Permafrost, Phillips, Springman & Arenson (eds)
© 2003 Swets & Zeitlinger, Lisse, ISBN 90 5809 582 7
Contemporary periglacial processes in the Swiss Alps: seasonal, inter-annual and
long-term variations
N. Matsuoka & A. Ikeda
Institute of Geoscience, University of Tsukuba, Ibaraki, Japan
K. Hirakawa & T. Watanabe
Graduate School of Environmental Earth Science, Hokkaido University, Sapporo, Japan
ABSTRACT: Comprehensive monitoring of periglacial weathering and mass wasting has been undertaken near
the lower limit of the mountain permafrost belt. Seven years of monitoring highlight both seasonal and interannual variations. On the seasonal scale, three types of movements are identified: (A) small magnitude events
associated with diurnal freeze-thaw cycles, (B) larger events during early seasonal freezing and (C) sporadic
events originating from refreezing of meltwater during seasonal thawing. Type A produces pebbles or smaller
fragments from rockwalls and shallow (10 cm) frost creep on debris slopes. Types B and C are responsible for
larger debris production and deeper (50 cm) frost creep/gelifluction. Some of these events contribute to permanent opening of rock joints and advance of solifluction lobes. Sporadic large boulder falls enhance inter-annual
variation in rockwall retreat rates. On some debris slopes, prolonged snow melting occasionally triggers rapid soil
flow, which causes inter-annual variation in rates of soil movement.
10º00'E
9º40'E
Real-time monitoring of periglacial slope processes is
useful to predict ongoing slope instability problems in
alpine regions. Such a prediction, however, needs longterm variations in slope processes caused by climate
change to be distinguished from inter-annual scale variations. The latter may mask the long-term trends by
affecting the annual freeze-thaw depth. In addition, partial melting of permafrost, which could trigger a large
mass movement, may result either from an episodic
warming event or from long-term warming. These situations call for long-term monitoring of slope processes.
In this context, a monitoring project has been undertaken since 1994 near the lower limit of the mountain
permafrost belt in the Upper Engadin, Swiss Alps
(Matsuoka et al. 1997, 1998). The monitoring involves
measurements of bedrock shattering, rock glacier
creep (discussed elsewhere in this volume: Ikeda et al.
2003), soil movement and associated parameters. This
paper presents data from the first seven years, focusing
on seasonal, inter-annual and long-term variability of
these processes.
The monitoring sites described here include four
rockwalls (Murtèl, Büz, TFN, TFS) and two debris
slopes (Valletta, Padella) (Fig. 1). The Murtèl site
(N-facing, 2890 m ASL) consists of greenschists while
the Büz site (N-facing, 2880 m ASL) consists of shale.
TFN and TFS (both 2850 m ASL) are located on the
northern and southern faces of a small peak, respectively, which consists of massive limestone. The
Valletta site (SW-facing, 2810 m ASL) is located near
the top of a small hill and displays miniature sorted
Piz Kesch
3418
Switzerland
Inn
Piz d'Err
3378
Piz Ot
3246
46º30'E
Italia
Samedan
A
St. Moritz
1822
Pontresina
46º30'E
1 INTRODUCTION
B
Piz Corvatsch
3451
Piz Bernina
4049
Italia
9º40'E
10º00'E
Figure 1. Location map. The area A includes the Valletta,
Padella, Büz, TFN and TFS sites and the area B includes the
Murtèl site.
stripes. The Padella site (E-facing, ca. 2690 m ASL) is
located on a debris-mantled slope, where numerous
stone-banked lobes are developed.
2 ROCKWALL PROCESSES
Milimetre-to-decimetre scale bedrock shattering has
been investigated by rock joint opening and debris
dislocation from painted rock faces. The volume of
large boulder falls was also investigated in the thawing period of 1997.
735
2.1
0.1–0.5 mm accompanied seasonal freezing in early
winter (type B). Superimposed on type B was opening
that occurred at the onset of seasonal thawing when
the rock surface was situated in the zero-curtain (type
C). Snow-melt water would fill the space of the rock
joint still at a subfreezing temperature and its refreezing may cause opening (Matsuoka 2001a). Although
the type C events did not recur every year, individual
opening amounted to 0.5 mm or more. Furthermore,
this event usually induced permanent opening after
complete thawing, while most of the type A and B
events were temporary. The mean opening rate over
1994–2001 was ⬃0.1 mm a1 with a significant interannual variation (Table 1). All three events took place
Rock joint opening
A crack extensometer connected to a data logger
recorded automatically the width of a rock joint at 1-h
intervals and thermal probes measured rock temperatures in the joint (for details see Matsuoka et al. 1997).
Significant movement occurred at the Murtèl rockwall. Three types of movements (A–C) were identified (Fig. 2). The repetition of opening and closing of
the order of 102 mm occurred frequently in autumn,
accompanying diurnal freeze-thaw cycles (type A).
Joint width also slightly fluctuated during summer,
possibly related to wet–dry or warm–cool cycles, but
the opening was much smaller. An expansion of
Expansion (mm)
2.0
(A) Crack movement, 1994-2001
1.5
type C
1.0
type B
type A
0.5
0.0
1994
1995
1996
1997
1999
2000
1-Jan
1-May
1-Sep
1-May
1-Jan
1-Sep
1-Jan
1998
1-May
1-Sep
1-May
1-Jan
1-Sep
1-Jan
1-May
1-Sep
1-May
1-Jan
1-Sep
1-May
(B) Crack-top temperature, 1994-2001
1-Jan
20
15
10
5
0
-5
-10
-15
1-Sep
Temperature (ºC)
-0.5
2001
Figure 2. Rock joint opening on the Murtèl rockwall, 1994–2001.
Table 1. Summary of periglacial monitoring, 1994–2001.
Year
Murtèl (rockwall, 2890 m ASL)
Mean annual rock temperature at 10 cm depth (°C)
Maximum joint opening (mm)
Annual joint opening (mm a1)
Valletta (sorted stripes, 2810 m ASL)
Mean annual soil temperature at 10 cm depth (°C)
Seasonal frost depth (cm)
Seasonal frost heave (cm)
Annual surface movement shown by strain probe (cm a1)
Annual surface movement shown by painted line (cm a1)
Padella (solifluction lobe, 2690 m ASL)
Mean annual soil temperature at 10 cm depth (°C)
Seasonal frost depth (cm)
Seasonal frost heave (cm)
Annual surface movement shown by painted line (cm a1)
Maximum snow depth (cm)
NA Data not available.
736
94/95
95/96
96/97
97/98
98/99
99/00
00/01
1.8
0.85
0.22
2.5
0.14
0.12
1.7
0.52
0.00
1.6
2.01
0.40
1.9
0.82
0.10
1.3
0.29
0.08
0.2
0.05
0.08
0.0
⬃200
0.9
–
–
0.2
200
0.6
1.1
–
0.7
100
1.6
0.2
–
0.8
200
0.9
0.6
–
0.6
⬃170
1.2
0.1
–
0.4
200
1.2
1.0
2.4
0.9
80
2.9
0.8
1.9
0.7
170
4.8
–
NA
0.5
200
5.3
–
NA
NA
130
5.1
–
150
NA
180
4.8
–
110
NA
NA
NA
3.7
180
1.0
190
5.1
3.2
NA
1.5
50
5.5
1.1
320
et al. 1999). It is most likely that the frequent production of pebbles or smaller debris contributes to only
a small part of the long-term rockwall retreat, while
occasional boulder falls govern the retreat. In fact, the
volume of a large boulder fall from the Murtèl rockwall during the thawing period of 1997, was equivalent to the mean long-term retreat rate.
mostly when the rock surface temperature reached or
remained just below 0°C, indicating in-situ freezing
as a primary cause of expansion. The type A and B
events occurred also on the Büz rockwall.
2.2
Rockfalls
The repetition of opening and closing of joints may
eventually lead to rockfalls. Such rockfalls were evaluated from rock fragments detached from 13 painted
quadrangles (50 cm 50 cm). The volume of fragments was measured every summer and their total
then converted to annual rockwall retreat for each
quadrangle.
Whereas a south-facing rockwall (TFS) produced
rock debris constantly over 7 years, north-facing rockwalls (TFN, Murtèl) showed irregular annual retreat
rates with an extraordinary rate (1.5 mm a1) occurring once at TFN1 (Fig. 3). This contrast may reflect,
at least partly, the type of joint opening. South-facing
rockwalls experience numerous short-term freezethaw cycles even in mid-winter because of the lack of
snow cover. This condition favours surficial, small
but frequent joint opening (type A). In contrast, as
indicated by data at Murtèl, the type B and C events
probably prevail on north-facing rockwalls. Despite
their infrequent occurrence, the latter two events
produce deeper and more intensive opening, which
may result in greater inter-annual variations in the
retreat rate.
However, most of the quadrangles showed very
small retreat rates (0.1 mm a1), despite highly fractured nature (joint spacing 10 cm). The retreat rates
are much smaller than the long-term rates estimated
from the volume of alpine talus cones or rock glaciers
(e.g. 1–2 mm a1 at the Murtèl rockwall: Haeberli
3 DEBRIS SLOPE PROCESSES
Automated monitoring of soil movement was conducted at the Valletta and Padella sites. Vertical and
downslope movements were measured with dilatometers and strain probes, respectively, and soil temperature was monitored at various depths (for details see
Matsuoka et al. 1997). Data loggers recorded these
quantities at 1–3 h intervals.
3.1
Figure 4 displays five years of soil movement on sorted
stripes at the Valletta site. Mean annual near-surface
soil temperatures were close to 0°C (Table 1), which
implies the possible presence of permafrost below a
thick active layer. However, permafrost is unlikely to
contribute to soil movement, because it lies, if present,
far below the regolith-bedrock interface at ⬃60 cm
depth. The ground temperatures showed significant
inter-annual variability, such as frequent diurnal fluctuations even in mid-winter (1995/96), the absence of
both diurnal and seasonal fluctuations in winter
(1996/97) and in-between conditions in the other
winters (Fig. 4C).
Three types of frost heave, equivalent to types A–C
of joint opening, were observed on a fine stripe
(Fig. 4B). Diurnal frost heave cycles (type A) took
place frequently in both autumn and spring.
Extremely high frequency variations were recorded
when snow cover was lacking in winter (1995/96).
Heaving (ice lens growth) was confined to the top
5 cm of soil. Despite the small heave amounts
(1 cm), differential heave often took place between
the coarse and fine stripes (Matsuoka et al. 2002). The
amount of seasonal heave (mostly type B) varied from
0.6 to 2.9 cm (Table 1). Relatively large heave was
associated with significant winter snow cover. A small
heave event (type C) occurred during some zerocurtain (seasonal thawing) periods. A comparison
between soil temperature profiles and seasonal heave
indicated that ice lenses grew largely within the top
20 cm during the type B and C events.
Downslope soil movement mirrored frost heave
activity (Fig. 4A). Whereas the surficial soil (0–12 cm
deep) responded mainly to the type A heave events,
1.6
MU6 (Greenschist, N, 60º,
J = 4.2 cm)
1.4
Erosion (mm/a)
1.2
TFN1 (Limestone, N, 70º,
J = 5.3 cm)
1
TFS2 (Limestone, SE, 75º,
J = 2.5 cm)
0.8
0.6
0.4
0.2
0
94/95
95/96
96/97
97/98
Period
98/99
99/00
Movement of sorted stripes
00/01
Figure 3. Erosion rates of three painted quadrangles on
rockwalls, 1994–2001. Legends involve lithology, aspect,
gradient and mean joint interval (J).
737
4
Depth (cm)
Displacement (cm)
5
3
2
1
Displacement (cm)
-1 0 1 2 3 4 Profile by
0
excavation on
10
24 July 2001
20
30
40
A. Deformation of strain probe
0 cm
24 cm
12 cm
36 cm
0
-1
Heave (cm)
2
B. Frost heave
1
0
-1
-2
Temperature (ºC)
40
C. Soil temperature
30
0 cm
30 cm
150 cm
20
10
0
1-Aug-00
1-Jun-00
1-Apr-00
1-Feb-00
1-Dec-99
1-Oct-99
1-Aug-99
1-Jun-99
1-Apr-99
1-Feb-99
1-Dec-98
1-Oct-98
1-Aug-98
1-Jun-98
1-Apr-98
1-Feb-98
1-Dec-97
1-Oct-97
1-Aug-97
1-Jun-97
1-Apr-97
1-Feb-97
1-Oct-96
1-Dec-96
1-Aug-96
1-Jun-96
1-Apr-96
1-Feb-96
1-Dec-95
1-Aug-95
-20
1-Oct-95
-10
Figure 4. Soil movement (downslope and vertical) and temperatures on sorted stripes, Valletta site, 1995–2000.
1 cm. The seasonal heave (mostly type B) was much
larger than the type A events, amounting to ⬃5 cm
regardless of the seasonal frost depth (Table 1). A
large part of the type B heave occurred before the
frost table reached a depth of 50 cm, suggesting that
ice lenses formed largely within the top 50 cm. A type
C heave event was sometimes superimposed on the
type B (e.g. in 1998), but the magnitude was much
smaller than the latter (Fig. 5B).
Although monitoring with a strain probe was successful only in the 1998–2000 period, the available
data indicated a nearly constant surface velocity
(2–3 cm a1), a maximum depth of movement of
40 cm, and a straight-to-concave downslope velocity
profile (Fig. 5A). These characteristics were consistent
with manual measurements with painted lines and
flexible tubes. The velocity profile mainly reflected
seasonal frost heaving, suggesting the primary role of
annual frost creep and gelifluction (cf. Matsuoka
2001b). Such a deeper movement in comparison with
that at the Valletta site reflects the thick fine sediment
(
2 m) at the foot slope location.
A different type of movement took place on another
lobe located 50 m upslope of the Padella site, where
prolonged water supply from a late-lying snow patch
can raise soil water content above a critical level for a
the subsoil (12–24 cm deep) moved with annual frost
heave cycles (types B, C). As a result, the velocity
profile was concave downslope (see the inset in
Fig. 4A), which suggests the primary role of diurnal
frost creep (cf. Matsuoka 2001b). Such a shallow
movement mainly reflects the thin fine debris layer.
The mean surface velocity was ⬃0.5 cm a1 over 6
years, with the highest value of 1.1 cm a1 in the first
year (Table 1).
3.2
Movement of solifluction lobes
Results of monitoring on a solifluction lobe at the
Padella site are summarized in Table 1 and Figure 5.
This site recorded 0.6–0.7°C higher mean annual soil
temperatures than the Valletta site. Permafrost is probably absent, but seasonal frost penetrates deeply, with
a large inter-annual variation in depth (50–200 cm)
according to snow conditions.
Short-term frost heave cycles (type A) occurred in
autumn, but they were rare in spring because of the
late-lying snow cover (Fig. 5B). A large heave event
(5.6 cm) occurred in early October 1999, which
accompanied short-term freezing to a depth of 20 cm.
With this exception, the type A heave rarely exceeded
738
Profile by excavation
on 1 Aug. 2000
A. Deformation of strain probe
0
4
Depth (cm)
Displacement (cm)
6
0 cm
12 cm
2
Logging start
24 cm
36 cm
0
Displacement (cm)
-2 0 2 4 6 8
10
20
30
40
50
-2
Heave (cm)
6
B. Frost heave
4
2
Frame bent by
snow pressure
Data not available
in 1998-1999
0
-2
-4
30
C. Soil temperature
0 cm
30 cm
Data not available
in 1998-1999
10
225 cm
0
1-Aug-01
1-Jun-01
1-Apr-01
1-Feb-01
1-Dec-00
1-Oct-00
1-Aug-00
1-Jun-00
1-Apr-00
1-Feb-00
1-Dec-99
1-Oct-99
1-Aug-99
1-Jun-99
1-Apr-99
1-Feb-99
1-Dec-98
1-Oct-98
1-Aug-98
1-Jun-98
1-Apr-98
1-Feb-98
1-Dec-97
-20
1-Oct-97
-10
1-Aug-97
Temperature (ºC)
20
Figure 5. Soil movement (downslope and vertical) and temperatures on a solifluction lobe, Padella site, 1997–2001.
0
-20
50
100
Distance (cm)
150 200 250
300
350
4 SEASONAL, INTER-ANNUAL AND
LONG-TERM VARIATIONS
400
0
The seven years of monitoring have highlighted temporal changes in alpine periglacial processes, both on
seasonal and inter-annual time scales.
Firstly, on the seasonal time scale, three types of
frost action operate during different periods. The
type A action originates from short-term freeze-thaw
cycles which take place mainly before seasonal freezing and after seasonal thawing. Despite low magnitude, its high frequency, regularity and ubiquity allow
type A to dominate over a wide area and to promote
surficial but rapid movement. Such a movement is
probably responsible for pebble falls and small-scale
patterned ground. Seasonal freezing involves the type
B (accompanying frost penetration in early winter)
and C (generated by refreezing of melt water) actions.
On thawing, these two types combine to induce
deeper and more voluminous movement and, in
terms of the erosion rate, much more important than
type A.
Displacement (cm)
20
40
60
80
100
120
140
95/96
96/97
97/98
98/99
99/00
00/01
160
Figure 6. Annual surface movement on a solifluction
lobe, upslope of the Padella site, 1995–2001.
rapid flow. In fact, painted lines demonstrated the
occurrence of a rapid soil flow, with downslope movement of about 100 cm, during the thawing periods of
1996 and 2000 (Fig. 6).
739
Dramis, F., Govi, M., Gugliemin, M. & Mortara, G. 1995.
Mountain permafrost and slope instability in the Italian
Alps: the Val Pola landslide. Permafrost Periglac.
Process. 6: 73–82.
Haeberli, W. 1996. On the morphodynamics of ice/debristransport systems in cold mountain areas. Norsk
Geogr. Tidsskr. 50: 3–9.
Haeberli, W., Wegmann, M. & Vonder Mühll, D. 1997.
Slope stability problems related to glacier shrinkage
and permafrost degradation in the Alps. Eclogae Geol.
Helvetiae 90: 407–414.
Haeberli, W., Kääb, A., Wagner, S., Vonder Mühll, D.,
Geissler, P., Haas, J.N., Glatzel-Mattheier, H. &
Wagenbach, D. 1999. Pollen analysis and 14C age of
moss remains in a permafrost core recovered from the
active rock glacier Murtèl-Corvatsch, Swiss Alps: geomorphological and glaciological implications. Jour.
Glaciol. 45: 1–8.
Harris, S.A. 2001. Twenty years of data on climatepermafrost-active layer variations at the lower limit of
alpine permafrost, Marmot Basin, Jasper National
Park, Canada. Geogr. Ann. 83A: 1–13.
Ikeda, A., Matsuoka, N. & Kääb, A. 2003. A rapidly moving small rock glacier at the lower limit of the mountain permafrost belt in Swiss Alps. In this volume.
Lewkowicz, A.G. & Clarke, S. 1998. Late-summer solifluction and active layer depths, Fosheim Peninsula,
Ellesmere Island, Canada. In A.G. Lewkowicz &
M. Allard (eds.), Proc., 6th Intern. Conf. Permafrost,
Yellowknife, Canada: 641–666. Centre d’études
nordiques, Univ. Laval: Sainte-Foy.
Matsuoka, N. 2001a. Direct observation of frost wedging in
alpine bedrock. Earth Surf. Process. Landforms 26:
601–614.
Matsuoka, N. 2001b. Solifluction rates, processes and landforms: a global review. Earth-Sci. Rev. 55: 107–134.
Matsuoka, N. & Sakai, H. 1999. Rockfall activity from an
alpine cliff during thawing periods. Geomorphology
28: 309–328.
Matsuoka, N., Abe, M. & Ijiri, M. 2002. Differential frost
heave and sorted patterned ground: field measurements and a laboratory experiment. Geomorphology:
in press.
Matsuoka, N., Hirakawa, K., Watanabe, T. & Moriwaki, K.
1997. Monitoring of periglacial slope processes in the
Swiss Alps: the first two years of frost shattering,
heave and creep. Permafrost Periglac. Process. 8:
155–177.
Matsuoka, N., Hirakawa, K., Watanabe, T., Haeberli, W. &
Keller, F. 1998. The role of diurnal, annual and millennial freeze-thaw cycles in controlling alpine slope
instability. In A.G. Lewkowicz & M. Allard (eds.),
Proc., 7th Intern. Conf. Permafrost, Yellowknife,
Canada: 711–717. Centre d’études nordiques, Univ.
Laval: Sainte-Foy.
Wegmann, M. & Gudmundsson, G.H. 1999. Thermally
induced temporal strain variations in rock walls
observed at subzero temperatures. Proc. 6th Intern.
Symp. Thermal Engineering and Sciences for Cold
Regions, 511–518. Springer-Verlag: Heidelberg.
Secondly, three types of movements are subject to
inter-annual variation. The annual frequency of type A
events varies mainly with the duration of the snowcover period, and this variation may affect the annual
movement. The inter-annual variability of type B and
C events depends on the seasonal frost (or thaw) depth
and snow conditions. The amounts of seasonal frost
heave and solifluction may significantly change in
regions with cold permafrost, where upward freezing
from the permafrost table causes ice segregation near
the base of the active layer (e.g. Lewkowicz & Clarke
1998). In contrast, inter-annual variation in the
solifluction rate is likely to be small in regions with
deep seasonal frost or warm permafrost like the study
sites, because frost heave and solifluction occur largely
within the top 50 cm of soil regardless of the seasonal
frost (or thaw) depth. In such an environment, interannual variation in soil movement depends mainly on
prolonged snow melting that triggers a rapid soil flow.
The annual rockwall retreat would change considerably with the occurrence of a large boulder fall, which
requires a number of annual freeze-thaw cycles and
removal of the underlying smaller clasts (Matsuoka &
Sakai, 1999).
The final remark is on the effect of long-term
climate change on periglacial processes. Indeed, a
number of monitoring/modelling projects have been
concerned with the influence of global warming on
alpine periglacial processes (e.g. Haeberli 1996,
Wegmann & Gudmundsson 1999, Davies et al. 2001).
Long-term warming results in thinning of the seasonal frost depth in non-permafrost sites. This potentially impedes frost-induced processes, where ice
segregation occurs in the lower part of the seasonal
frost. Warming would affect more significantly the
active layer processes in permafrost sites, particularly
where melting of ice lenses accompanies the active
layer deepening. On a time scale of decades or shorter,
however, inter-annual fluctuation or an episodic warm
year may often hinder such a long-term trend, because
it may involve temporary melting of the uppermost
few decimetres of permafrost. In contrast, except
where permafrost is very thin, inter-annual fluctuation
or an episodic event may not result in basal melting of
permafrost (cf. Harris 2001), which potentially destabilizes a decametre-thick material (e.g. Dramis et al.
1995, Haeberli et al. 1997).
REFERENCES
Davies, M., Hamza, O. & Harris, C. 2001. The effect of rise
in mean annual temperature on the stability of rock
slopes containing ice-filled discontinuities. Permafrost
Periglac. Process. 12: 137–144.
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