Ninth International Conference on Permafrost ... - IARC Research

Rock Glacier Distribution in the Absaroka/Beartooth Wilderness, Montana, USAZach M. Seligman, Anna E. KleneDepartment of Geography, University of Montana, Missoula, 59812, USAIntroductionRock glaciers are relatively understudied glacialfeatures found in many alpine environments around theworld. Because they are rock-covered and often similar inappearance to talus fields and moraines, their presence andhydrologic significance has gone widely unnoticed (Millar& Westfall 2007). However, they play an important role inalpine environments. Rock glaciers provide a mechanismfor transport of headwall debris (Humlum 2000) and,similar to glaciers, can act as a source of year-round waterin high alpine catchments where late summer precipitationis minimal (Johnson 2007). Schrott (1996) determined thatthese features can contribute up to 30% of river dischargeduring summer months in the Andes.Additionally, rock glaciers potentially contain significantclimatic information within their spatial distribution(Humlum 1998). While a number of studies have focusedon these relationships (Kerschner 1978, Brazier et al. 1998,Humlum 1998), a paucity of relevant climate stations oftenlimits such efforts (Brazier et al. 1998). Other research hasexamined characteristics of rock glacier age (Aoyama 2005),movement (Chueca & Julian 2005), structure (Arenson et al.2002), and geomorphology (Berthling & Etzelmuller 2007).In the Absaroka/Beartooth wilderness, rock glaciersnumber in the hundreds (unpublished data), existingsimultaneously with cirque glaciers and permanentsnowfields, yet general information about them is sparse,and hydrological research is non-existent. This study willexamine the spatial distribution of rock glaciers to understandthe relative local importance of topoclimatic and geologicfactors. This understanding will allow further investigationsinto the relationships between rock glacier distribution, icevolume, and downstream ecology. The interplay of thesefactors has important implications in light of recent andongoing climatic changes.Research will be performed in two phases. Phase oneincludes analysis through GIS and remote imagery, whichwill explore trends in rock glacier distribution relativeto topoclimatic factors. The second phase will be fieldverification of the digital data, which will subsequentlyinvestigate the link between spatial characteristics of rockglaciers and water availability in alpine catchments.BackgroundTopoclimatic and geologic controlsPrevious research in New Zealand shows that activerock glaciers tend to favor relatively higher elevations andmore southerly aspects (Brazier et al. 1998). In the samestudy, modern distribution of relict rock glaciers favoredlower elevations on all aspects. Similarly, Humlum (1998)describes rock glacier presence to be “a complex functionof responses to air temperature, insolation, wind, andseasonal precipitation over a considerable period.” Just astopoclimatic factors play a major role in ice formation andretention of rock glaciers, lithology has also been shown to bean important component of rock glacier initiation (Johnsonet al. 2007). This study will use GIS to compare topoclimaticand geologic controls on rock glacier distribution.Ice volume and distributional controlsRock glacier ice volume may also correlate strongly withtopographical distribution in the same ways that rock glacieractivity is linked to topographical and altitudinal controls(Humlum 1988). As rock glacier activity is dependent onice volume for its classification, it should follow that icevolume is subject to the same variables that affect rockglacier activity. This study will explore topographical andaltitudinal controls on rock glacier ice volume.Ice volume and vegetationInvestigations of relationships which may exist betweenrock glacier distribution, ice volume, and downstreamecology can be based upon the relationships currently knownto exist between glacial systems and ecological successionin the region. Previous research has looked at vegetativeadvancement in response to glacial recession in Africa (e.g.,Kazuheru 2003). Locally, Hall and Fagre (2003) used modelsto project vegetation succession patterns of glacial forelandsin Glacier National Park, Montana. Perhaps a similarrelationship exists for alpine catchments where rock glaciers,instead of ice glaciers, are the dominant glacial feature. Thisstudy will estimate rock glacier ice volume in comparisonwith percentage per area of appropriate vegetation typesdownhill of the rock glacier terminus.Implications for climateTopological and altitudinal distribution of rock glaciers,in itself, has the potential to contain unique climaticinformation (Humlum 1998). By comparing ages andelevations of active and relict rock glaciers and interpretingchanges in equilibrium line altitudes, timing of glaciationsand temperature differences have been determined (Millar& Westfall 2007). Regionally, results of vegetative patternsassociated with spatial distribution of rock glaciers may alsoharbor additional climatic information.Study AreaThis study will focus, in the first phase, on the distributionof rock glaciers within Absaroka/Beartooth wilderness areain southwest Montana. Phase two will look at approximately30 representative rock glaciers within the wilderness area.279