# Geomorphic properties of a complex subarctic slope and dynamic implications: granulometric characteristics and tree-ring patterns (Raspberry slope, Wiyâshâkimî lake, Nunavik, Canada)

Armelle Decaulne, Najat Bhiry, Ann Delwaide

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Armelle Decaulne, Najat Bhiry, Ann Delwaide. Geomorphic properties of a complex subarctic slope and dynamic implications: granulometric characteristics and tree-ring patterns (Raspberry slope, Wiyâshâkimî lake, Nunavik, Canada). Géomorphologie: relief, processus, environnement, 2025, Formes et processus périglaciaires des milieux montagnards, 31 (1), 10.4000/13w4n. hal-05536572

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# Geomorphic properties of a complex subarctic slope and dynamic implications: granulometric characteristics and tree-ring patterns (Raspberry slope, Wiyâshâkimî lake, Nunavik, Canada)

## Propriétés géomorphologiques d'un versant subarctique complexe et ses implications dynamiques : caractéristiques granulométriques et dendrochronologie (versant Framboisier, lac Wiyâshâkimî, Nunavik, Canada)

Armelle Decaulne<sup>a*</sup>, Najat Bhiry<sup>b</sup>, Ann Delwaide<sup>c</sup>

## ABSTRACT

This paper concerns a study of slope dynamics in the Nunavik region (northern Québec), specifically on a northern slope of Lepage Island, at Lake Wiyâshâkimî. This area, characterized by a subarctic climate, features active geomorphological processes. The aim of this study is to document the evolution of a slope that consists of a coarse debris talus in the apical zone, followed by a forested slope below a flat area, with particular attention to slope dynamics and recent geomorphological activity.

Fieldwork includes topographical profiles of the slope, an inventory of the morphometric properties of the rock debris, and visual estimation of the vegetal cover on the clasts. Dendrochronology methods were also used to identify the periods of disturbances in black spruce growth, and suggest recurrent surface instabilities since 1790. Results show that the upper part of the slope is dominated by large and coarse boulders with continuous vegetation cover, indicating little recent geomorphological activity on the majority of the slope. In contrast, the lower part shows signs of destabilization, notably after 1980. Results indicate that current geomorphological processes, such as snow avalanches, rockfall or landslides, are limited, although there are signs of past readjustments and recent disturbances.

**Keywords:** morphometry, debris, avalanches, periglacial, dendrochronology, Nunavik.

## RÉSUMÉ

Cet article porte sur les dynamiques de pente dans la région de Nunavik (Québec nordique), spécifiquement sur un versant nord de l'île Lepage, au lac Wiyâshâkimî. Cette région, caractérisée par un climat subarctique, présente des processus géomorphologiques actifs. L'objectif de l'étude est de documenter l'évolution d'un versant composé d'un talus de débris grossier en zone apicale, puis d'un talus enforesté sous un replat, avec une attention particulière portée à la dynamique des pentes et à l'activité géomorphologique récente.

Les travaux de terrain incluent des profils topographiques du versant, un inventaire des propriétés morphométriques des débris rocheux, et une estimation de la couverture végétale sur les clastes. Des méthodes de dendrochronologie ont également été utilisées pour identifier les périodes de perturbations de croissance des épinettes noires, suggérant une instabilité du dépôt de surface récurrente depuis 1790. Les résultats montrent que la partie supérieure du versant est dominée par un talus formé de blocs rocheux larges et angleux à couverture végétale continue, indiquant la faible activité géomorphologique récente sur la majorité du versant, tandis que la partie inférieure présente des signes de déstabilisation, en particulier après 1980. Les résultats suggèrent que les processus géomorphologiques actuels, comme les avalanches, les chutes de pierres ou les glissements de terrain, sont limités, bien que des indices de réajustements passés et des perturbations récentes aient été observés.

**Mots-clés :** morphométrie, débris, avalanches, périglaciaire, dendrochronologie, Nunavik.

## ARTICLE INFORMATION

Received February 2, 2025.

Accepted March 21, 2025.

E-mail adresses:

armelle.decaulne@univ-nantes.fr (A. Decaulne)

najat.bhiry@cen.ulaval.ca (N. Bhiry)

ann.delwaide@ggr.ulaval.ca (Delwaide)

## 1. Introduction

Hillslopes are a common terrestrial landform key component of the understanding of mass wasting geomorphic dynamics, providing indications on the types and recurrence of processes that contribute to build up landforms on slopes (Easterbrooks, 1999). The study of hillslopes is essential to understand their long-term

complex evolution, and the recognition of processes responsible for slope denudation is achieved through the identification of forms (Selby, 2005). However, changes in slope forms vary through time, depending on the intensity of influences they encounter (van Steijn, 2002). Talus deposits are widespread in cold climate mountain environments, and are shaped by a range of contributing processes (e.g., Caine, 1974; Kirkby and Statham, 1975; Gardner,

<footnote><sup>a</sup> CNRS LETG-Nantes, Université de Nantes, France.</footnote>

<footnote><sup>b</sup> Centre d'études nordiques & Département de Géographie, Université Laval, Québec, Canada.</footnote>

<footnote><sup>c</sup> Département de Géographie, Université Laval, Québec, Canada.</footnote>

<footnote>* Corresponding author. Tel: +33 253487658</footnote>
1979; Brunsden and Prior, 1984; Selby, 2005; Germain and Hétu, 2016). Slope accumulations reveal also climatic changes through debris organisation and natural archives (e.g., Blikra and Nemeç, 1998; Hétu and Gray, 2000; McCarroll et al., 2002; van Steijn et al., 2002; Decaulne et al., 2007; Slaymaker, 2008; Germain et al., 2009; Bhiry et al., 2019)

In the rolling landscape of Nunavik, with its subarctic climate, the presence of erodible bedrock, freeze-thaw cycles, frost cracking, frost wedging and vegetation dynamics all contribute to geomorphic processes on slopes, as highlighted by this study. Deciphering slope dynamics in the region is a recent effort in the international literature, with the first studies published from the end of the 20th century (Bégin and Filion, 1985; Marion et al., 1995). Over the last decade, the identification of active slope processes has been necessary for hazards recognition and vulnerability assessment in the region. This is particularly relevant due to the recently settled populations and subsequent extension of human infrastructures (Decaulne et al., 2021; Joliet et al., 2024); snow avalanches are one of the main targeted hazards (Germain, 2016). The geology of most of Nunavik is dominated by gneiss and granite and is not prone to the development of large slope accumulations: few deposits are found in the distal part of slopes. In areas with more erodible bedrocks such as sedimentary rocks and basalts such as Umiujaq northern village region, talus develop with recurrent accumulation of debris originating from various slope processes (Veilleux et al., 2020), and snow-avalanche occurrence has been clearly documented (Veilleux et al., 2021; Grenier et al., 2023). However, the number of sites investigated in Nunavik (almost 445,000 km²) is so far very limited, and more slope accumulations have to be studied to encompass the variety of processes and talus development during the Holocene in the region. South of the tree line in Nunavik, the presence of forest fringes supplies an additional proxy in their tree-ring patterns to date potential slope activity periods.

The objective of this work is to gather keys to explain the functioning of a complex slope composed of an apical open work talus separated from a forested portion by a local horizontal step that abruptly breaks the slope continuity.

## 2. Study site

The study site is located within Lake Wiyashâkimî (56°12'56.91"N; 74°30'54.37"O), in south western Nunavik (Canada), which is the area of northern Québec lying north of the 55th parallel. Lake Wiyashâkimî (Cree name, also found as Lac à l'Éau Claire in French or Clearwater Lake in English on maps on in the literature, although the indigenous name is henceforth promoted) stands in southwestern Nunavik (fig. 1), about 130 km southeast from Umiujaq northern village, and within the eastern boundaries of Tursujuq National Park, the largest protected area in Québec established in 2013. The lake is 36 km wide and was formed by a meteorite impact at about 286 Ma (Schmieder et al., 2015), producing friable volcanic breccia, also coherent volcanic breccia, and massive quartz latite (Bostock, 1969), i.e., impact-melt-bearing (lava-like) units about 100-m thick that totally transformed the original Archean metamorphic rocks (Dence, 1964; Simonds et al., 1978). Typical impact patterns are exhibited, with a 17-km wide inner ring of islands with a greater slope gradient on the outer side of the crater. The largest islands are

Lepage (in the north; Wiskichanikw in Cree), Aux Foreurs (in the east; Kamiskutanikaw in Cree) and Atkinson (in the south); in the west are the small Tétard islands.

According to Payette (1984) and Allard and Séguin (1985), the Lake Wiyashâkimî area was deglaciated by 5300 BP, and the inner islands were ice free by 5050 BP, with the vegetation colonization starting shortly after. The subsequent depression was filled by a proglacial lake (Marion et al., 1995). Glacial and fluvioglacial deposits from the Wisconsin glaciation, mostly till, cover most areas of the Lake Wiyashâkimî archipelago.

The climatic characterization of the area varies slightly between authors. According to the Litynski climatic classification (1988), and the climate model proposed by Gerardin and McKenney (2001), the climate of Lake Wiyashâkimî archipelago is subarctic, with temperatures which qualify as cold subpolar (mean annual temperature from -6 to -1.5° C), with moderate precipitation (470-799 mm/year) and a very short growing season (90-119 days). Results of the climatic model proposed by Charron (2015) indicate mean annual air temperature from -5 to -4° C and annual precipitation from 750 to 850 mm; snow cover lasts for 221-240 days (according to model estimates, the water equivalent varies from 122-150 to 201-225 mm).

Weather stations are few in Nunavik; however, the Centre d'études Nordiques station on the northern shore of Lake Wiyashâkimî has operated since 2005 (data available from the SILA network website: http://www.cen.ulaval.ca/sila.php?xml=cartesila&lt=72&lg=-79&zm=3). The annual data for 2006, 2007, and 2011-2015, indicate a mean annual temperature of -3.6 °C. The number of freeze-thaw cycles is unknown at the site; a regional study (Charron, 2015) indicated that the months of April to June and September to November have the highest number of days with at least one freeze-thaw cycle (from a comparison of the maximum and minimum daily temperature).

In this study, we focused on a north-facing slope on the central part of Lepage island that we arbitrarily named Raspberry slope (fig. 1). The slope, below a 200 m-long edge, extends from the lake bank, at 238 m a.s.l., to the island plateau, at 300 m a.s.l. The slope is complex in its shape and succession of landforms, with an apical openwork talus slope followed in the mid- and distal part by a fully vegetated slope, partially covered with black spruce (*Picea mariana*) and other local bushes species (*Betula glandulosa*, *Rhododendron groenlandicum*) growing on a sphagnum peat (Payette, 1984, 1988).

## 3. Methods

### 3.1. Long profiles of Raspberry slope

A survey of all the north-facing Raspberry slope was conducted by a ground survey, to identify the present-day geomorphological activity. In this type of research, precise knowledge of slope microtopography is essential, and therefore a differential global positioning system (dGPS) was used to survey six long-profiles along Raspberry slope. The profiles enabled the general form and shape of the slope to be determined (Selby 2005). In addition, determining slope profiles with a high degree of accuracy and precision highlights changes in slope gradients and identifies the
<figure><img src="image_2.png" /><figcaption>Figure 1 - Location of the site area and view from the upper west slope. (photo A. Decaulne, August 2017).</figcaption></figure>

<caption>Figure 1 - Localisation du secteur d'étude et vue depuis l'amont-ouest du versant. (photo A. Decaulne, août 2017).</caption>

preferential locations for slope deposit accumulation. The position and α-angle (reach angle measured with an inclinometer from the boulder to the apical slope edge) of 17 large boulders (volume >1 m³) were gathered. Slope evolution was estimated using the Ho/ Hi index, which compares the height of the talus (Ho) with the height of the full slope (Hi); the closer the ratio to 1, the more developed the slope, as previously documented by Francou (1988) and Sellier (1992, 2001).

## 3.2. Clast and vegetation survey

The upper slope talus was surveyed along four long-profiles for granulometric assessment: at each station (stations 1 being the uppermost ones) 25 boulders were measured with a tape and calipers along a 10-m line, providing their length (a-axis), width (b-axis) and thickness (c-axis). The lithology of the clasts was noted, to estimate the part of locally produced clasts (volcanic breccia) versus allochthonous ones (gneiss and granite) inherited from glacial transport.

A total of 1650 measurements were made and the data were analyzed with Excel and R softwares to produce a statistical analysis of the clast population at each station along each profile. The shape of the clasts has been described with a series of calculation and

indexes (after Pérez, 1998; Hétu and Gray, 2000; Fournier et al., 2012). Ratio width/length (b/a) and thickness/width (c/b) are used to built up Zingg graphs (Zingg, 1935; Bringgs, 1977; Marion et al., 1995; Germain and Filion, 2002; Ouellet and Germain, 2014), with divide the clast shapes into four categories: discs, spheres, rods and blades. In addition, the flatness and sphericity indexes are calculated.

The flatness index (following Cailleux et Tricart, 1965) was calculated as:

$$ If = \frac{(a+b)}{2c} \quad [1] $$

where a and b are the length and width of the clast and c is clast thickness. The greater the value of Ia, the flatter the clast. Since flat clasts are the most prone to slide across the talus and escape the openwork texture traps, their spatial distribution across the talus is very informative. The sphericity index (following Krumbein, 1941) was calculated as:

$$ Is = \left( \frac{bc}{a^2} \right)^{1/3} \quad [2] $$
a value of 1 indicates that a, b and c are of equal measure; thus, an
angular clast would be cubic.

On the openwork talus, vegetation cover on the clasts was also visually assessed, separating visual recognition into four classes. Complete absence of vegetation indicates a fresh deposit, while presence of a single lichen species, or several lichen or moss species, indicates increasing relative presence of the clast on the talus.

3.3. Dendrochronology

A total of 20 black spruces (Picea mariana), 15 dead (13 were still standing) and five alive, providing 22 discs, were sampled in the mid- to distal slope forest stand. Being located in the Tursujuq National Park boudaries, the number of trees alive is voluntarily very limited, while most of the samples come from dead trees, in order to estimate the age of the stand and the growth accidents the forest stand encountered. We focussed on erect trees and ignored the stunted ones, and samples were done either with a chainsaw or a hand saw as close to the collar or stem base possible. We then followed the classical dendrogeomorphic procedures (Shroder, 1978; Butler, Malanson, 1985): for each tree sampled, information regarding their spatial location (GPS records), and the type of damage (tilted stem, candelabra shape, topped stem, etc.) were noted. Samples were dried and finely sanded until the wood cells were visible under a binocular microscope. Annual growth rings were measured with a Velmex micrometer (0.002 mm) at a magnification of 40x.Two opposite radii per stem sample was measured as we specifically focus on eccentric growth, as a proxy of slope destabilisation. Trees #5, 17 and 18 were not measured due to poor reading of the rings of these dead trees. This work was conducted in the dendrology laboratory of Centre d'études Nordiques at Laval Université.

Samples were visually dated under a binocular microscope by
identifying light ring patterns, following previous procedure in
dendrochronology in Nunavik (Filion et al., 1986; Delwaide et al.,
2021). Light rings are made of latewood tracheids delineated by very
thin cell walls (Wang et al., 2000). They are often formed in years
with unusually low summer temperatures (Liang et al., 1997; Wang
et al., 2002), sometimes due to the cooling effect of major volcanic
eruptions (Gennaretti et al., 2014). Crossdating accuracy of all
measured stems was also assessed using the program COFECHA
(Holmes, 1983).

3.4. Programmed shutter-release camera

In summer 2017, an automatic camera was installed by Raspberry
slope to document any geomorphic events occurring on the upper
talus. The distance from the talus (60 to 170 m) and the resolution
of the Reconyx PC800 Hyperfire camera is favorable to track snow-
avalanche events over winter. Programmed to record one picture
every hour from 9:00 am to 04:00 pm, the camera functions year-
round with 8 pictures daily, and enables the documentation of several
daily snow-avalanche events. The angle of the camera was modified
in the fall 2017 by an animal that damaged part of its ties, deflecting
the lens from the view on the talus over winter 2017-2018. However,
the camera's position was corrected in summer 2018, and the survey
of the slope by this means has been ongoing since that date.

The workflow of the paper is presented in Figure 2.

<figure><img src="image_3.png" /><figcaption>Figure 2 – Workflow of the study of Raspberry slope.</figcaption></figure>

<caption>Figure 2 – Déroulement méthodologique de l'étude du versant Framboisier.</caption>

4. Results

4.1. Morphometric properties of the talus

- Ho/Hi:

The slope shows advanced evolution with a minimal Ho/Hi ratio of 0.84 (Ho = 54 m; Hi = 64 m) in the west and a maximal Ho/Hi ratio of 0.93 (Ho = 60 m; Hi = 64 m) in the east, almost reaching complete evolution. The limited rockface height produces minimal debris to the talus below. The clearly retreating rockwall, with only a short height remaining active, also diminishes its potential contribution of large debris volume to the slope, therefore limiting its longitudinal reach towards the distal part of the slope.

- Long profiles and boulder reach:

Raspberry Slope's long profiles, with average angles ranging from 20° to 28°, display varied shapes (fig. 3). While almost rectilinear or slightly concave in the eastern part of the slope (long profiles A and B), the profiles become clearly concavo-convex for profiles C, D and E due to a significant reduction of the slope angle around 260 m a.s.l., reaching an intermediate slope break, a plateau (fig. 3), downhill followed with another concave segment. Profiles D, E and F are significantly shorter, reaching the western talweg. Out of profiles A and B, the upper segments of all other profiles are around 33°, i.e., the angle of repose, which is seldom overpassed.
<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /><figcaption>Figure 3 – Position of the long profiles of Raspberry slope and schematic details of each of the six long profiles.</figcaption></figure>

1: rockwall; 2: coarse angular surface debris; 3: broadleaved bushes (mainly dwarf birch - *Betula glandulosa*); 4: stand of black spruce (*Picea mariana*). Photo by Armelle Decaulne, August 2017.

<caption>Figure 3 – Position des profils longitudinaux du versant Framboisier et détails schématiques de chacun des six profils en long.</caption>

1 : paroi rocheuse ; 2 : débris de surface anguleux et grossiers ; 3 : buissons de feuillus (surtout le bouleau glanduleux - Betula glandulosa) ; 4 : boisé d'épinettes noires (Picea mariana).

The long profiles exhibit also contrasted vegetation patterns. While openwork debris accumulation in the apical part of the slope are mostly depraved from erected vegetation, bushes of *Betula glandulosa* are anyway present in the apex of profile B; broadleaved bushes are found also on the horizontal surface at the boundary between the debris talus and black spruce stand, where the undergrowth is also largely represented by small bushes of dwarf birch and Labrador tea.

The slope is short; however, scree have clearly formed on the upper part of the slope, with an openworked talus. Also, large boulders are scattered over the whole slope: the 17 largest red breccia boulders (>1 m³, maximum measured at 8 m³) are found at different positions within the lower part of the slope (fig. 4), the

furthest ones with a α-angle of 27° only. These furthest boulders are located on the banks of the lake, meaning that the maximum reach for boulders originating from the top rockwall may extend to the lake, overpassing 130 m of horizontal distance, or 150 m of oblique distance long profiles A and B. However, all these boulders have been settled for decades, as they all exhibit complete vegetation coverage, ranging from lichens to mosses.

### - Clast characteristics and spatial distribution:

The vast majority of clasts measured on Raspberry slope are red impactite breccia: this type of lithology represents 96.5 % of the total analysed clasts; 2.4 % white impactite breccia, and the
remaining 1.1 % are allochthonous granites or gneiss. Therefore, we can conclude that the lithology of the talus is uniform, and has no influence on the shape distribution of the clasts.

The measure of clasts at different stations along the four profiles A to D show first that all kinds of shape are represented. Zingg

diagrams (fig. 5) do not exhibit preferential forms, indicating that the rockwall supply a mix of clasts. If spheres are almost absent from profile D, from the upper station of profile B, and third station of profile A, they are found elsewhere, as well as other shapes.

The spatial distribution of clasts is presented in fig. 6. If the mean

<figure><img src="image_6.png" /><figcaption>Figure 4 – Position of large boulders (> 1 m³) along Raspberry slope and their respective α-angle (reach angle).</figcaption></figure>

(photo by A. Decaulne, August 2015).

<caption>Figure 4 – Position des blocs les plus gros (> 1 m³) sur le versant Framboisier, et leur angle de portée α.</caption>

(photo A. Decaulne, août 2015).

<figure><img src="image_7.png" /><figcaption>Figure 5 – Zingg diagrams showing the distribution of debris according to four major shapes: discs, spheres, rods and blades.</figcaption></figure>

On the left, the Zingg diagram gathers the 1650 clasts measured, distributed by profile and stations on the right.

<caption>Figure 5 – Diagrammes de Zingg montrant la répartition des débris selon quatre formes majeures : disques, sphères, aiguilles et lames.</caption>

A gauche, le diagramme de Zingg comprend tous les fragments mesurés, eux-mêmes distribués par profils et stations à droite.
a-axis is 0.44 cm, only 5.8 % of clasts are longer than 1 m (with a max at 3.50 m in lower profile C). This trend is specifically true in the distal part of profiles B and D, although it is not highly pronounced. The flatness index does not show any clear trend either, except from profile D that shows slightly higher values; overall, flatness index values are rather low, which impedes the displacements of clasts from the openwork texture, i.e., escaping the upper slope talus. That's also where the rockwall is most developed. The sphericity index shows variable values from one station to another and between profiles, with more "spheric" clasts distributed unevenly on the profiles.

- Vegetal cover distribution on clasts:

The visual estimation of vegetal cover on clasts shows the clear dominance of totally covered clasts with mosses and lichens (fig. 7), which have remained on the talus for decades with no mobility. Profile D, then C, are clearly the parts of the talus that are the most stabilized (the western parts), with the higher representation of the more developed stage of vegetal cover on clasts. On the opposite, profile B shows the greatest mobility potential, with the freshest clasts evenly distributed along the talus, except from the distal station. This indicates present-day debris supply from the rockwall (free fall, delivering of scree), as well as other reworking processes such as snow avalanches. On profile A, the few freshest boulders are located at mid-talus.

<figure><img src="image_8.png" /><figcaption>Figure 6 – Box and whisker plots comparing the morphometric properties (a-axis, flatness and sphericity indexes) of clasts along profiles A, B, C and D.</figcaption></figure>

<caption>Figure 6 – Diagramme boîte à moustaches comparant les propriétés morphométriques (grand axe, indices d'aplatissement et de sphéricité) des fragments le long des profils A, B, C et D.</caption>

## 4.2. Dendrochronology within the mid- to low slope forest stand

Trees were sampled all over the stand, from the lake to the openwork talus slope (fig. 8A). The oldest tree-ring dates back to 1790 CE; all samples cover the period 1950-1990 (except for tree #7, much younger than all others), and all except one the period 1900-1990 (fig. 8B). The coverage of earlier decades, as well as 1990-2017, is done by part of the trees sampled.

In Figure 9, we represent eccentric years per tree, arrange per spatial sampling areas: left column are trees #1, 2, 3 and 4, located in the distal part of the slope; middle column are trees #6, 7, 8, 9 located in the upper-east part of the stand; and trees #19, 20 from the western side of the stand; the right column gathers trees sampled in the mid-part of the stand, #10, 11, 12, 13, 14, 15 and 16. Dendrochronological data highlight two periods where the radial growth of trees is particularly eccentric (period 1880-1920 and period after 1980). All trees located in the distal part of the slope (1, 1bis, 2, 2bis and 4), with the exception of tree 3, show growth ring eccentricity during the period 1880-1920. Tree 19 and to a lesser extent, tree 6, also display eccentricity during this period. Eccentricity data, observed for several trees located throughout the slope, suggest also a period of instability after 1980.

Tilting eccentricity in the slope direction dominates (positive values); however, eccentricities due to tilting towards the upper slope direction are also observed (recurrent negative values in trees #01bis, 02bis, 03, 04, 09, 10, 11, 19), indicating that stress

<figure><img src="image_9.png" /><figcaption>Figure 7 – Spatial distribution of vegetal cover on clasts over the openwork talus.</figcaption></figure>

1: none; 2: one lichen species; 3: several lichen species; 4: lichens and mosses.

<caption>Figure 7 – Répartition spatiale de la couverture végétale sur les débris le long du talus.</caption>

1 : absence ; 2 : une espèce de lichens ; 3 : plusieurs espèces de lichens ; 4 : lichens et mousses.
<figure><img src="image_10.png" /><figcaption>A. Sampled tree spatial distribution</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>B. Tree-ring temporal distribution</figcaption></figure>

<caption>Figure 8 - Location of trees sampled (A), and their lifespan, with sample depth in dashed line (B).</caption>

The grey zone representing the common period 1900-1990 to all trees (except for #07). Background photo by A. Decaulne, August 2015.

<caption>Figure 8 - Localisation des arbres échantillonnés (A), leurs durées de vie, et le nombre annuel d'échantillons (en ligne pointillée), (B).</caption>

La zone en grisé représente la période de vie commune à tous les arbres (excepté #07). Photo d'A. Decaulne, août 2015.

on the stem is not only due to aerial dynamics, but also internal, i.e., the slope surface has been unstable, affecting the root system from one place to another: the spatial dispersion of tree-ring patterns illustrate multiple responses to various stresses.

Schaerer, 1993, as initiated by radiation input, releasing isolated snow blocks in the shape of various size snow balls). Over the documented period, seven snow avalanches have reached the distal part of the talus slope.

## 4.3. Recent snow-avalanche activity

Although short, as noted earlier, Raspberry slope has the competence to develop slope process, as several clasts devoid of lichen and moss were found. Snow avalanches are an active process within the boundaries of the upper talus slope, as attested through a programmed shutter-release camera. Figure 10 (A and B) provides the calendar of 32 avalanche days and the contour lines of 37 snow avalanches that occurred on the upper talus. These snow avalanches are mostly linked to snow-cornice collapse triggering a slab avalanche below; as well, several sluffing activities (defined according to McClung and

## 5. Discussion and conclusions

Ho/Hi values, long profiles as well as clast organization on slope accumulations are classical features to provide indication on slope activity (Selby, 2005; Bertran et al., 1997). For Raspberry slope, Ho/Hi values range 0.84-0.93, which is similar to those obtained for Caribou slope located about 3.5 km to the west (Decaulne et al., 2018). If the Ho/Hi values are equivalent for both sites, other features show different results. At Caribou slope, which displays a similar length talus slope, long profiles are rectilinear to concave; the median of a-axis is similar however Raspberry slope counts much larger debris at the 75th
<figure><img src="image_12.png" /><figcaption>Figure 9 – Raw eccentricity values derived from the measure of the opposite radii in the slope axis.</figcaption></figure>

Graphs are ordered by tree location groups: distal trees on the left, upper east trees and mid-west in the central column, and central mid-slope trees in the right column. The periods with similar eccentricity patterns in several trees are highlighted (1880-1920 and 1980-2017). Photos by A. Delwaide.

<caption>Figure 9 – Valeurs brutes d'excentricité dérivées des mesures des rayons opposés dans l'axe du versant.</caption>

Les graphiques sont ordonnés par localisation : sur la gauche les arbres de la zone distale ; les arbres de la zone est et centre-ouest dans la colonne centrale, et les arbres à mi-versant dans la colonne de droite. Les périodes avec des schémas d'excentricité similaires dans différents arbres sont surlignées (1880-1920 and 1980-2017). Photos d'A. Delwaide.
<figure><img src="image_13.png" /></figure>

<figure><img src="image_14.png" /><figcaption>Figure 10 – Snow-avalanche activity recorded on Raspberry upper talus by automatic cameras over the six winters 2018 to 2024.</figcaption></figure>

A: calendar of recent snow-avalanche events (1: none; 2: slab avalanche; 3: sluffing); B: contours of snow-avalanche deposits and example of some of the longest events (1: observed contours; 2: hypothetic contours hidden by the forest; 3: sluffing visible track and position of the distal snow block).

<caption>Figure 10 – Activité avalancheuse enregistrée sur le talus amont du versant Framboisier par un appareil photographique à déclenchement automatique durant les six hivres 2018 à 2024.</caption>

A : calendrier des avalanches récentes (1 : aucune, 2 : avalanche de plaque ; 3 : rupture partielle de corniche de neige libérant des blocs isolés) ; B : contours des dépôts avalancheux et exemples d'événements dont la distance de parcours est la plus longue (1 : contours observés ; B : contours hypothétiques cachés par la forêt ; 3 : trajectoire visible et position distale des blocs de neige isolés).
percentile with numerous outliers; the flatness index is generally less at Raspberry than at Caribou site; and the sphericity index is much higher at Raspberry than Caribou site. Caribou talus also displays debris with dense vegetation cover (including lichens and mosses). However, a few fresh clasts are visible at various locations, indicating recent deposits, including in the distal part of the talus. This suggests that the surface of the talus has been reworked in the recent past, notably by snow avalanches that could have transported clasts to the bottom of the talus. These observations are not made at Raspberry site. At both slopes, the transport of debris from the rockwall to the distal talus is extremely limited. Therefore, we hypothesize that any spheric clast is either supplied by the locally favorable joint network that fragments the rockwall, or originates from the few allochthonous rocks transported by the Laurentide Ice Sheet and deposited during the glacial retreat. In fact, both taluses are made of coarse debris, which contrasts with other slopes studied in Québec, notably those from Gaspésie. The landscape there also displays short slopes and rolling plateau, similar to Nunavik relief. In Gaspésie, slopes developed from the denudation of sedimentary rocks, delivering much smaller clasts, around maximum a-axis of 20 cm in a loosely cohesive structure and subhorizontal beddings in an alluvial fan (Ouellet and Germain, 2014), or a-axis of 6 cm in the stratified scree of the Chic-Choc (Hétu and Gray, 2000; Germain and Hétu, 2016).

On Raspberry slope, the presence of a mid-slope plateau rises questions regarding its origin. If long profiles A and B show a slight convexity around 260 m a.s.l., just uphill from the first spruces, the convexity of the distal talus is marked for profiles C and D, with a distinct plateau. The plateau, which is 65 m long and about 8 m large, extends from the west of profile B to profile F. The mid-slope plateau suggests a disconnection between the apical, i.e., the openwork talus, and the distal part, i.e., the woody slope. On the wooded slope below, tree-ring results, with a maximum age of *Picea mariana* of 227 years in 2017, indicate that this part of the slope reached a stage of geomorphic stability before 1790 CE that permitted tree growth. Marion et al. (1995) has analysed tree rings from 117 trees on the nearby Aux Foreurs islands, finding out the first growth disturbances in 1760 CE; Bégin and Filion (1985) studied 52 trees, also on Aux Foreurs island, reaching back to 1750 CE. These two studies highlight the occurrence of multiple slope instabilities, either since 1785 (Bégin and Filion, 1985), or throughout the Holocene (Marion et al., 1995).

On Raspberry slope, trees reacted asynchronously across the slope, even for individuals close to each other. However, two periods were identified on Raspberry slopes with common eccentricities in several tree rings, regardless their position: 1880-1920 and 1980-2017, with a majority of downward tilting of the stems, and backward as well. Avalanches and creeping snow tend to impact trees in the direction of the slope, provoking sabre growth (Schweingrüber, 1996), which is a stem shape observed in the field, although it is not dominant. Rather, stems were strait but tilted, towards the lake as well as towards the slope, indicative of slope movements. Bégin and Filion (1985) documented multiphases landslide activity on Lepage island starting in 1750 CE, which culminated in 1933 CE. On the other hand, Marion et al. (1995) documented the slope development on Aux Foreurs island since 5050 BP, emphasizing the role of paraglacial processes following deglaciation, and dated the onset of gelifluction back to around 3200-

3000 BP. This period was followed by a relative stability until 900 BP, when a series of fires initiated mass movements. Mass movements have been recurrent during the last millennium at the study site., favored by the till deposit that mantled the slopes, inherited from the glacial period and prone to gliding during water saturation periods. Marion et al. (1995) explain that Holocene fires have depleted the vegetation on the summital plateaux of the islands in Wiyâshâkimî lake, which in turn favored the lower slope paludification by accumulating excess of water since 530 BP due to higher snow accumulation in the distal forest from the windblown island plateau. That process favored the aggradation of permafrost under the forest fringe, where *Sphagnum* cover prevented permafrost from thawing (Bhiry and Robert, 2006; Bhiry et al., 2007). Permafrost prevented water infiltration, contributing to the oversaturation of the active layer, thus provoked surface movements of the debris mass (Roy et al., 2012). Over the last decades, the degrading permafrost conditions in Wiyâshâkimî lake region led to the deepening of the active layer (Langlais et al., 2021), which also favors local mass movements.

Following these previous researches on the slopes of Lake Wiyâshâkimî islands, which suggest different kinds of slope movements, we hypothesize that Raspberry slope encountered a massive landslide (fig. 11). The forested area would grow on the landslide mass, on which accumulated the apical slope dynamics that developed into the scarp. This process filled the reverse slope and isolated the lower slopes from present-day slope processes. Black spruce subsequently developed on the mid to low slope, characterized by an uneven surface with spread large boulders. The landside mass was later affected by permafrost degradation (Marion et al., 1995; Langlais et al., 2021). Although the present study lacks dating to document Raspberry slope development over the Holocene, the paraglacial crisis has been documented for the nearby Caribou slope (Bhiry et al., 2019), with minerogenic contribution to a distal peatland from 4905 to 4660 cal. yr BP, while abundant charcoal is found over the period 1595-115 cal. yr BP, supporting Marion et al. (1995) results. However, according to Bhiry et al. (2019), fires would not have favored slope processes at Caribou slope, as the peatland do not bear the signature of massive minerogenic input afterwards. Based on the literature in Wiyâshâkimî lake area, we can partly infer the following sequences qt Raspberry slope:

- deglaciation of Wiyâshâkimî lake, with the area being totally ice free by 5300 cal yr BP;

- the paraglacial period, i.e., from 7000 to 5050 cal. yr BP, would have supplied debris from successive rockfall, scree and other slope dynamics, including snow avalanches;

- the boreal forest, mainly represented by balsam fir (*Abies balsamea*) according to Richard et al. (1982) settled from 4900 to 3000 cal. yr BP;

- nine fire-induced deforestation periods from 2350-200 cal. yr BP, which were notably destructive on Lepage island (Millet and Payette, 1987); the last fire period corresponds to the tree-ring dating obtained in the forest of lower Raspberry slope, as well as in neighboring slopes (Bégin et Filion, 1985; Marion et al., 1995). The consequent depletion on forest cover modifies snow distribution and thereby the subsurface temperature, and raises the permafrost table by reducing the thickness of the active layer if permafrost is present, provoking slope destabilization; the Little Ice Age period, at the end of this stage, is known to have contributed to the rockwall retreat (e.g., McCarroll et al., 2002);
<figure><img src="image_15.png" /><figcaption>(ii) PARAGLACIAL STAGE: ~7000-3000 cal. yr BP</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>(iii) BOREAL FOREST: ~4900-2000 cal. yr BP</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>(iv) FIRE-INDUCED DEFORESTATION: ~2350-200 cal. yr BP</figcaption></figure>

<figure><img src="image_18.png" /><figcaption>(v) PERMAFROST AGGRADATION: FROM ~900 cal yr BP</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>(vi) PRESENT DAY: DISCRETE GEOMORPHIC ACTIVITY ON THE SLOPE</figcaption></figure>

<figure><img src="image_20.png" /><figcaption>**Figure 11 - Slope development considerations at Raspberry slope based on the literature.**</figcaption></figure>

1: bedrock; 2: glacial till and erratics; 3: openwork talus slope; 4: boreal forest, mainly composed of balsam fir (Abies balsamea); 5: landslide deposit; 6: post-fire forest, mainly composed of black spruce (Picea mariana).

<caption>**Figure 11 - Considérations d'évolution du site du versants Framboisier basé sur la littérature.**</caption>

1 : roche mère ; 2 : till glaciaire et erratiques ; 3 : talus à texture ouverte ; 4 : forêt boréale, composée principalement de sapin baumier (Abies balsamea) ; 5 : dépôt de glissement ; 6 : forêt post-feux, composée principalement d'épinettes noires (Picea mariana).

<figure><img src="image_21.png" /></figure>

- permafrost aggradation is favored by the absence or low accumulation of snow, which acts as an insulator. Thus, cold waves penetrate deeply and contribute to the aggradation of permafrost. On the other hand, the persistence of permafrost in peatlands is favored by the presence of an overlying layer of mosses and *Sphagnum*, which acts as an insulator, preventing heat from penetrating deeply and melting the ice within the permafrost (Bhiry et al. 2007);

- nowadays, climate warming causes permafrost degradation, with multiple evidence in Wiyâshâkîmi lake such as the formation or expansion of thermokarst ponds (Langlais et al., 2021). This process might be responsible for the asynchronous tilting of stems at different spots on the lower slope deposit;

- additionally, recent snow-avalanche activity is attested.

However, the documented events did not overpass the upper forest fringe, showing a limited reach. Interestingly, on the most frequent snow-avalanche paths determined over the six last winters, only the eastern part has some fresh deposits, which might have been deposited by snow avalanches. Meanwhile fresh clasts are absent from the centralwestern part, where snow avalanches seem to have no reworking role. The first results show that Raspberry slope has been formed and shaped by various postglacial and paraglacial processes over the last millennia; however, at present time it displays a weak geomorphic activity. The upper openwork talus is formed of large angular boulders with a well-developed vegetal cover, mostly mosses. The middle-western part exhibits fresher surficial clasts indicative of recent debris supply (free fall from the rockwall) and rework (snow avalanches), however not reaching the distal part of the talus. Clasts do not display specific shapes; their low sphericity and flatness indexes do not favor their exportation out of the coarse debris talus. The lower part of the slope exhibit recent signs of destabilisation (particularly after 1980-2000) as illustrated in the eccentricity of tree-rings, from a chronology extending to 1790 CE. Numerous surficial movements seem to have affected the forested part of the slope since 1880 CE. Nevertheless, the clear relation with

slope dynamics has to be more specifically established. This would require examining permafrost degradation in the area, along with the development of climatic models for the last centuries, as weather data has only been available intermittently in the recent year. In addition, further data should be acquired from Raspberry site to refine the chronology proposed here based on the literature. Raspberry slope is a very interesting place for such research with a paleoenvironmental background, as its topography is peculiar in the area: while several other slopes present openwork taluses in the islands of Wiyâshâkîmi lake, Raspberry slope is the only one investigated that associates an openwork upper talus resting on a convexity suggesting the occurrence of a prior landslide. The peat present at different sites in the island, and on the slope, might provide new insights into the development of Raspberry slope.

## Acknowledgements

This research is funded by Labex DRIIHM program "Investissements d'avenir" referenced ANR-11-LABX-0010 and OHMi Nunavik; we also received support from Institut Polaire Paul-Emile Victor (IPEV, FRance), research project #1148 DeSiGN, and from NSERG (Canada)

We also wish to thank Julien Lebrun, Samuel Veilleux, Borsteinn Sæmundsson for field assistance during the 2017 campaign.

## References

- **Allard M., Séguin M.K. (1985)** - La déglaciation d'une partie du versant hudsonien québécois : bassins des rivières Nastapoca, Sheldrake et à l'Eau Claire. Géographie Physique et Quaternaire, 39 (1),13-24. Geological Survey of Canadian Journal, 178, 63 p.

- **Bégin C, Filion L. (1985)** - Analyse dendrochronologique d'un glissement de terrain de la région du Lac à l'Eau Claire (Québec nordique). Canadian Journal of Earth Science, 22, 175-182.
Bertran P., Hétu B., Texier J.P., van Steijn H. (1997) – Fabric characteristics of subaerial slope deposits. Sedimentology, 44, 1–16.
DOI: 10.1111/j.1365-3091.1997.tb00421.x

Bhiry N., Decaulne A., Bourgon-Desroches M. (2019) – Development of a subarctic peatland linked to slope dynamics at Lac Wiyàshàkimi (Nunavik, Canada). The Holocene, 29 (9), 1459–1467. DOI: 10.1177/095968361985

Bhiry N., Payette S., Robert E.C. (2007) – Peatland development at the arctic tree line (Québec, Canada) influenced by flooding and permafrost. Quaternary Research, 67, 426–437. DOI: doi:10.1016/j.yqres.2006.11.009

Bhiry N., Robert E.C. (2006) – Reconstruction of changes in vegetation and trophic conditions of a palsa in a permafrost peatland, subarctic Québec, Canada. Ecoscience, 13, 56–65. DOI: 10.2980/1195-6860(2006)13[56:ROCIVA]2.0.CO;2

Blikra L.H., Nemec W. (1998) – Postglacial colluvium in western Norway: depositional processes, facies and paleoclimatic records. Sedimentology, 45, 909–959. DOI: 10.1046/j.1365-3091.1998.00200.x

Bringgs D. (1977) – Sediments. Butterworths, London, 192 p.

Bostock H.H. (1969) – The Clearwater complex, New Quebec. Geological Survey Canadian Bulletin, 178, 63 p.

Brunsden D., Prior D.B. (1984) – Slope instability. John Wiley and Sons, UK, 620 p.

Bulter D.R, Malanson G.P. (1985) – A History of High-Magnitude Snow Avalanches, Southern Glacier National Park, Montana, U.S.A. Mountain Research and Development, 5 (2), 175–182. DOI: 10.2307/3673256

Cailleux A., Tricart J. (1965) – Initiation à l'étude des sables et des galets. SEDES, Paris, 369 p.

Caine N. (1974) – The geomorphic processes of the alpine environment. In Barry R.G., Ives J.D. (eds): Arctic and Alpine Environments. London, Methuen, 721–748.

Charron I. (2015) – Elaboration du portrait climatique régional du Nunavik. Ouranos, Montréal, 86 p.

Decaulne A., Sæmundsson Þ., Jónsson H.P., Sandberg O. (2007) – Changes in deposition on a colluvial fan during the upper Holocene in the Tindastóll Mountain, Skagafjörður district, North Iceland: preliminary results. Geogafriska Annaler, 89, 51–63. DOI: 10.1111/j.1468-0459.2007.00307.x

Decaulne A., Bhiry N., Faucher-Roy J., Boily C.P. (2021) – The development of Kangiqsualujjuq and the threat of snow avalanches in a permafrost degradation context, Nunavik, Canada. Espace, Populations, Sociétés, 1, 10497. DOI: 10.4000/eps.10497

Decaulne A., Bhiry N., Lebrun J., Veilleux S. Sarrazin, D. (2018) – Geomorphic evidence of slope dynamics on the Canadian Shield throughout the Holocene–A study from Lac à l’Eau-Claire, western Nunavik. Ecoscience 25, 343–357. DOI: 10.1080/11956860.2018.1431376

Delwaide A., Asselin H., Arseneault D., Lavoie C., Payette S. (2021) – A 2233-year tree-ring chronology of subarctic black spruce (Picea mariana): growth forms response to long-term climate change, Écoscience, 28 (3-4), 399–419. DOI: 10.1080/11956860.2021.1952014

Dence M.R. (1964) – A comparative structural and petrographic study of probable Canadian meteorite craters. Meteorite and Planet Science, 2 (3), 249–270.

Easterbrooks D.J. (1999) – Surface processes and landforms. Prentice Hall, Upper Saddle River, New Jearsey. 546 p.

Filion L., Payette S., Gauthier L., Boutin Y. (1986) – Light rings in subarctic conifers as a dendrochronological tool. Quaternary Research, 26 (2), 272–279. DOI:10.1016/0033-5894(86)90111-0.

Fournier J., Bonnot-Courtois C., Paris R., Voldoire O., Le Vot M. (2012) – Analyses granulométriques, principes et méthodes. CNRS, Dinard, 100 p.

Francou B. (1988) – L'éboulisation en haute-montagne – Andes et Alpes – six contributions à l'étude du système corniche-éboulis en système périglaciaire. PhD thesis, Paris, Université Paris 7.

Gardner J.S. (1979) – The movement of material on debris slopes in the Canadian Rocky Mountains. Zeitschrift für Geomorphologie, N.F. 23, 45-57.

Gennaretti F., Arseneault D., Nicault A., Perreault L., Bégin Y. (2014) – Volcano-induced regime shifts in millennial tree-ring chronologies from northeastern North America. Proceedings of the National Academy of Sciences, 111 (28), 10077–1008. DOI: 10.1073/ pnas.1324220111

Gerardin V., McKenney K. (2001) – Une classification climatique du Québec à partir de modèles de distribution spatiale de données climatiques mensuelles : vers une définition des bioclimats du Québec. Direction du patrimoine écologique et du développement durable, ministère du Développement durable, de l'Environnement et de Lutte contre les changements climatiques. http://www.mddelcc. gouv.qc.ca/changements/classification/

Germain D. (2016) – Snow avalanche hazard assessment and risk management in northern Quebec, Canada. Natural Hazards, 80, 1303–1321.

Germain D., Filion L., Hétu B. (2009) – Snow avalanche regime and climatic conditions in the Chic-Choc Range, eastern Canada. Climatic Change, 92, 141–167. DOI: 10.1007/s10584-008-9439-4

Germain D., Filion L. (2002) – Description morpho-sédimentologique d'un système éolien de haut de falaise, au cap Sandtop à l'île d'Anticosti (Québec). Géographie physique et Quaternaire, 56 (1), 81–95. DOI: 10.7202/008606ar

Germain D. Hétu B. (2016) – Hillslope processes and related sediment fluxes on a fine-grained scree slope of Eastern Canada. In Beylich A.A., Dixon J.C., Zwolinski Z. (Eds): Source-to -sink fluxes in undisturbed cold environments. Cambridge University Press, Cambridge, UK, 79–95.

Grenier J., Bhiry N., Decaulne A. (2023) – Meteorological conditions and snow-avalanche occurrence over three snow seasons (2017–2020) in Tasiapik Valley, Umiujaq, Nunavik. Arctic, Antarctic, and Alpine Research 55(1), 2194492. DOI: 10.1080/15230430.2023.2194492

Hétu B., Gray J.T. (2000) – Effects of environmental change on scree development throughout the postglacial period in the Chic-Choc Mountains in the Northern Gaspé Peninsula, Québec. Geomorphology, 32, 335–355. DOI: 10.1016/S0169-555X(99)00103-8

Holmes RL. (1983) – Computer-assisted quality control in tree ring dating and measurement. Tree-ring Bull. 43:69-78.

Joliet F., Chanteloup L., Herrmann T.M., Gibout S., Haillot D., Bhiry N., Coxam V., Decaulne A. (2024) – Urban emergence in inuit territory: impacts on the Nunavik socio-ecosystem. Comptes-Rendu de l'Académie des Sciences (CRAS), section Géosciences, 265. DOI: 10.5802/crgeos.265

Kirkby M.J., Statham I. (1975) – Surface stone movement and scree formation. Journal of Geology, 83, 349-362.

Krumbein W.C. (1941) – Measurement and geological significance
of shape and roundness of sedimentary particles. Journal of Sedimentary Petrology, 11, 64–72.

Langlais K., Bhiry N., Lavoie M. (2021) – Holocene dynamics of an inland palsa peatland at Wiyâshâkimî Lake (Nunavik, Canada), Écoscience, 28(3-4), 269–282. DOI: 10.1080/11956860.2021.1907975

Liang C, Filion L, Cournoyer L. (1997) – Wood structure of biotically and climatically induced light rings in eastern larch (Larix laricina). Can J Forest Res. 27(10), 1538–1547. DOI: 10.1139/x97-117.

Litynski J. (1988) – Climat du Québec d'après la classification numérique. Montreal: Éditions Gamma.

Marion J., Filion L., Hétu B. (1995) – The Holocene development of a debris slope in subarctic Québec, Canada. The Holocene, 5 (4), 409–419.

McCarroll D., Shakesby R.A., Matthews J.A. (2002) – Enhanced rockfall activity during the Little Ice Age: further lichenometric evidence from a Norwegian talus. Permafrost and Periglacial Processes, 12, 157–164.

McClung D., Schaerer P. (1993) – The Avalanche Handbook. Seattle, The Mountaineers, 271 p.

Millet J., Payette S. (1987) – Influence des feux sur la déforestation des îles centrales du lac à l’Eau Claire, Québec nordique. Quaternaire, 41 (1), 76–86. DOI: 10.7202/032666ar

Ouellet M.A., Germain D. (2014) – Hyperconcentrated flows on a forested alluvial fan of eastern Canada: geomorphic characteristics, return period, and triggering scenarios. Earth Surface Processes and Landforms, 39, 1876–1887. DOI: 10.1002/esp.3581

Payette S. (1984) – Peat inception and climatic change in Northern Quebec. In: Marner N.A., Karlèn W. (eds.): Climatic change on a yearly to millennial basis. Boston, Reidel, 173–179.

Payette S. (1988) – Late Holocene development of subarctic ombrothrophic peatlands: allogenic and autogenic succession. Ecology, 69, 516–531.

Pérez F.L. (1998) – Talus fabric, clast morphology, and botanical Indicators of Slope Processes on the Chaos Crags (California Cascades), U.S.A. Géographie Physique et Quaternaire, 521, 47–68.

Roy N., Bhiry N., Woollett J. (2012) – Environmental change and terrestrial resource use by the Thule and Inuit of Labrador, Canada. Geoarchaeology, 27, 18–33.

Schmieder M., Schwarz W.H., Trieloff M., Tohver E., Buchner E., Hopp J., Osinski G.R. (2015) – New 40Ar/39Ar dating of the Clearwater Lake impact structures (Québec, Canada) – not the binary asteroid impact it seems? Geochemistry and Cosmochemistry Acta, 148, 304–324.

Schweingrüber F.H. (1996) – Tree Rings and Environment: Dendroecology. Paul Haupt editions, Berne, Switzerland, 609 p.

Selby M.J. (2005) – Hillslope materials and processes. Oxford University Press, Oxford. 451 p.

Sellier D. (1992) – Évolution comparée de versants quartzitiques des Highlands d’Écosse et de Norvège centrale. Bulletin De l’Association des Géographes Français, 69 (3), 236–241.

Sellier D. (2001) – Géomorphologie des versants quartzitiques en milieux froids : l’exemple des montagnes de l’Europe du nord-ouest, thèse d’Etat, Université Paris 1. Vol. 3, 1888 p.

Shroder J.F. (1978) – Dendrogeomorphological analysis of mass movement on Table Cliffs Plateau, Utah. Quaternary Research, 9, 168–185.

Simonds C.H., Phinney W.C., McGee P.E., Cochran A. (1978) – West Clearwater, Quebec impact structure. In: Lunar and Planetary Science Conference Proceedings vol. 9. Proceedings of the 9th Lunar and Planetary Science Conference; Mar 13-17; Houston (TX). 2633–2693.

Slaymaker O. (2008) – Sediment budget and sediment flux studies under accelerating global change in cold environments. Zeitschrift für Geomorphologie, supplementary issue 52, 123–148. DOI: 10.1127/0372-8854/2008/0052S1-0123

Van Steijn H. (2002) – Long-term landform evolution: evidence from talus studied. Earth Surface Processes and Landforms, 27, 1189–1199. DOI: 10.1002/esp.420

Van Steijn H., Boelhouwers J., Harris S., Hétu B. (2002) – Recent research on the nature, origin and climatic relations of blocky and stratified slope deposits. Progress in Physical Geography, 26, 551–575. DOI: 10.1191/0309133302pp35

Veilleux S., Bhiry N., Decaulne A. (2020) – Talus slope characterization in Tasiapik Valley (subarctic Québec): evidence of past and present slope processes. Geomorphology, 349, 106911. DOI: 10.1016/j.geomorph.2019.106911

Veilleux S., Decaulne A., Bhiry N. (2021) – Snow cornice and snow avalanche monitoring using automatic time lapse cameras in Tasiapik Valley, Nunavik (Québec) during the winter of 2017–2018. Arctic Science, 7, 798–812. DOI: 10.1139/as-2020-0013

Wang L, Payette S, Bégin Y. (2000) – A quantitative definition of light rings in black spruce (Picea mariana) at the Arctic treeline in Northern Québec, Canada. Arctic, Antarctic and Alpine Research, 32 (3), 324–330. DOI: 10.1080/15230430.2000.12003370.

Wang L, Payette S, Bégin Y. (2002) – Relationships between anatomical and densitometric characteristics of black spruce and summer temperature at tree line in northern Quebec. Canadian Journal of Forestry Research, 32(3), 477–486. DOI: 10.1139/x01-208.

Zingg, T. (1935) – Beitrag zür schotteranalyse. **Schweizerische Mineralogische und Petrographische Mitteilungen**, 15, 39–140.

## Version abrégée en français

Cette étude porte sur les dynamiques géomorphologiques d'un versant situé sur l'île Lepage, au lac Wiyâshâkimî, au Nunavik (Québec nordique, Canada). Cette région, caractérisée par un climat subarctique, est favorable aux processus géomorphologiques sur les pentes, bien qu'elles soient courtes (60-65 m de dénivelé). L'objectif principal est de comprendre le fonctionnement d'un versant complexe, composé d'un talus à texture ouverte et d'une pente douce enforestée d'épinettes noires, séparés par un replat à mi-pente. L'étude s'intéresse à l'évolution de ce versant, en analysant à la fois les caractéristiques géomorphologiques actuelles et les signes de perturbations passées.

Le versant étudié, situé dans le parc national Tursujuq (fig. 1), est une zone géologique particulière car elle est formée par un impact météoristique datant de 286 millions d'années. La région est couverte de dépôts glaciaires et fluvioglaciaires de la dernière glaciation-déglaciation wisconsienne. Le climat est froid, avec une saison de croissance végétative courte et une couverture neigeuse importante, ce qui influence les processus géomorphologiques.

Pour étudier ce versant, plusieurs méthodes ont été utilisées
(fig. 2). Des profils topographiques longitudinaux ont été réalisés à l'aide d'un système de positionnement global différentiel (dGPS), permettant de décrire la forme générale de la pente et de mesurer les variations de l'angle de la pente, ainsi que la distribution des débris. Les profils montrent des pentes de formes variées : formes rectiligne, concave ou concavo-convexe indiquant une évolution complète du versant, avec une faible activité géomorphologique récente (fig. 3), parsemés de larges blocs (> 1 m³, fig. 4).

L'étude des débris sur le talus à texture ouverte a montré que la majorité est composée de brèches d'impact rouge, avec peu de formes caractéristiques (fig. 5). Ils sont anguleux, indiquant que le transport sur la pente a été limité. Cela est confirmé par les indices de forme, comme la sphéricité et l'aplatissement, expliquant que le transport des débris de la paroi rocheuse vers le talus est restreint (fig. 6). Les quelques débris récents présentent une couverture végétale minimale (fig. 7), suggérant des réajustements géomorphologiques récents mineurs, comme des chutes de blocs ou des avalanches de neige, dans la partie supérieure du versant.

L'étude dendrochronologique a permis d'identifier des périodes de perturbations de croissance des épinettes noires dans la forêt au bas du versant. Les cernes de croissance des arbres, couvrant la période

de 1790 à 2017 (fig. 8), ont montré des anomalies de croissance dues à des stress variés. L'excentricité des cernes suggère que des mouvements de surface ont affecté la stabilité du versant à différentes périodes, notamment après 2000 (fig. 9). Les instabilités de la masse glissée et le dégel du pergélisol pourraient en être la cause.

La zone apicale, constituée de débris à texture ouverte, est principalement stable, avec une végétation bien établie, et l'activité géomorphologique récente semble faible, bien qu'une trentaine d'avalanches de neige soient documentées au cours des derniers hivers (fig. 10). Les indices recueillis, comme la distribution des débris, leurs caractéristiques et les anomalies de croissance des arbres, suggèrent que le versant a connu plusieurs épisodes de dynamiques variées.

Enfin, l'étude ouvre des pistes quant aux causes de la présence d'une rupture de pente topographique à mi-versant, avec une préférence vers l'hypothèse d'un glissement de terrain ayant affecté la totalité du versant (fig. 11), réactivant la fourniture de débris dans la cicatrice d'arrachement où se trouverait le talus à texture ouverte, alors que la masse glissée, dorénavant colonisée par l'épinette noire, poursuit son évolution avec des pertes d'équilibres locales.