Earth Surface Processes and Landforms
Mapping
monitoring
of rockglacier
Earth Surf.and
Process.
Landforms
(in press) activity
Published online in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/esp.1496
1
Rockglacier activity studies on a regional scale:
comparison of geomorphological mapping and
photogrammetric monitoring
Isabelle Roer1,2* and Michael Nyenhuis1†
1
2
Department of Geography, University of Bonn, Bonn, Germany
Swiss Federal Institute for Forest, Snow and Landscape Research, Birmensdorf, Switzerland
*Correspondence to: Dr. Isabelle
Roer, Swiss Federal Institute for
Forest, Snow and Landscape
Research, Zürcherstrasse 111,
8903 Birmensdorf, Switzerland.
E-mail: [email protected]
†
Present address: Federal
Institute of Hydrology (BfG),
Koblenz, Germany.
Received 13 April 2006;
Revised 14 December 2006;
Accepted 3 January 2007
Abstract
In their spatial distribution as well as in their different states of activity, rockglaciers imply
important information on former and recent permafrost conditions. Two different methods
were applied in one study area (Turtmann Valley, Swiss Alps) in order to compare their
suitability in assessing rockglacier activity. The comparison of geomorphological mapping
and photogrammetric monitoring demonstrated a good accordance, especially on a regional
scale. On a local scale, some differences in delimitation of the landforms as well as in the
degree of activity were found. One reason for the observed differences is the qualitative
character of geomorphological mapping resulting from the variable suitability of single
parameters and combinations thereof in the determination of rockglacier activity.
Based on these results, geomorphological mapping of rockglaciers can be improved by
data from photogrammetric monitoring. Therefore, at best the two methods are combined
when analysing former and present permafrost distribution. Copyright © 2007 John Wiley
& Sons, Ltd.
Keywords: rockglacier; permafrost; geomorphological mapping; photogrammetry; high
mountains
Introduction
The history of rockglacier research is characterized by a long-standing discussion on origin, nomenclature and ongoing processes (see, e.g., Humlum, 2000) and generated two main positions. One position focused on the glacial origin
of rockglaciers (e.g. Potter, 1972; Whalley, 1974; Humlum, 1982, 1996; Evans, 1993; Hamilton and Whalley, 1995)
while the others argued for a general periglacial origin (e.g. Wahrhaftig and Cox, 1959; Haeberli, 1985, 2006; Barsch,
1977, 1992; Frauenfelder, 2005). The study presented here does not aim to discuss the different positions; it follows
the periglacial reasoning, and in order to emphasize the autonomy of the phenomenon, the term ‘rockglacier’ is
written in one word, following Barsch (1988). Thus, rockglaciers are significant indicators of past and present permafrost distribution and related climatological changes. In particular, their spatial distribution in different degrees of
activity implies important evidence of former and recent permafrost conditions. Therefore they are considered as
useful landforms for the analysis of climatic changes within high mountain geosystems. In addition, rockglaciers
represent capacious storages and archives of sediment within the alpine geosystem and thus allow for an estimation of
material production since the last glacial maximum.
Due to their ice content and flow behaviour, rockglaciers are classified into the following types: active, inactive and
relict (Haeberli, 1985; Barsch, 1996). Often the different types are situated one over the other, forming a cascade of
active rockglaciers at higher altitudes to relict rockglaciers at lower altitudes. Thus, their spatial setting depicts a
complex archive of a geosystem’s development since the last glaciation.
A steep terminal front (>35°) with loose boulders and without vegetation indicates the activity of a rockglacier,
whereas inactive landforms, which still contain ice but actually do not move, have a gentler front with stable boulders
and partial or full vegetation. Because of their ice content, active and inactive rockglaciers are grouped together as
‘intact’ rockglaciers (cf. Haeberli, 1985).
Copyright © 2007 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms (in press)
DOI: 10.1002/esp
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I. Roer and M. Nyenhuis
Figure 1. Relict rockglacier on the south-exposed slope in the Hungerlitälli, Turtmann Valley, Swiss Alps (front altitude 2580 m
a.s.l.). Note the collapsed surface structure of the landform, and vegetation abundance in areas with fine grained material.
Regarding the inactivity of rockglaciers, Barsch (1996) emphasized two causes for deactivation, depending on
thermal and mechanical factors. On the one hand, climatically induced inactivity is characterized by a thickening of
the active layer due to melting of the frozen core and therefore only occurs at the lower limit of the discontinuous
permafrost belt (cf. Ikeda and Matsuoka, 2002). On the other hand, dynamically induced inactivity results from a
reduction in shear stress due to a reduced input of debris and ice or a downslope decrease in slope gradient (Barsch,
1996).
Relict rockglaciers show a collapsed surface due to melting of the ice (Figure 1). The furrows and ridges are still
visible, but the front has a lower angle and the rockglacier surface features a dense vegetation cover – at least in areas
with fine material. Thus, relict rockglaciers are valuable indicators for palaeoclimatic reconstructions (cf. Kerschner,
1985; Van Tatenhove and Dikau, 1990; Konrad et al., 1999; Frauenfelder and Kääb, 2000; Frauenfelder et al., 2001).
Initially, the activity of rockglaciers was determined by the direct measurement of their movement. Simple methods
such as remeasurement of painted stone-lines were used to detect rockglacier movements (see, e.g., Chaix, 1923).
Then, geodetic techniques were applied (Wahrhaftig and Cox, 1959; Vietoris, 1972; Barsch and Zick, 1991; Francou
and Reynaud, 1992; Lambiel and Delaloye, 2004), while later diverse air- and space-borne remote sensing methods
were exploited (Messerli and Zurbuchen, 1968; Barsch and Hell, 1975; Kääb and Vollmer, 2000; Kaufmann and
Ladstädter, 2003; Kenyi and Kaufmann, 2003; Strozzi et al., 2004; Kääb, 2005; Roer et al., 2005a). The latter are
useful, particularly to monitor remote areas that are difficult to access for in situ measurements, and to cover large
areas within regional-scale studies.
In addition to the measurements, rockglacier activity is estimated by characteristic geomorphological, structural
and thermal conditions (cf. Ikeda and Matsuoka, 2002). In several studies the state of activity has been assessed by
geomorphological criteria such as position (altitude, aspect), steepness of the front and surface structure as well as
by characteristics (distribution, density) of the vegetation cover (cf. Wahrhaftig and Cox, 1959; Haeberli, 1985;
Krummenacher et al., 1998; Barsch, 1996; Imhof, 1996; Frauenfelder, 1998; Burger et al., 1999; Ikeda and Matsuoka,
2002; Nyenhuis, 2005; Nyenhuis et al., 2005). Apart from direct measurements, geomorphological mapping is one of
the most feasible and reliable methods to assess rockglacier activity on a regional scale.
This paper compares two independent rockglacier activity studies based on different regional-scale methods within
the same area. The main research question of this study is to what extent the mapped states of activity correspond to
the measured movement rates. Hence, the purpose is the verification and evaluation of the primarily qualitative
geomorphological mapping by movement rates quantified from digital photogrammetric measurements. Improved
accuracy in rockglacier mapping is desirable as an important basis for the further development of reliable models of
past and present permafrost distribution.
Copyright © 2007 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms (in press)
DOI: 10.1002/esp
Mapping and monitoring of rockglacier activity
3
After a short overview of the basic data, the study focuses on the agreements and disagreements of the findings in
order to evaluate the potentials of the two methods. Since the investigations are not conducted on a single landform
but cover a wide area with a large number of rockglaciers in all states of activity, the comparison allows a conclusive
validation of the applied methods. A profound analysis of the entire geosystem regarding permafrost distribution is
enabled by the findings presented in this paper.
Study Site
The Turtmann Valley is a tributary of the River Rhone and is located in southern Switzerland between the Matter
Valley and the Anniviers Valley (about 46° 13′ N/7° 38′ E, Figure 2). Due to its inner-alpine location, the area is
characterized by an intramontane climate with an annual precipitation of 600–900 mm/a at c.2000 m a.s.l., and the
0 °C isotherm of mean annual air temperature (MAAT) is at c.2300 m a.s.l. (Van Tatenhove and Dikau, 1990). The
valley’s lithology mainly consists of Palaeozoic gneisses and schists. Its geomorphology is dominated by two large
glaciers in the valley head and several hanging valleys above the shoulders of the trough. Here, periglacial landforms
such as gelifluction lobes, ploughing boulders and rockglaciers are numerous (Otto and Dikau, 2004). Rockglaciers
are the most striking landforms (covering 4.2% of the total area of 110 km2) and occur in different states of activity.
The high density of rockglaciers is one characteristic of the study area and facilitates intense investigation of the
phenomenon.
Methods
Two independent approaches are compared in this study: first, the assessment of rockglacier activity by geomorphological
mapping, and second, the quantification of rockglacier movement by the application of photogrammetric techniques.
Figure 2. Location of the study site (Turtmann Valley) within Switzerland (black rectangle).
Copyright © 2007 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms (in press)
DOI: 10.1002/esp
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I. Roer and M. Nyenhuis
Geomorphological mapping
Active, inactive and relict rockglaciers have been mapped by interpretation of high resolution aerial images and a
digital terrain model (DTM) with a resolution of 1 m as well as by geomorphological mapping in the field during
several field campaigns. The panchromatic and multispectral aerial images have been created by an airborne high
resolution stereo camera (HRSC-A) – a pushbroom scanner developed by the German Aerospace Centre (DLR). The
images of the study area have a resolution of 50 cm and a photogrammetric precision of 15–20 cm (Hoffmann and
Lehmann, 2000; Roer et al., 2005a). The corresponding DTM serves mainly as a database for geomorphometric
analyses of the rockglaciers to determine, e.g. the altitudes of the front and rooting zone, data on spatial dimensions,
slope, aspect and curvature as well as the form type according to Barsch (1996). Additionally, the geomorphological
setting of both the rockglaciers and their surrounding areas was determined by the use of HRSC image and digital
elevation data (Otto et al., in press). Three-dimensional visualizations of the DTM provided a better overview of the
landscape and enabled the mapping of landforms even in inaccessible and dangerous terrain. Figure 3 shows shaded
relief visualizations of the HRSC-DTM and a multispectral image of an active rockglacier in one of the hanging
valleys of the study area. The front and side slopes of the landform can clearly be recognized in Figure 3(A), (B).
Moreover, the typical surface structure of the rockglacier, characterized by ridges, furrows and lobes, becomes apparent in the visualizations. On the multispectral image, vegetation is represented in red colours; as expected, the active
rockglacier depicted here shows only a sparse vegetation cover (Figure 3(C)).
To evaluate and replenish HRSC analyses, fieldwork conducted on the rockglaciers provided geomorphologically
relevant information such as vegetation abundance, appearance of the front, stability of boulders, occurrence of ice
Figure 3. Different views of one rockglacier in the Turtmann valley (see Figure 4 for orientation). (A) 3D shaded relief visualization
of the HRSC-DTM. (B) Shaded relief visualization (bird’s eye view). (C) Composite of the multispectral sensors resulting from
HRSC survey. Note the distinct surface structure and the lack of vegetation (in red) on the landform.
Copyright © 2007 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms (in press)
DOI: 10.1002/esp
Mapping and monitoring of rockglacier activity
5
or collapse structures, spring temperatures and perennial snow patches. The occurrence of vegetation depends on a
multitude of parameters, for example the existence of fine material between the large boulders (cf. Frauenfelder,
1998). A full list of the geomorphological and geomorphometric data determined within this study is given by
Nyenhuis et al. (2005) and an evaluation of single parameters is given in Table I.
Due to their steep side and front slopes, rockglaciers are in most cases clearly distinguishable from surrounding
landforms in DTM and HRSC image visualizations. Nevertheless, geomorphological mapping in the field proved to
be essential to verify these results and represents the basis for the activity classification. The distinction between
active and inactive rockglaciers proved to be especially difficult on the basis of HRSC data alone. Accurate activity
classification of a rockglacier requires in situ mapping of its surface and information on geomorphological and
geomorphometric characteristics of the landform. Generally, vegetation on rockglaciers is regarded as an indicator of
reduced activity. Since vegetation is visible on the multispectral images of the HRSC (Figure 3(C)), relict rockglaciers
have been determined with high certainty. Furthermore, characteristic geomorphological features of relict rockglaciers
such as a subdued surface due to melting of interstitial ice can be mapped accurately by 3D visualizations of the
DTM.
Geomorphological and geomorphometric characteristics of the rockglaciers determined by analysis of HRSC
data and by fieldwork have been compiled in a rockglacier inventory, which is presented in detail in Nyenhuis
(2005) and Nyenhuis et al. (2005). The inventory contains information on the activity status of the rockglaciers and
serves primarily as a database for the development of a regional permafrost distribution model (Nyenhuis et al., in
preparation).
Table I. Evaluation of geomorphological, geomorphometric and ecological parameters for the determination of rockglacier
activity
Suitability for differentiation
Method/indicator
Determined data
Data type
Active or
inactive?
Inactive or
relict?
Active or
relict?
Slope angle of rockglacier front
Vegetation or lichen abundance
Geomorphological appearance
of rockglacier front
Occurrence of stable/unstable boulders
Occurrence of ice outcrops
Occurrence of thermokarst
Spring water temperatures close to 0 °C
Temperature monitoring/BTS
(Bottom Temperature of Snow)
Perennial snow patches
Slope angle: steep/flat
Spatial distribution
Micro-scale geomorphic forms
indicating movement
Spatial distribution
Location and size of outcrop
Location of feature
Temperature (summer)
Spring temperatures (below −2 °C)
beneath snow cover of >0·8 m
Location of feature
Quantitative
Descriptive
Descriptive
––
O1
++
–
+
–
+
++
++
Descriptive
Descriptive
Descriptive
Quantitative
Quantitative
++
––
O3
– –4
– –5
––
– –/+ +
O3
– –/+4
+5
Descriptive
– –6
– –/+ +6
2
++
– –/+ +2
O3
– –/+4
+5
– –/+ +6
Suitability of differentiation between active, inactive or relict status of the rockglacier:
++
very good
+
good
–
poor
––
not suitable
n/y
case differentiation: regarding condition formulated in column 1
O
it depends.
1
Lithology and other factors controlling vegetation have to be examined as well (see discussion in the text).
2
The occurrence of ice shows that the rockglacier is not relict but inactive or active. From absence of ice outcrops no activity state can be inferred.
3
The absence of thermokarst does not necessarily mean that the rockglacier is active or inactive. If thermokarst is present, it has to be characterized
further. If the thermokarst exposes ice, the rockglacier might be active or inactive, but not relict.
4
In a strict sense, hydrological pathways within the rockglacier have to be known to evaluate this parameter. A temperature close to 0 °C implies that
it has flowed over ice, thus indicating an active or inactive rockglacier, but a higher temperature does not necessarily mean that there is no ice within the
rockglacier—the water might also have taken an ice-free route.
5
BTS data reflect permafrost conditions (BTS > −2 °C = no permafrost, BTS < −3 °C = probable permafrost). Hence, a differentiation between relict
and intact (active and inactive) rockglaciers is permitted by such temperature monitoring.
6
The absence of perennial snow does not indicate permafrost-free terrain and does not indicate any rockglacier activity state. However, perennial snow
patches are indicators of permafrost (see, e.g., Haeberli, 1975) and thus of active and inactive rockglaciers.
Copyright © 2007 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms (in press)
DOI: 10.1002/esp
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I. Roer and M. Nyenhuis
Digital photogrammetry
In order to verify the mapping results, information on rockglacier kinematics is required. Therefore, digital
photogrammetry was utilized for the quantification of rockglacier creep and finally the determination of the state
of activity (Roer, 2005; Roer et al., 2005a). For the Turtmann Valley, analogue aerial stereo photographs for the
years 1975 and 1993 were selected and combined with digital data (DTM and orthophotographs) from a survey
with the HRSC-A in 2001. This combination was applied for the first time in rockglacier studies (Roer et al., 2005a).
It enabled the monitoring of permafrost creep on a regional scale over a 26-year period, divided into two periods
(1975–1993, 1993–2001). Regarding the lifetime of rockglaciers of some thousand years (cf. Frauenfelder and
Kääb, 2000), this monitoring does not cover a long time, but in comparison to other studies this is quite a long data
series.
First of all, the available aerial images were analysed to map rockglaciers – independently of the mapping described
above. Based on this analysis, extensive measurement of kinematics was accomplished on the landforms mapped as
active and inactive (n = 34).
With the image correlation software CIAS developed by Kääb and Vollmer (2000), horizontal displacements
of single blocks at the rockglacier surfaces were quantified. The program outputs the coordinates (x, y), the changes in
x and y and the velocity and direction of the moving blocks as well as the correlation coefficient of the measurements.
In order to reveal a statistically significant quantity and to derive complete horizontal deformation fields, a large
number of blocks was measured on each rockglacier (Roer, 2005). The results were depicted as 2D flow vectors (see
Figures 5(B) and 6(B) below). In addition, vertical changes were derived from subtraction of multitemporal DTMs.
The accuracy of the horizontal and vertical displacements is estimated to lie in the range of 0·06–0·13 m/a, depending
on the interval considered. In some areas, measurements were inhibited due to shadows or snow cover in the aerial
images. Further details on raw data, processing and accuracies are given in the work of Roer et al. (2005a), Wangensteen
et al. (2006) and Kääb and Vollmer (2000).
The final determination of the state of activity is mainly based on the measured horizontal displacements. On
inactive rockglaciers, the flow vectors indicate very small displacements, mainly within the range of uncertainty and in
diverse directions. Against this, blocks on active permafrost bodies display a clear movement in a uniform direction.
Single landforms may have both active and inactive lobes.
Results and Discussion
On the east side of the Turtmann Valley all rockglaciers were monitored and mapped by the two methods described
before. Therefore, the comparison of the methods presented here focuses on this part of the study area. A general
overview of the findings is given in Figure 4. As becomes apparent, different activity classes are investigated by the
two methods. It is apparent that active, inactive and relict rockglaciers are described by geomorphological mapping
(Figure 4(A)), while photogrammetric measurements only distinguish active and inactive landforms (Figure 4(B)).
This is due to the different capabilities of the methods applied; while geomorphological mapping allows the differentiation of all states of activity, the application of digital photogrammetry enables the determination of creeping and
non-creeping masses. Since some relict rockglaciers were undoubtedly identified by geomorphological mapping prior
to the investigation of kinematics, no photogrammetric measurements were conducted on these landforms.
Regarding the intact rockglaciers, geomorphic mapping exposed 39 features (25 (64%) active, 14 (36%) inactive),
while the measurements by digital photogrammetry compiled 34 rockglaciers (17 (50%) active, 17 (50%) inactive).
Comparing Figure 4(A) and (B), it becomes apparent that most of the investigated landforms coincide well in their
state of activity classified by the two methods. In particular, the rockglaciers in the Hungerlitälli and in the Grüobtälli,
where most of the fieldwork was conducted, indicate a good accordance. In the Niggelingtälli the number of active
rockglaciers is clearly overestimated by the geomorphological mapping.
Beside this general comparison, two examples are given in the following to substantiate the differences in rockglacier
boundaries as well as the differences in rockglacier activity.
Differences in rockglacier boundaries
As mentioned before, the recognition as well as the classification of landforms depends to a great extent on the
experience of the scientist (cf. Van Westen et al., 1999). In general, a rockglacier – independent of its state of
activity – is readily identifiable in the field or on aerial photographs, but the delimitation of the landform in the rooting
zone as well as in connection to other lobes offers some difficulties.
Copyright © 2007 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms (in press)
DOI: 10.1002/esp
Mapping and monitoring of rockglacier activity
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Figure 4. Comparison of two independent approaches determining rockglacier activities on the east side of the Turtmann Valley.
On the left side (A), active (red), inactive (yellow) and relict (green) rockglaciers are depicted as determined by geomorphological
mapping, while the right side (B) shows a combination of geomorphological mapping and photogrammetric monitoring of rockglacier
kinematics. Due to the quantification of rockglacier movement, the latter study concentrated on the differentiation of active (red)
and inactive (yellow) landforms. Differences in outlines of some landforms result from the independently conducted mappings. The
rectangles mark the rockglaciers that are considered in detail in Figures 3, 5 and 6.
The rooting zones of the rockglaciers under investigation connected either to a cirque or to a glacial forefield
represent transition zones lacking prominent landforms such as furrows or ridges indicating compressive or extending
flow (Figure 5). Therefore, borders in the rooting zone can only be defined with knowledge of kinematics. Hence, a
continuous creeping mass can be distinguished from non-moving terrain or areas affected by other processes such as
Copyright © 2007 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms (in press)
DOI: 10.1002/esp
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I. Roer and M. Nyenhuis
Figure 5. Rockglacier complex in the Brändjitälli: comparison of the state of rockglacier activity estimated from (A) geomorphological
mapping and (B) annual horizontal velocities between 1993 and 2001 derived from photogrammetric measurements.
rock fall or gelifluction. This process-related determination is limited in situations where frozen talus slopes occur and
creep downslope at rates similar to rockglaciers.
In the lower part of complex rockglaciers, where they are frequently connected to other lobes representing different
states of activity, the delimitation is even harder. With information on kinematics, active lobes can clearly be separated
from non-moving lobes. However, the question is whether this differentiation is reasonable in a geomorphological
sense, since it is one complex landform originating from one source area. On the other hand, it is important to know
how the complex feature is set up and the differentiation is valuable in an ecological or climatological context, since
inactive and relict rockglaciers are indicators for the former permafrost distribution (see above).
In our example, the focus is on one rockglacier complex in the Brändjitälli, which was defined in different ways by
the two methods applied (Figure 5; for orientation see Figure 4). By geomorphological mapping four different
landforms were identified in this hanging valley (Figure 5(A)): one active rockglacier with a small inactive lobe below
Copyright © 2007 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms (in press)
DOI: 10.1002/esp
Mapping and monitoring of rockglacier activity
9
on the north side of the valley, and on the south side an inactive rockglacier in the upper part and a small active lobe
originating from the side. The borders of the rockglaciers were mapped according to the geomorphological situation in
the field. The border between the northern active and the southern inactive rockglacier was represented by a clear
ridge in the field. Nevertheless, the flow vectors measured by photogrammetrical analysis reveal another situation;
here, the complex described before consists of two landforms: one large rockglacier which branched into two tongues,
showing a distinct activity in the upper part (horizontal velocities up to 2 m/y) and very small movement rates in the
lower part, is displayed in Figure 5(B). In addition, another active landform is situated below; with its source area on
the southern slope of the valley (see the rockglacier boundaries in Figure 4(B)). Geomorphologically, these two
features are separated from each other by the steep front of the large rockglacier. But the deformation field indicates
that movement of the lower rockglacier affects the tongue above and results in a reactivation.
Differences in rockglacier activity
In a second hanging valley (Pipjitälli; for orientation see Figure 4) very different findings are noticeable. The landforms
depicted (Figure 6) are delimited in the same way, apart from the rockglacier on the north side of the valley, where the
boundary in the root zone was hard to determine by geomorphological mapping.
The large lobate-shaped rockglacier on the north-exposed side of the valley has a very steep front as well as distinct
furrows and ridges. In combination with a lack of vegetation, a clear activity of this landform is indicated. However,
by photogrammetric measurements, no movement of blocks at the rockglacier surface was measured and thus the
activity of the landform was not ascertained (and is therefore not depicted in Figure 6). The two rockglaciers on the
northern side of the hanging valley are interpreted as inactive and relict by geomorphological mapping because of
their concave surface, indicating melting of the ice (Figure 6(A)). However, they show distinct velocities of several
decimetres per year (Figure 6(B)). Their kinematics indicate similar deformation rates over the whole period (1975–
2001), even though only the period 1993–2001 is depicted in Figure 6(B).
The reason for the disagreement in the state of activity is due to several reasons. As described above, geomorphological
mapping derives rockglacier activity from geomorphological and geomorphometric parameters as well as from vegetation occurrence, while photogrammetric methods quantify movements of single blocks at the rockglacier surface. In
this valley, the geomorphological and geomorphometric structures as well as vegetation patterns seem not to reflect
the ongoing processes. The misinterpretations described above might be attributed to the special lithological characteristics of this hanging valley. Unlike the remaining study area, where metamorphic rocks are present, the southern part
of this hanging valley consists of sedimentary rocks (dolomite). One of the most important differences of this rock
type is that weathering produces debris of much smaller grain sizes. The material available for rockglacier development presumably leads to a different flow behaviour of the rockglaciers and develops a different surface structure. In
addition, due to the relatively low nutrient content of the dolomite, vegetation cover is much sparser than on metamorphic rocks. Apparently, vegetation mapping for determining the activity state of these rockglaciers is of restricted use
here and has to be applied carefully. Thus, geomorphological parameters have to be evaluated for each region in terms
of their suitability to determine the activity state of rockglaciers (compare Table I).
The comparison of geomorphological mapping and photogrammetric monitoring for the purpose of rockglacier
activity studies demonstrates good accordance, especially on a regional scale. On a local scale, some differences in
delimitation of the landforms as well as in the determination of their state of activity exist. Of course, an important
reason for these differences is the qualitative approach of geomorphological mapping. Here, the activity classification
is based on a combination of different parameters regarded to be indicative of a certain state of activity (Table I). But
the significance of the single parameters might differ depending on the geomorphological rockglacier context. Therefore, it appears to be crucial to evaluate the different parameters determined by geomorphological mapping with care,
whenever the activity of a rockglacier has to be determined (Table I).
Conclusions
Geomorphological mapping allows for a valuable estimation of rockglacier activity and consequently for a reliable
assessment of permafrost distribution. But in a strict sense, the evidence of activity is provided only by quantification
of rockglacier movement. Based on these results, geomorphological mapping of rockglaciers can be validated and
improved by data from photogrammetric monitoring. Therefore, at best both methods are combined to enable the
mapping of rockglaciers in all different states of activity.
These findings promote knowledge of the regional distribution of active, inactive and relict rockglaciers. On the
local scale, a better delimitation of the landforms is facilitated. By incorporating the results of the comparison
Copyright © 2007 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms (in press)
DOI: 10.1002/esp
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I. Roer and M. Nyenhuis
Figure 6. Rockglacier complex in the Pipjitälli: comparison of the state of rockglacier activity estimated from (A) geomorphological
mapping and (B) annual horizontal velocities between 1993 and 2001 derived from photogrammetric measurements.
presented here, the database for empirical–statistical permafrost distribution models is improved further (Nyenhuis
et al., 2005, in preparation).
Current investigations ascertained strong spatio-temporal variations and a general increase in rockglacier movement, which seem to be related to the general increase in air temperature (Roer et al., 2005b; Kääb et al., 2006).
Therefore, future studies focus on a repeated monitoring and mapping in order to investigate morphological changes
on the rockglaciers, as they react to the measured acceleration.
Copyright © 2007 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms (in press)
DOI: 10.1002/esp
Mapping and monitoring of rockglacier activity
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Acknowledgments
The described investigations were funded by the Research Training Group 437 (Landform – a structured and variable boundary
layer) of the Deutsche Forschungsgemeinschaft (DFG). Thanks are given to the Swiss Federal Office of Topography (Swisstopo) for
access to the aerial photographs. Special thanks are dedicated to several assistants in the field. We gratefully acknowledge valuable
comments by our colleagues at the Department of Geography in Bonn and two anonymous reviewers on an earlier version of
the manuscript.
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