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Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
13
DOI: 10.4408/IJEGE.2011-03.B-002
INFLUENCE OF THE CONNECTIVITY WITH PERMAFROST
ON THE DEBRIS-FLOW TRIGGERING IN HIGH-ALPINE ENVIRONMENT
E. BARDOU, G. FAVRE-BULLE, P. ORNSTEIN & J.-D. ROUILLER
(*)
(*)
Research Center on Alpine Environment CREALP, r. de l'Industrie 45, CH-1950 SION - Email: eric.bardou@crealp.vs.ch
INTRODUCTION
Results from a case study of debris-flow events
involving permafrost-related features provide new in-
formation regarding the relationship between debris-
flow hazard and permafrost in an alpine environment.
In the European Alps, a series of debris flows at
the end of the 1990's already highlighted the connec-
tion between permafrost (or so-called recently degla-
ciated area) and debris flow (H
aebeRli
et alii, 1991;
H
aRRis
& G
ustafson
, 1993; R
iCkenmann
& z
immeR
-
mann
, 1993). This sensitivity of the high-altitude en-
vironment is similar in other mountain ranges (e.g.
s
einova
, 1991; P
alaCios
et alii, 1999, s
einova
& z
ol
-
otaRev
, 2003). In the same period, with the accumu-
lation of evidence on global warming many authors
have predicted an increase in debris flows triggered by
melting of previously frozen sediments (z
immeRmann
& H
aebeRli
, 1992; R
ebetez
et alii, 1997).
Frozen soils have been the subject of several geo-
technical studies aimed at understanding the micro-
mechanisms leading to their deformation (e.g. d
ysli
,
1993; H
aRRis
et alii, 2003; a
Renson
& P
almeR
, 2005;
a
Renson
& s
PRinGman
, 2005). However, as noted by
d
ysli
(2007), only a few studies concentrated on the
processes during thaw. Owing to the logistical difficul-
ties, most of these studies are done in the labs. To our
knowledge, only a few are directly done in the field
(t
eysseiRe
et alii, 2000; s
PRinGman
& t
eysseiRe
, 2001).
This work shows how debris-flow triggering is
connected to permafrost at a macro-scale manage-
ABSTRACT
The study area is the Bonnard glacier which lies
in the Anniviers Valley, Valais, Switzerland. Two
glacial torrents originate from a source area that
is composed of 60% of creeping permafrost which
supplies loose material. Heavy rainfall events trig-
ger debris flows on the steep slopes of the lower
permafrost complex. Three scarps are visible, two
of them from the last event in 2008. In scar n°1 the
permafrost plays a key role in triggering debris flow
by loading the streambed with unstable materials and
creating an impervious layer due to the presence of
ice and/or frozen ground. In scar n° 2 the triggering
follows shallow landslide liquefaction with no signs
of permafrost, though we know that it surrounds this
area. There, we assume that the water circulation,
influenced by frozen layer upstream is a key factor.
Scar n°3 shows only superficial erosion that contrib-
utes to gully recharge. Four processes of debris-flow
triggering related to permafrost can be highlighted:
cohesion loss of sediments due to thaw in the ma-
trix, cohesion reduction due to the constant creep-
ing, spatio-temporal changes in water circulation and
constant rejuvenation of sediment on the slope. For
this site, the permafrost complex is a key factor for
the triggering of debris flow, although we should take
into consideration all other geomechanical processes
that may occur in loose sediments.
K
ey
words
: alpine debris flow, triggering, permafrost
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E. BARDOU, G. FAVRE-BULLE, P. ORNSTEIN & J.-D. ROUILLER
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
the scope of this paper to outline in detail these parts
of the catchments and we will refer to it below as the
permafrost complex or the Bonnard glacier.
The geology of the source area is located on the
contact between the thrust sheets of the Dent Blanche
and Tsaté systems (P
illoud
& s
aRtoRi
1981). The
granitic gneisses of the Dent Blanche covering the
Bonnard glacier fall from the cliffs that surround
Diablons summit. The outcrops directly around the
glacier and moraine bastion are made of gabbros. The
outcrops and the cliffs are fractured and produce a
very large amount of blocks that rarely exceed 1 m
in diameter. Scree fans completely encircle the gla-
cial system as can be seen on Figure 4. The slopes
below the source area are mainly formed by hanging
till from the Zinal glacier and others slopes deposits.
The slope downstream from the source area is
very steep (Figg. 4 and 6), exceeding 80% just after
the initiation zone. Below 2500 m a.s.l., the slope fall
to less than 40% occasionally inducing debris-flow
deposition. In the last third of the long profile a rock
cliff increases the slope before the gentle reduction on
the alluvial fan (with a mean slope of ~18%).
PERMAFROST FEATURES
The permafrost zone of the Bonnard glacier is
very complex, with a combination of feature includ-
ing rock glacier, moraine, push moraine and covered
glacier or at least shreds of a former glacial edifice
able in the field. In presenting 4 chains of
processes leading to debris flow formation, the
studied site stands as an interesting outdoor
laboratory. These 4 different ways of connect-
ing permafrost to debris flow may be combined
providing a glimpse of the complexity of the
high-alpine environment as already noted by
others (e.g. H
aebeRli
, 1992). However, this
work is not an exhaustive presentation of the
possible connection between debris flow and
permafrost, but it presents a first step toward a
functional analysis at a macro-scale of alpine
catchments suffering permafrost degradation.
Traditionally in mountainous environments,
streams are influenced by water and sediments.
Thus, catchments may be divided into (s
uRell
,
1841; m
eunieR
, 1991):
1. a source area (or production area for water
as well as for sediments);
2. a transient area (where erosion and deposition
may occurs alternatively);
3. a deposition area (on the alluvial fan where the
deposition is the preponderant process).
During our study it became clear that at this mac-
ro-scale we have to distinguish between two debris
flow stages: an initial stage encompassing the onset of
the movement phase to the preliminary flow under a
debris-flow form and an advanced debris flow stage in
which the characteristics derived from the initial stage
have evolved during the flow downstream. The evolu-
tion concerns not only the volume (e.g. k
inG
, 1996)
as it will be emphasized here, but also other intrinsic
characteristics such as the grain size distribution and
the relative mineralogical composition, which in turn
may change the flow behaviour (b
aRdou
et alii, 2007).
STUDY AREA
GENERAL SETTINGS
The study area is located in the Canton of Valais,
Southwestern Switzerland (Figure 1). The catchments
range in altitude between of 1660 and 3548 m
asl
. It
implies that low temperature (freezing) and snow play
an important role in the water balance across the year.
The area concerned is about 3 km
2
of which the source
area represents ~1.7 km
2
. Two torrents originate from
there, the Pétérey in the North and the Tracuit's torrent
in the South. Approximately 60% of the source area
is composed by creeping permafrost. It is beyond of
Fig. 1 - Location of the study area
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INFLUENCE OF THE CONNECTIVITY WITH PERMAFROST ON THE DEBRIS-FLOW TRIGGERING IN HIGH-ALPINE ENVIRONMENT
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
15
clue about this activity: indeed, in former dialect,
Pétérey means quagmire. Considering events de-
tected by dendrochronology analysis (s
toffel
&
b
ollsCHweileR
, 2009), a total of at least 15 major
events have been recorded for the Pétérey (Fig. 3).
People living near the torrent's bank speak of a mean
of 1, with up to 3 debris flows per year. However the
sensitivity of local inhabitants (Zinal has been in-
habited year round only since 1961) increases with
time as roughly depicted by the detection threshold
on Figure 3. The building of the retention dam (since
1958) increased this threshold at the beginning, but
has been less effective since 1980 due to less main-
tenance as a result of rising costs.
Conversely, only 2 major events are reported
for the Tracuit's torrent, probably due to the lack
of historical data. However, these two debris flows
originated from an area corresponding to the shal-
low landslide scar at the border of the permafrost
complex, mainly formed here by what we think is a
push moraine (Figure 4).
RESULTS OF FIELD OBSERVATIONS
PERMAFROST AREA & TRIGGERING POINTS
As shown by the geomorphological map (Fig. 4),
the debris flow triggering zones are located in the lower
part of the permafrost complex. However, all starting
points present different features. The detailed map of
this area (Fig. 5) illustrates these differences.
Scar n°1 delimits the terrain where Figure 2 is
located. The ice near the surface is covered with
unstable blocks with matrix elements at the base.
Most recent "initial debris flows" seem to origi-
nate from this zone, lying at the end of one of the
major mapped sub-channels (see below). Field
evidence and older photographies do not exclude
triggering from the other stream branch, but fresh
tracks were not visible during our field campaigns.
Scar n° 2 represents the starting zone for two re-
ported debris flows in Tracuit's torrent. Field obser-
vations made in the scar after the last event (in 2008)
didn’t show any humidity or ice traces. The scoured
depth was approximately 1.5 m, with an estimated
500 m
3
of material that started moving as a shallow
landslide. The downstream channel presents fresh
erosion marks. It is of interest to note that in 2009,
even on this >35° slope, some material was already
stored in the channel, which is a similar timescale to
(visible on the maps of XIX century). Indeed, massive
ice was sometimes observed (Fig. 2).
This permafrost complex feeds the two tor-
rents with loose material, but debris-flow frequency
in each torrent differs notably. The displacement
measurement made by differential global position-
ing system (DGPS) on more than 150 points on the
whole area show that since 2006 the average dis-
placements have been around 0.5 m/a.
EVENT HISTORY
The Pétérey, that originates from the north lobe
of the complex outbreaks frequently. The etymol-
ogy of this very active torrent itself gives us a first
Fig. 2 - Massive ice observed at the Péterey's triggering zone
Fig. 3 - Historical chronic of events recorded for the Pétérey.
The magnitude-index is derived form the level of damag-
es or area covered by debris: 1 is for middle-sized event,
2 for rare and 3 for extreme (information about dendro-
chronology is from S
toffel
& B
ollSchweiler
, 2009)
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E. BARDOU, G. FAVRE-BULLE, P. ORNSTEIN & J.-D. ROUILLER
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
Fig. 4 - Simplified geomorphological map of the Bonnard glacier complex. Debris-flow triggering zones investigated are on
the headwaters of the torrents (roughly on the 2800 m contour line)
Fig. 5 - Map of the debris flow triggering zones as observed during field campaigns achieved between 2007 and 2009
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INFLUENCE OF THE CONNECTIVITY WITH PERMAFROST ON THE DEBRIS-FLOW TRIGGERING IN HIGH-ALPINE ENVIRONMENT
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
17
one reported by b
ovis
& J
akob
(1999) and far more
rapid than one reported by b
enda
& d
unne
(1997).
Small initial debris flows also started from
zone n°3. This source area presents a diffuse
erosion pattern linked to thin superficial runoff
(small rills) without evidences of water supply
from the upstream permafrost complex. A part
of the material that originates from scar n°3 has
already been deposited downstream as scree (on
slope >35°). Further downstream, at ~2630 m
a.s.l., other fresh intermediate deposits (levees
and complete snout) could be seen after the 2008
survey on a slope between 30-33°.
During the summer of 2007, in scar n°1 we per-
formed a tracer test in water running along the upper
part of the cover material. The estimated transit veloc-
ity of 4'000 m/d is ~10 times slower than what can be
expected for free surface runoff and ~1000 times faster
than in a very porous material. Calculated values are
representative of fractured aquifers and these magni-
tudes are semi-quantitative proxies for describing sub-
surface hydrological processes. They are very rapid in
this area (north lobe), which contrasts with the absence
of surface water in the south lobe of the complex.
OTHERS PARAMETERS INFLUENCING THE FINAL
MAGNITUDE OF DEBRIS FLOw
As shown simplified in Figure 4, in addition to
the permafrost complex, other processes may con-
tribute to the final debris-flow volume (detailed map-
ping performed in the study). These processes include
shallow and deep-seated landslides (e.g. b
auR
et alii,
1992; i
veRson
et alii, 1997; J
akob
et alii, 1997; R
eid
et alii, 2003), and slope of the reach, which influences
deposition (proportionally to the debris-flow magni-
tude). These processes can contribute to recharging
the gully, which in turn balances the probability of
occurrence of large debris flows (J
akob
et alii, 2005).
If we consider the cumulative volume of the 2008
debris flow that occurs in the Pétérey one could see
that the initial volume of debris directly linked to the
permafrost area is only 17% of the total volume (Fig.
6). It should be noted that this ratio is only representa-
tive for this particular event, which is, according to the
debris-flow history, a middle-sized event (magnitude-
index of 1 on Fig. 3). For other magnitudes or in other
environments this ratio may change (e.g. k
inG
, 1996;
J
oHnson
et alii, 2008).
During the same rainfall event, a ~1'500 m
3
debris
flow occurred in the Tracuit's torrent. Evidence shows
that the main source area is scar n°2 (Fig. 5). Here, the
initial debris flow represents 25% of the whole volume.
DISCUSSION
SCAR N°1
In scar n°1 (Fig. 5), permafrost plays a key role in the
triggering of debris flows. However, this role is defined by
several mechanisms. First, due to the slope (38-40°) and
the constant movement induced by Bonnard glacier com-
plex, sediments of all sizes are at the limit of equilibrium.
Individual elements are available for mass wasting and
in close connection with the thalweg's torrent. Unstable
material on these slopes may be regarded as very likely
to develop debris flow (R
iCkenmann
, 1999). After resur-
gence of water, bed erosion thickness itself can be greater
than 5 m in this environment (k
RonfellneR
-k
Raus
, 1984;
R
iCkenmann
& z
immeRmann
, 1993).
Second the presence of ice (lens or shreds from
former the glacier) and/or frozen soil tend to facilitate
the concentration of water as observed in other perma-
frost complexes (e.g. k
RaineR
& m
ostleR
, 2002). From
the strict point of view of debris-flow triggering, sudden
water supply is sufficient to mobilize sediments, due to
drag forces and/or increase of pore pressure in the soil
(a
ndeRson
& s
itaR
, 1995; R
eid
et alii, 1997). However
in the case of Pétérey, due to the nature of the deposits,
pore pressure increase should dissipate rapidly after the
onset of movement. It is difficult to determine whether
the pore pressure increase is a preponderant process or
not. In addition, thin layers of similar material lying on
bedrock in a non permafrost area could experience ini-
tial debris flow of the same magnitude.
Fig. 6 - Cumulative volume of the 2008 debris flow as sur-
veyed in the field. The major part of the deposition
occurs in a sediment trap
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E. BARDOU, G. FAVRE-BULLE, P. ORNSTEIN & J.-D. ROUILLER
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
ficient to saturate the soil at 1.5 m depth, as observed.
Thus here, the permafrost has influenced the water
supply but not the geotechnical characteristics.
SCAR N° 3
The material starting to move from scar n°3 with-
in the area that has undergone important displacement
(≥1 m/a) in the south lobe of the complex. There, the
thrust from the upstream creeping permafrost continu-
ously rejuvenates the sediments in the slope, keeping
it naturally at the limit of the friction angle. This collu-
vial material may be the primary source of sediments
transfer (m
ontGomeRy
& b
uffinGton
, 1997), which
in turn may concentrate to form debris flows. This
could be similar to the hydrologicaltriggering type
described by m
eunieR
(1991). Based on the current
observations, it is impossible to quantify the propor-
tion of material originating directly from this scar as
an initial debris flow with the proportion of material
eroded along the path that contributed to the final total
debris flows volume deposited on the fan. The onset
of particle movement due to the development of drag
forces can be derived from the work of many authors,
although not explicitly described as a triggering phe-
nomenon (e.g. J
ulien
, 1998; t
akken
& G
oveRs
, 2000;
e
GasHiRa
et alii, 2001). For now it is not clear if this
source represents a small part of the volume for each
debris flow, or if it contributes to gully recharge, lead-
ing to more intense future debris flows.
SCAR N° 2
In this zone, the triggering mechanism is similar
to a shallow landslide liquefaction classically reported
as a factor in debris flow formation (e.g. s
assa
, 1984;
f
leminG
et alii, 1989; i
veRson
et alii, 1997). Altough
we have no evidence of permafrost in this scar, we
know it surrounds the zone. A possible direct effect of
permafrost on the onset of movement may be due to
the decrease in apparent cohesion with melting of ice
particles (a
Renson
& s
PRinGman
, 2005).
By combining information about connectivity and
the sediment dynamics on a long profile, we show
the importance of the permafrost complex relative
to other mass wasting processes. Figure 7 shows that
only a very short part of the stream is connected to the
permafrost complex. Intuitively, with regard to other
downstream sediment feeding mechanisms, the part of
the debris flow material possibly linked with perma-
frost should represent only a part of the whole volume.
An indirect effect of permafrost may be changes
in the near surface flow paths upstream of the scar.
Several authors have noted that these processes may
lead to triggering (P
alaCios
et alii, 1999; C
HiaRle
et
alii, 2007). In our case, no moisture is observed in the
scar, and compared with tests performed in similar en-
vironments by t
eysseiRe
et alii (2000) it is unlikely
that the rainfall can percolate deep into the ground,
thus intermittent water supplies must come from up-
stream. Indeed, the 1
st
July 2008 rainfall was not suf-
Fig. 7 - Long profile wrapped with: the major dynamic (white or gray background); quality of the substratum (patterns);
extension of the permafrost complex. There is no information about material depth, vertical separation are there only
for graphic purpose
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INFLUENCE OF THE CONNECTIVITY WITH PERMAFROST ON THE DEBRIS-FLOW TRIGGERING IN HIGH-ALPINE ENVIRONMENT
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
19
CONCLUSION
The compilation of post-event observations, geo-
morphological mapping and DGPS monitoring allow
us to distinguish four processes of debris-flow trigger-
ing related to permafrost:
1. cohesion loss of sediment formerly cemented by
ice and/or frozen matrix (case of scar n° 1);
2. cohesion reduction due to the constant movement in-
duced by dynamics of the above permafrost complex;
3. spatio-temporal changes in water circulation, lea-
ding to sudden variations in water supply (case of
scars n° 1 and 2);
4. constant rejuvenation of sediment accumulated on
slope due to the thrust of creeping permafrost, kee-
ping it at the limit of equilibrium (case of scar n° 3).
In addition, we must take into consideration all
other geomechanical processes, non-permafrost relat-
ed, that may occur in loose sediments hanging on steep
slopes (due to increases in internal pore pressure).
In the present case study, the Bonnard glacier per-
mafrost complex appears to be a key factor in the forma-
tion of initial debris flows. The recorded events and ob-
servations made since 2006 demonstrate that all events
originate from this area. Notwithstanding, we could not
exclude debris flows originating from other catchments
parts below the altitude of the permafrost belt, the vol-
ume of initial debris flow can nevertheless be seen as a
“detonator” for more intense advanced events.
To conclude, the debris-flow hazard for the down-
stream communities should only be analysed in a glo-
bal framework as the permafrost related volume rep-
resents only a fraction of the total volume. The event
magnitude is thus closely dependent on:
1. the local interaction between the cryospheric and
lithospheric features (i.e. geometry, constituents,
stream connection type);
2. the rate of deformation of the permafrost complex;
3. the connectivity of the downstream non-perma-
frost mass wasting phenomenon.
ACKNOWLEDGEMENTS
The authors wish to thank the Canton of Valais
for supporting data acquisition and field work as well
as the project INTERREG IV which provided fund-
ing for this study. We wish to thank to Douglas Cripe
for polishing the English. We much appreciate also the
comments of two anonymous reviewers, those having
greatly improved the early draft.
VOLUME ENTRAINED ON THE DOwNSTREAM
REACHES
As soon as the debris flow becomes channelized,
depending on the type of substratum, erosion (i.e.
volume addition) continues to occur. This channel
incision (e.g. k
RonfellneR
-k
Raus
, 1984; z
immeR
-
mann
, 1990) may be supplemented by connected
mass movements (e.g. J
oHnson
& R
odine
, 1984) to
form a landslidetriggering type (m
eunieR
, 1991).
Among the different methods of debris-flow volume
assessment, H
unGR
et alii (1984) propose summing
these two additional volumes at the reach scale to
estimate the final volume.
It must be remembered here that Figure 6 is
only valid for the event of the 1
st
of July 2008. This
initial volume of 17% does not stand as a rule for
torrents in general. Moreover, it may be different
for other environment or hydrometeorological situ-
ations as noticed by other authors who find that the
initial released volume contributes up to 92% of the
total (J
oHnson
et alii, 2008).
The results presented in Figure 6 are consistent
with the work of other authors, but as stressed by b
en
-
da
et alii (2005), it is important to link the depicted
figure there with the probability of occurrence. Here,
the linkage could be done only in a qualitative way.
Indeed, the addition of volume to the initial debris
flow triggered from the permafrost area is a strongly
stochastic process (b
enda
& d
unne
, 1997; m
ay
&
G
Resswell
, 2003; b
aRdou
& J
aboyedoff
, 2008). The
volume involved in the formation of initial debris
flow in the permafrost area is constrained by local ge-
ometry (vicinity of scar n° 1). The geomorphological
estimations in Pétérey show that the initial volume of
initial debris-flow volume may be expanded by a fac-
tor 3 to 4, while the downstream (advanced) debris-
flow volume may be increased by a factor 6 to 10
(mainly due to the presence of active landslides, in
the last third of the torrent see map Fig. 4).
The magnitude of additional downstream volume
entrainment can be linked with the magnitude of the
initial debris-flow volume and the ratio of the initial
volume to the whole volume deposited on the alluvial
fan is likely to be the same or less, except for dramatic
processes involved in general destabilization of the
permafrost complex, such as Kolka-Karamadon ca-
tastrophe's kind (e.g. H
aebeRli
et alii, 2004).
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E. BARDOU, G. FAVRE-BULLE, P. ORNSTEIN & J.-D. ROUILLER
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
REFERENCES
a
ndeRson
s.a. & s
itaR
n. (1995) - Analysis of rainfall induced debris-flow. Journal of Geotechnical Engineering, 121(7): 544-552.
a
Renson
l.u. & P
almeR
a. (2005) - Rock glaciers, fault gouge and asphalt Hard particles in a nonlinear creeping matrix. Cold
Regions Science and Technology, 43 (3): 117-127.
a
Renson
l.u. & s
PRinGman
s.M. (2005) - Mathematical descriptions for the behaviour of ice-rich frozen soils at temperatures
close to 0 C. Canadian Geotechnic Journal, 42 (2): 431-442.
b
aRdou
e., b
oivin
P. & P
feifeR
H. (2007) - Properties of debris flow deposits and source materials compared: implications for
debris flow characterization. Sedimentology, 54 (2): 469-480.
b
aRdou
e. & J
aboyedoff
M. (2008) - Debris flows as a factor of hillslope evolution controlled by a continuous or a pulse
process? In: G
allaGHeR
k., J
ones
s.J. & w
ainwRiGHt
J. (Editors), Landscape Evolution: Denudation, Climate and Tectonics
Over Different Time and Space Scales. The Geological Society of London, London, pp. 63-78.
b
auR
m., e
dmaieR
b. & s
Paun
G. (1992) - Talzuschübe als geschiebeherde für Murgangeriegnisse in Saalbach und Rauris
(Land Salzburg). In: F.f.v. Hochwasserbekämpfung (Editor), InsInternational Symposium Interpraevent. Birkäuser Verlag,
Bern: 165-180.
b
enda
l.e. & d
unne
T. (1997) - Stochastic forcing of sediment supply to channel networks from landsliding and debris flow.
Water Resource Research, 33 (12): 2849-2863.
b
enda
l.e., H
assan
m.a., C
HuRCH
m.a. & m
ay
C.L. (2005) - Geomorphology of steepland headwaters: the transition from
hillslopes to channels. Journal of the Amercian Water Resource Association, 41 (4): 835-851.
b
ovis
, m. & J
akob
m. (1999) - The role of debris supply conditions in predicting debris flow activity. Earth Surface Process and
Landforms, 24: 1039-1054.
C
HiaRle
m., i
annotti
s., m
oRtaRa
G. & d
eline
P. (2007) - Recent debris flow occurrences associated with glaciers in the Alps.
Global and Planetary Change, 56: 123-136.
d
ysli
M. (1993) - where does the water go during ice lenses thaw? 2
nd
Int. Symp. on Frost in Geotechnical Engineering,
Anchorage: 45-50.
d
ysli
M. (2007) - Etude expérimentale du dégel d'un limon argileux. Application aux chaussées et pergélisols alpins. Thesis
n°3792 Thesis, EPFL, Lausanne.
e
GasHiRa
s., H
onda
n. & i
toH
T. (2001) - Experimental study on the Entrainement of bed material into debris flow. Physics and
Chemistry of the Earth, Part C: Solar-Terrestrial and Planetary Science, 26 (9): 645-650.
f
leminG
R.w., e
llen
s.d. & m
itCHell
a.A. (1989) - Transformation of dilative and contractive landslide debris into debris
flows, an example from Marin county, California. Engineering Geology, 27: 201-223.
H
aebeRli
W. (1992) - Construction, environmental problems and natural hazards in periglacial mountain belts. Permafrost and
Periglacial Processes, 3 (2): 111-124.
H
aebeRli
w. et alii (2004) - The kolka-karmadon rock/ice slide of 20 September 2002: An extraordinary event of historical
dimensions in North Ossetia, Russian Caucasus. Journal of Glaciology, 50 (171): 533-546.
H
aebeRli
w., R
iCkenmann
d. & z
immeRmann
M. (1991) - Murgänge, Ursacheanalyse der Hochwasser 1987. Ergebnisse der
Untersuchung. Mitt. Nr. 14. Landeshydrologie und -geologie, Bern.
H
aRRis
C., d
avies
m. & R
ea
b. (2003) - Gelifluction: viscous flow or plastic creep? Earth Surf. Process. Landforms, 28 (12): 1289-1301.
H
aRRis
s.a. & G
ustafson
C.A. (1993) - Debris flow characteristics in an area of continuous permafrost, St Elias range, Yukon
Territory. Zeitschrift für Geomorphologie, 37 (1): 41-56.
H
unGR
o., m
oRGan
G.C. & k
elleRHals
R. (1984) - Quantitative analysis of debris torrent hazards for design of remedial
measures. Canadian Geotechnical Journal, 21: 663-677.
i
veRson
R.m., R
eid
m.e. & l
a
H
usen
R.G. (1997) - Debris-flow mobilization from landslides. Annual Review of Earth and
Planetary science, 25: 85-138.
J
akob
m., b
ovis
m.J. & o
deH
m. (2005) - The significance of channel recharge rates for estimating debris-flow magnitude and
frequency. Earth Surf. Process. Landforms, 30 (6).
J
akob
m., H
unGR
o. & t
Homson
B. (1997) - Two debris flow with anomalously high magnitude. In: C.-l. Chen (Editor), 1st International
Conference on Debris-Flow Hazards Mitigation, Mechanics, Prediction and Assessment. ASCE, San Fransico, pp. 382-394.
J
oHnson
a.m. & R
odine
J.D. (1984) - Debris flow. In: D. B
Rundsen
& d.b. P
RioR
(Editors), Slope Instability. Wiley, New York.
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J
oHnson
R.m., w
aRbuRton
J. & m
ills
a.J. (2008) - Hillslope-channel sediment transfer in a slope failure event: wet Swine Gill,
Lake District, northern England. Earth Surface Processes and Landforms, 33: 394-413.
J
ulien
P.Y. (1998) - Erosion and sedimentation. Cambridge University Press, Cambridge.
k
inG
J. (1996) - Tsing Shan Debris Flow. Special Project Report SPR 6/96, Geotechnical Engineering Office, Hong Kong.
k
RaineR
k. & m
ostleR
W. (2002) - Hydrology of active rock glaciers: examples from the Austrian Alps. Artic, Antarctic, and
Alpine Research, 34(2): 142-149.
k
RonfellneR
-k
Raus
G. (1984) - Extreme Festofffrachten und Grabenbildungen von wildbächen, INTERPRAEVENT. VHB,
Villach: 109-118.
m
ay
C.l. & G
Resswell
R.E. (2003) - Processes and rates of sediment and wood accumulation in headwater treams of the
Oregon Coast Range, USA. Earth surface processes and landforms, 28: 409-424.
m
eunieR
m. (1991) - Eléments d'Hydraulique torrentielle. CEMAGREF, Grenoble.
m
ontGomeRy
d.R. & b
uffinGton
J.M. (1997) - Channel-reach morphology in mountain drainage basins. Geological Society of
America Bulletin, 109 (5): 596-611.
P
alaCios
d., P
aRilla
G. & z
amoRano
J.J. (1999) - Paraglacial and postglacial debris flows on a Little Ice Age terminal moraine:
Jamapa Glacier, Pico de Orizaba (Mexico). Geomorphology, 28: 95-118.
P
illoud
C. & s
aRtoRi
m. (1981) - Etude géologique et pétrographique de la region des Diablons (Val de Zinal, VS). MSc. Thesis,
University of Lausanne, unpublished
R
ebetez
m., l
uGon
R. & b
aeRiswyl
P. (1997) - Climatic change and debris flows in high mountain regions: The case study of
the Ritigraben torrent (Swiss Alps). Climatic Change, 36 (3): 371-389.
R
eid
m.e. et alii (2003) - Debris-flow initiation from large, slow-moving landslides. In: D. R
iCkenmann
& C. C
HenG
-
lunG
(Editors), 3
rd
International Conference on Debris-Flow Hazards Mitigation, Mechanics, Prediction and Assessment, Davos: 155-166.
R
eid
m.e., l
a
H
usen
R.G. & i
veRson
R.M. (1997) - Debris flow initiation experiements using diverse hydrologic triggers. In: C.-
l. C
Hen
(Editor), 1
st
International Conference on Debris-Flow Hazards Mitigation, Mechanics, Prediction and Assessment.
ASCE, San Francisco, pp. 44-53.
R
iCkenmann
D. (1999) - Empirical relationships for debris flows. Natural Hazards, (19): 47-77.
R
iCkenmann
d. & z
immeRmann
M. (1993) - The 1987 debris flows in Switzerland: documentation and analysis. Geomorphology,
8 (2-3): 175- 189.
s
assa
K. (1984) - The mechanism starting liquefied landslides and debris flows, IV International symposium on landslides,
Toronto: 349-354.
s
einova
I.B. (1991) - Past and present changes of mudflow intensity in the central Caucasus. Mountain Research and
Developpement, 11 (1): 13- 17.
s
einova
i.b. & z
olotaRev
E. (2003) - The evolution of glaciers and debris flows in the vicinity of Elbrus, central Caucasus. In:
D. R
iCkenmann
& C. C
HenG
-
lunG
(Editors), 3rd International Conference on Debris-Flow Hazards Mitigation, Mechanics,
Prediction and Assessment, Davos, pp. 189-198.
s
PRinGman
s. & t
eysseiRe
P. (2001) - Artificially induced rainfall instabilities on moraine slopes. In: k
üHne
m., e
instein
H.H., k
RauteR
e., k
laPPeRiCH
H. & P
öttleR
R. (Editors), International Conference on Landslides, Causes, Impacts and
Countermeasures. Verlag Glückauf Essen, Davos, pp. 209-223.
s
toffel
m. & b
ollsCHweileR
M. (2009) - Tree-ring reconstruction of past debris flows based on a small number of samples-
possibilities and limitations. Landslides, 6: 225-230.
s
uRell
A. (1841) - Étude sur les torrents des Hautes-Alpes. Carilian-Goeury and V. Dalmont, Paris. Reprint C. Lacour, Nîmes, 2002.
t
akken
i. & G
oveRs
G. (2000) - Hydraulics of interrill overland flow on rough, bare soil surfaces. Earth Surface Process and
Landforms, 25: 1387-1402.
t
eysseiRe
P., C
oRtona
l. & s
PRinGman
S. (2000) - water retention in a steep moraine slope during periods of heavy rain. In: T.
R
aHaRdJo
, l
eonG
(Editor), Unsaturated soils for Asia. Balkema, Rotterdam: 831-836.
z
immeRmann
M. (1990) - Debris flows 1987 in Switzerland: geomorphological and meteorological aspects. In: R.O. s
inniGeR
& m.
m
onbaRon
(Editors), Hydrology in mountainous regions II: artificial reservoirs, water and slopes. IAHS, Lausanne, pp. 387-393.
z
immeRmann
m. & H
aebeRli
, W. (1992) - Climatic change and debris flow activity in high-mountain areas. In: M. b
oeR
& e.
k
osteR
(Editors), Catena Supplement, pp. 59-72.
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