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

TLDR: In this paper, Schmidt-hammer and weathering rind measurements were used to date rock glaciers in the Albula area of the eastern Swiss Alps, and the results showed that the number of active and relict glaciers increased with increasing surface ages.

Abstract: To 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.

Figures

Table 3. Cosmogenic Nuclide Concentrations and Calculated Exposure Ages for the Albula-Region. Ages were Calculated Using an Erosion Rate of 3 mm per 1000 Years. To Emphasize the Influence of Erosion and Snow Coverage, Values without Correction (A) are Shown as Well as Ages with Two Different Estimated Snow Heights, in Each Case Only for Snow (B, D) and Additionally for Erosion (C, E)

Table 4. Radiocarbon Dating of the Stable Soil Organic Matter of the Site Peidra Mora. Calibrated 14 C Ages are Given in the 2- Range

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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!
!
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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Institute of Ion Beam Physics, ETH-Hönggerberg, CH-8093 Zurich, Switzerland
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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.

Frequently asked questions

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.