Journal rifGlaciology, Vo!. 45, No. 149, 1999
Pollen analysis and 14e age of moss remains in a pertnafrost
core recovered frotn the active rock glacier Mur tel-Corvatsch,
Swiss Alps: geotnorphological and glaciological implications
WILFRIED HAEBERLI/ ANDREAS KAAB,I STEPHAN WAGNER,2* DANIEL VONDER MUHLL,2
PATRICIA GEISSLER," J EAN NICOLAS HAAS,4t HOLGER GLATZEL-MATTHEIER,5 DIETMAR WAGENBAC H5
I
Department rifGeography, Universi£y rif <,iirich-hclzel, Winterthurerstrasse 190, C H -8057 Zurich, Switzerland
2
Versuchan staltjiir r Vasserbau, H)dwlogie und Glaziologie, Eidgeniissi sche Teclmische Hochschule, ETH-<ent rum, CH-8092 Zurich, Switzerland
3
Con servatoire etJa rdin Botaniques de la Ville de Geneve, c.p 60, CH-1292 Chambesy, Switzerland
4De/Jartment ofBotany, Universiry of Basel, Schb"nbein st rasse 6, CH-4056 Ba sel, Switzerland
S
In stitutjur UmweltjJ/�ysik. Universiry qf Heidelberg, D-69120 Heidelberg, German)
ABSTRACT. Within t he framework of core-drilling t hrough the permafrost of t h e
act ive rock glacier MurteI-Con'atsch in the Swiss Alps, subfossil stem remains o f seven
d ifferent bryophyte species were found at a depth of 6 m below surface and about 3 m
below the permafrost table in samples from massive ice. The composition of the moss spe­
cies points to t he former growth of t h e recovered mosses in t he nearest surroundings of t h e
d ri l l site. A total of 127 pollen and spores captured b y t h e mosses and representing 23 taxa
were determined. The local vegetation during deposition time must be characterized as a
moss-rich alpine grassland meadow rich in Cyperaceae, Poaceae, Chenopodiaceae and
14
Asteraceae, comparable to today's flora present a round t he study site. For C analysis,
accelerator mass spect rometry h a d to be used d u e to t h e smal l sample mass ( about
14
0.5 mg Carbon content). The mean conventional C age of 2250 ± 100 years (I (J variabil­
ity) corresponds to ranges in the cal ibrated calendar age of470-170 BC and 800 BC toAD 0
at statistical probabi lities of68% and 95 % , respect ively. This result is c ompared with t he
present-day now field as determined by high-precision photogrammetr y and with infor­
m ation about the t hickness, vertical st ructure and flow of the perma frost from borehole
measurements.1otal age of the rock glacier as a land form is on the order of 104 years; the
de\·elopment of t h e rock glacier most probably started around the onset of t he Holocene,
when the area it now occupies became definitely deglaciated. The bulk of t he ice/rock mix­
ture within the creeping permafrost must be several t housand years old. Characteristic
average values are est i mated for (I) surface velocities t h rough time (cm a \ (2) long-term
ice a nd sediment accretion rates ( m m a I) on the debris cone from which t he rock glacier
develops, (3) retreat rates (1-2 mm a I) of the cliff which supplies the debris to the debris
cone and rock glacier, and (4) ice content of the c reeping ice/rock mixtur e (50-90% by
volume). The pronounced supersatu ration of the permafrost explains t he steady-state
creep mode of the rock glacier.
INTRODUCTION
Permafrost or negative ground temperat ure throughout the
year is characteristic of many high-mountain areas of the
world ( Cheng and Dramis, 1992; Haeberli and o thers,
1993). vVith such g round thermal conditions, large a mounts
of ice beneath t he surface can exist o\"Cr extended time peri­
ods. Ice supersaturation and t he existence of massive ice
st rongly affect geotechnical propert i es of the frequent ly oc­
curr i ng perennially frozen scree a nd moraine deposits,
leading to slow viscous nolV and t he formation of lava­
stream-like landforms usually termed rock glaciers ( \Vahr* Present address: Bitzi, CH-954 2 Ebnat-Kappel, Switzer­
t
land.
Present address: Department of Bot any, University of
Toronto, 25 Wi llcocks Street, Toronto, Ontario M 5 S 3B2,
Canada.
haftig and Cox, 1 959; Haeberli, 1985; Barsch, 1996). Evidence
from o utcrops, drillings, borehole loggi ng and geophysical
soundings indicates t hat the ground ice concerned is most
likely to b e polygenetic in origin, with interst itial, segrega­
tion and buried snow-bank ice probably being the predomi­
nant c omponents. Measured electrical d . c. resistivity
values - a key indicator for variable ice origins - together
with the coupled thermodynamic conditions of ice forma­
tion and preservation lead to the assumption t hat the ice
types concerned must systematically vary along flow trajec­
tories and form, over characteristic time periods of mil len­
nia, on top ( permafrost t able) of as well as at t he bottom
(perm a frost base) of the creeping rock glaciers ( H aeberli
and Yonder Ml1hll, 1996).
I n 1987, scientific core-drilling was carried out through
the active rock glacier Murtel-Corvatsch ( Figs I and 2),
eastern Swiss Alps (er. Haeberli and ot hers, 1988, for infor­
mat ion about site select ion, goals, drilling logist ics and first
results). The borehole is sit uated on the central nowl ine,
JournalofClaciology
SITE AND SAMPLING
Fig. 1. Location map and oblique view of the l\l!urtel rock
glacier. Photograph taken by At. Hoelde, 1994.
Fig. 2. Aerial photograph of Murtel rock glacier taken by the
Swiss Federal Offic e of Cadastral Surveys on 11 September
1996,flight-line 066155, photo 2435.
about halfway trom t he headwall to the front, and reaches
bedrock. Onc ot the prim ary goals of this project was to
search for organic remains within the recovered cores in
order to directly date ice from mountain permafrost and to
acqui re evidence about the age of the investigated groun d
ice. This age determination would b e independent o f earlier
est imates from kinematic considerations. Surprisingly
enough, only one layer wit hin massive ice contained moss
remains at a dept h of about 6 m below surface. The results
from HC dating and botanical analyses confirm the con­
cepts developed so far about the creep of mountain perma­
frost and enable some general conclusions to be drawn about
long-term flow yelocities, l andform genesis, rates of ice for­
mation, rockfall activity and cliff retreat at an active rock
glacier. The present contribution reviews t h e background
of the drill site and core-sampling, documents the botani­
cal/bryological analysis of t he recovered moss remains with
their pollen spectra, reports on the " C dating (cf. early 14C
datings of Arctic permafrost by Brown, 1965) and briefly dis­
cusses t he geomorphological and glaciological implications
of the result obtained.
2
The active Murtcl-Corvatsch rock glacier has developed
within a former cirque from perennially frozen, north­
westerly exposed scree slopes at 2850-2620 m a.s.1. Extend­
ing flow characterizes the upper part of the rock glacier,
whereas longitudi nal compression causes pronounced
ogive-like transverse ridges in t h e lower part. The steep, ap­
proximately 20 m high front is l a rgely free of vegetation and
slowly advances over permafrost-free granodiorite bedrock.
High-resolution vertical aerial photographs were t aken by
t he Swiss Federal O ffice of Cadastral Surveys in t he fall of
t he years 1987 a nd 1996. Using special computer-aided
photogrammetric techniques ( Kaab and others, 1997), the
horizontal velocity field ( Fig. 3, left side) as wel l as area­
wide changes in surface elevation were determined from
t hese photographs. Horizontal velocities reach m aximum
1
values of 15 c m a and more in t h e upper part of t h e rock
glacier just below the rock wall delimiting t h e creeping
permafrost. A l ong t he 110wl ines, t hey decrease to about 5
1
cm a behind t h e front, where increasing surface slopes
a nd sliding or t i lting of individual rocks lead to h igher sur­
face velocities again. In fu ll agreement with borehole de­
formation measu rements (vVagner, 1992; Yonder Miihll,
1996), the photogrammetric compilations show horizontal
1
surface velocities of about 6- 7 c m a at the borehole. The
changes in surface elevation at t h e front hint at an advance
rate of the rock glacier Murte! of about 1.5-2 cm a lover the
period 1987-96. Assuming constant creep rates t h rough the
last millennia, traj ectories were computed trom the velocity
f ield 1987-96 for a number of m anually selected points ( Fig.
3, right side). These tr�ectories show the time it t a kes for a
particle to t ravel down the rock-glacier surface under pres­
ent-day conditions. Because flow must have been quite dit­
ferent from today at the beginning of rock-glacier evolution
( Olyphant, 1983, 1987), such a calculation allows only for a
rough (probably minimum) age estimate (cr discussion at
the end ot the paper).
The 60 m deep borehole on t he active rock glacier Mur­
te! was placed at 2670 m a.s.1. Alpine permafrost in the area
surrounding t h e drill site exh ibits a discontinuous distribu­
tion pattern (Hoelzle, 1996). C o re analyses and borehole
measurements ( Fig. 4; Yonder Mlihll and Haeberli, 1990;
Yonder Mlihll and Holub, 1992; Wagner, 1992; Yonder
Mlihl l, 1996) showed that t h e permafrost underneath the
3 m thick active l ayer essentially consists of two l ayers: an
upper one with an extremely high ice content (90- 100 % by
volume), and a lower one consisting of coarse blocks with
ice-filled pores but almost completely without fine rock par­
ticles. Se\'enty-five per cent of t h e total horizontal displace­
I
ment (6 cm a- at the surface) takes place within the
t ransition zone between the t wo l ayers at 28-30 m depth,
with the upper (strongly supersaturated) layer undergoing
steady-state creep and overriding the non-deforming (struc­
tured) lower l ayer. Mean annual ground temperature at
11 m depth increased from -2.3°C ( 1987) to - 1 .4°C (1994)
but was intermi t tently cooling again due to thin snow cover
in t he winters of 1994-95 and 1995-96 (Fig. 5; Yonder Mlihll
and others, in press). It is reasonable to assume t h at perma­
frost conditions existed at t he drill site throughout the
younger Holocene time period a t least. At 52-58 m depth,
temperature variations around O°C are observed in a seas­
onal talik (Vonder Mi.ihll, 1992). Total permafrost t hickness
reaches far into t h e bedrock which underlies the rock-glacier
Haebedi and others: Pollen analysis and I-IC age qfmoss remains
10cma-1
•
20m
borehole
100m
... .. . .
1000
.
.
... ...
•
a
100 a
.
Fig. 3.
and tmjectories/suiface ages computed from this velocityfield (right).
sediments, and is estimated at about 100 m. This is in sharp
contrast wilh the absencc of permafrosl in front of t he rock
glacier and indicates m arked horizontal gradients in
ground lhermal conditions. Electrical d . c. resistivity of t he
perennially frozen m aterial is up lO 2 MQm in the massive
ice, decreasing to around 10 kQm or even l ess above bcd­
rock. Together with t he short dislance (200 m ) between thc
rock wall and the drill site, such resistivit ies exclude the pos­
sibility of a predominanr sedimentary ("ftrn") origin for t h e
Gamma-Gamma
1500
o
Stratigraphy
density
1000
500cps 0
massive ice encoU11lered ( H aeberli and Vonder l\1iih ll, 1996).
I t is much more plausible to assume a polygenetic origin of
the massive ice with burial of superimposed ice from small
perennial snow banks fed by snow a\'alanches ( Figs I and 2),
probably in c ombination with l ater addition of ice from sec­
ondary frost heave within the permafrost and from fl"eezing
processes taking place at t he permafrost table (cr. H aeberli
and Vonder Miihll, 1996; Elconin and LaChapcllc, 1997).
Careful visual inspection connected to t he melting of
Horizontal
o
displacement (cm)
40
20
-20 +---t--'<;--t----j
E
:5 -30
Q.
'"
o
+---+---+",-.....--j
-401---t---+��
-60�--�--�-�
-r---+----+--� 40
El
�
�
".
0
�
III
Missing
50
Blocks
Ice
Frozen sa nd
Frozen blocks, ice
Bedrock
�. I I
I
J
I
I
60
Fig. 4. Principal results from core analyses and borehole measurements at the active rock glacier Nlurtel-Corllatsc/l.
the 3m thick active layer with coarse blocks, the density log ("(-"() alld the stratigra/J/�y show two main la)'ers: (1) massive ice
(9 0- 100% ice content by volume) with thin layers qf
almost cam/Jletely wit/lOutfine rock particles down to bedrock at about 57 m depth. Three-quarters qfthe total Iwri::.ontal dis/Jlace­
ment (6 cm a I at the surface) takes place within a pronounced shear horiz:ofllll the transitioll z:one between the two l�yers at 28
30 m depth as revealed by the borehole difor
by ovenides the non-diforming (structured) lower laye1: Seasonal temperature variations are well develo/Je!1 within approxi­
mately the uppermost 20 m, alld mean annual permafrost temperature at the permaji'OSt table (3m depth) is estimated at -2.5
to -3°G.
3
Journa loJGlaciology
8.0
6.0
_
E
..
...
:l
�..
4.0
2.0
0.0
,
� ·2.0
�
after, t h e moss remains were prepared for radiocarbon dat­
ing at t he Institute of Environmental Physics of the
University of Heidelberg. Analysis of t h e final target was
done at ETH Zurich.
1
i.6m
\01
-4.0
·6.0
·8.0
1.0
0.0
E
·1.0
�
E
..
I�
BOTANICAL/BRYOLOGICAL ANALYSIS
u
87 88 89 90 91 92 93 94 95 96 97
J
3.6m
� I Ii
J1 Jl ,.,
� ·2.0
•
� ·3.0
I-
�
r�
I' f1 11
-4.0
·5.0
-6.0
0.0
E
·1.0
� -2.0
:l
� -3.0
�
�
87 88 89 90 91 92 93 94 95 96 97
1
5.6m
I
J
I f
�
�
/I
J
I
�
-4.0
-5.0
-1.0
-1.2
87 88 89 90 91 92 93 94 95 96 97
t-n-rtr'-'+�f-,-rrtnnf-,"""'f,-r-rtr'-'+�f-,-rrtnrrl
ii.6m
-1.4
U
2- -1.6
�
�
-1.8
..
-2.0
Il.
�
I-
-2.2
-2.4
-2.6
-2.8
87 88 89 90 91 92 93 94 95 96 97
Fig. 5. Borehole temperatures within the active Murtel-Cor­
vatsch rock glacier betweenJuly1987 a n dJuly1997, at depths
if 1.6 m (active layer) 3.6 m (un derneath the permafrost
table) 5.6 m (nearest thermistor with respect to the moss)
an d 11.6 m (time-phase lag about halfa year). Permafrost
temjJeratures are strongly influence d by snow conditions in
in divi dual years (especially thin snow cover in 1988-89 an d
1995-96).
ice-core samples for water isotope analyses revealed one
piece of moss remains within core Murtcl 2jI I j4 at a depth
of 5.94 m below surface. The sample was put into double­
distilled water with in a cleaned, d ried and sealed small
glass bottle and sent to t he Department of Botany of t h e
Universi t y o[ Basel for further analysis. Moss identification
was performed at the Botanical Garden of Geneva. There4
Subfossil stem remains of seven different bryophyte species
were found. Table 1 lists t he number of individuals counted
[or each species, together with short descriptions o[ thei r
ecological preferences following Amann and others (1918)
and Meylan (1924), as well as personal observations by one
o[ the authors (PG.) . A l l considered species commonly
occur within Alpine to nival altitude belts. The composition
of t he m oss species points to the growth o[ t he recovered
mosses in t he nearest surroundings o[ the d r i l l site Murtel.
Although the individual ecological preferences reflect differ­
ent h abitats, the small-scale density of bryophyte niches
may wcl l allow t he conclusion that t he seven moss species
grew c lose together before t hey were eroded and subse­
quently e mbedded within t he rock-glacier permafrost by a
process w hich is not known (snow avalanche, soil erosion,
debris flow, rockfall?). Since t he sample was found in good
preservation conditions, the mosses appear to have been
trapped in t he ice of the rock-glacier permafrost immedi­
ately after deposition. The large amount of Blindia acuta re­
mains m ay indicate that t he m ain original stand was a moist
rock.
A l l stems found were photographed after identification
and before being used [or pollen analysis and HC dating.
Figure 6 shows the species Distichium inclinatum as an
example. The extremely good preservat ion of the moss re­
mains w i thin the permafrost core is obvious: t he stems stil l
carry remains of leaflets, showing t hat secondary processes
of defo r mation were minimal during and after sedimenta­
tion. Because leafy mosses serve as ideal pollen traps by con­
centrating pollen and spores in between leaflets and stems, a
pollen analysis was performed on detritic material ex­
tracted by a paint-brush, following classical palynological
techniques (Moore and others, 1991) at a m agnification of
400 and 630 by using phase-contrast microscopy.
A total of 127 pollen and spores representing 23 taxa
were determined (Table 2). Percentages of 58% arboreal
pollen and 31 % non-arboreal pollen and spores (ferns and
mosses) were found. This ratio represents well the pollen
flora typical for sites above t imberline in t h e region (H eitz,
1975). T h e arboreal pollen h ad, t herefore, a l l been blown up
to the study site from lower altitudes and represents the re­
gional vegetation composition during the time of sedimen­
tation. The local vegetation during deposition t ime must be
characterized as a moss-rich alpine grassland meadow rich
in Cyperaceae, Poaceae, C henopodiaceae and Asteraceae,
comparable to the flora present around the study site today.
This glimpse into the former vegetation mosaic facilitated
the characterization of the relative importance of arboreal
and non-arboreal pollen influx, and the dating of the moss
remains by comparison wit h results from pollen-analytical
investigations on past vegetation at nearby sites (Kleiber,
1974; H ei tz, 1975; Welten, 1982; Punchakunnel, 1983; Zoller
and Brombacher, 1984; Burga, 1987). The appearance ofpollen
[ram fi r (Abies alba) and spruce (Picea abies) made it possible
to set a maximum age of the moss remains at approximately
8000 BP. Based on the lack of plant species typical for the
Haeberli and others: PoLLen ana(ysis and 14C age of moss remains
Table 1. Description and present-day ecological characteristics of moss remains found in the permafrost core of the active
glacier Murtel-Corvatsch at 5.94 m depth
Species
FamiLy
Mlmbers
rock
Ecology
Distribution
found
AnastrophyLlum minuturn (Schreb.) Schust.
BLindia aCl1ta (Hedw.) Bruch et Schimp.
Lophoziaccae
Seliger i aceae
34
Subalpine-alpine, up to
Subalpine nival, up to
3000 m a.s.l.
3500 m a.s.l.,
On siliceous rocks, rarely soil
On humid to very wet rocks
relatively common, subarctic-alpine
Desmatodon latifoLlus (Hedw.) Brid.
Po t tiaceae
3
{loral element
S ubalpine-nival, up to
very
Distichium incLinatum (Hedw.) Bruch et Schimp
Fahlia effilum (Schimp.) Mart.
Ditrichaeae
Bryaceae
5
2
common spec ies,
3500 m a.s.l.,
boreal sub­
alpine {loral element
Common 111 montane regions, 6503300 m a.s.l. , subarctic-subalpine floral
ele ment
On rich soil and open ground, also on
dry and luminous places
On
danlp soil, in rock crevices, often
on soil in late-snow areas
The specimen probably belongs to the
group of bulbiferous Pohlia species
often growing on soil 1I1 late- snow
areas. No propagules were preserved,
so it was not p ossible to identify the
Racomitri"m heterostichum (Hedw.) Brid. 5.1.
s p ecimen to species level
Subalpine-nival regions , up to
Grinlmiaceae
m
a.s.l.,
common
sp ecies,
montane floral element
Tritomaria scitula (Tayl.) J"rg.
Lophoziaceae
3
Roman Age Period, such as walnut (Juglans regia) and chest­
nut (Castanea satwa) - both very well distributed by atmos­
pheric currents ( Peeters and Zoller, 1988) - a minimum age
of 2000 BP was attributed to the moss remai ns. This younger
age limit was later confirmed by the 14C dating of the moss
remains to t he Iron Age Period.
During thc Iron Age (2800-2000 BP), t he upper tree limit
was composed oflarch (Larix decidua), pine (Pinus cembra) and
birch (Betula spec.) and must have been a t a n altitude of
< 2300 m a.s. l. At that t ime, it was already heavily influ­
enced by human activities a n d grazing (Zoller and Haas,
1995).
RADIOCARBON DATING
In order to narrow down t he botanical age estimates of the
moss sample, an attempt was made to date t he specimen in­
..
3300
Subalpine-alpine, relatively rare spe -
Cl es
On
dry, often exposed si I iceous rocks
boreal­
On hUl1lous soil or open
siliceous
rocks
strumentally by the I+ C method. I n this process, t he age is
determined from t he decay of t he cosmogenic I+C isotopc in­
corporated by t he moss during its assimilation period and
14
from an assumption about the original C content of the
atmospheric C O2. In our case, spec i fic crror sources to be
accounted for relate to possible sample contaminations by
other carbon pools (carbonate and organic soil compo­
nents). Furthermore, due to t he small sample mass ( about
0.5 mg Carbon content) positive or negativc age shifts may
arise from very old or from modern laboratory blanks, re­
spectively. For 14C analysis, accelerator mass spectrometry
( A MS) had to be used instcad of c onventional beta-counting
duc to thc small sample size. The sample preparation proce­
dure and carbon isotope analyses outlined below were carc­
fully cross-checked by processing a series of auxiliary
14
samples (modern sugar coal, C free charcoal and recent
moss species) a long with the MurteI sample.
According to various test r u ns on recent moss speci­
mens, the following procedure was applied for t h e Murtcl
sample at the Heidelberg Laboratory:
L
pooling of all plant fragments into one bu l k sample
which was t hen washed, dried, weighted and ground in
a mortar to a fine powder;
2. acid treatment of the powder i n d iluted H CI t o rcmove
carbonates. More rigorous steps to extract the organic
fraction not associatcd w i t h t he moss (pollen) matrix
were avoidcd in ordcr not to d i ssolve the sample;
3. stepwise t r a nsfer of the suspension onto two small, pre­
fired quartz fiber filters which were gcntly heated under
purified air until dry.
Fig. 6. Moss stems of Distichum inclinatum }i"om the
permafrost core driLLing MurteL-Corvatsch found at a depth
of 5.94 m. ( Magnification 6.)
I n this way, two practically identical aliquots of the M urtel
moss were obtained with a dry weight of 2.9 and 2.7 mg, re­
spectively. Combustion of the quartz filter samples within a
pure O2 atmosphere was initiated by an cxternal heat
source. The result ing CO2 amount was manomct rically de­
termined after purification by a n activatcd charcoal trap
and then cryogenically transferred i nto a glass vial for sub5
JournalofGlaciology
Table 3. N e results if A1urtel and the two respective test
samples. !Sevalues are given in b notation a s the deviation oJ
13 ,3
C! C ratios relative to the VPDB standard in per mil. NC
activities as !Se conected ratios relative to NBS-oxalic acid
in per mil
Table 2.
found on the subfossil moss remainsJrom the permafrost core­
drilling Murtel-Corvatsch
Numberfound
Species
Percentage
%
O"'e
Samj)/e name
Trees and Shrubs
% VPDB
Abies atba (Fir)
Alnus (Alder)
Betula ( Birch)
8
6.3
11
8.7
I
0.8
COI)'lus avellana (Hazel)
8
6.3
JUllipews Uuniper)
2
1.6
Picea abies (Spruce)
Pill us
(Pine)
6
4·.7
30
23.6
4
3.1
Quercus (Oak)
Salix (Willow)
Titia cordata-type
(Lime)
Ulmus (Elm)
Total
I
2
74
1.6
I
0.8
Astemceae (Composits)
2
1.6
Chellopodiaceae (Chcnopods)
2
1.6
11
8.7
Cyperaceae (Sedges)
I
Ericaceae (Heaths)
Poaceae (Grasses)
-2130
-27.97
40
235
21.27
-258
2340
21.19
242
2165
984.5
33100
2250
±
±
±
±
±
±
100
100
100
100
100
100
Process-blank \'aluc for moss correction.
2000 BP
1.6
27
2l.4
5
I
3.9
0'copodiullZ (Clubmoss-spores)
Bryophyta-tritete (Moss-spores)
3
2.4
P teridophyta (Fern-spores)
Bryophyta-inapertumte (Moss-spores)
3
2.4
9.5
Varia
6
4.7
lndctcrminata
8
6.3
14
11.0
Varia and Indeterrninata
"iotaI
Fungal spores and Charcoal particles
«
50 fllll)
1800 BP
0.8
12
Total
2400 BP
0.8
I
2
Ferns and Mosses
2600 BP
2000 BP
5.5
Urtica (Ncttle)
Total
5
15
20
sequent 813C analysis. Pilot runs on recent moss samples
from the Heidelberg area gave yields of approximately 6598 % , with a systematic enrichment of the 813C values to­
wards higher yields by up to 0.5 per mil. No large isotope­
fractionation effects were observed otherwise. Elemental
carbon required for the AMS measurement was obtained
by catalytic reduction of the CO2 sample in H2 at 570°C
(Schlosser and others, 1987). Procedures for preparation
and analysis of the final target at t he ETH Zurich AMS fa­
cility are described by Suter (1990).
The carbon-isotope results from t he two Murtel moss
subsamples are summarized in Table 3 along with t he
respective reference samples. As illustrated by Figure 7, the
mean conventional 14 C age of t he Murtel moss of 2250 ± 100
years (1 (J variability) corresponds to ranges in the calibrated
calendar age of 470- 170 BC and 8 0 0 BC to AD 0 at statistical
probabilities of68 % and 95 % , respectively. The 8 14C values
from t he recent moss and the recent sugar-coal reference
sample appear to be underestimated by up to 60%0, suggest­
ing a contamination by some old c a rbon components. This
systematic deviation was depicted from comparisons with
t he current atmospheric 14 C02 record at Heidelberg (per6
312
0.8
Rosaceae (Roses)
Total
19.5
58.3
Artemisia (Mugwort)
Fu ngal spores
24.97
2800 BP
Herbs
Charcoal particles
•
years BP
%
Sugar coal
�durtel I (ETH-Kr. 14228)
1'.IuneI II (ETH-;'\r.14229)
Murtel average Illl
0.8
Cage
·
Trenl0nia coal
Recent 1l10SS
0.8
14
800 BC
400 BC
AD
AD 400
Calibrated date
Calibration if conventional NC age of moss sample
(2250 ±100 BP) after Stuiver and Reimer (1993) giving
calibrated date ranges if 400 Bc-16 0 BC at la (short
horizontal bar) and 800 BC-AD 0 at 2a (long bar) con­
fidence levels; normally distributed !4C ages are indicated at
the ordinate.
Fig. 7
sonal communication from I . Le\'in, 1995) and with low­
level counting results giving 8H C
362%0 ± 3%0 for the
sugar-coal sample (personal communication from B.
Krol11er, 1995). As shown by the low process blank of the
14
C free Tremonia coal, no significant contamination by
modern carbon has to be considered, however. On the other
hand, referring to the adopted overall analytical uncer­
tainty in the I+ C analysis of approximately 10 per mil, there
14
is perfect agreement between the C values of the two
Murtel a liquots, making random contamination less likely.
For t his reason, no downward correction of the Murtel l-fC
ages d ue to dead c a rbon contami nation (which wou l d
account for a maximum o f 500 years) was performed.
T h e relatively well-preserved habitus of the moss
remains as well as of t he pollen scavenged by t hem suggesLs
an insignificant residence t ime of the material on the rock­
glacier surface before becoming ultimately isolated from its
ambient environment by incorporation into the ice mat rix.
Hence, t he 14 C age of the moss may not be much influenced
by other carbon pools a n d is expected to be well representa­
tive of the age of the hosting ice layer. A l though no further
macroscopic plant fragments have been detected so far in
t he MurtCl cores, micro-plant debris may be abundant
(though not easily recognized on visual inspection). Hence,
=
Haeberl i an d others: Pol len an a!Js is and
extracting t his material by selective concentration steps
would lead to bulk particulate organic c arbon ( POC)
samples, s ufficiently large for further AMS Icf C d at ings. The
same is expected for dissoh-ed organic carbon ( DOC ) com­
ponents event ually washed down from overlying soil
patches or even from sparsely colonized rock debris.
GE OMORPHOLOGICAL
AND
GLACIOLOGICAL
INTERPRETATION
+
The I C dating of t he moss remains found in t he permafrost
core recovered from the active rock glacier r-.1uncl now con­
stitutes t h e fi rst absolute age determination of creeping
Alpine permafrost available: ground ice at t he site of the
core-dri l l i ng within Murtel rock glacier has existed for at
least 2000 years. Earlier estim ates from flow considerations
arc, thus, clearly confirmed: t he ice within active rock
glaciers is t housands of years old and by far predates recent
climatic events s uch as the Little Ice Age. r-. 10reover, t his ab­
solute age determination of a permafrost layer allows some
general conclusions to be d rawn about long-term flow
velocities, l and form genesis, rates of ice form ation, rockfall
acti\'ity and cliff retreat at an active rock glacier as well as
about conditions for preservation of old ice in cold moun­
t ain areas.
With t h e time of existence of the sample being known,
the average flow velocity of t he creeping permafrost during
t he considered time period can be estimated if t he place of
moss deposition and, hence, t he travel distance to t he drill
site can be defi ned. A (hardly realistic ) minimum t ra\-cl dis­
tance and long-term flow velocity (both 0) are given by the
assumption t hat t he moss had been directly deposited at t he
drill site in its present-day posit ion. A corresponding maxi­
mum limit can be established by assuming t hat t he moss
had been deposited at the very foot of the rock wall at t he
head of t h e rock glacier a nd t hen traveled by permafrost
creep over t h e fu ll distance to today'S borehole. In such a
case, t he average flow veloei ty along the traj ectory to t he
borehole would have been some 25 % higher t ha n at present.
The most plausible case is in bet ween the two ext remes: the
moss may have been transported from the head wall to t he
rock-glacier surface by a rockfall event or a snow avalanche
traveling over some runout dist ance but not reaching the
drill site in the current position. The present-day flow field
( Fig. 3), in fact, indicates t hat the moss remains may have
been deposited some 100 m from the foot of t h e rock wall.
I n any case, t he characteristic average long-term flow
velocity is in t he range of cm a \ closely corresponding to
values measured at present.
Such a n esti mated long-term surface velocity of a few
cm a I confi r m s t hat the fl ow of t he rock-glacier permafrost
indeed corresponds to a secondary (steady-state) viscous­
flow mode of ice-supersaturated debris, where constant
stress leads to constant strain rates (Olyphant, 1983, 1987;
Haeberli, 1985; \ Vagner, 1992). The constant rate of t he flow
over long t i me periods t hereby indicates that, during the
past two mi l lennia, dramatic changes in rheological charac­
teristics as influenced by m aterial propert ies or t hermal
conditions are unlikely to have taken place and t hat surface
slope and permafrost thickness which exert a predominant
influence on t he st ress field within the creepi ng ice/rock
mixt ure must have remained quite similar to t h e present
ones. The rock glacier as a l and form expressing t he cumula-
Ne ag e qfm oss
rem ain s
t ive straining of perennially frozen, ice-rich debri s m ust,
t herefore, be c o nsiderably older t han 2000 years.
Th(' total age of t he rock glacier, i.e. the beginning of its
formation, can b e estimated only roughly. In terms of speci­
fics, many questions remain unanswered. Estimates can be
based on (1) consideration of the obvious inertia a n d long­
t erm stability of t he flow field, and (2) extrapolation of the
vertical time-scale to greater depth . The photogrammetri­
cally determined velocities along t h e central trajectories of
1urtel rock glacier indicate a surface age of about
3000 years at t h e bore hole, where t he moss rem a i n s were
found, and a su rface age of about 6000 years at the a c tively
advancing front. Integration of t h e currently measured
ratio between t he rate of ad\'ance a nd the surface velocit ies
over present flow t raj ectories yields an age estimate [or t he
Murtel rock glacier of roughly 10+ years. Assuming t hat 6 m
of ice (3 m) and debris (3 m) had accumulated above t he
moss remains a n d t hat t he rate of ice and debris accumula­
t ion (3 mm a I) remained constant t h rough time, t h e age of
t he layers w i t h i n the shear horizon at 30 m dep t h s can,
again, be est i m ated at some lOci years. It appears quite
reasonable to a s s u me that rock-glacier formation m ay have
st arted during t he fi nal stages of t h e l ast Ice Age or w i t h t he
onset of the Holocene. The bulk o[ the creeping ice/rock
mixture is likely to be several t housand years old.
Ice format ion abO\'C the moss remains could have taken
place at a characteristic rate of m m a I by means of freezing
processes at t he permafrost table d u ring the buildi n g up of
t he surfic ial debris l ayer (at a comparable rate of m m a \
This part of ground ice formation would represent synge­
netic permafrost aggradation. The most li kely process
t hereby involved is refreezing of snow meltwater p ercolat­
ing into the still cold active layer during spring ( Keller and
G ubler, 1993) and producing high-resistivity ice w i t h a rel­
at ively low ion c ontent ( Haeberli a nd Vonder Muhll, 1996).
Taking into account the porosity of the coarse blocks at t hc
surface, the ice c ontent by volume over the total ice/debris
thickness above t he moss remains is about 50-70 % . Such a
supersaturation is commonly observed in A lpine perma­
frost boreholes ( Vonder r-. I llhll a nd Holub, 1992; Yonder
Muhll, 1996) a n d constitutes t he basis for the obsenTd
steady-state creep of the rock-glacier permafi·os t . The
amount of debris which has been deposited at t he rock­
glacier surface over t he past 2000 years along the central
flowline to the borehole roughly corresponds to a retreat of
the 200 m high rock headwall o[ 3 m or 1 -2 mm a I . Based
on an average w i d t h of the rock glacier ancl the rock head­
wall of 150-250 m, some 30- 100 m 3 of rocks are l i kely to
have fallen onto the rock-glacier surface every year. D u ring
t he entire Holocene t ime period, t hi s would add up to a total
3
of 300 000- 1 00 0 000 m of debris. A s suming that t h e rock­
glacier permafrost acts as a perfect sediment trap (no loss of
rock material fro m meltwater erosion) and comparing it
6 3
with a total rock-glacier volume of 2-3 x 10 m provides
again a characteristic ice content by volume of 50-9 0 % .
The largest and most conspicuous ice bodies in t he Alps
are the surfac e ice m asses of the numerous glaciers. \tVith
characteristic lengths of kilometers and characteristic flow
velocities of meters to tens of meters per year, however, t he
age of such ice in glaciers is usually limited to a few cen­
t uries. Much older ice can be found in cold-based parts of
glaciers on wi nd-exposed crests and at very high altit udes.
Examples arc t he s ummit ice ofTitlis ( Lorrain and H aeber­
li, 1990), the ice-c o re drilling site on Colle Gnifetti, Monte
7
)
Journal oJGlaciology
Rosa ( H aeberli , 1994; Wagenbach, 1994; Wagner, 1 994), or
t he ice on saddles, which, for insta nce, contained t he O tztal
ice man at H auslabjoch or t he archeological bows at
Lotschental ( H a eberli, 1994; Baroni and Orombelli, 1 996).
Ice considerably older than a few centuries has also been de­
tected in perennial snow banks o f t h eJapanese A lps ( Yama­
moto and Yoshida, 1987; Yoshida and others, 1990). A l l t hese
occurrences concern surface ice w it hin an environment of
mountain permafrost. The present study confirms t hat old
ice also exists within the permafrost itself. The scientific in­
vestigation of such old ice archives in mountain areas is at its
very beginning and deserves more attention.
besonderer Berucksichtigung der Fichteneinwanderung. Beitriige zurGeo­
botanischen Landesau.fnahme del' Schweiz, 55, I �63.
Hoclzle, M . 1996. i\!fapping and modelling of mountain permafrost distri­
bution in the Alps. Nor. Geogr. Tidsskr., 50 ( 1), I I � 15.
Kaab, A . , W. Haeberli and G. G udmundsson. 1997. Analysing the creep of
mountain permafrost using high precision aerial photogrammetry: 25
years of monitoring Grubcn Rock Glacier, Swiss Alps. Permafrost and
Periglacial Processes, 8 (4), 409�426.
Kcller, F. and H. U. Gubler. 1993. I nteraction between snow cover and high
mountain permafrost, M u rtCl Corvatsch, Swiss Alps. In Permafrost. Sixth
International COIlJerence. Proceedings, 1 101. 1, July 5-9 1993, Bey'ing, China.
G ua ngzhou, South C h i n a University oflechnology Press, 332 337.
Kleiber, H. 1974. Pollenanalytische Untersuchungen zum Eisruckzug und
z u r Vegetationsgeschichte i m Oberengadin 1 . Bot. Jahrb. Syst. Pflanzen­
gesch. Pflanzengeogr., 94 (1), I 53.
Lorrain, R. and W. Haeberli. 1990. Climatic change i n a high-altitudinal
alpine area suggested by the isotopic composition of cold basal glacier
ACKNOWLEDGEMENTS
Ann. Glaciol. , 14, 168� 171.
1924. Les hepatiques d e la Suisse. Beitl: zur Kryptogamelljlora der
Schweiz, 6 (1).
Moore, P. D. , J. A. Webb and M. E. Collinson. 199! . Pollen analysis. Oxford,
ice.
Thanks are due to 1 . Levin and B. Kromer for letting us use
t heir AMS target preparation devices and for i nval u able
discussions. VVe also thank G. Bonani and M. Suter for the
AMS analysis at the Institut fUr Mittclenergiephysik, ETH
Zurich, Switzerland. The photogrammetric i nvestigations
are based on t he aerial photographs taken by the Swiss Fed­
eral Office of Cadastral Surveys ( Eidgenossische Vermes­
s ungsdirektion) and were performed using the a nalytical
plotter of the Laboratory of H y drau lics, Hydrology and
Glaciology, ETH Zurich. Core-drilling, core analysis and
borehole measurements in the permafrost of the active rock
glacier Murtel�Corvatsch were supported by ETH research
grants. Photogrammetric analysis o f M urtel rock glacier is a
contribution to the permafrost-monitoring schem e of the
G laciological C o mmission within the Swiss Academy of
Sciences (SANW).
Meylan, Ch.
etc. , Blackwell Scientific Publications.
Olyphant, G. A. 1983. Computer simulation of rock-glacier development
under viscous and pseudo plastic flow.
Olyphant, G. A.
duction.
glaciers.
In
1987.
Geol. Soc. Am. Bull. , 94 (4) 499�505.
,
Rock glacier response to abrupt changes in talus pro­
Giardino, J. R . , J.
F.
Shroder, J r and J. D. Vitek,
London, Alien and Unwin,
G. and H. Zoller. 1988. Long range transport of Castanea sativa
Grana, 27, 203 207.
Punchakunnel, P. 1983. Pollenanalytische Untersuchungen zum Eisruckzug
Peeters, A.
pollen.
und
zur Vegetationsgeschichte im Oberengadin
All1ann, J , Ch. Meylan and
P.
Culll1ann.
1918. Flore des mousses de la Suisse.
Lausanne, 1 ll1prill1eries Reunies S.A.
Baroni,
C.
and G. Oroll1belli. 1996. The Alpine "iceman" and Holocene
Q.uat. Res. , 46 (1), 78�83.
Barsch, D. 1996. Rockglaciers: indicatorsfor the jJresent andformer geoecology in high
mountain environments. Berlin, etc., Springer-Verlag. ( Springer Series in
Physical Environment 16.)
Brown, J 1965. Radiocarbon dating, Barrow, Alaska. Arctic, 18 (1), 37�48.
Burga, C. A. 1987. G l etscher- und Vegetationsgeschichte der Sudrat ischen
Alpen seit del' Spateiszeit ( Puschl av, Livigno, Bormiese). Denkschr.
Schweiz. Natu.ifonch. Ges. , 101, I � 162.
Cheng Guodong and F. Dramis. 1992. Distribution of mountain permafrost
and climate. Pemzajimt and Periglacial Processes, 3(2), 83�9!'
Elconin, R. F. and E. R. LaChapelle. 1997. Flow and internal structure of a
rock glacier. ] Glaciol., 43 ( 144), 238�244 .
Haeberli, \'V. 1985. Creep of mountain permafrost: internal structure and
flow of Alpine rock glaciers. Eidg. Teclz. Hochschule, ::f
: iriclz. Versuchsanst.
Wasserbau, Hydro!. Glaziol. Mitt. 77.
Haeberli, W 1994. Glaciological basis of ice-core drilling on mid-latitude
glaciers. VA I V/E THZArbeitshift 14, 3�9.
climatic change.
Haeberli, W and D. Vonder Mohl!. 1996. O n the characteristics and possible
origins of ice in rock glacier permafrost. Z
band
104, 43�57.
W, J Huder,
Geomorphol. ,
Supplement­
1988.
Core drilling through rock glacier-permafrost. In Senneset, K . , ed.
Permafrost. Fifth international Conference. Proceedings. Vol. 2. August 2�5, 1988.
Haeberli,
H.-R. Keusen, J. Pika and H. Rbt h lisberger.
1J'ondheim, Tap i r Publishers, 937�942.
W, M .
Wagner. 1993.
Haebcrli,
Hoelzle,
F.
Keller,
W
Schmid,
D. S. Vonder
M u h l l and S.
l\10nitoring the long-term evolution ofmountain perma­
In Permafrost. Sixth International Conference. Proceed­
ings, 1101. 1, July 5�9 1993, Beijing, China. Guangzhou, South China
frost in the Swiss Alps.
University onechnology Press, 214�219.
Heitz, Ch.
1975. Vegetationsentwicklung
und Waldgrenzschwan kungen des
Spat- und Postglazials im Oberhalbstein (Graubundenj Schweiz) mit
(Lej
Marsch,
Radiocarbon, 2 9 (3), 347 352.
14
and PJ. Reimer. 1993. Extender!
C data base and revised
14
C A Ll B 3.0 C age calibration program. I<adiocarbon, 35(1), 215�230.
samples by accelerator mass spectrometry.
Stuiver,
M.
Suter, M. 1990. Accelerator mass spectrometry: state of the art in 1 990.
instrum. Methods Pilys. Res. , Ser. B,
29,
21 1 �223.
Ni,cI.
Vonder Muhll, D. S. 1992. Evidence of intrapermafrost groundwater flow
Processes, 3 (2), 169� 173.
Vonder Muhll, D. S. 1996.
50 (1), 17� 24.
Permafrost and Periglacial
D r i l l i ng in Alpine permafrost.
Nor. Geogr. Tidsskr.,
Vonder l\ li.i hll, D. and W. Haeberli. 1990. Thermal characteristics of the
permafrost within an active rock glacier ( Murtelj Corvatsch, Grisons,
Glacial. , 3 6 (123), 151 �158.
P Holub. 1992. Borehole logging in Alpine perma­
frost, upper Engadine, Swiss Alps. Permafrost and Periglacial Processes, 3 (2),
125� 132.
Swiss Alps). ]
Vonder Muhll, D. S. and
Vonder Miihll, D., Th. Stucki and W. Haeberli. In press. Borehole tempera­
tures i n Alpine permafrost: a ten-year series. in 7th international Conference
on Permafrost, 23�27 June 1998, Yellowknije, NWT, Canada. Proceedings. Otta­
wa, Ont., Geological Survey of Canada.
Wagenbach, D. 1994. Results from the Colic Gnifetti ice-core programme.
VAW/ETHZArbeitscheft 14, 19�22.
Wagner, S. 1992. Creep of alpine permafrost investigated on the Murtel rock
Permafrost and Periglacial Processes, 3 (2), 157� 162.
1994. Three-dimensional flow and age distribution at a h i g h­
a l t itude ice-core d r i l l i n g site. VAW/ETHZArbeitsheft H, 33�39.
Wahrhaftig, C. and A. Cox. 1959. Rock glaciers in the Alaska Range. Geol.
Soc. Am. Bull. , 70 (4), 383�436.
glacier.
Wagner, S.
\'Velten,
M.
1982.
geschichte des
Pollenallalytische
ntersuchungen zur Vegetations­
Schweizcrischen Nationalparks.
Schweiz. Nationalpark, 16 ( 80), I �43.
Yamall1oto, K. and M. Yoshida. 1987.
Ergeb. Wiss. Unten.
Impulse radar sounding of foss i l ice
within the Kuranosuke perennial snow patch, centralJapan.
ciol. ,
218�220.
M., K. YamamolO,
9,
T.
Naka­
1000�
1700 year B P. inJapan.
Zoller, H. and Ch.
K. H iguchi. H . l ida,
T.
Ann. Gla­
mura. 1990. Correspondence. First discovery of fossil ice of
Yoshida,
Ohata and
Glaciol., 36 (123), 258�259.
Brombacher. 1984. Das Pollenprofil
]
"Chalavus" bei St.
Moritz: ein Beitrag zur vVald- und Landwirtschaftsgeschichte im Ober­
377 398.
1995. War Mitteleuropa u rsprunglich eine halbof­
fene Weidelandschaft odeI' von geschlossenen \ Valdern bedeckt? Schweiz.
Z Forstwes. , 146 (5), 321 � 354.
engadin.
Diss. Bot. 72,
Festschrift Wclten,
Zoller, H . and]. N. Haas.
MS received 12 September 199 7 and accepted in revisedJorm 12 March 1998
8
Il
Mau ntschas, Stazerwald). ( l nauguraldissertation, Universitat Base!.)
14
Schlosser, P. and 7 others. 1987. l\1easurement of small volume oceanic
C
beneath an active rock glacier i n the Swiss Alps.
REFERENCES
eds. Rock
55�64.