Search

Tsunamis and storms cause considerable coastal flooding, numerous fatalities, destruction of structures, and erosion. The characterization of energy and frequency associated with each wave contribute to the risk assessment in coastal regions. Coastal boulder deposits represent a physical proof of extreme inundation and allow us to study the effects of marine floods further back in time than instrumental and historical records. Age estimation of these deposits is challenging due to lack of materials (such as sand, shells, corals, or organic matter) that retain information about the passage of time. Lichenometry, a simple age estimation method, which is cost-effective, quick to apply, and non-destructive, is here proposed as a solution. A lichen growth model for a calcium-tolerant lichen species was developed and used to estimate the age of a boulder deposit related to extreme marine inundation(s) in Portugal. Estimated ages indicate several very recent events (

In arid landscapes across the globe, aeolian processes are key drivers of landscape change, but arid Arctic regions are often overlooked. In the Kangerlussuaq region of West Greenland, strong katabatic winds have removed discrete patches of soil and vegetation, exposing unproductive glacial till and bedrock. Although lake-sediment records suggest that landscape destabilization began approximately 1000 years ago, the upland soil erosion has never been directly dated. We use a novel application of lichenometry to estimate the rates and timing of soil erosion. We show that the formation of deflation patches occurred approximately 800–230 years ago, in general agreement with lake-sediment records. In West Greenland, the ‘Little Ice Age’ (AD 1350–1880) was characterized by a cold and arid climate, conditions that increased susceptibility to erosion. On average, deflation patches are expanding at a rate of 2.5 cm yr−1, and variation in the rate of patch expansion cannot be explained by proximity to the Greenland Ice Sheet (GrIS), slope, aspect, elevation, or patch size. An erosional threshold exists in this aeolian system, with climate conditions necessary for patch formation likely harsher than those necessary for continued patch expansion, a result that has implications for land management in arid regions. Currently, deflation patches are expanding throughout the study region and are forming in areas close to the GrIS, but future deflation rates are dependent on projected climate and potential land-use changes. Our results stress the importance of aeolian processes in arid polar landscapes such as Kangerlussuaq, and demonstrate the use of aeolian landforms in paleoclimate reconstructions and predicting future landscape change.

Coarse-grained flood deposits, including 52 discrete berms, bars, terraces, splays and sheets, were investigated along a 6.6 km stretch of the Leira river, in a catchment containing several alpine glaciers. These landforms were mapped, characterized in terms of clast size and reconstructed hydrological parameters, and dated using several techniques with differing temporal range and resolution. High-resolution lichenometric dating indicated that 60–65% of the deposits date from the 20th century whereas 5.7% are 300–600 years old. In contrast, low-resolution Schmidt-hammer exposure-age dating (SHD) indicated that 85% of deposits have an age

In the context of reconstruction of Holocene glacier chronologies, there has been a clear tendency during the past few decades towards imprecise use of the term ‘high resolution’. Furthermore, it seems to be increasingly assumed that recently developed terrestrial cosmogenic nuclide dating (TCND) is replacing earlier dating methods. Although recent glaciological knowledge clearly reveals the futility of oversimplified global and inter-hemispheric correlation on the basis of few ‘key’ sites, such comparisons are widely attempted. Stimulated by the example of a recently published article relating to the Southern Alps of New Zealand (Schaefer et al., 2009, Science 324: 622—625) we highlight some related potential problems with the interpretation of Holocene glacier chronologies. In particular, we consider (1) that the term ‘high resolution’ should be applied only to decadal-scale resolution or better and, therefore, not to TCND-based chronologies; (2) that discontinuous moraine chronologies should not be termed high resolution and that their potential geomorphological limitations should be acknowledged; and (3) that TCND-based moraine chronologies should not automatically replace evidence available from other dating techniques but that they should be regarded as complementary and an opportunity for mutual evaluation. Owing to local and regional patterns in glacier response to climate, it is concluded (4) that intra-hemispheric synchroneity in high-resolution Holocene glacier variations is still unproven, and hence (5) that inter-hemispheric comparison is arguably premature, if not impossible. Finally, it is suggested (6) that the first priority for research in this field should be to establish the spatial patterns in glacier behaviour evident at various scales in Holocene records.

Glaciar León is a temperate, grounded outlet of the eastern North Patagonian Icefield (NPI). It terminates at an active calving margin in Lago Leones, a 10 km long proglacial lake. We take a multidisciplinary approach to its description and use ASTER imagery and clast sedimentology to describe the geomorphology of the glacier and its associated moraines. We date periods of glacier retreat over the last 2500 years using a combination of lichenometric, dendrochronological, cosmogenic and optically stimulated luminescence techniques and show that the glacier receded from a large terminal moraine complex some 2500 years ago and underwent further significant recession from nineteenth-century moraine limits. The moraine dates indicate varying retreat rates, in conjunction with significant downwasting. The bathymetry of Lago Leones is characterized by distinct ridges interpreted as moraine ridges that dissect the lake into several basins, with water depths reaching 360 m. The fluctuations of Glaciar León appear to have been controlled by the interplay between climatic forcing and calving dynamics.

Based on lacustrine and morpho-stratigraphical evidence from Lyngen in Troms, northern Norway, 13 marginal moraines have been mapped in front of Lenangsbreene in Strupskardet. Moraines M1-M13 are inferred to represent glacier halts or advance/readvance taking place during the Lateglacial and Holocene. The presence of collapse depressions suggests that some of them were ice cored (M1-M3). A chronological framework, taking into account a combination of former shorelines and related glacier-meltwater channels, lichenometry and AMS radiocarbon-dated lacustrine sediments spanning the last 20 000 cal. yr BP, has been established. The distal glacier-fed lake Aspvatnet was isolated from the sea c 10 300 cal. yr BP, and the lacustrine sediments have been investigated by use of loss-on-ignition (LOI) magnetic susceptibility, water content, wet and dry bulk density (DBD), and the magnetic parameters anhysteretic remanent magnetization (ARM) and saturation remanent magnetization (SIRM). There is, in general, good agreement between physical sediment parameters and magnetic parameters. DBD, a combination of medium and fine silt and the two statistical parameters ‘sorting’ and ‘mean’ have been used to construct a high-resolution glacier-fluctuation curve for the last 3800 cal. yr BP. Based on an accumulation-area ratio (AAR) of 0.6 and an ablation-accumulation balance ratio (ABR) approach, a continuous temperature-precipitation-wind equilibrium-line altitude (TPW-ELA) curve for the last 20000 cal. yr BP has been constructed. Using an established exponential relationship between mean ablation-season temperature and mean annual solid precipitation at the ELA of Norwegian glaciers, variations in mean winter precipitation (snow) are quantified using an independent proxy for summer temperature. Mean annual winter precipitation varied from 500 to 5000 mm water equivalent, and on average, Holocene estimates are c. 50% higher than similar figures from the Lateglacial. The two driest periods occurred during Heinrich events 1 (HI) (17 500-16 500) and 0 (HO) (13 000-12 200), whereas freshwater pulses to the North Atlantic had apparently no systematic impact on mean winter precipitation. Based on the winter precipitation curve from Lyngen, the atmospheric circulation responded to the sea surface temperature (SST) lowering associated with HI and HO. The dry and cold climate during the events led to formation of talus-derived rock glaciers at sea level.

On examining the scientific literature of recent years, one notices an increase in the number of studies of global warming and its impact on the Earth’s various environments. Research has been undertaken in various fields such as geomorphology, hydrology and many others. In the context of climatic change, there is growing interest in the study of past floods, or palaeofloods. Researchers are attempting to reconstitute the chronology of past floods, especially with respect to past or subrecent climatic changes. The work involves using different methodological approaches borrowed from various disciplines including geology, geomorphology and ecology. The reconstruction of ancient hydrological events such as palaeofloods in fact requires that different methods and techniques be combined in order to trace the chronology of events as precisely as possible using different biophysical parameters. A wide variety of indicators are used in the chronological reconstruction of ancient fluvial environments, whether in humid, subhumid or desert regions. These indicators involve analysing stratigraphic sequences and sedimentary deposits, organic matter and macrorest deposits, as well as using radiocarbon dating(14C), thermoluminescence (TL), and dendrochronology and lichenometry. In fact, most work on the reconstitution of the frequency and magnitude of ancient floods uses several methods and techniques to obtain the long-term chronology of flood events in relation to the specific conditions (e.g., climate, geomorphology) of a region or study area. With the publication of several studies in palaeohydrology, it was interesting to examine, through a literature review, the various approaches used in the study of palaeofloods. This kind of study has seen major advances, which can be explained partly by the interest generated by global climate change and its effect on river-system dynamics.

Lichenometric dating studies using the yellow-green Rhizocarpon subgenus at the Eugenie, Hooker, Mueller and Tasman Glaciers in Mt Cook National Park, Southern Alps, New Zealand, reveal a ‘Little Ice Age’ maximum during the mid-eighteenth century (around AD 1725-1740). Lichenometric dating curves, constructed for Mueller Glacier in a preliminary study, were modified using local control points at the other glaciers. Modification was necessary because of variations in local ecological conditions. The ‘Little Ice Age’ chronology is similar for three out of the four glaciers studied. All except Tasman Glacier underwent a major glacier front oscillation directly following the ‘Little Ice Age’ maximum. After a slow but constant retreat during the second half of the eighteenth and the first half of the nineteenth centuries, the glaciers experienced major readvances during the second half of the nineteenth century (around AD 1860 and 1890/95), and during the early decades of the twentieth century. Tasman Glacier, as the exception, returned to its ‘Little Ice Age’ maximum frontal position during the late nineteenth century, overtopping pre-existing ‘Little Ice Age’ moraines, and therefore preventing detailed dating of these moraines. Differences in dating from previous lichenometric studies may be due to the different methods used.

Lichenometric evidence and Schmidt hammer R-values are used to date Holocene moraine sequences in front of six high-altitude (> 1500 m) glaciers in Breheimen, central southern Norway. At three glacier forelands with southerly aspects (Høgsetbreen, Vestre Høybre and Østre Høybre), relatively small (≤4 m high) discrete boulder moraine ridges are shown to date from the ‘Little Ice Age’. The remaining three glaciers (Østre Tundradalskyrkjabre, Nordre Tundradalskyrkjabre and Hestdalshøgdibreen), with northerly or easterly aspects and large, multiridged, rampart-like moraine complexes (15-30m), thought to be ice-cored and of the ‘push-deformation’ type, lie above the local altitudinal limit of permafrost. Negatively skewed R-value distributions from these moraine complexes provide critical evidence for pre-‘Little Ice Age’ glacier expansion as they indicate the survival of long-weathered boulders on moraine surfaces where late-lying snow may reduce or prevent lichen growth. Formation of the moraine complexes appears to have begun in Preboreal times, most likely during the Erdalen Event, but much of their present character was determined by repeated Neoglacial glacier expansion, moraine deformation and ridge formation in the late Holocene, culminating in the ‘Little Ice Age’ readvance.

A small-scale rock-slope failure firmly dated by historical photographic evidence, supported by lichenometry, to between ad 1977 and 1991 is described from the glacier foreland of Marzellferner and Schalf ferner, Ö tztal Alps, Austria. There was a timelag of 90–100 years between deglacierization of the site around ad 1890 and slope failure. An extreme rainfall event in ad 1987 is suggested as the most likely trigger factor affecting a rock slope weakened by several possible processes including debuttressing (producing dilation joints), fluctuating cleft-water pressure, and permafrost aggradation and degradation. The rock topple is considered to represent an example of subaerial geomorphological processes conditioned by‘Little Ice Age’ glacierization; similar neoparaglacial effects can be expected to follow other neoglacial events.

Lake sediments from Waskey Lake, Ahklun Mountains, southwestern Alaska were studied to decipher the history of upvalley glacier fluctuations during the Holocene. Several indicators of glacier activity were measured including: magnetic susceptibility, organic-matter content, grain-size distribution, bulk-sediment mineralogy and diatom assemblages. Seven radiocarbon ages on macrofossils, along with cross-checks by tephrochronology, provide the chronology of the cores. The results from core WL-1 indicate that glaciers lingered near Waskey Lake until 9100 cal. yr BP, perhaps under conditions of high winter accumulation. Peak organic-matter content occurs at 7400 cal. yr BP, when precipitation might have shifted to summer. The onset of Neoglaciation occurred 3100 cal. yr BP, and glaciers reached their maximum extenñ700 cal. yr BP. This chronology is consistent with the lichenometrically dated moraines from the glacier forefields. Although the ages are tentative, the youngest and most widespread group of moraines was deposited sometime between 650 and 200 cal. yr BP (during the‘Little Ice Age’). Since then, glaciers in the Waskey Lake area have shrunk bñ50% and equilibrium-line altitudes (ELA) have risen by 35± 22 m. This rise in ELA is much less than the 100 to 200 m rise observed elsewhere in Alaska and indicates considerable spatial variability in late-Holocene climatic change.

Lichenometric-dating studies using the yellow-green Rhizocarpon subgenus at Mueller Glacier in the region of Mt Cook, Southern Alps, New Zealand, reveal a ‘Little Ice Age’ maximum about ad 1725/1730. Differences from previous studies are shown to result from different methods, especially the type of mathematical functions used for calculating the lichenometric dating curves. Previous work also used variable sample sizes, distal moraine slopes, and, to some extent, different fixed points. Schmidt hammer measurements enable the differentiation of ‘Little Ice Age’ from pre-‘Little Ice Age’ frontal moraines in the outer glacier foreland and confirm the status of the ‘Little Ice Age’ as a separate glacier advance among several advances during the Holocene.

We present a late-Holocene glacial and environmental history of three valleys within Miki and I.C. Jacobsen Fjords, East Greenland (68°N). The fjords have no direct connection with the main ice sheet and are presently glacierized by a series of local ice caps and glaciers. Little sediment has been deposited within the study area, but bedrock is distinctly glacially striated, which suggests that extensive valley glaciers reached the present coastline in the past. Moraines are the prominent morphological features including distinct end and lateral moraines. Most of the moraines are related to the existing glaciers in the area. Apparent moraines extend as far as 2 to 2.5 km in front of present-day glaciers. Based on morphological and stratigraphical studies of the sediments in these valleys, five glacier advances during the late Holocene are implied. Stabilization of the oldest moraines is lichenometrically dated to c. 1450 to 1650 years ago. Younger moraines in both Miki and I.C. Jacobsen Fjords are lichenometrically dated to c. 1050–1100 years ago, c. 750–950 years ago and c. 600–700 years ago. The youngest moraines containing measurable lichens stabilized c. 300–400 years ago. The timing of this moraine formation correlates to marine records from previous research on the inner part of Miki Fjord, where apparent intensification in sediment stratification is related to a glacier advance into the fjord c. 290 years ago. This glacial advance may correlate to the‘Little Ice Age’ cooling observed in many records from the North Atlantic region. Our glacial record from Miki and I.C. Jacobsen Fjords also shows good correlation with temperature proxies within the GRIP ice core in Greenland and foraminifera records from Nansen Fjord, East Greenland. Less pronounced correlation is observed with the Icelandic Sea Ice Index and records of glacier fluctuation in Iceland during the last .1000 years. These results suggest that widespread climatic cooling was the direct cause of many of the late-Holocene glacier variations documented in this study, although the glacial advance at c. 1050–1100 years ago coincides with the so-called‘Medieval Warm Period’, and could reflect the response of glaciers to increased precipitation within the area.

This study employs sedimentological indices and lichenometric dating on the lichen species Plac opsis patagonica to investigate the nature and age of debris cones which have accumulated at the margins of the downwasting San Rafael Glacier in Chilean Patagonia. These cones appear to have accumulated by the resedimentation of glacigenic deposits by debris flows, with debris movement starting in the early 1980s. Cone activity follows a pattern of intense initial activity and sediment mobilisation followed by increased stability and colonization by vegetation. Three of the four cones had stabilized within 15 years of sediment movement initiation. These features may be seen as being conditioned by glacial activity with second order controls provided by the local climate and sediment supply. The cones have accumulated in a 'paraglacial' environment.

Further evidence for an early 'Little Ice Age' in the Sandane area, southern Norway, is presented in support of the lichen data of Evans et al. (1994) and in response to the reassessment of Matthews et al. (1996). The geomorphological evidence for three phases of moraine deposition is clarified and relative age dating based upon Schmidt hammer R-values and soil development is presented. These data, in combination with the lichenometry reported earlier, indicate that the moraines of the Jardalen/Fagerdalen cirque in particular are not all of the same age (pre 'Little Ice Age' as suggested by Matthews et al. (1996) but instead date either to post-Preboreal/Younger Dryas times (Stage 1 moraines) or to the 'Little Ice Age' (Stage 2 and 3 moraines). The gradual increase in lichen diameters, R-values and soil depths from the youngest 'Little Ice Age' (Stage 3) moraine to the outermost and oldest Stage 2 moraine lends further support to the suggestion that the 'Little Ice Age' in western Nor way may have begun much earlier than previously documented in the literature. Problems in using the Schmidt hammer for relative age dating in mountainous terrain, where the moraines being dated are often con structed from old glacial deposits and fresh rock fall debris, are also dis cussed.

Lichenometric dating of moraines deposited by eight glaciers in the northeastern Brooks Range suggests major glacial advances or stillstands at about 2600, 1000, 450, and 60 lichenometric (L) years BP. The latter two advances of the early-middle and latest part of the 'Little Ice Age', respectively, formed promi nent moraines at all glaciers studied. In response to overall twentieth-century warming, these glaciers have retreated at average rates of 2 to 19 m yr-1 from the distinct ridges formed in AD 1890. Glacier thinning at rates of 0.7 to 0.9 m yr-1 accounts for over 90% of the ice loss.

Evidence for the timing and extent of late-Holocene glacial advances in the Tian Shan mountains, central Asia, is based on lichenometric and radiocarbon dating of end-moraines. Three phases of glacial advance occurred at 1700-2100 and 1100-1300 lichenometric (L) years ago, and then during the 'Little Ice Age', 150- 700 (L) years ago. Differences in the pattern of glacier variations between the northwestern frontal and inner areas of the Tian Shan are reflected in the equilibrium line altitude (ELA) depression of 23 glaciers studied at nine selected sites. The peripheral glaciers appear to have been significantly more extensive during late- Holocene advances than the glaciers of the inner areas. This difference seems to be explained by regional differences in humidification: in the northwestern periphery of the Tian Shan, the cold periods of the late Holocene were more humid than the warm period of the mid-Holocene; whereas, in the inner areas, the pattern of climate changes was the opposite (a warm and humid mid-Holocene was followed by a cold and arid late Holocene).

A new approach to lichenometry, based on large samples of the single largest lichen on each boulder, is presented. On surfaces of uniform age, lichen sizes measured in this way are near normally distributed, so the mean value can be used in constructing lichenometric-dating curves. By combining mean values from several sites, statistically defined confidence limits can be assigned to predicted dates. In a pilot study, dates obtained for 'Little Ice Age' moraines of two glaciers in southern Norway are consistent with those obtained using other approaches. Unlike standard lichenometry, the new approach can be used to investigate the age-frequency of boulders on diachronous surfaces formed by continuous or periodic accretion or disturbance. It has been used successfully to access the record of late-Holocene snow avalanche activity retained on avalanche boulder ramparts in upper Jostedalen, western Norway. Pilot studies are also presented of its use on a talus slope, solifluction lobes and periglacial patterned ground. Although there are some problems and limitations to its use, in many circumstances these are likely to be outweighed by the advantages of the new approach over standard lichenometry.

Moraine sequences, protalus ramparts, rock glaciers and various slope deposits in seven separate glacier basins provide lichenometric ages for glacier retreat in an upland area of Sogn-og- Fjordane, southern Norway. Geomorphological mapping, relative dating based on section Rhizocarpon size-frequency distributions, observations on vegetation cover, and numeric dating based on a regional lichen dating curve for section Rhizocarpon, place moraines into three groups: Stage 1 moraines of likely Preboreal or Younger Dryas age; Stage 2 moraines of pre- or early 'Little Ice Age' but post-Preboreal age (thirteenth-fourteenth centuries); and Stage 3 moraines of fifteenth-century age and younger. The occurrence of thirteenth-sixteenth century (pre- or early 'Little Ice Age') moraines at low altitudes in the Sandane area is thought to relate to greater availability of moisture and to the capture of wind- drifted snow. These moraines are some of the oldest 'Little Ice Age' moraines dated by lichenometry in southern Norway. In some cirques, glaciers retreated from their fifteenth-century positions allowing protalus rampart development, scree accumulation and debris-flow activity to continue until the present.

Multiple geochronologic techniques, when used in an integrated approach, provide a powerful means of deciphering the stratigraphy of Holocene moraine sequences. The Jarvis Creek Ash, deposited across central Alaska at 3650 ± 125 BP, underlies a mid-Holocene lateral moraine of the Gulkana Glacier. This tephrochronological datum provides new control on long-term Rhizocarpon geographicum growth rates in central Alaska, and suggests that this species grows at approximately 4mm per century in the central Alaska Range. Lichenometry, together with tephrochronology and radiocarbon dates from buried organic horizons, indicate Holocene advances of the Gulkana Glacier occurred c. 5700 ± 260 BP, 4100 ± 800 BP, 3600 ± 700 BP, 800 ± 125 BP and 150-200 years ago.

The object of this paper is to reconstruct the history of glaciation and the dynamics of mudflow activity as part of the development of landscapes in the Aksay Valley, Kirgizsky Ridge, over the last 2000 years. Glacial, mudflow and slope deposits were dated by lichenometry and the radiocarbon method. The results of 14C dating of buried soils shows that at about 1700 BP a period of activization of slope processes took place in the valley. The zone of alpine meadow was situated at that time at an elevation of about 2750 m and glacier termini were situated at about 3100-3200 m. The oldest mudflow surface, which was investigated by lichenometry, dates from the same time. New equations for the rate of growth of the lichens Aspicilia tianshanica and Rhizocarpon geographicum use the oldest mudflow surface as a control point. Two periods of reduced mudflow activity are identified by lichenometry, i.e., 350-450 and 130-240 BP, and the latter is confirmed by 14C dating of peat-soil interlayers in a mudflow stratum with the specific activity of samples exceeding NBS standard. Thus, a new modification of the 14C-dating method is demonstrated. Lichenometry on moraines of the Aksay Glacier shows that advances of the glacier took place in the fourteenth and late- nineteenth centuries as well as at the beginning of this century. The depression of equilibrium-line altitude (ELA) for the fourteenth and nineteenth centuries was 150-170 m and 100-120 m, respectively.

Comparison of the equilibrium line altitudes (ELAS) for the present (1980s) and the maximum 'Little Ice Age' depression determined for glaciers in the Skíõadalur/Svarfaõardalur area of the Tröllaskagi peninsula, northern Iceland, shows a rise of c. 50 m over the last 100-150 years. Meteoro logical data suggest that over the same period the mean summer temperature at the equilibrium line changed by at least 2.0°C. Application of a model of the relationship between mean summer temperature and winter accumulation at the ELA for glaciers in southern Norway suggests that such a temperature change should have led to a movement of up to 300 m in the ELA. The discrepancy between the observed and expected results is accounted for by an almost two-fold increase in winter accumulation. The application of this model highlights the potential importance of interpreting changes in ELA in terms of both temperature and precipitation, and the results from northern Iceland demonstrate that in some areas accumulation changes can almost balance considerable changes in temperature. There is also potential through this method for hypothesizing atmospheric changes as explanations of the climatic changes interpreted.

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.

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.

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.