas that for the capacity of river systems to respond to cli- were overridden by ice in later glaciations. In matic v. anthropogenic forcings (Meybeck 2003; addition, as interglacials progress, pre-existing Juen et al. 2007). Further, Wilkinson & McElroy periglacial and paraglacial sediments and structures (2007) argued that current rates of continental denu- are probably destroyed by plant growth and soil dation are far higher than background rates over past development. These limitations suggest that little glacial–interglacial cycles, hence that human is known about past macroscale dynamics of activity is more significant than other processes in periglacial and paraglacial environments, and that shaping Holocene landscapes. This is significant the principle of uniformitarianism is not always because it suggests that paraglacial sediment appropriate to apply. systems are being (or have been since the late Interglaciations, including the present Holocene, Holocene) overwhelmed by a direct anthropo- are characterized by low continental ice volume and genic overprint controlled by deforestation, ecosys- land surfaces dominated by plants. As interglacials tem changes, etc. In addition, future enhanced develop, therefore, the geographical zones in global warming (and changing temperature and which periglacial and paraglacial processes operate precipitation regimes) is going to impact most retreat towards core high- and high-altitude strongly on the climatically determined environ- areas. This means that these processes are time ments where periglacial and paraglacial processes transgressive across the landscape as climate belts take place, in particular in upland and glaciated shift, and that their environments become smaller catchments. and more geographically isolated over time. As A probable effect of anthropogenic climate interglacials develop, geological records from warming is that the present interglacial is extended these environments reflect local-scale controls beyond the timescale determined solely by Milan- rather than regional-scale climate, and there are kovitch forcing (Mitchell 1972; Mo¨rner 1972), associated problems of correlation. Interglacial which has been largely responsible for controlled records are therefore sparser and their interpret- interglacial length in the past (e.g. Tziperman ations limited. The present situation of anthropo- et al. 2006). As periglacial and paraglacial processes genically enhanced climate changes (global are, on the macroscale, determined by climate, it is warming), superimposed upon the already warm to be anticipated that sediment generation and Holocene, is unprecedented. The net future climatic supply will decrease over time as the land area effects (in both precipitation and in air and ground under these favourable climates decreases also. temperature) are uncertain (Rosenzweig et al. This follows the paraglacial sediment exhaustion 2008; Scott et al. 2008). This poses many questions model of Ballantyne (2002). Under an extended as to how periglacial and paraglacial processes and (and warmer) interglacial, it is probable that sedi- environments will respond, and how quickly ment fluxes from the headwaters of mid-latitude gla- (Warburton 2007), under climatic contexts for ciated basins will decrease dramatically, leading to which there is no preserved analogue. This clearly sediment starvation and, eventually, cannibalization illustrates the limitations of uniformitarianism as a of river lowlands and coastal fringes. In high- tool to understand future changes in periglacial latitude areas, melt and reduced sea ice and paraglacial environments. protection is already leading to enhanced coastal and sediment supply (Lawrence et al. 2008). Global warming, therefore, is already Discussion and outlook to the future leading to a decrease in the continuity and intercon- nectedness of permafrost and associated periglacial Human impacts on late Holocene climate and Earth processes (Lemke et al. 2007). A sediment budget systems have dramatically affected land surface approach (e.g. Syvitski et al. 2003; Phillips & stability and associated sediment fluxes, and led to Slattery 2006) can help monitor the progression of the late Holocene period being informally termed this breakup. the Anthropocene (Ruddiman 2003). The impact of human activity on landscape dynamics has been discussed in a number of studies (e.g. Hooke Imperatives in the understanding of 2000; Ehlen et al. 2005; Wilkinson 2005). Other periglacial and paraglacial environments studies have focused more specifically on human- related changes in sediment budgets in different The foregoing discussion identifies the subtle inter- physical settings. For example, Hooke (1999) and relationships between periglacial and paraglacial Wilkinson & McElroy (2007) argued that human environments and climates of the past and future. Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021

INTRODUCTION 3

Understanding these interrelationships is important of sediment supply using examples from Europe, because present decreases in the distribution and North America and Asia. The paper by Curry thickness of permafrost, particularly in continental et al. considers the geotechnical and geomorphic interiors (Camill 2005), have implications for eco- implications on ongoing paraglaciation. Specific system and landscape stability, human activities examples of paraglacial landscape responses from and engineering solutions, and CO2 degassing British Columbia are shown in the papers by from thawing permafrost (Lawrence et al. 2008). Wilkie & Clague and Friele & Clague. The This is mirrored in sensitive and marginal perigla- paper by Hewitt considers paraglaciation in cial Alpine environments that are presently experi- Pakistan as a transient landscape response to cli- encing increased rockfall and mass movement, matic disturbance. The final paper in the volume, including solifluction, rock instability and by Harrison, addresses the sensitivity of periglacial changes in sediment release to downstream rivers and paraglacial geomorphic systems to climatic (Juen et al. 2007; Warburton 2007). Likewise, a forcing, which is particularly important when one major initiative in sensitive glaciated mountain considers that these environments are most at environments is to understand the processes of geo- threat from future climate change. morphic change, the rate of landscape modification and the nature of resulting paraglacial landsystems. The papers in this volume are largely the outcome of a In considering how periglacial and paraglacial meeting held at the Geological Society, London (UK) in environments are going to respond to future January 2007, on the theme of Periglacial and Paraglacial climate changes, two key questions present them- Processes and Environments, Past, Present and Future. The meeting was held jointly between the Geological Society selves. First, given that renewed paraglaciation of London and the Quaternary Research Association who will accompany future glacier retreat and decreased are thanked for their financial support. extent of periglacial environments under global The editors wish to thank the authors for their contri- warming, how will we accommodate such geomor- butions, and acknowledge the following reviewers: phological instability into our models of economic N. Betts, J. Boelhouwers, J. Catt, J. Carrivick, and social use of both mountain and lowland cold- P. Christoffersen, M. Clark, J. Desloges, J. Dixon, climate regions? Second, how far can models of B. Etzelmuller, A. Findlayson, D. Giles, S. Gurney, paraglaciation, and periglacial slope processes, be K. Hall, P. Hughes, K. Huntington, O. Humlum, used to interpret the geomorphic evolution of J. Kemp, M. Konen, O. Korup, W. Mitchell, A. Nesje, S. Payette, R. Pine, B. Rea, A. Strom, D. Swift, these landscapes under future climate scenarios? R. Tipping, F. Tweed, C. Whiteman and C. Zangerl. These questions, and related issues, are explored in this volume in an inter- and multidisciplinary framework, through case studies from both contem- porary and Quaternary periglacial and paraglacial References settings. ANDRE´ , M.-F. 2003. Do periglacial landscapes evolve This volume is organized into three sections. The under periglacial conditions? , 52, first section focuses on periglacial processes and 149–164. environments. The paper by Andre´ sets periglacial BALLANTYNE, C. K. 2002. Paraglacial geomorphology. studies into a wider and historical context. Perigla- Quaternary Science Reviews, 21, 1935–2017. cial weathering and processes are examined BLIKRA,L.H.&NEMEC, W. 1998. Postglacial colluvium in the papers by Nicholson, and Seppa¨la¨ & in western Norway: depositional processes, facies and Kujala, respectively. The papers by Waller et al. palaeoclimatic record. 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4 J. KNIGHT & S. HARRISON

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