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Journal ArticleDOI

A Combination of Relative-Numerical Dating Methods Indicates Two High Alpine Rock Glacier Activity Phases After the Glacier Advance of the Younger Dryas

18 Jan 2011-The Open Geography Journal (Bentham Open)-Vol. 4, Iss: 1, pp 115-130

AbstractTo exploit the potential of rock glaciers as indicators of past climate condition it is first necessary to date them. The combined application of both relative and absolute dating techniques is a promising approach. In this study, we present Schmidt-hammer rebound value measurements and weathering rind thicknesses on four active and one relict rock glacier in the Albula area of the eastern Swiss Alps. Associated landforms such as the moraines in front of rock glaciers and glacially polished bedrock also were used to set up the temporal framework. This was done using soil chemical analyses, radiocarbon dating of the stable fraction of soil organic matter and surface exposure dating of boulders. Schmidt-hammer and weathering rind measurements showed, in most cases, well-pronounced trends with increasing surface ages. These values are in line with measurements from other nearby rock glaciers with comparable lithologies. Use of this information together with the numeric ages makes it possible to derive two main activity phases: one started soon after the ice retreat following the Younger Dryas, the main activity occurred most likely in the early Holocene and lasted approximately until the Holocene climate optimum. The second activity phase continues today and had an unclear start between 10 to 6 cal ky BP.

Topics: Rock glacier (69%), Weathering rind (62%), Absolute dating (61%), Glacier mass balance (60%), Surface exposure dating (59%)

Summary (3 min read)

INTRODUCTION

  • Rock glaciers as distinct tongue-shaped landforms are perennially frozen and ice-rich debris on non-glacierised mountain slopes creeps steadily under the influence of gravity [1].
  • With time, the surface of rock glaciers is increasingly subject to weathering processes.
  • Relative and numeric age dating by measuring the weathering rind thickness or the Schmidt-hammer rebound value was successfully performed on moraines and rock glaciers developed on sandstones in New Zealand [4-8], basaltic and andesitic boulders in North America and Japan [9, 10] and on granites and gneiss in the Alps [2, 11].
  • A ‘cross-check’ of these methods allows an extended interpretation and reciprocal control of the results.

STUDY AREA

  • The study area is located in the eastern Swiss Alps (Fig. 1).
  • The area of the Albula pass is characterised by many glacial and geomorphic features such as moraines, polished bedrock with roches moutonnées, scree slopes, rock glaciers, traces of glacial erosion (such as grooves, striations, etc.) and plucking processes.
  • The mean annual precipitation is rather low with around 900 mm in the lower parts near Preda and up to 1100 mm towards the mountain ridges [21].
  • While the active rock glaciers show a simple structure with a clearly identifiable rooting zone and a compact steep tongue, the conditions in case of the rock glacier Alvra are more complex.
  • In close vicinity, previously-reported data of a peat bog was available [25].

Schmidt-Hammer Rebound Values

  • The measured Schmidt-hammer rebound values for all rock glaciers are given in Fig. (8A-D).
  • The standard error after [30] was in most cases relatively small.
  • Close to the cirque, the values were usually near 50-55.
  • This suggests that the activity of rock glacier Alvra began soon after the retreat of the Egesen-age glaciers.
  • The measured Schmidt-hammer values at the distal front of these rock glaciers correspond approximately to the initial values of rock glacier Alvra (near 40-45).

Soil Chemistry and Physics

  • The soil samples were air-dried, large aggregates were gently broken by hand and sieved to <2 mm.
  • Total C and N contents of the soil were measured with a C/H/N analyser (Elementar Vario EL, Elementar Analysensysteme GmbH) using oven-dried and ball-milled fine earth.
  • Oven-dried samples were dissolved using a mixture of HF, HCl, HNO3, and H3BO3 in a closed system [38] (microwave oven and under high pressure, 25 bar).
  • Concentrations were determined by AAS (Atomic Absorption Spectrometry – AAnalyst 700, Perkin Elmer, USA).
  • The dithionite- and oxalate-extractable fractions were measured for the elements Fe, Al and Si [39].

Fractionation of Organic Matter

  • Acting on the assumption that chemical oxidation mimics natural oxidative processes, the authors treated the soils with 10% H2O2 to eliminate the more labile organic material from the more refractory organic matter [41-44].
  • Profile photos and horizon designations of the investigated soils (see also Fig. 1).
  • First organic matter formed in the sediment after glacier retreat [45] and may, under certain circumstances, provide a minimum age of deposition of the moraines and of deglaciation.
  • The beakers were closed with two layers of parafilm to avoid evaporation of the reagent.
  • At the end of the treatment the samples were washed three times with 40 ml deionised water, freeze-dried, weighed, analysed for total C and N and 14 C dated.

Cosmogenic Dating

  • The cosmogenic nuclide concentrations (e.g. 10 Be) in the surface of moraine boulders and polished bedrock exposure reflect the time that has passed since the moraine stabilised [48] and the ice retreated and exposed the landform to cosmic ray flux.
  • The rock samples were crushed, sieved and leached in order to obtain pure quartz following [50, 51].
  • The Be was isolated using anion and cation exchange columns followed by selective pH Be(OH)2 precipitation [51].
  • Production-rate scaling for latitude and altitude was based on [52] and corrected for sample thickness assuming an exponential depth profile, a rock density of 2.65 g cm -3 and an effective radiation attenuation length of 155 g/cm 2 [48].
  • The theoretical snow height for the sample site was estimated using a mean snow height gradient of 0.08 m/100 m altitude difference [54].

Weathering rind Thicknesses

  • The weathering rinds were generally very thin (Fig. 7).
  • Nonetheless, the median and mean values showed a clear increase from the youngest part near the rockwall to the frontal talus of the rock glacier (Fig. 7A-E).
  • Thicknesses of weathering rinds increased towards the distal front of the rock glaciers.
  • The literature indicates that the modal values should be used to delineate trends along a rock glacier.
  • The time dependent tendency looked, however, more disturbed.

Soils and Weathering Losses

  • The physical and chemical characteristics of the soils are given in Tables 1 and 2.
  • The parameter Alo + 0.5Feo (Table 2) clearly reflects the spodic characteristics of the soil at Igls Plans (see [55]).
  • Long-term weathering rates of soils were derived using immobile element contents [56-58].
  • This gives another indication of the minimum age of the present-day active rock glaciers and an indication of when the rock glacier Alvra became inactive.

DISCUSSION

  • Frauenfelder et al. [2] and Laustela et al. [11] measured Schmidt-hammer rebound values that varied from approx.
  • The median as well as the modal values of weathering rind measurements [11] are equally suitable to delineate the increasing weathering rind thicknesses with the duration of exposure.
  • The soil “Igls Plans” is more weathered than soil “Peidra Mora” and shows relative element losses that are close to soils that developed over post-Egesen time [60, 61, 64, 65].
  • This finding was only made possible using a multi-parameter approach that consequently clearly shows its advantages [66, 67].
  • Two main phases of rock glacier activity could be derived: one starting immediately after the retreat of glaciers during the Younger Dryas (Egesen glacial states) and the other one during the Holocene.

CONCLUSIONS

  • The authors obtained the following main findings: A distinct increase in weathering rind thickness and decrease of the Schmidt hammer rebound values along the rock glaciers (i.e. with increasing age) could be measured.
  • Both methods reflect equally well the effect of weathering with increasing age.
  • Soil analyses confirmed and added an additional time constraint.
  • The older soil, in front of the relict rock glacier, was highly weathered and must have started its evolution in the Lateglacial (shortly after the Younger Dryas).
  • This leads to additional datasets, provides the ability to cross-check each of the methods and to revise previous interpretations.

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ZurichOpenRepositoryand
Archive
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www.zora.uzh.ch
Year:2011
Acombinationofrelative-numericaldatingmethodsindicatestwohigh
AlpinerockglacieractivityphasesaftertheglacieradvanceoftheYounger
Dryas
Böhlert,R;Compeer,M;Egli,M;Brandova,D;Maisch,M;Kubik,PW;Haeberli,W
Abstract:To exploitthe potentialof rockglaciers as indicatorsof pastclimate conditionit isrst
necessarytodatethem.Thecombinedapplicationofbothrelativeandabsolutedatingtechniquesis
apromising approach.Inthis study, wepresentSchmidt-hammerrebound valuemeasurementsand
weatheringrindthicknessesonfouractiveandonerelictrockglacierintheAlbulaareaoftheeastern
SwissAlps.Associatedlandformssuchasthemorainesinfrontofrockglaciersandglaciallypolished
bedrockalsowereusedtosetupthetemporalframework.Thiswasdoneusingsoilchemicalanalyses,
radiocarbondatingofthestablefractionofsoilorganicmatterandsurfaceexposuredatingofboulders.
Schmidt-hammerandweatheringrindmeasurementsshowed,inmostcases,well-pronouncedtrendswith
increasingsurfaceages.Thesevaluesareinlinewithmeasurementsfromothernearbyrockglacierswith
comparablelithologies.Useofthisinformationtogetherwiththenumericagesmakesitpossibletoderive
twomainactivityphases: onestartedsoonaftertheiceretreatfollowingtheYoungerDryas,themain
activityoccurredmostlikelyintheearlyHoloceneandlastedapproximatelyuntiltheHoloceneclimate
optimum.Thesecondactivityphasecontinuestodayandhadanunclearstartbetween10to6calky
BP.
DOI:https://doi.org/10.2174/1874923201104010115
PostedattheZurichOpenRepositoryandArchive,UniversityofZurich
ZORAURL:https://doi.org/10.5167/uzh-42941
JournalArticle
Originallypublishedat:
Böhlert,R; Compeer,M; Egli, M; Brandova,D; Maisch,M; Kubik, P W; Haeberli,W (2011).A
combinationofrelative-numericaldatingmethodsindicatestwohighAlpinerockglacieractivityphases
aftertheglacieradvanceoftheYoungerDryas.OpenGeographyJournal,(4):115-130.
DOI:https://doi.org/10.2174/1874923201104010115

The Open Geography Journal, 2010, 3, 281-296 281!
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1874-9232/10 2010 Bentham Open
Open Access
A Combination of Relative-Numerical Dating Methods Indicates Two High
Alpine Rock Glacier Activity Phases After the Glacier Advance of the
Younger Dryas
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Rock Glacier Activity in a High Alpine Region The Open Geography Journal, 2010, Volume 3 283
MATERIALS AND METHODS
Schmidt-Hammer Rebound Values
The Schmidt-hammer is a portable instrument originally
developed to test concrete quality in a non-destructive way
[28]. A spring-loaded bolt impacting a surface yields a
rebound- or R-value, which is proportional to the hardness
(compressive strength) of a rock surface. Applied in
geomorphology, old rock surfaces exposed to weathering
processes for a long time provide low R-values and vice
versa. Since the 1980s the method has also been successfully
used for relative age dating of gemorphologic features such
as moraines [14, 29, 30], rock glaciers ([2, 31] or rockfall
deposits [32]. Recent publications increasingly discuss the
possibilities and limitations to calibrate R-values, for
instance with results from
10
Be and
14
C-analyses [33, 34] or
optically stimulated luminescence and photogrammetrical
measurements [2, 17].
In this study the N-type Schmidt-Hammer (Proceq,
Switzerland) was used. On each mapped unit (e.g. moraine,
rock glacier lobe) 50 randomly selected boulders/sites were
measured, avoiding edges of boulders [35], spots that
Fig. (2). Spatial distribution of local (sporadic) and continuous permafrost in the investigation area (data source: [27]).
Fig. (3). Aerial photo (with a view in southern direction) of the investigated rock glaciers A-D.

284 The Open Geography Journal, 2010, Volume 3 Böhlert et al.
showed lichen growth as well as visual fissures or cracks.
Only flat parts under dry conditions were considered. The
hardness of an analysed form is represented by the arithmetic
mean of the individual records. Following the suggestions by
[30], we used a standard error based on the standard
deviation in a 95% confidence interval to get statistically
significant hardness variations and by extensions age
differences:
x ± 1.96
/ n
()
(1)
where
x
is the arithmetic mean,
the standard deviation
and
n
corresponds to the number of measurements.
Fig. (4). Detailed view of the investigated rock glaciers A-D. The uppermost part of the relict rock is shown in E1 and the middle and lower
part in E2.

Citations
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Journal ArticleDOI
01 Dec 2013-Catena
Abstract: In order to evaluate the potential of the Schmidt hammer for relative age dating of Late Pleistocene moraines and rock glaciers, rebound (R) values were collected at 38 sites in two formerly glaciated valleys in the Western Tatras in northern Slovakia. A large statistical population of measurements obtained from moraine and rock glacier surfaces was used to analyze the variability of mean R-values in the same lithology and overall southern valley exposition. Four separate sets of glacial/periglacial morphosystems are present at different positions in the Western Tatras starting from valley outlets to the highest cirques, which represent successive phases of deglaciation. R-value means and 95% confidence intervals for selected Last Glacial Maximum (LGM), and Late Glacial (LG-1, LG-2 and LG-3) stages (respectively, 40.1 ± 1.1, 46 ± 0.5, 53.5 ± 1.0 and 60.5 ± 0.3) are significantly statistically different and values for each age category are comparable for the two analyzed valleys. The results of weathering indexes used in conjunction with geomorphological relationships were taken together to reconstruct the pattern of deglaciation on southern Tatra slopes. It is stated that the Schmidt hammer technique may be successfully used as a relative age dating tool for Late Pleistocene glacial and periglacial deposits, and with this method, it is possible to differentiate between Late Glacial moraines and rock glacier systems of different age.

29 citations


Journal ArticleDOI
Abstract: Relict rock glaciers provide information on past discontinuous permafrost and former mean annual air temperatures. A lack of records showing former permafrost distribution along the northern Alpine fringe prompted the investigation and numerical dating of a belt of relict rock glaciers in the Karwendel Mountains of the Northern Calcareous Austrian Alps. In two neighbouring cirques that were still glaciated during the early Younger Dryas, eleven 36Cl exposure ages from boulder surfaces were obtained. The ages imply the onset of rock glacier activity around ~ 12.3 ka with subsequent stabilization and permafrost melt out no later than ~ 10.1 ka. Hence, rock glacier formation coincided with glacier retreat in the cirques around the mid-Younger Dryas and continued into the early Holocene. As permafrost induced features, the rock glacier termini indicate the local past lower limit of discontinuous permafrost in open cirque floors at ~ 2000 m asl, which is around 400 m lower than during the mid-twentieth century at comparable locations in the Karwendel Mountains. Thus, a mean annual air temperature reduction of ~− 2.6 to − 3.8 °C relative to the mid-twentieth century is inferred. Based on a minimum glacier equilibrium line altitude in the cirques, a summer temperature reduction of less than − 2.6 to − 1.8 °C is shown, suggesting an increased seasonality at the time of rock glacier activity.

28 citations


Journal ArticleDOI
Abstract: Two rock glaciers in the valley head of Irishman Stream in the central Ben Ohau Range, Southern Alps/New Zealand, have been investigated using the electronic Schmidt-hammer (SilverSchmidt). Longitu...

22 citations


Journal ArticleDOI
Abstract: The Piec Stawow Polskich-Roztoka Valley in the High Tatras (Western Carpathians) features typical alpine-type relief with a deeply incised glacial trough and large, compound trough head cirque. The prominent hypsographic maximum in the valley (1680–2000 m) along with a broad cirque bottom had provided a vast space for recording glacial and periglacial landforms, specifically the most recent Lateglacial advances. The valley has been intensively studied before in the context of glacial chronology. In this paper, we re-establish the post-Last Glacial Maximum (LGM) glacial chronology of the valley via detailed geomorphologic mapping, equilibrium line altitude (ELA) reconstruction, and Schmidt hammer (SH) dating, along with a critical review of previously published cosmogenic exposure age data ( 36 Cl) and lacustrine sediment chronology. Our results indicate that the first four of the five distinguished Lateglacial stages (Roztoka I–III, Pusta I) occurred before the Bolling/Allerod (B/A) interstadial; thus, virtually the entire valley became deglaciated in course of the Oldest Dryas cold phase. A distinct reorganization of deglacial patterns from valley-type to marginal-type occurred before B/A warming when the ELA increased above the valley hypsographic maximum concentrated at the cirque bottom elevation. It shows that noticeable deglaciation step can be caused due to topographic reason with a minimal climate forcing. This points also to an important role of glaciated valley hypsography in regulating the distribution of moraines which is rarely taken into account in paleoglaciological reconstructions. We infer that glaciers vanished in the Tatra Mountains during the B/A interstadial. Later, a renewed advance during the Younger Dryas (Pusta II) formed a nearly continuous, festoon shaped pattern of moraines and rock glaciers in close distance to cirque backwalls. Furthermore, we discus some paleoenvironmental significance of the geomorphological record in the valley, as well, the applicability of SH dating in constructing glacial chronology.

18 citations


Journal ArticleDOI
Abstract: Rock glaciers contain valuable information about the spatial and temporal distribution of permafrost. The wide distribution of these landforms in high mountains promotes them as useful archives for the deciphering of the environmental conditions during their formation and evolution. However, age constraints are needed to unravel the palaeoclimatic context of rock glaciers, but numerical dating is difficult. Here, we present a case study assessing the potential of luminescence techniques (OSL, IRSL) to date the inner sand-rich layer of active rock glaciers. We focus on the signal properties and the resetting of the signal prior to deposition by investigating single grains. While most quartz shows low signal intensities and problematic luminescence characteristics, K-feldspar exhibits much brighter and well-performing signals. Most signals from plagioclases do not show suitable properties. Luminescence signals far below saturation indicate distinct but differential bleaching. The finite mixture model was used to determine the prominent populations in the equivalent dose distributions. The luminescence ages represent travel times of grains since incorporation into the rock glacier and hence, minimum ages of rock glacier formation. Luminescence ages between 3 ka and 8 ka for three rock glaciers from the Upper Engadine and Albula region (Swiss Alps) agree well with independent age estimates from relative and semi-quantitative approaches. Therefore, luminescence seems to have the potential of revealing age constraints about processes related to the formation of rock glaciers, but further investigations are required for solving some of the problems remaining and reducing the dating uncertainties.

16 citations


Cites background from "A Combination of Relative-Numerical..."

  • ...…(SED) of a roches moutonnes using 10Be, 14C dating of a peat bog, palynological investigations as well as glaciomorphologic mapping (?) delimited the maximum age of the Lateglacial permafrost activity that apparently started shortly after the Younger Dryas (about 11.6 kyr; Böhlert et al. 2011a)....

    [...]

  • ...Soil analyses support these time constraints for the second activity phase that hypothetically started sometime around 6 kyr ago and continues today (Böhlert et al., 2011a)....

    [...]

  • ...The glacier stages were numerically dated measuring in-situ produced 10Be in boulders on moraines, polished bedrocks, and roches moutonnes (Ivy-Ochs et al., 1996; Böhlert et al., 2011b,c)....

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  • ...The values are typical for rock glaciers having a maximum surface age of several thousand years that suggest Holocene rock glacier formation (Böhlert et al., 2011a)....

    [...]

  • ...Exposure ages from a glacially polished rock barrier showed that this area was ice-free at the end of the Younger Dryas ((9.0± 0.7) kyr and (11.9± 0.9) kyr; Böhlert et al. 2011b)....

    [...]


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"A Combination of Relative-Numerical..." refers methods in this paper

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Abstract: A new calibration curve for the conversion of radiocarbon ages to calibrated (cal) ages has been constructed and internationally ratified to replace IntCal98, which extended from 0-24 cal kyr BP (Before Present, 0 cal BP = AD 1950). The new calibration data set for terrestrial samples extends from 0-26 cal kyr BP, but with much higher resolution beyond 11.4 cal kyr BP than IntCal98. Dendrochronologically-dated tree-ring samples cover the period from 0-12.4 cal kyr BP. Beyond the end of the tree rings, data from marine records (corals and foraminifera) are converted to the atmospheric equivalent with a site-specific marine reservoir correction to provide terrestrial calibration from 12.4-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a coherent statistical approach based on a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The tree-ring data sets, sources of uncertainty, and regional offsets are discussed here. The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed in brief, but details are presented in Hughen et al. (this issue a). We do not make a recommendation for calibration beyond 26 cal kyr BP at this time; however, potential calibration data sets are compared in another paper (van der Plicht et al., this issue).

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"A Combination of Relative-Numerical..." refers methods in this paper

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Abstract: The cosmic ray flux increases at higher altitude as air pressure and the shielding effect of the atmosphere decrease. Altitude-dependent scaling factors are required to compensate for this effect in calculating cosmic ray exposure ages. Scaling factors in current use assume a uniform relationship between altitude and atmospheric pressure over the Earth's surface. This masks regional differences in mean annual pressure and spatial variation in cosmogenic isotope production rates. Outside Antarctica, air pressures over land depart from the standard atmosphere by ±4.4 hPa (1σ) near sea level, corresponding to offsets of ±3–4% in isotope production rates. Greater offsets occur in regions of persistent high and low pressure such as Siberia and Iceland, where conventional scaling factors predict production rates in error by ±10%. The largest deviations occur over Antarctica where ground level pressures are 20–40 hPa lower than the standard atmosphere at all altitudes. Isotope production rates in Antarctica are therefore 25–30% higher than values calculated by scaling Northern Hemisphere production rates with conventional scaling factors. Exposure ages of old Antarctic surfaces, especially those based on cosmogenic radionuclides at levels close to saturation, may be millions of years younger than published estimates.

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"A Combination of Relative-Numerical..." refers background or methods in this paper

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TL;DR: This paper highlights some of the main developments to the radiocarbon calibration program, OxCal, including changes to the sampling algorithms used which improve the convergence of the Bayesian analysis.
Abstract: This paper highlights some of the main developments to the radiocarbon calibration program, OxCal In addition to many cosmetic changes, the latest version of OxCal uses some different algorithms for the treatment of multiple phases The theoretical framework behind these is discussed and some model calculations demonstrated Significant changes have also been made to the sampling algorithms used which improve the convergence of the Bayesian analysis The convergence itself is also reported in a more comprehensive way so that problems can be traced to specific parts of the model The use of convergence data, and other techniques for testing the implications of particular models, are described

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"A Combination of Relative-Numerical..." refers methods in this paper

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Journal ArticleDOI
Abstract: An isolation method relying totally on chemical steps was developed to separate large quantities (10-200 g) of clean mono-minerallic quartz samples from a variety of terrestrial rocks and soils for the purpose of measuring Be-10 (t1/2 = 1.5 Myr) and Al-26 (t1/2 = 0.705 Myr) produced by cosmic rays in situ in the quartz phase. The procedure consists of grinding the sample, heating it in HCl, and treating it with a series of leaches using a dilute HF/HNO3 mixture in a heated ultrasonic tank. The purified quartz was also used for the measurements of in situ cosmic-ray-produced Ne-21 and C-14 (t1/2 = 5730 yr). The method is applicable to any problem requiring purified quartz on a large scale.

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Frequently Asked Questions (1)
Q1. What have the authors contributed in "A combination of relative-numerical dating methods indicates two high alpine rock glacier activity phases after the glacier advance of the younger dryas" ?

In this study, the authors present Schmidt-hammer rebound value measurements and weathering rind thicknesses on four active and one relict rock glacier in the Albula area of the eastern Swiss Alps. Use of this information together with the numeric ages makes it possible to derive two main activity phases: one started soon after the ice retreat following the Younger Dryas, the main activity occurred most likely in the early Holocene and lasted approximately until the Holocene climate optimum.