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Where snow avalanches descend steeply into large rivers, displacing bedload, avalanche boulder-ramparts may accumulate, retaining a record of late-Holocene snow-avalanche frequency. The age frequency of surface boulders on 12 such features in upper Jostedalen, southern Norway, was investigated using the size-frequency distribution of lichens. A model was constructed to simulate the influence of variations in avalanche frequency since AD 1325 on lichen-size-frequency distributions. Using this modelling approach it is not possible to define a unique pattern of avalanche activity to account for the observed lichen-size-frequency distributions, but it is possible to place strict limits on the range of scenarios that are acceptable. The results suggest that maximum avalanche activity occurred during the 19th century, after the peak of the Little Ice Age. This conflicts with historical records of avalanche damage to property at lower altitude in nearby valleys, which may reflect avalanche activity only during a short period of extreme climatic conditions. Close agreement between the records of snow avalanches and debris flows suggests that both reflect periods of high winter snowfall and rapid spring melting rather than low temperature. Future ‘greenhouse warming’ may therefore result in increased avalanche activity in southern Norway.

Measurements of Rhizocarpon subgenus Rhizocarpon thalli in fixed-area (100-m 2) sample plots at 295 randomly selected localities above timberline in the Colorado Front Range suggest six episodes of widespread, shallow, lichen snowkill during and immediately following the Audubon glacial interval. Recolonization of lichen-free areas began in cal. AD 210, 375, 570, 700, 1025, and 1255. In contrast to the 'Little Ice Age', when snowkill was restricted to narrow bands peripheral to modern late- lying snowpatches, Audubon snowkill destroyed all crustose lichens in more than 90% of the study area. Heavy April or May snowstorms, occurring after redistribution of snow by wind had diminished, are thought to have been responsible; cool, cloudy summers and warm subnivean winter temperatures may also have been involved. Audubon snowkill episodes lasted for relatively brief periods, and were superimposed on the broader pattern of late-Holocene climatic change. They did not necessarily trigger glaciation or cause geomorphic instability, but are thought to have temporarily discouraged human use of the Front Range alpine region through their adverse effects on large-game-animal populations. Lichenometric dates for landforms in areas of potential snowkill should be evaluated using rock- weathering criteria or other independent age evidence.

Complex moraine-ridge sequences in front of seven outlet glaciers of the Jostedalsbreen ice-cap (Austerdalsbreen, Bergsetbreen, Fabergstolsbreen, Lodalsbreen, Stegaholbreen, Tuftebreen, Bodalsbreen) are dated using families of lichenometric dating curves established previously at an eighth outlet (Nigardsbreen). Applicability of the Nigardsbreen curves at the regional level is tested using independent historical evidence: moraines deposited during the present century are dated to an accuracy of ± 9.4 yr (16.0%), and most of them are dated to an accuracy of ± 5.5 yr (9.4%). Results from the moraine sequences are combined to form a composite ‘Jostedalsbreen’ record. Median predicted dates for moraine ridges cluster around AD 1939 ± 2 yr, 1929 ± 3, 1908 ± 3, 1886 ± 5, 1875 ± 2, 1867 ± 4, 1855 ± 3, 1842 ± 5, 1822 ± 5, 1807 ± 4 and 1785 ± 5. At least four glaciers reached their ‘Little ice age’ maxima prior to AD 1780, two (Nigardsbreen and Bodalsbreen) at ca. 1750, one (Fabergstolsbreen) at ca. 1705. Stegaholbreen attained its maximum ca. 1863. Since the ‘Little ice age’ maximum, and despite large differences in glacier size, frontal variations of the various outlets have exhibited a high degree of synchroneity, which suggests that the moraine sequences contain a sensitive record of high-frequency climatic variations over the last ca. 250 yr. During the early twentieth century, measured readvances of the order of 5–150 m over 1–10 yr led to moraine formation. Dendroclimatic evidence indicates that since the late eighteenth century, moraine ridges formed about 5 yr after summer temperature minima and correlate with runs of cool summers (temperature depression of 0.5–1.0°C below the AD 1700–1950 average). Almost simultaneous glacier advances appear to have been caused by reduced ablation. This near-immediate response to climatic variation, by glacier tongues that descend to relative low altitudes, is superimposed upon the longer-term dynamic response of the ice cap to climate.

The air-photo interpretations and the casual field observations in the Navajo Glacier area, the uppermost reaches of the South St. Vrain Creek, Colorado Front Range, led to the speculation that the Triple Lakes “protalus ramparts” which were identified by Benedict (1968) can be classified into the following three different landforms:(1) a ridge located at the highest altitude (U1) regarded as a protalus rampart, while another in the center can be subdivided and classified into (2) a protalus rampart (U2: upper unit) and (3) a lateral moraine (L: lower unit). Several lines of evidence support the above classification. Firstly, the lower unit (L) has a flat surface with vegetation cover. Secondly, the lower unit (L) continues to an arcshaped ridge downvalley. Thirdly, the upper unit (U2) has the same sinuosity as that of U1 and the talus slope but the lower unit (L) does not. Finally, the lower unit (L) has fine matrix whereas the upper unit (U2) does not.Multiple relative dating methods, such as lichenometry (lichen diameter, percent lichen cover, and ratio of green lichens/{brown and black lichens}), weathering rind thickness, SGW I (surface granite weathering index of Benedict, 1985), and pit depth, provided the estimated age of Triple Lakes (3, 000-5, 200 y. B. P.) for both the moraine and the protalus rampart classified above. However, soil profiles and soil color indices (Buntley-Westin and Hurst color indices) indicate that the moraine is older than the protalus rampart. It is probable that the lichenometric and weathering feature data collected from the lateral moraine surface have been influenced by rockfall activity which modified the moraine surface during the Triple Lakes period. The protalus rampart (U2) is estimated to have been formed in the Triple Lakes Stade, as Benedict (1968) states. However, the moraine seems to be of the Satanta Peak Stade (10, 000-12, 000 y. B. P.), which is recognized elsewhere in the Colorado Front Range (Birkeland et al., 1987).Using this result together with the method for estimating glacier ice thickness of Porter et al.(1983), this study has also attempted to reconstruct the Navajo Glacier in the Late Stade of Pinedale and the Satanta Peak and Triple Lakes stades. The glacier is believed to have terminated at an altitude of 3, 250-3, 300m in this valley in the Late Stade of Pinedale (-14, 000 y. B. P.)(Madole, 1969), at which time the area and thickness of the glacier are estimated to have been 5.6km2 and 250m, respectively. In the Satanta Peak Stade (12, 000-10, 000 y. B. P.), the glacier retreated to 3, 480m, and its area and thickness decreased to 1.0km 2 and 100m, respectively. The Triple Lakes glacier terminated at an altitude of 3, 680m in the cirque, with an area of 0.2km 2 and a thickness of 25-30m.

Introduction The steep, crumbly and wet mountains of New Zealand have frequent mass movements and floods, and landscape instability related to glaciers. The Southern Alps sit astride the Australian–Pacific plate boundary (Figure 2.1) with its highly active dextral-oblique thrust faults, active volcanoes, and subduction zones. This chapter summarizes a hazardous geomorphological consequence of widespread seismic shaking in the South Island of New Zealand. Rocks tumble downhill during earthquakes and the times of arrival on a scree slope can be dated by measuring the largest lichen of Rhizocarpon subgenus Rhizocarpon on many blocks. This discussion focuses on how to use lichenometry to better understand the intensity and history of hazardous seismic shaking so as to minimize risk. A typical study site is described, the precision of dating is noted, and maps revealing areal intensities of seismic shaking are examined to better understand sizes and sequences of earthquakes. Lichenometry site characteristics The Mt. John site summarizes the desirable features needed for seismic-hazard evaluations. The valley side here was trimmed by a late Pleistocene glacier, creating cliffy outcrops of crumbly greywacke sandstone that have shed blocks to be stored in talus accumulation areas. Hazards such as snow avalanches and water floods are absent. I would have chosen an active talus cone if I had wanted to study the frequency and sizes of avalanches. Rhizocarpon subgenus Rhizocarpon grows well at this altitude and climate, but locally is impinged upon by other lichens and by mosses.

Moraine ridges are present in the highest cirques of the Durmitor massif in Montenegro and post-date the widespread Pleistocene moraines of this area. Lichenometry suggests that at least eight glaciers were present in the 19th century and correlate with the culmination of the Little Ice Age in the European Alps. Cooler temperatures combined with local topoclimatic controls, including windblown and avalanching snow as well as shading, were crucial for the formation and survival of these glaciers below the regional equilibrium–line altitude. The resultant regional equilibrium line altitude (ELA) was positioned close to the highest peaks between 2400 and 2500 m, with local controls such as avalanche, windblown snow and shading depressing the ELA in the northern cirques to 2130–2210 m. This ELA position was very low for this latitude and lower than for most glaciers in the European Alps at any time during the Holocene, and even equivalent to many Alpine glaciers during the Younger Dryas. Today, one glacier still survives in Montenegro, in a deep northeast-facing cirque characterized by the largest combined areas of potential avalanche and windblown snow. Copyright © 2009 John Wiley & Sons, Ltd.

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Sediment transport of four boulder bed rivers is studied using lichenometry. The presence of lichens on boulders in the river channel is used to date the last mobilization of the blocks. Using size frequency diagrams and regional growth curves calibrated with dated reference points it is possible to determine the flood event responsible for the last mobilization of each boulder with lichens present. The specific stream power of flood events over the last 60 years is then calculated, and thresholds of sediment transport based on the sediment size are calculated. The results from the four studied rivers are compared to similar relationships in the literature. Sediment motion thresholds appear to be very variable within the same type of river (mountainous boulder bed rivers). The critical specific stream power necessary to mobilize a particle of a given diameter may vary by up to 10 times from one river to the next. Bed sediment size and river slope may explain this large range of stream powers. Calculation of the relative size of the transported particles (Di/D50) also shows that both hiding and protrusion effects, as well as channels slope, are important factors in sediment transport. Copyright © 2010 John Wiley & Sons, Ltd.

Scotland, a maritime subpolar environment (55–60°N), has seen relatively few applications of lichenometry – even though it offers much potential. Perhaps surprisingly, direct measurements of Rhizocarpon geographicum growth rates in Scotland are so far lacking. This study reports on the growth of this crustose areolate species from two sites in Assynt, NW Scotland, between 2002 and 2009. Repeat photography of 23 non-competing thalli growing under identical environmental conditions on a single vertical surface over 5 years at Inchnadamph showed growth rates to be a function of size – with larger thalli (10–30 mm) growing significantly faster than the smallest thalli (10 mm are 0.67 mm yr−1 (s.d. = 0.16). Studies on a second vertical surface near Lochinver, over 7 years, yielded complex growth data on a more mature population of R. geographicum thalli (10 mm) are slower (0.29 mm yr−1; s.d. = 0.12) than those at Inchnadamph. However, at this site, competition with other species rules out any meaningful comparison of growth rates between the two sites. Other growth processes were monitored over the five to seven-year study period, including hypothallus growth, areolae development, thallus coalescence, and inter-species competition – all have important implications for the use of Rhizocarpon species in lichenometry.

Crustose species are the slowest growing of all lichens. Their slow growth and longevity, especially of the yellow-green Rhizocarpon group, has made them important for surface-exposure dating (‘lichenometry’). This review considers various aspects of the growth of crustose lichens revealed by direct measurement including: 1) early growth and development, 2) radial growth rates (RGR, mm yr-1), 3) the growth rate-size curve, and 4) the influence of environmental factors. Many crustose species comprise discrete areolae that contain the algal partner growing on the surface of a non-lichenised fungal hypothallus. Recent data suggest that ‘primary’ areolae may develop from free-living algal cells on the substratum while ‘secondary’ areolae develop from zoospores produced within the thallus. In more extreme environments, the RGR of crustose species may be exceptionally slow but considerably faster rates of growth have been recorded under more favourable conditions. The growth curves of crustose lichens with a marginal hypothallus may differ from the ‘asymptotic’ type of curve recorded in foliose and placodioid species and the latter are characterized by a phase of increasing RGR to a maximum and may be followed by a phase of decreasing growth. The decline in RGR in larger thalli may be attributable to a reduction in the efficiency of translocation of carbohydrate to the thallus margin or to an increased allocation of carbon to support mature ‘reproductive’ areolae. Crustose species have a low RGR accompanied by a low demand for nutrients and an increased allocation of carbon for stress resistance; therefore enabling colonization of more extreme environments.

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Certain species of crustose lichens have concentrically zoned margins which probably represent yearly growth rings. These marginal growth rings offer an alternative method of studying annual growth fluctuations, establishing growth rate–size curves, and determining the age of thalli for certain crustose species. Hence, marginal growth rings represent a potentially valuable, unexploited, tool in lichenometry. In a preliminary study, we measured the widths of the successive marginal rings in 25 thalli of Ochrolechia parella (L.) Massal., growing at a maritime site in north Wales. Mean ring widths of all thalli varied from a minimum of 1.02 mm (the outermost ring) to a maximum of 2.06 mm (the third ring from the margin). There is some suggestion that marginal ring width and thallus size are positively correlated; and hence that growth rates increase in larger thalli in this small population. In a further study on recently exposed bedrock adjacent to Breiðarlon, SE Iceland, we examined the potential for using marginal growth rings to estimate thallus age of a lichen tentatively identified as a Rhizocarpon (possibly R. concentricum (Davies) Beltram.) and thus confirm the timing of surface exposure (c. 50 years). Collectively, these results suggest: 1) the measurement of marginal rings is a possible alternative method of studying the growth of crustose lichens; 2) O. parella may grow differently to other crustose species, exhibiting a rapidly increasing radial growth rate in thalli >40 mm; 3) where lichens with marginal rings grow on recently exposed surfaces (

Rockfall represents the most intensely studied geomorphic process in mountainous areas. Nevertheless, very little information exists on how rockfall frequencies and magnitudes vary over time and how hazards and risks posed by rockfall could be reliably assessed. Former studies have mainly focused on short-term observations of contemporary rockfall activity (Luckman 1976, Douglas 1980), rendering it difficult to estimate long-term accretion rates. Long-term estimates of rockfall accumulation rates have, in contrast, been derived from accumulated talus volumes (Rapp 1960), but such rates may neither be representative of the present-day rockfall activities nor of those that prevailed in the past. On slopes composed of siliceous lithologies, lichenometry has repeatedly been used to evaluate the mean age or activity of talus surfaces (Andre 1997) or to estimate rates of rockfall accretion (Luckman and Fiske 1995).

Investigations of plant colonization patterns and lichenometry have provided new insights regarding past and present slope processes on Svalbard. Major stages in slope evolution during the Holocene have been identified, and the Neoglacial period (3500–2000 B.P.) is suggested as the starting point for the formation of lobate rock glaciers. Estimates of the frequency of episodic meteorological events, which have geo‐morphological implications, indicate a recurrence interval of rainstorm‐triggered debris flows and slush avalanches of 70 to 600 years. Active and stable slope deposits have been distinguished and the importance of runoff during spring melt and subsurface percolation later in the summer is implied. In order to interpret the data it is necessary to take into account lithology and to realize that some plant communities provide better indications than others. In contrast with the great variability of phanerogamic and moss communities, which primarily reflect ecological conditions, the stab...

Families of lichenometric dating curves are constructed using four historically-dated moraine ridges on the glacier foreland of Nigardsbreen (Jostedalsbreen ice cap), southern Norway. A further 20 'Little Ice Age' moraine ridges are dated in terms of median-predicted dates derived from the families of curves. Four approaches are used to assess the accuracy of the median-predicted dates: (1) the extent to which the dates form a temporal sequence; (2) the extent to which they agree with local independent evidence of glacier variations; (3) the extent to which dates agree when the moraine sequences on the two sides of the glacier foreland are dated separately; and (4) the extent to which they agree when section Rhizocarpon is differentiated from lichens of the Rhizocarpon subgenus as a whole. It is concluded that under conditions favourable for lichenometric dating, median-predicted dates have attained an accuracy of ~10% on the 'Little Ice Age' timescale. Realistic error limits are considered to be of the order of ±20 years for the oldest moraines and ±5 years for the youngest. Previous dates for the Nigardsbreen moraine sequence derived from single lichenometric dating curves may be ~5% less accurate. It is suggested that the range of predicted dates obtained from families of lichenometric dating curves can be used as a conservative surrogate for accuracy.

Measurements of Rhizocarpon subgenus Rhizocarpon thalli on moraines the ages of which are constrained by six radiocarbon dates, two pre-Colombian structures, and one historically-dated flood deposit indicate that lichenometry can be used to estimate the age of stabilization of glacial deposits that date to the last c. 7 ka on the west side of the Cordillera Blanca, Perú (8°40′-9°40'S; 77°00′-77°40'W). The preliminary growth curve for subgenus Rhizocarpon resembles those derived for alpine areas in Alaska and Colorado, and can be subdivided into an initial, rapid phase of growth (c. 0.4 mm yr-1) that lasts c. 100 years, a c. 500-to 1000-year-long phase of decelerating growth, and a period of slow linear growth (0.016 mm yr-1) that commences after c. 1000 years. Size clustering of subgenus Rhizocarpon thalli supports a four-fold subdivision of cirque moraines at altitudes between 4200 and 4650 m. The oldest moraines stabilized between c. 7000 and 6000 BP, and the three younger groups between c. 3350 and 1800 BP, between c. 1250 and 400 BP. and within the last 100 years. This subdivision is supported by limiting radiocarbon dates from the Cordillera Blanca and from several cordilleras in southern Perú, and indicates that the Holocene glacial chronology of the Cordillera Blanca is the most complete heretofore recognized in the tropical Andes.

This commentary article discusses the relative merits of new mathematical approaches to lichenometry. It highlights their strong reliance on complex statistics; their user un-friendliness; and their occasional mistreatment of existing lichenometric techniques. The article proposes that the success of lichenometric dating over the past 50 years has stemmed from its relative simplicity, transparency, and general field applicability. It concludes that any new techniques which ignore these principles are likely to be unjustified, unsuitable to the user community and inappropriate for the subject matter. Furthermore, the article raises a more general philosophical question: can statistical complexity and high precision in a ‘geobotanical’ dating technique, fraught with high degrees of environmental variability and in-built uncertainty, ever be scientifically valid?

Lichenometry is a dating method widely used to study Little Ice Age (LIA) glacial fluctuations in many arctic and alpine mountainous areas where historical data are sparse. In the Alps, very few studies have attempted to use lichenometry because of the more reliable nature of archive documents and dendroglaciological investigations, and because of the lichen growth pattern under mid-latitude climate. Despite of these limitations, lichenometry remains the unique tool to build a LIA glacial chronology for regions like the Massif des Ecrins, where other dating methods are unsuitable. A growth curve for Rhizocarpon subgenus Rhizocarpon built in the Veneon valley allowed us (i) to date late LIA and contemporary retreat glacial deposits with a good accuracy (± 5-25 years), and (ii) to propose two scenarii for older deposits formation. Over the most recent period, results have been compared with available historical evidence. The methodological problems encountered have also been discussed., La lichenométrie est une méthode de datation fréquemment utilisée pour reconstituer les fluctuations glaciaires du Petit Age de Glace (PAG) dans des massifs montagneux pour lesquels les données historiques sont très fragmentaires. Dans les Alpes, son utilisation est restreinte par des facteurs liés à la croissance du lichen sous les latitudes moyennes et par l 'usage d'autres méthodes de datation plus précises (e.g. archives historiques ou dendrochronologie). Toutefois, dans les massifs où ces méthodes ne peuvent être mises en œuvre, elle constitue le seul moyen d'établir un cadre chronologique des fluctuations glaciaires sur la période considérée. La construction d 'une courbe de croissance pour Rhizocarpon sous-genre Rhizocarpon dans la vallée du Vénéon a permis de dater les moraines de la fin du PAG et de la décrue qui a suivi avec une précision de ± 5-25 ans, et de proposer deux scénarios de mise en place des dépôts plus anciens. Les résultats ont été validés pour le XXe siècle à l 'aide de documents historiques. Les problèmes méthodologiques rencontrés sont également discutés., Le Roy Melaine, Deline Philip. Étude des fluctuations glaciaires du Petit Âge de Glace dans le Massif des Écrins : apports de la lichénometrie. In: Collection EDYTEM. Cahiers de géographie, numéro 8, 2009. Neige et glace de montagne. Reconstitution, dynamique, pratiques. pp. 51-64.

The aim of this paper is to document the evolution of glaciers in the tropical Andes (between 10 degrees N and 16 degrees S) for the last millennium, based on moraines dated by lichenometry and radiocarbon, lake sediment records and historical documents. Viewed collectively, several glacial advances occurred synchronously. The first advance is dated around AD 1200-1350. The maximum glacial extent (MGE), defined as the furthest down-valley extent recorded synchronously by the majority of glaciers, occurred around 1630-1680 in Bolivia and Peru (the outer tropics) and around AD 1730 in Ecuador, Colombia and Venezuela (the inner tropics). Subsequently. during the 18th and 19th centuries, glaciers retreated continuously with only minor synchronous readvances. In the outer tropics, minor glacial advances occurred around 1730,1760,1800,1850, and 1870. In the inner tropics, synchronous minor advances occurred around 1760,1820 and 1880. Between the MGE and the early 20th century, glaciers lost about 30% of their total length. The retreat was slow between the 17th and 18th centuries but then became more marked. Use of the accumulation area ratio (AAR) method or historical observations in the different cordilleras revealed an increase in the equilibrium line altitude (ELA) of about 300 m from the MGE onward. Palaeoclimatic hypotheses, based on glaciological models run in different countries, suggest a cool and humid period in the 16-18th centuries followed by a colder and drier period in the 19th century. The reduction of glaciers observed from the middle of the 19th century is due to increasingly warmer conditions than before. Here, quantitative estimates are proposed to explain the evolution of the glaciers. In Venezuela, results indicate for the period 1250-1820 that mean air temperatures were 3.2 +/- 1.4 degrees C cooler and precipitation was about 22% higher than at present. In Ecuador, temperatures of between 0.8 degrees and 1.1 degrees C lower than today, and between 25% and 35% higher accumulation than today, appear to have occurred in the 18th century, followed by a short drier but colder period at the beginning of the 19th century. In Bolivia, the MGE could be a consequence of a decrease in temperature of 1.1 to 1.2 degrees C, and a 20 to 30% increase in accumulation or an increase in cloudiness of about 1-2/10. We discuss not only external climatic forcing but also the coincidence between glacier expansion and a decrease in solar irradiance. Dating uncertainties, however, have made the role of volcanism in glacier fluctuations impossible to determine. Finally, we discuss the relationships between ENSO and glacier fluctuations in recent centuries, which do not match directly with current knowledge of modern teleconnections between tropical Pacific SSTs and variations in glacier mass balance.

International audience; The Little Ice Age (LIA) maximum glacial extent of 13 glaciers located in SE Iceland was dated by lichenometry to check for intraregional variations. Different lichenometric approaches were applied to date maximum LIA moraines, and they all showed high variability between glaciers. According to the Extreme Value Theory and Bayesian approach, LIA advances in the region occurred in or around A.D. 1740–1760, A.D. 1810–1820 and A.D. 1840–1880 with confidence intervals of between 8 and 21 years. The dates were correlated with geomorphic characteristics of glacier tongues: hypsometric and slope parameters can be considered as determining factors in the variability of glacier timing during the LIA, as previously observed in Norway and in the Alps. In terms of timing, results obtained in SE Iceland were similar to those obtained for other glacier regions around the North Atlantic.

The past decade has seen the development and application of over a dozen new methods for quantitative age-determinations of geomorphic surfaces. Some surface exposure dating methods are numerical, including the accumulation of cosmogenic radionuclides 10Be, 14C, 26Al, 36Cl, and 41Ca, accumulation of cosmogenic stable nuclides 3He and 21Ne, 14C dating of organic matter encapsulated in rock coatings, and dendrogeomorphology. Calendar ages are obtained by dendrogeomorphological analysis. Calibrated ages can be obtained by analysis of rock-varnish chemistry, lichenometry, weathering, and soils. Various methods can be used in combination to overcome individual limitations. Whereas conventional methods provide age control on stratigraphic profiles, surface-exposure dating methods are especially suitable for geographic problems, such as analyzing not only temporal, but also spatial variations in the rates of geomorphic processes. [Key words: geomorphology, process, geochronology, cosmogenic nuclides, Quaternary,...

Lichenometric and weathering-based techniques are employed in an investigation of the chronology of large-scale sorted circles in Jotunheimen, southern Norway. Comparison of diameter measurements of Rhizocarpon geographicum agg. with local growth curves, and size-frequency analysis of lichen population data, indicate that all the sorted circles originated prior to the mid-eighteenth century 'Little Ice Age' maximum. Parts of the circle borders appear to have been stable since before the twelfth century, although minor disturbances to border clasts were widespread between about AD 1640 and 1740. Large proportions of the smaller surface clasts in circle centres have stabilized only since the 'Little Ice Age' maximum. The thickness of surface weathering rinds and measurements of rock surface hardness (R-values obtained using a Schmidt hammer) indicate long periods of clast exposure in circle borders (at least 1500 years at some sites) and shorter exposure times for central clasts. Despite difficulties in inferring the nature of rind thickness/age and R-value/age curves, the evidence based on weathering criteria strongly points to early Holocene origins. These results demonstrate the potential for using relative-age dating techniques in chronological and palaeoenvironmental investigations of sorted patterned ground, and suggest that a similar approach may be applicable in studies of other stony periglacial features.

Dating moraines by lichenometry enabled us to reconstruct glacier recession in the Bolivian Andes since the Little Ice Age maximum. On the 15 proglacial margins studied, we identified a system of ten principal moraines that marks the successive positions of glaciers over the last four centuries. Moraines were dated by performing statistical analysis of lichen measurements based on the extreme values theory. Like glaciers in many mid-latitude mountain areas, Bolivian glaciers reached their maximal extent during the second half of the 17th century. This glacier maximum coincides with the Maunder minimum of solar irradiance. By reconstructing the equilibrium-line altitude and changes in mass-balance, we think the glacier maximum may be due to a 20 to 30% increase in precipitation and a 1.1 to 1.2 °C decrease in temperature compared with present conditions. In the early 18th century, glaciers started to retreat at varying rates until the late 19th to early 20th century; this trend was generally associated with decreasing accumulation rates. By contrast, glacier recession in the 20th century was mainly the consequence of an increase in temperature and humidity. These results are consistent with observations made in the study region based on other proxies.

La dynamique fluviale des vallées en gorge du rebord cévenol du Massif central est encore mal connue. L’étude des formations alluviales périglaciaires et actuelles dans le bassin du Chassezac (Cévennes) permet de retracer l’évolution des talwegs depuis la dernière période froide. On peut ainsi montrer qu’on est passé d’un lit würmien remblayé et caractérisé par des écoulements très compétents et une dynamique de tressage à un fond de gorge où alternent des secteurs rocheux et des bancs caillouteux qui traduisent un déficit sédimentaire. La répartition longitudinale de ces formes alluviales, inféodée à celle des vestiges périglaciaires comme leur composition granulométrique très grossière, pose le problème de la mobilité de la charge de fond actuelle. L’étude lichénométrique des unités alluviales permet de déterminer la relation liant la taille des particules aux puissances spécifiques nécessaires à leur mise en mouvement. On peut alors prolonger la courbe enveloppe de la mobilité pour des blocs dont le diamètre est compris entre 100 cm et 230 cm, valeurs absentes de la littérature jusqu’ici, et montrer en même temps que seuls les débits exceptionnels (supérieurs à 2 500 m3/s) sont morphogènes à l’Holocène. The fluvial dynamics of the gorge valleys of the Cévennes, in the southeastern part of the French Massif central, are not well known. The study of the Pleistocene and present-day alluvial forms in the Chassezac watershed have allowed us to reconstruct the evolution of thalwegs since the last Pleistocene cold period. Field observations suggest that the Würmian thalweg was filled with alluvium and characterised by flow conditions of high competence with braided channels. The Holocene channel consists of a combination of bedrock reaches and boulder bars. The spatial distribution of these bars, controlled by the location of inherited periglacial alluvium, and their very coarse grain size, suggest that the mobility of the bedload is now limited. A lichenometric study of bedload has allowed us to determine the relationship between grain size and stream power, in the range of diameters from 1 to 2.3 m. The results reveal that only exceptional discharges (i.e. 2 500 m3.s-1 and more) are effective for removing the coarse bedload and for shaping the alluvial features during the Holocene.

Le Changement climatique global observé depuis la fin du Petit Age glaciaire en Islande entraîne un retrait généralisé des fronts glaciaires. Ce retrait engendre de nouvelles dynamiques sur les surfaces déglacées, liées à la libération d’eau de fonte et à la détente postglaciaire. La datation par la lichénométrie des arcs morainiques et des terrasses fluviatiles permettent de reconstruire l’évolution des marges proglaciaires du Morsárjökull et du Skaftafellsjökull (sud-est de l’Islande) depuis la fin du Petit Âge glaciaire. Les versants sont le théâtre d’importants processus d’éboulisation et de chutes de blocs, tandis que l’on observe des phénomènes d’incision et de diminution du tressage au niveau des cours d’eau.The Global Warming which occurs since the end of the Little Ice Age in Iceland leads to the retreat of the glacier fronts. This retreat has induced new dynamics in the glacier foreland, especially related to glacial meltwater and post-glacial release. Lichenometrics measures on moraines ridges and paleosandurs provide us the opportunity to reconstruct the evolution of the proglacial areas of the Morsárjökull and the Skaftafellsjökull (South-east Iceland) since the end of the Little Ice Age. Important processes of rockslides and rockfalls occur on slopes, whereas proglacial rivers undergo phenomena of incision and abandon of minor channels.

Dating moraines by lichenometry enabled us to reconstruct glacier recession in the Bolivian Andes since the Little Ice Age maximum. On the 15 proglacial margins studied, we identified a system of tell principal moraines that marks the successive positions of glaciers over the last four Centuries. Moraines were dated by perl'onning statistical analysis of lichen rneaSUrenients based on the extrerne values theory. Like glaciers ill many mid-latitude mountain areas, Bolivian glaciers reached their maximal extent during the second half of the 17th century. This glacier maximum coincides with the Maunder minimum of solar irradiance. By reconstructing the equilibrium-line altitude and changes in mass-balance, we think the glacier maximum may be due to a 20 to 30% increase in precipitation and a 1.1 to 1.2 degrees C decrease in temperature compared with present conditions. In the early 18th century, glaciers started to retreat at varying rates until the late 19th to early 20th century; this trend was generally associated with decreasing accumulation rates. By contrast, glacier recession in the 20th century was mainly the consequence of an increase in temperature and humidity. These results are consistent with observations made ill the study region based on other proxies.

International audience; Depuis la fin du petit age glaciaire, les langues glaciaires sud-islandaises ont enregistre un recul prononce qui modifie a priori les conditions hydrosedimentaires offertes aux cours d'eau proglaciaires. A partir de datations lichenometriques et de mesures topographiques, cette etude montre que l'ajustement des sandar proximaux au recul glaciaire s'effectue en deux phases. La premiere correspond au temps de reponse du sandur, durant lequel l'incision de la plaine fluvio-glaciaire proximale est empechee soit par la stagnation du front glaciaire soit par un apport de sediments d'origine paraglaciaire. La seconde correspond au declenchement de l'incision du sandur proximal lorsque l'apport de sediments paraglaciaires n'est plus suffisant pour maintenir la plaine fluvio-glaciaire dans un etat stable. Lors de cette seconde phase, la vitesse d'incision du sandur proximal a tendance a ralentir au fur et a mesure que le front du glacier recule. La question de l'impact des re-avancees glaciaires sur la vitesse d'incision du sandur proximal est posee. En realimentant le stock sedimentaire de la marge proglaciaire, les re-avancees glaciaires seraient en mesure de provoquer un ralentissement quasiment immediat de l'incision du sandur proximal. Since the end of the Little Ice Age, glacial outlets of southern Iceland have undergone a substantial retreat, which has modified hydrological and sedimentological settings and caused fluvial adjustments. Based on lichenometric dating and topographical measurements, this study demonstrates that proximal sandar adjustment to glacier retreat follows two distinctive stages. The first one can be regarded as the reaction time of the sandur, during which the incision of the outwash plain is inhibited due to glacier front stagnation or paraglacial sediment release, which maintains the marginal sediment budget in a stable state. The second stage is characterized by the proximal sandur incision, which is triggered from the moment when the paraglacial sediment supply is insufficient to keep the sandar stable. During the second stage, the proximal sandur incision rate decreases as the glacier front retreats. The effect of glacier front readvances on the rate of proximal sandur incision is discussed. We found that glacier readvances could be able to slow down the proximal sandur incision, without time lag, by enhancing the marginal sedimentary stock.

The chronology for the younger Marquee and Arrowsmith moraine sets of the Cameron Glacier is revised. This is done by using new lichen growth curves for Rhizocarpon geographicum and R. candidum, developed for moraines of the Mueller Glacier at Mount Cook and calibrated with ages determined from rock weathering rind thicknesses. A new rock weathering rind curve was established for this purpose. The new lichenometric dates (greatest age estimated by either lichen, years B.P.) for the Cameron Glacier moraines are: Arrowsmith set: A1 c.170|A2 c.410|A2b c.480|A3 c.1010;A4 c. 1480|A5 c. 1960|Younger Marquee set: B1 c. 2320|B2 c. 3080|B3 c. 4480|B4 c. 5390. The kinds of vegetation and soils on the morainic time series are briefly indicated.

Geomorphic features as indicators of climatic fluctuations in a periglacial environment, northern Sweden

The relative ages of Neogfacial deposits above 2900m near Cloudveil Dome, Middle Teton, and Teepe glaciers, central Teton Range, western Wyoming, were determined using topographic position, weathering features, lichenometry, vegetation characteristics, and soils. A three-fold deposit sequence is identified and correlated with the Gannett Peak, Audubon and Indian Basin Neoglacial advances described elsewhere in the Teton and nearby Wind River ranges. While soil profile morphology proved very useful in distinguishing deposits of different age, other age indicators such as clay mineralogy and soil chemistry, proved of only marginal value in age discrimination. This chronosequence, emplaced over the last ∼5000yr, provides an excellent setting upon which to test changes in plant species composition and its use as a relative dating method. Vascular plant species composition cannot be used to discriminate deposits of the different advances, possibly because of random colonisation and establishment combined with extensive mass wasting during the Neoglacial. However, certain vegetation features, such as total cover and species densities, appear useful as relative dating methods.

In this paper, we discuss the advantages and drawbacks of the most classical approaches used in lichenometry. In particular, we perform a detailed comparison among methods based on the statistical analysis of either the largest lichen diameters recorded on geomorphic features or the frequency of all lichens. To assess the performance of each method, a careful comparison design with well-defined criteria is proposed and applied to two distinct data sets. First, we study 350 tombstones. This represents an ideal test bed because tombstone dates are known and, therefore, the quality of the estimated lichen growth curve can be easily tested for the different techniques. Secondly, 37 moraines from two tropical glaciers are investigated. This analysis corresponds to our real case study. For both data sets, we apply our list of criteria that reflects precision, error measurements and their theoretical foundations when proposing estimated ages and their associated confidence intervals. From this comparison, it clearly appears that two methods, the mean of the n largest lichen diameters and the recent Bayesian method based on extreme value theory, offer the most reliable estimates of moraine and tombstones dates. Concerning the spread of the error, the latter approach provides the smallest uncertainty and it is the only one that takes advantage of the statistical nature of the observations by fitting an extreme value distribution to the largest diameters.

This paper is a comparison and compilation of lichenometric and geomorphic studies performed by two independent teams in the Cordillera Blanca, Peru, in 1996 and 2002 on 66 “Little Ice Age” moraines of 14 glaciers. Using eleven new control points, we recalibrated the initial rapid growth phase of the previously established Rhizocarpon subgenus Rhizocarpon growth curve. This curve was then used to estimate the age of “Little Ice Age” moraines. The time of deposition of the most prominent and numerous terminal and lateral moraines on the Pacific-facing side of the Cordillera Blanca (between AD 1590 and AD 1720) corresponds to the coldest and wettest phase in the tropical Andes as revealed by ice-core data. Less prominent advances occurred between AD 1780 and 1880.

International audience; To date glacial and periglacial landforms, lichenometry is a valuable method but, to improve efficiency, the estimated surface dates derived from traditional methods need to be more accurate. In other words, the statistical uncertainty associated with inferred dates has to be reduced. How to perform such a reduction is the main question that we will address in this paper. An interdisciplinary approach (lichenometry and statistics) allows reduction in the main sources of uncertainty: lichen diameters and their associated ages. Around 2600 lichen measurements collected on moraines from the Charquini glacier in Bolivia (Cordillera Real) are used to illustrate the advantages of our approach over past studies.As for any statistical estimation procedure, the error analysis in lichenometry is directly linked to the type of observations and the statistical model used to represent accurately these data. The attribute of lichenometry studies is that the measurements are not averages but maxima; only the largest lichen diameters provide information about the surface ages. To take this characteristic into account, we propose a novel statistical way to model maximum lichen diameters. Our model, based on the extreme value theory, allows us to compute small confidence intervals for the inferred surface ages. In addition, it offers three other advantages: (1) a global statistical model, as all our data (dated surfaces and all lichen maximum diameters) are represented with a unique function; (2) a mathematical framework within which the maximum lichen distribution is derived from a statistical theory; and (3) flexibility, as different types of growing curves can be investigated.

We focused our study on the retreat of a typical valley glacier Kashkatash, located in the Elbrus Area. We compared the old photographs of the glacier forefields (H. Burmester, 1911; H. Altberg, 1927; E.N. Lukasheva, 1932; unknown author, 1939) with the aerial photograph of 1957, 1965, 1987, maps of scale 1:100 000 (1890) and 1:25 000 (1950s), satellite images (CORONA of 1971, ASTER of 2005, EROS of 2006), oblique photographs taken in 1980s – 2000s and plans, created by different researches. Using cartographic material and old photographs we reconstructed 14 positions of glacier tongue over the last 120 years. We estimated the linear glacier retreat and the age of numerous stadial moraines basing on geomorphic, tree-ring and lichenometric data and correlated our results with previous sparse glacier fluctuation reconstructions in this region. We identified at least 13 end moraines within the distance of 900 meters from the up-to-date glacier front position. The minimum age of the outer moraine is 450 years according to the tree-ring data. One tree growing on this moraine was damaged by a boulder falling down from a younger moraine under formation in the period from autumn 1839 to spring 1840. Three moraines were deposited in 1870s – 1890s. In 20 th century the glacier advanced in 1910-s, 1920-s, and 1970 – 1980-s.

Based on remote mapping and field studies inGrand Rapids, Tumansky,Hasynsky,Del-Urechen Ridges as well as Dukchinsky and Kilgansky Mountain Massifs there were identified about 1160 landforms which morphologically are similar to the rock glaciers or they develop in close association with them. Besides tongue-shaped cirque rock glaciers originated due to ablation, a large number of lobate-shaped slope-associated rock glaciers were recognized. Significant quantity of such forms are developing within the active neotectonic areas, in zones of seismic-tectonic badland and in association with active earthquakes-controlling faults. Multiplication of regional data on volcanic-ash-chronology, lichenometry, Schmidt Hammer Test, pollen spectra and single radiocarbon data, most of the active rock glaciers were preliminary attributed to the Late Holocene.

In this article we present the reconstruction of fluctuations of Alibek valley glacier situated in the Teberda valley, Western Caucasus. The former positions of glacier of the past 120 years were reconstructed basing on the old photographs of 1904, 1921, remote sensing data of 1955, 1987, 2007, 2008 and 2012, plans created in 20th century. Since the middle of 20th century Alibek Glacier decreased by 650 m in length and by 0,67 km2 in area and its tongue has risen by 110 m.

Cerro Charquini, Bolivia (Cordillera Real, 5392 ma.s.l.) was selected as a site to reconstruct glacier recession since the maximum of the Little Ice Age (LIA) in the central Andes. Five glaciers, located on differently exposed slopes, present comprehensive and well-preserved morainic systems attributed to former centuries. The moraines were dated by lichenometry and show a consistent organization on the different slopes. The past geometry of the glaciers was reconstructed using ground topography and aerophotogrammetry. Lichenometric dating shows that the LIA maximum occurred in the second half of the 17th century, after which the glaciers have receded nearly continuously. Over the last decades of the 20th century (1983–97), recession rates increased by a factor of four. On the northern and western slopes, glaciers receded more than on the southern and eastern slopes (by 78% and 65% of their LIA maximum area, respectively). The mean equilibrium-line altitude (ELA) rose by about 160 m between the LIA maximum and 1997. Recession rates were analysed in terms of climatic signal, suggesting that glacier recession since the LIA maximum was mainly due to a change in precipitation and that the 19th century may have been drier. For the 20th century, a temperature rise of about 0.6°C appears to be the main cause of glacier recession. Recent climatic conditions from 1983 to 1997 correspond to a mass deficit of about 1.36m w.e.a–1. If such conditions persist, the small glaciers below 5300ma.s.l. in the Cordillera Real should disappear completely in the near future.

International audience; Holocene glacier variations pre-dating the Little Ice Age are poorly known in the western Alps. Studied for two centuries, the Miage morainic amphitheatre (MMA) is composed of three subconcentric sets of c. 25 moraines. Because of its location and of a dominant mode of morainic accretion, the MMA is a well-preserved marker of the glacier dynamics during the Neoglacial. Radiocarbon dates were obtained by digging and coring in inter-morainic depressions of the MMA and through a deep core drilling in a dammed-lake infill (Combal); complementary data for the inner MMA were obtained by lichenometry and dendrochronology. Radiocarbon chronology shows that (i) the MMA not only pre-dates the Little Ice Age (LIA), but was built at least since 5029–4648 cal. yr BP (beginning of the Neoglacial); (ii) outer sets of moraines pre-date 2748–2362 cal. yr BP; (iii) the MMA dammed the Lake Combal from 4.8 to 1.5 cal. kyr BP, while lakes/ponds formed inside the moraines (e.g. from 2147–1928 to 1506–1295 cal. yr BP). The ‘Neoglacial model' proposed here considers that the MMA formed during the whole Neoglacial by a succession of glacier advances at 4.8–4.6 cal. ky BP (early Neoglacial), around 2.5 cal. ky BP (end of Göschener I), at AD 600–900 (end of Göschener II) and during the LIA, separated by raising phases of the right-lateral moraine by active dumping because of the Miage debris cover.

The evolution of about fifteen glaciers of the Bolivian Eastern Cordillera (16-17°S; 68°W), since their Little Ice Age (LIA) maximum till the late 20th century, has been reconstructed on the basis on ten main moraines observed on the glacier forelands and six aerial photographs. A correspondence between the moraines from a glacier margin to another has been established using geomorphological criteria. These moraines have been dated by lichenometry (Rhizocarpon geographicum s.l.) using a new statistical method based on the extreme values theory. Glacier maximal extent has been dated from the second half of the 17th century. Glaciers kept, until the first half of the 18th century, a quite similar position. From the 1730s – 40s, they began to retreat nearly continuously. The most important moraines attest to periods of standstill or small advances which were never strong enough to remove former moraines. Glacier retreat accelerated during the late 19th and early 20th centuries. Over the 20th century retreat remains fast. Over the whole studied period, glaciers lost about 60% of their maximal extent and the ELA rose by about 135 m. Moraines' dating as well as Bolivian glaciers' evolution since the late 19th century are in good agreement with data available in other places of the tropical Andes such as in Peru and Equator. A synchronism in glacier evolution at a regional scale due to a common climatic forcing can be stressed. We suppose that the Bolivian glaciers' maximal extent was forced by enhanced precipitation (20 to 30% higher than current mean) and reduced temperature (0.4 to 0.6°C lower than current mean). In addition, we can note the concomitance between periods of low solar activity and periods of glacier advances. Retreat from the first half of the 18th century could be mainly due to a decrease in precipitation. These hypothesis agree with the results obtained from the scarce climate proxies available in this part of the Andes such as the ice core retrieved in the southern Peru Quelccaya ice cap. During the late 19 – early 20th century, numerous and intense El Niño events, pointed out by several indicators, could be responsible of the accelerated glacier recession which precipitated the LIA ending in the tropical Andes. Unlike the former periods during which glacier evolution appears to have been mainly controlled by precipitation, their retreat during the 20th century seems to have been the result from a combined increase in temperature and humidity., L'évolution d'une quinzaine de glaciers de la Cordillère Orientale de Bolivie (16-17°S ; 68°W), depuis leur phase d'extension maximale du Petit Age Glaciaire (PAG) jusqu'à la fin du 20ème siècle, a pu être reconstruite sur la base des dix principales moraines observées sur les marges proglaciaires et de six couples de photographies aériennes. L'ensemble des moraines, dont la correspondance géomorphologique a pu être établie d'un glacier à l'autre, a été daté par lichenométrie (Rhizocarpon geographicum s.l.) en utilisant une nouvelle méthode de traitement statistique des données basée sur la théorie des valeurs extrêmes. Le maximum d'extension des glaciers est daté de la deuxième moitié du 17ème siècle. Les glaciers ont gardé, jusque durant la première moitié du 18ème siècle, une position quasiment équivalente à ce maximum. A partir des années 1730-40 s'amorce une phase de retrait continue des glaciers. Les moraines les plus importantes attestent de périodes de stagnation des fronts ou de réavancées n'ayant cependant jamais été d'ampleur suffisante pour remanier les dépôts morainiques précédemment mis en place. La fin du 19ème et le début du 20ème siècle sont marqués par une accélération du recul des glaciers. Durant le 20ème siècle, la décrue reste rapide. Sur l'ensemble de la période d'étude, les glaciers enregistrent une perte moyenne de près de 60% de leur surface maximale, ce qui correspond à une remontée d'environ 135 m de l'altitude de leur ligne d'équilibre. Les datations du maximum du PAG et des stades morainiques ultérieurs, aussi bien que l'évolution des glaciers boliviens depuis la fin du 19ème siècle sont concordants avec les données disponibles dans d'autres massifs des Andes intertropicales, notamment au Pérou et en Equateur. On émet l'hypothèse d'un synchronisme de l'évolution des glaciers à l'échelle régionale en réponse à un forçage climatique commun. L'interprétation paléoclimatique des données obtenues permet de supposer que l'extension maximale des glaciers boliviens correspond à une période pendant laquelle les précipitations étaient supérieures de 20 à 30% à leur niveau actuel et les températures inférieures de 0,4 à 0,6°C. En outre, on note la concomitance entre les périodes de moindre activité solaire et celles d'avancée des glaciers. Le retrait, à partir de la première moitié du 18ème siècle, serait en grande partie dû à une baisse des précipitations. Ces hypothèses sont en accord avec les indications issues d'autres « proxies » du climat, encore peu nombreux dans cette région des Andes, que sont par exemple les carottes de glace extraites de la calotte glaciaire de Quelccaya au sud du Pérou. L'occurrence de nombreux et intenses phénomènes El Niño à la fin du 19ème et au début du 20ème siècle, mise en évidence par plusieurs indicateurs, pourrait être responsable de l'accélération du retrait des glaciers à cette période et aurait sans doute précipité la fin du PAG à l'échelle des tropiques andins. Contrairement aux périodes précédentes pendant lesquelles l'évolution des glaciers semble avoir été principalement contrôlée par les précipitations, leur retrait durant le 20ème siècle apparaît comme résultant d'une hausse combinée des températures et de l'humidité.

International audience; Fluctuations of the Charquini glaciers (Cordillera Real, Bolivia) have been reconstructed for the Little Ice Age (LIA) from a set of 10 moraines extending below the present glacier termini. A lichenometric method using the Rhizocarpon geographicum was used to date the moraines and reconstruct the main glacier fluctuations over the period. The maximum glacier extent occurred in the second half of the 17th century, followed by nearly continuous retreat with three interruptions during the 18th and the 19th centuries, marked by stabilisation or minor advances. Results obtained in the Charquini area are first compared with other dating performed in the Peruvian Cordillera Blanca and then with the fluctuations of documented glaciers in the Northern Hemisphere. Glacier fluctuations along the tropical Andes (Bolivia and Peru) were in phase during the LIA and the solar forcing appears to be important during the period of glacier advance. Compared with the Northern Hemisphere mid-latitudes, the major advance observed on these glaciers during the first half of the 19th century is not present in the tropical Andes. This discrepancy may be due to regional scale climate variations.

A new approach to regional lichenometric dating is developed and applied to‘Little Ice Age’ moraine-ridge sequences on 16 glacier forelands in Jotunheimen, southern Norway. Lichenometric-dating curves, based on the Rhizocarpon subgenus, are constructed independently for west, central and east Jotunheimen. Although there are differences between the subregions, a composite regional moraine chronology for Jotunheimen identifies 12 episodes of moraine formation in AD 1743-1750 (the regional‘Little Ice Age’ glacier maximum), 1762-1771, 1782-1790, 1796-1802, 1811-1818, 1833-1838, 1845-1854, 1860-1868, 1871-1879, 1886-1898, 1915-1922 and 1927-1934. Spatial and temporal patterns in glacier behaviour between the subregions and between Jotunheimen and the neighbouring Jostedalsbreen are explained in terms of the interaction of annual to decadal variations in summer temperature and winter precipitation: glacier advances and moraine-formation events driven primarily by winter-precipitation variations exhibit subregional patterns while summer-temperature forcing affects more synchronous glacier behaviour across the region. Regionally controlled lichenometric dating improves the accuracy of dating by up to about±20 years on relatively old moraines and is dependent on regional patterns in the rate of lichen growth. On relatively young surfaces, mean cumulative growth rate declines from about 0.75mm yr-1in maritime west Jotunheimen to about 0.55mm yr-1in continental east Jotunheimen (though the differential in growth rate is less on older surfaces).

Fluctuations of the Charquini glaciers (Cordillera Real, Bolivia) have been reconstructed for the Little Ice Age (LIA) from a set of 10 moraines extending below the present glacier termini. A lichenometric method using the Rhizocarpon geographicum was used to date the moraines and reconstruct the main glacier fluctuations over the period. The maximum glacier extent occurred in the second half of the 17th century, followed by nearly continuous retreat with three interruptions during the 18th and the 19th centuries, marked by stabilisation or minor advances. Results obtained in the Charquini area are first compared with other dating performed in the Peruvian Cordillera Blanca and then with the fluctuations of documented glaciers in the Northern Hemisphere. Glacier fluctuations along the tropical Andes (Bolivia and Peru) were in phase during the LIA and the solar forcing appears to be important during the period of glacier advance. Compared with the Northern Hemisphere mid-latitudes, the major advance observed on these glaciers during the first half of the 19th century is not present in the tropical Andes. This discrepancy may be due to regional scale climate variations. To cite this article: A. Rabatel et al., C R. Geoscience 337 (2005). (c) 2005 Academie des sciences. Published by Elsevier SAS. All rights reserved.

In the area of Piz Corvatsch (Upper Engadin, Grisons, Switzerland), the actual vegetation on active and inactive rock glacier surfaces has been mapped. The floristic composition (vascular plants and lichens) of the different rock glacier surfaces has be en mapped and compared with photogrammetrical measurements of surface movements of the active rock glaciers. In general, the active rock glacier surfaces show a very low cover of vascular plants. Most of them are located at the edge and at the front of the rock glacier where fine-grained soil material occurs in small pockets. Lichenometry has been used as an additional method on Murtel rock glacier and on the protalus rampart. Measurements of Rhizocarpon geographicumthalli revealed increasing sizes from the root zone of the rock glacier to its front. On the Murtel rock glacier, Rhizocarpon geographicumthalli with a diameter > 4cm occur on surfaces with ages between 5000 and 6000 years B.P. The statistical analysis (MULVA-5) of the dense vegetation cover of the inactive and relict rock glaciers revealed four plant sociological groups, which are composed of species reflecting well consolidated sites : alpine grassland, subalpine dwarf shrubs and small patches with single small trees of Swiss stone pine ( Pinus cembra) and larch (Larix decidua).

Lichens of the subspecies Rhizocarpon geographicum s.l were measured on 25 avalanche boulder tongues in the Massif des Ecrins to elucidate the Little Ice Age history of avalanche activity. Results show: (1) an increase of lichen size from the median to the distal zone of deposits, and a decrease from the edges to the centre; (2) three types of lichen settlement. From the uppermost to the median zone, lichens are absent, because avalanche activity is very active. Down-slope, lichens occur in two different zones: the median zone is colonized by 5–20 mm size lichens on sides of blocks protected from the abrasional action of avalanches, while in the distal zone lichen diameters are largest (>30 mm) and occur on all sides of the blocks. The spatial distribution of the lichens and their size according to elevation make it possible to distinguish different phases during which avalanche activity has increased. At high elevation, the avalanche activity was at a maximum before ad 1650 and between ad 1730 and 1830. During these two periods avalanches had sufficient magnitude to reach the basal zone of the deposits. At low elevation since ad 1650 the magnitude and frequency of avalanches have declined. Copyright © 2004 John Wiley & Sons, Ltd.

This paper describes software to accompany McCarroll, D. 1993. ‘Modelling late-Holocene snow-avalanche activity: incorporating a new approach to lichenometry’, Earth Surface Processes and Landforms18, 527–539; and McCarroll, D., Matthews, J. A. and Shakesby, R. A. 1995. ‘Late-Holocene snow-avalanche activity in southern Norway: interpreting lichen-size-frequency distributions using an alternative to simulation modelling’, Earth Surface Processes and Landforms20, 465–471.