Rock glaciers of the Southern French Alps, specifically the Marinet Rock Glacier, are commonly thought to have a 'permafrost origin'. However, there are other rock glaciers in the Southern French Alps found in association with small corrie glaciers, suggesting that glacier ice has a role to play in their formation. At the Marinet Rock Glacier, results from ground surveys, relationships between debris and ice input, lichen dating and historical documentation suggest a glacial rather than a permafrost origin. Rock glacier palaeovelocities, calculated for an ice core within the rock glacier, suggest that it once moved much faster (up to 20 ma -1 ) than at present (<0.04 ma -1 ). This difference can be accommodated by a glacial explanation with development of the rock glacier over a 300 year period from the beginning of the Little Ice Age (derived from lichenometry). This relatively recent origin, compared to that required for a permafrost origin, accounts for the unstable nature of the rock glacier surface and its lack of vegetation. The very limited rock glacier movement shown at present (< 0.04 ma -1 ) is explained by the thinning of the ice core underneath a rock debris cover.
Sr/iool of (;eo,lril'/l((',I. Til l' Qjlffll ' ,I [ 'lIil'NSi(J' of B rijrls/ . IJeij(ls/ 1550-1850 ) m o ra ine of' the Feegletsc hcr, \ 'a lai s. S\\-itz e riand \\-as compared with th e actual \'olume being tran spo rted c urrc nth-1)\-the g lac ie r. Th e latte r is small e r by a f~\nor of'about t\\-o. In Tro ll as kagi, no rth Icela nd , a surfa ce co\'C r or d c bri s o n top o r a l'C ry slO\\' mOl'ing g lac ie r ice ma ss g lac ie r no ir. roc k g lac itT h as b ee n dated by li e h e nome tn', Th e age of' th e o lcl es t part is eo mm cll surat e \I'irh L IA mora in es in the area. Kn ow ing th e volum e of'de bri s o r a g i\'e n age a ll o\\'s an es tim a te o f' the d e bris supp ly to th e g lacier in a g i\'e n tim e. Again, there appears to han' bee n Cl sig n ificant reduction in d e hri s to the g lac ie r sincc th e turn o f'th e 19 th ce ntury, Dehri s input in th e ear ly LIA see m s to ha \'e bee n parti c u larh-co pi o us and thi s mal-be impo rta nt in the formation of so m e g lac ier depos iti o nal form s suc h as roc k g la cie rs,8
Sr/iool of (;eo,lril'/l((',I. Til l' Qjlffll ' ,I [ 'lIil'NSi(J' of B rijrls/ . IJeij(ls/ 8 T7 1. \ : \ -. , \ -o r/it em i rdalld \BSTRACT Th e \-o lum e or d e bri s in th e left -lateral , Little lee A ge (LlA:\i) 1550-1850 ) m o ra ine of' the Feegletsc hcr, \ 'a lai s. S\\-itz e riand \\-as compared with th e actual \'olume being tran spo rted c urrc nth-1)\-the g lac ie r. Th e latte r is small e r by a f~\nor of'about t\\-o. In Tro ll as kagi, no rth Icela nd , a surfa ce co\'C r or d c bri s o n top o r a l'C ry slO\\' mOl'ing g lac ie r ice ma ss g lac ie r no ir. roc k g lac itT h as b ee n dated by li e h e nome tn', Th e age of' th e o lcl es t part is eo mm cll surat e \I'irh L IA mora in es in the area. Kn ow ing th e volum e of'de bri s o r a g i\'e n age a ll o\\'s an es tim a te o f' the d e bris supp ly to th e g lacier in a g i\'e n tim e. Again, there appears to han' bee n Cl sig n ificant reduction in d e hri s to the g lac ie r sincc th e turn o f'th e 19 th ce ntury, Dehri s input in th e ear ly LIA see m s to ha \'e bee n parti c u larh-co pi o us and thi s mal-be impo rta nt in the formation of so m e g lac ier depos iti o nal form s suc h as roc k g la cie rs,
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