Rock Glacier

Rock glaciers are masses of coarse angular debris that display steep fronts and a system of transverse surface ridges and furrows, indicating a downward catamenia motility (Wahrhaftig and Cox, 1959).

From: Past Antarctica , 2020

Rock Glaciers

J.R. Janke , T. Bolch , in Reference Module in Earth Systems and Environmental Sciences, 2021

Abstruse

Rock glaciers, a central chemical element of alpine mountain geomorphic systems, consist of coarse surface debris that insulates an ice-core or ice-debris mixture. Rates of movement of active stone glaciers vary from 1 to more than 100  cm   year−   i. Rock glaciers exist in all major mountain ranges where permafrost occurs just are more than common in dryer climates with high talus accumulation rates. New geospatial techniques, high-resolution data sources, and improved technology will contribute to a better understanding of these landforms. This chapter provides an in-depth summary of important research findings pertaining to stone glaciers and offers insight to futurity research.

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Glacial and Periglacial Geomorphology

J.R. Janke , ... J.D. Vitek , in Treatise on Geomorphology, 2013

Abstract

Rock glaciers, a key element of alpine mountain geomorphic systems, consist of coarse surface droppings that insulates an water ice-core or water ice-droppings mixture. Rates of movement of rock glaciers vary from ane to 100 cm yr –1. Rock glaciers exist in mainly continental dry out climates in areas that have loftier rates of talus aggregating. New geospatial techniques, high-resolution data sources, and improved technology will contribute to a better understanding of these features on Globe and perhaps on Mars. This chapter provides an in-depth summary of important research findings pertaining to rock glaciers and offers insight to future research.

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PERMAFROST AND PERIGLACIAL FEATURES | Rock Glaciers and Protalus Forms

A. Kääb , in Encyclopedia of Quaternary Science (Second Edition), 2013

Environmental Change and Climatic Significance

Stone glaciers are intimately dependent on their geoecological surroundings ( Barsch, 1996). Thus, changes in these conditions take a potentially strong outcome on the rock glacier system. Millennia-calibration climatic changes – for case, temperature shifts such equally betwixt the Concluding Glacial Maximum, the Tardily Glacial flow, and the Holocene – affect, among others, the thermal conditions, and the production and availability of debris. An increment in ground temperatures, possibly above the 0   °C threshold, and/or a reduction of headwall weathering and rockfall onto underlying rock glaciers (Olyphant, 1987) are, for instance, most likely responsible for the decline in activeness of rock glaciers at the beginning of the Holocene. Similarly, the atmospheric warming trends since the terminate of the Piddling Water ice Age observed in most common cold mount regions may be responsible for the recent decay of rock glaciers. Indeed, the altitudinal belts where agile, inactive, and relict stone glaciers are found advise that temperature changes are an important driver of changes in rock glacier activity (Frauenfelder et al., 2001, 2008).

Significantly less well investigated, just potentially of similar importance to temperature, is the influence of long-term changes in precipitation regime. Related changes in mass supply or ground temperature may besides be due to spatiotemporal changes in snow cover. Changes in the climatic regime may also indirectly favor or hinder stone glacier evolution. Thus, stone glaciers may exist overridden by glaciers in times of climatic change or rock glaciers may develop or recover at locations previously occupied by glaciers (see section 'Thermal Atmospheric condition'; Kääb and Kneisel, 2006; Maisch et al., 2003).

As yet, as well petty is known about the exact climatic significance of stone glaciers in order to use them reliably for paleoclimate reconstruction (Brazier et al., 1998; Frauenfelder et al., 2001; Humlum, 1998). The typical climate of modern agile rock glaciers seems similar to the atmospheric condition found at the equilibrium line distance of modern glaciers, though it is somewhat drier. Thus, the altitudinal belts where active, inactive, and relict stone glaciers are found can be used equally proxies for paleoclimatic atmospheric condition that were suitable for active rock glaciers to develop (Frauenfelder et al., 2001). Such reconstruction is, however, substantially complicated past the fact that rock glacier evolution depends not only on climatic weather, but as well on droppings supply and interactions with glaciation. For instance, insufficient debris production may inhibit formation of a stone glacier nether otherwise suitable geoecological atmospheric condition. Or, the topographic and local climate conditions may favor a glacier to occupy the potential geoecological niche of a rock glacier. In addition, quondam rock glacier forms may have been removed by glacial erosion or covered by modern glaciers. As a result, reconstruction of ancient rock glaciers and their paleoclimate requires the consideration of the complete and complex spatiotemporal history of periglacial, glacial, and mass-wasting processes throughout the existence of the rock glaciers investigated (Frauenfelder et al., 2001; Maisch et al., 2003).

Geostatistical investigations on the basis of surface velocity measurements and climatic parameters, laboratory tests, and numerical modeling show that the deformation rate of rock glaciers is dependent, amid other factors (e.m., slope, composition, or thickness), on the ground temperature (Kääb et al., 2007). Warmer rock glaciers bear witness, in full general, higher surface velocities than colder ones do. Consequently, ground-temperature warming as a result of atmospheric warming or changes in snow encompass is expected to increment rock glacier deformation. Indeed, early investigations confirm a significant contempo acceleration of many rock glaciers in the European Alps where an air temperature increase of close to +   ane   °C has been observed since the 1980s (Kääb et al., 2007).

From theoretical considerations, rock glacier permafrost volition react in 3 stages to atmospheric warming (Haeberli, 1992): (i) increase in seasonal thaw depth (i.e., active-layer thickness), (two) ground-temperature warming, and (iii) thermal adjustment toward a new thermal equilibrium accompanied by reduced thickness of the permafrost body (descending permafrost table and rising permafrost base).

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Mass Movement Processes Related to Permafrost and Glaciation

Robert Kenner , ... Lorenz Grämiger , in Reference Module in Earth Systems and Environmental Sciences, 2021

two.1.2 Dynamics

Rock glaciers advance in a conveyer chugalug blazon mode, which significantly differs to glacier flow, where basal sliding at the interface betwixt the lesser of the glacier and the underlying terrain is the fundamental machinery. This major difference, compared to a glacier, explains the widespread absenteeism of push moraines at the forepart of a rock glaciers. Fig. ii shows a typical deformation profile of a rock glacier. Mostly, a Layer A of upwardly to several decameters thickness and relatively small-scale internal strain rates was observed on top of a well-divers Layer B of several decimeters or a few meters thickness with relatively high strain rates. In some cases, more than ane sequence of superimposing A-B layers was identified (Hausmann et al., 2007; Roer et al., 2008; Delaloye et al., 2010a). Plastic deformation of the ice-rich permafrost trunk, post-obit Glen's Law is considered the dominant process for Layer A. This type of deformation is normally referred to as creep and is highly stress- and temperature-dependent (Glen, 1955; Cicoira et al., 2019; Cicoira et al., 2021). Layer B is characterized by having considerably stronger pitter-patter, shearing or a combination of both. In full general, pitter-patter is associated with the dislocation of the fabric's microstructure, while shearing results from continuous failure within the microstructure. To simplify the distinction betwixt both layers, we refer to them every bit a zone of plastic deformation (Layer A) and a zone of shearing (Layer B), although 'concentrated creep inside a constricted layer' may be the appropriate clarification for the processes in Layer B in some cases. The transition from creep-dominated to shear-dominated rock glacier deformation is circuitous, depends on local atmospheric condition and tin thus typically not be clearly discerned.

Fig. 2

Fig. 2. Arenson et al. showing the deformation of boreholes 1 and two (B1 and B2) in the Schafberg rock glacier in Switzerland. A well-divers shear horizon at 15 m (B1) and 25 m depth (B2) is clearly visible. While plastic deformation contributes nearly l% to the full deformation in borehole 2 it is barely existent in borehole i. The base of permafrost is at approximately threescore thousand (B1) and 40 m depth (B2).

 Reproduction of Fig. 9 from Arenson L, Hoelzle Thou, and Springman S (2002) Borehole deformation measurements and internal structure of some rock glaciers in Switzerland. Permafrost and Periglacial Processes thirteen(2): 117–135, doi: doi:10.1002/ppp.414.

In the root zone of stone glaciers or in rather small or cold rock glaciers, creep deformation can contribute 50% or more to the deformation process (Springman et al., 2012) (Fig. 2). The deformation of the stone and ice conglomerate initiated by pitter-patter deformation causes the shear zone to develop downslope of the root zone (Frehner et al., 2015). The ratio of shearing on the total stone glacier deformation increases downslope and with increasing gradient angle (Delaloye et al., 2013; Kenner et al., 2017). If the shear zone (a layer in which deformation is dominated by shear deformation) is located in (water ice-poor) permafrost, shearing velocity may also be temperature dependent (Cicoira et al., 2019). Many of the investigated rock glacier shear zones are located close to the permafrost base of operations (Arenson et al., 2002), likely related to the ideal combination of highest permafrost temperatures, highest stress and coexistence of water and excess ice. While creep deformation only contributes a few decimeters per year at nearly to the total deformation (Arenson et al., 2002; Springman et al., 2012), shearing may cause rock glacier displacement of several meters per year, or in extreme cases, even of decameters (Delaloye et al., 2013; Marcer et al., 2019). For faster rock glaciers (>   1   thou/year) shearing is probable the dominant process, specifically in the example of large rock glaciers in steep terrain (Marcer et al., 2019). As this blazon of rock glacier is most relevant for the release of rapid mass movements such as rock autumn and debris flows from the rock glacier front, information technology is the focus of the discussion below.

Changes in the deformation velocity of rock glaciers tin can occur at daily, seasonal, interannual and multiannual time scales (Jansen and Hergarten, 2006; Delaloye et al., 2010a; Wirz et al., 2015; Kenner et al., 2017). In fast moving stone glaciers, as described above, these accelerations are most likely triggered by changes in water supply (Buchli et al., 2012; Wirz et al., 2016) and the acceleration takes place in the shearing zone (Kenner et al., 2017). The shearing velocity is controlled by the water supply to the shear zone and an associated subtract in effective stress (Jansen and Hergarten, 2006; Cicoira et al., 2019). Precipitation events and snow cook tin explain short-term and seasonal rock glacier velocity variations. The seasonal dispatch of rock glaciers is generally triggered past the beginning of the snowfall melt (Fig. three). At time scales of a few hours, rock glaciers prove a stick-slip deformation pattern, in which the skid deformation oftentimes coincides with rainfall (Jansen and Hergarten, 2006; Kenner et al., 2017; Buchli et al., 2018).

Fig. 3

Fig. 3. The time series prove the simultaneous onset (vertical blackness lines) of (ane) snow melt (blue), (2) warming of a talik, indicating a water flux toward the shear horizon (turquoise) and (three) acceleration of the rock glacier "Ritigraben" (red & green markings) in the Swiss Alps.

 Reproduction of Fig. eight in Kenner R, Phillips 1000, Beutel J, Hiller M, Limpach P, Pointner Eastward, and Volken G (2017) Factors controlling velocity variations at brusk-term, seasonal and multiyear fourth dimension scales, Ritigraben stone glacier, Western Swiss Alps. Permafrost and Periglacial Processes 28(4): 675–684, doi: ten.1002/ppp.1953.

In addition to the reduction in effective stress, advective heat transfer, i.due east. the infiltration of estrus with the water to greater depths within the permafrost, adds to subtract in resistance and a potential increase in stone glacier deformation.

At annual and multiannual scales, precipitation and snow melt rates in non-barren regions are likewise homogeneous to cause strong variations in rock glacier velocity (Frei and Schär, 1998; Kenner et al., 2019b). Here, other factors dominate, which are likely directly linked to climate:

Beginning, the menstruum of the yr during which water supply to the rock glacier shear horizon is maintained (Menses of water supply - PWS). Seasonal warming typically has piddling result on rock glacier deformation velocity, as ground temperatures almost the shear zone are already shut to 0 °C. Winter cooling, however, has an indirect outcome on the PWS (Kenner et al., 2019b). The PWS can be quantified equally the number of days during which the active layer is not completely frozen, i.e. temperatures are either positive or a zero drapery indicates the presence of liquid water. This catamenia is delimited by the showtime of the snow melt in jump and by the end of the fall zero mantle in (early) winter. Notably, this menstruum varies by up to 4 months between individual years and is highly correlated to the rock glacier deformation velocity, in detail to the degree of winter deceleration (Kenner et al., 2019b). Interannual variations of the autumn zero pall end date are controlled by the early winter snow comprehend. Little snow in early wintertime allows rut extraction, hence rapid freezing of the agile layer, while a thick snow encompass delays freezing. Given that wintertime precipitation rates exercise non decrease strongly, climate warming will shift the autumn zero drapery cease engagement farther into the wintertime season in the long-term. The date of the kickoff of the snowfall melt in jump is direct related to weather conditions such as air temperature and radiation and thus to long-term changes in climate.

A 2nd influencing gene is the ratio between quick menses and base flow runoff (Krainer and Mostler, 2002). While quick flow describes the office of the runoff which originates from upslope, drains on top of the permafrost body and does not reach the shear horizon, base flow is the runoff which actually reaches the shear horizon and affects rock glacier velocity. A shift in the ratio of quick- and base of operations menses tin occur due to ongoing development of a drainage systems within the permafrost body in response to ongoing permafrost degradation (Zenklusen Mutter and Phillips, 2012b) and can therefore cause a long-term acceleration of the rock glacier (Kenner et al., 2017). The overall hydraulic electrical conductivity of a rock glacier can increase due to higher permafrost ice temperatures in the long-term and the development of a well-established drainage organization (Zenklusen Complain and Phillips, 2012b); like to those found in glaciers (Fountain and Walder, 1998).

In recent years, several collapsing rock glaciers have been reported (Roer et al., 2008; Delaloye et al., 2013; Iribarren Anacona et al., 2015; Marcer et al., 2019). Collapses of rock glaciers are non referred to every bit catastrophic mass movements, only involve a significant acceleration of the unabridged rock glacier or parts of information technology, which is more typical, by at least one guild of magnitude. Mostly, this occurs in terrain with average slopes close to 30° and is mostly accompanied past the evolution of transverse tension cracks or shear horizons (Buchli et al., 2018). Such a significant rock glacier acceleration may pb to failure of large parts of the rock glacier and subsequent rock- and ice avalanches (Roer et al., 2008). Nonetheless, due to the extremely express number of known cases, collapses of rock glaciers have not been investigated in detail. In full general terms, contributing factors are probable like to those influencing deformation velocities, likewise as overloading furnishings in the root zone of these rock glaciers.

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By geomorphic processes: The function of permafrost and periglacial processes in ice-free environments

Mauro Guglielmin , in Past Antarctica, 2020

Rock glaciers and protalus ramparts

Stone glaciers are masses of coarse athwart debris that brandish steep fronts and a system of transverse surface ridges and furrows, indicating a downward period move ( Wahrhaftig and Cox, 1959). These landforms are quite widespread besides in Antarctica (Hassinger and Mayewski, 1983; Humlum, 1998; Serrano and López-Martínez, 2000; Swanger et al., 2010; López-Martínez et al., 2012; Vieira et al., 2012; Bockheim, 2014).

Despite several geomorphological and geophysical works, their internal structure is not then well known; indeed, in Antarctica, only a couple of rock glaciers were investigated with boreholes, one at the Tumbledown Crags rock glacier on James Ross Island (Fukui et al., 2008) and at Adelie Cove stone glacier shut to Mario Zucchelli Station (Guglielmin et al., 2018). In both cases a cadre of buried relict glacial water ice was found in some shallow excavations or natural exposure (Fig. 6; Swanger et al., 2010; Strelin and Sone, 1998; Vieira et al., 2012; Bockheim, 2014). Guglielmin et al. (2018) integrating different geophysical investigations (GPR and electrical tomography) with borehole and geomorphological analyses highlight that rock glaciers with cores of cached glacier ice can be considered features due to the creep of the buried ice and therefore not permafrost creeping phenomena. Less common are talus-derived rock glaciers, which generally originate from vast accumulations of droppings scree at the pes of volcanic mesas of James Ross Island with buried snowfall derived from interstitial ice (Davies et al., 2013).

Fig. 6

Fig. vi. Relict buried glacier ice exposure of a stone glacier shut Lachman, James Ross Island.

Too protalus ramparts are a common landform observed at the foot of steep scree slopes in Maritime Antarctica (Ermolin et al., 2002; Davies et al., 2013; Nozal et al., 2013; Mlčoch et al., 2018; Ruiz-Fernández et al., 2019).

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Monitoring of Earth Surface Movement and Geomorphologic Processes by Optical Paradigm Correlation

André Stumpf , ... Julien Travelletti , in State Surface Remote Sensing, 2016

5.five.ii Applications to water ice- and rock glaciers

Ice- and rock glaciers are of crucial importance in regional hydrological cycles and are sensitive to changes in the global climate. Glacier retreat may therefore pb to seasonal reductions of fresh h2o supplies that will affect the downstream environs and local population. Glacier fluctuations tin also induce natural hazards such equally outbursts of glacial lakes, avalanches and droppings flows. Especially for fast-moving glaciers with displacement rates of up to several meters per 24-hour interval and frequent changes of their surface features, it remains very challenging to use techniques such as InSAR or in situ techniques such equally permanent dGPS. Equally a result, DIC is often the only feasible approach to quantify the glacier velocities over larger areas and with comprehensive spatial coverage. Furthermore, remote sensing archives such as the Landsat database can be exploited to get together historical data on the glacier extents and velocities upwards to the present mean solar day and allow studying the long-term response of glaciers to environmental changes.

The outcomes of a contempo written report on the monitoring of the Greenland water ice sheet outlet glaciers from Landsat images covering the catamenia of 1999–2012 are presented in Figure 5.7(a). In accordance with previous investigations, the written report institute the many of the outlet glaciers have undergone acceleration during this period. It, however, also highlighted that in that location are likewise many glaciers whose surface velocity does non evidence a clear trend or have even slowed down during the by decade. Long-term and seasonal trends are more often than not very inhomogeneous in infinite and fourth dimension and tin be influenced past thinning of the ice canvas and structural changes in the glacier connectivity. This emphasizes the importance of considering such variables when relating changes in the glacier velocities to climate change [ROS 15a].

Figure 5.seven. Examples of surface deportation measurements on glaciers and rock glaciers: a) Median displacement rates (2010–2012) and changes in displacement rates for individual outlet glaciers (circles) of Central West Greenland ice sheet derived from the correlation of Landsat images from the period 1999–2012. Color-coded squares point the estimates of the flow-velocity trend for the three periods 1999–2003, 2004–2007 and 2008–2012 [ROS 15a]; b) Annual velocity of the Karakoram glaciers (Islamic republic of pakistan, Republic of india and Mainland china) for the year 2000 derived from cross-correlation of multiple Landsat images [DEH 15]; c) Surface displacement of the Muragl rock glacier (Switzerland) for the menstruation 1981–1994 measured by cross-correlation of aerial images [DEB xi]. For a colour version of this figure, meet world wide web.iste.co.uk/baghdadi/6.nada

Figure 5.7(b) presents an average deportation charge per unit for glaciers in the Karakoram mountains obtained through the assay of a subset of the Landsat archive spanning from 1999 to 2001. The exploitation of long fourth dimension serial is not only useful to decipher long-term trend but also helps to increment the spatial coverage and reduces the measurement uncertainty [DEH 15]. Like studies have shown a dandy variability in the glacier response to climate change depending on the droppings covers, topography and atmospheric precipitation government [SCH 11].

While glaciers can easily reach displacement rates of hundreds of meters per year, rock glaciers feature significantly slower displacement rates making cantankerous-correlation of aerial photographs an ideal tool to written report the long-term behavior. Effigy 5.vii(c) shows the motion field of the Muragl rock glacier in Switzerland, which has an average speed of about 0.5 m/year. The report showed that nearly of the stone glacier's displacement field is relatively smooth, while some significant shear occurs on inactive side lobes [KAA 02].

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Ice loss from glaciers and permafrost and related slope instability in high-mount regions

Philip Deline , ... Samuel Weber , in Snow and Ice-Related Hazards, Risks, and Disasters (Second Edition), 2021

fifteen.iii.5 Droppings slopes in permafrost areas

Hazards related to permafrost degradation in debris slopes can be subdivided into (1) direct effects of accelerated creep of cohesive masses of frozen debris such as rock glaciers; (2) indirect furnishings of debris supply from moving masses; and (3) thermokarst.

15.3.5.1 Rock glacier movement

Several types of behavior of rock glaciers and other landforms affected past permafrost creep can be distinguished based on surface kinematics ( Fig. 15.15; Schoeneich et al., 2014):

Fig. 15.15

Fig. xv.15. Evolution trajectories of rock-glacier behavior with increasing temperature (Schoeneich et al., 2014).
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Type i: Moderate acceleration, modulated by multi-annual velocity fluctuations in the range of a few cm   yr−   one to >   2   m   year−   1 (Delaloye et al., 2008; Staub et al., 2016; PERMOS, 2019).

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Type 2a: Aberrant acceleration of the entire or almost of the moving mass with opening of crevasses, scarps, or cracks on the surface (Roer et al., 2008; Darrow et al., 2016; Scotti et al., 2016; Marcer et al., 2019) with velocities ranging from about 1 to >   10   1000   year−   1.

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Blazon 2b: Very strong acceleration with known velocities >   80   chiliad   year−   one, which tin can last a few years (Delaloye et al., 2013; Eriksen et al., 2018).

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Type 2c: Acceleration and dislocation of the lower part of the moving mass, with the formation of scarps (Roer et al., 2008; Delaloye and Morard, 2011; Delaloye et al., 2013).

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Blazon 3: Collapse of the lower part of the frozen moving mass, which breaks down as a debris flow; a new front develops from the scarp (Bodin et al., 2017).

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Type 4: Deceleration of Types 2 and 3 during months to decades after destabilization.

Blazon 1 Laurichard rock glacier (Ecrins massif, French republic) provides 1 of the longest available series of surface deportation (Bodin et al., 2009, 2018). Its velocity has increased during 1988–2018, likely in response to permafrost warming, and its multi-annual behavior has been like to observations in the Swiss Alps (PERMOS, 2019). Afterwards a first peak in 2004, velocity abruptly decreased until 2007, before increasing again until 2016. Every bit shown past Staub et al. (2016) for the Becs-de-Bosson rock glacier, this beliefs tin be related to the lagged upshot of the ground surface temperature deviation over the previous two years.

Types ii–3 are often referred to as "destabilized" and many of these phenomena started in the post-1980s warm decades, although possible cases of earlier initiation are also known (e.g., Marcer et al., 2016). For instance, the destabilization of Blazon 2c Petit-Vélan and Type 2b Tsaté rock glaciers (Valais) in 1988–1995 followed the strong increase in permafrost temperature that occurred around 1990 (Delaloye and Morard, 2011; Lambiel, 2011), and the collapse of the Bérard rock glacier (Southern French Alps) was possibly triggered by the summertime heat-waves of 2003 and 2006 (Bodin et al., 2017).

The internal limerick of the moving mass is an important control of destabilization: The Blazon 4 Bérard moving mass (Southern French Alps), composed of fine schist droppings decumbent to sliding when water saturated, corresponds to a "pebbly" or "fine-grained" rock glacier co-ordinate to Ikeda and Matsuoka (2006). The initiation of a destabilization phase results from the combined influence of thermal (permafrost temperature), geometrical/topographical (gradual changes in geometry of the moving mass over a given topography), and mechanical (e.g., increased loading induced by pregnant rockfall deposits) factors over different fourth dimension scales. Every bit such, it may not be but the response to permafrost warming (Delaloye et al., 2013).

The basal topography over which a stone glacier is moving is a meaning cistron influencing its destabilization (Avian et al., 2009; Marcer et al., 2019). A steep slope causes higher shear stress, and a convex long-profile topography induces extending period and hence favors stretching and fifty-fifty splitting of the moving rock glacier, equally shown by all reported destabilizations/ruptures of the lower part of rock glaciers. Deposits of stone avalanche or rockfall may add mass to a rock glacier and contribute to destabilization (Delaloye et al., 2013; Scotti et al., 2016). If this affects the rooting zone, a longer time is necessary for the effects to achieve the terminal part of the stone glacier, e.g., 25 years to reach the "mechanical surge" of the 400-m-long Grabengufer rock glacier (Valais, Switzerland) in 2008–2012 (Delaloye et al., 2013).

15.3.v.two Debris supply from permafrost areas

The connections between permafrost deposition and debris flows have received increased attention in the aftermath of the catastrophic rain and flooding in the Swiss Alps during the summer of 1987, which triggered numerous debris flows on steep till-covered slopes deglaciated during the past 150 years (Zimmermann and Haeberli, 1992 ). Rock glacier fronts provide droppings downstream into mount torrents ( Zischg et al., 2011), although the link is non necessarily direct. At agile rock-glacier fronts, debris supply to the torrent system is modulated past velocity variations of the stone glacier (Kummert et al., 2018). The rate of droppings supply is usually in the range of tens to a few hundred miii  year−   one. Episodic acceleration or destabilization phases can increment this to several ten thousand 10003  twelvemonth−   ane (Kummert and Delaloye, 2018). Melting of ground ice in debris masses may leave a big amount of loose material available to erosion, which may be limited by the coarse size of debris and a facilitated infiltration of water into the footing.

The consequences of this variation in debris supply depend on the characteristics of the torrent organization. In debris-express systems, additional debris supply due to permafrost degradation may pb to an increase in the magnitude and frequency of droppings flows (Kummert et al., 2018). For example, an enhanced torrent activity was triggered by increased debris supply from the overhanging Dérochoir rock glacier front end in the Arandellys catchment in the Mont Blanc massif (France) in the late 1890s (Mougin, 1914; Marcer et al., 2016).

xv.3.5.three Ground ice melting and thermokarst

In the European Alps, thermokarst phenomena are commonly related to cached glacier water ice or avalanche deposits, and more rarely to excess ice formed in the ground. The long-term conservation of buried water ice is favored by permafrost atmospheric condition. The most hitting phenomena are thermokarst lakes and associated outburst floods (e.g., Gruben Glacier expanse: Haeberli et al., 2001). In the southern French Alps, the Lac Chauvet (2800   m a.s.l.) is an ephemeral lake on debris-covered expressionless ice in a proglacial area that grows for a couple of years earlier draining through a glacial tunnel, triggering droppings flows that tin dam the chief river (Assier, 1996). The phenomenon repeated at least six times since the 1930s, once in 2008. Geophysical investigations show that the ice and frozen droppings are still >   40   chiliad thick.

In recent years, several cases of ground ice revealed by thermokarst features were reported in the Alps in places where no presence of ground water ice was suspected. This could point to an increase in the melt rate of buried ice bodies, representing an emerging risk in periglacial mountain areas. Mapping of proglacial areas combined with permafrost distribution modeling could help identifying the potential areas of thermokarst development.

Ice-cemented droppings layers tin occur in aggrading talus slopes where debris and barrage snow are deposited. The Dents Blanches (Valais) rockfall in 2006 provided a rare exposure of such a permafrost body (Gruber and Haeberli, 2009). The melt of the pore water ice and the interwoven ice layers brand sediment hitherto preserved from erosion available for transport. Every bit a effect, droppings flows of unpredictable magnitude may originate from unexpected locations within talus slopes that contain water ice.

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Response of Periglacial Geomorphic Processes to Global Modify☆

John C. Dixon , in Reference Module in Earth Systems and Ecology Sciences, 2020

4.ii Rock glaciers

During recent decades, the velocity of rock glaciers in the European Alps exceeded values of the belatedly 20th century. Some stone glaciers prove increasing velocity as a response to warming and water input, although continued permafrost deposition would eventually inactivate them ( Ikeda and Matsuoka, 2002). Rock glacier velocities observed in the European Alps in the 1990s were on the society of a few decimeters per year, simply during approximately the by 15   years they often were about 2–10 times higher (Bodin et al., 2009; Lugon and Stoffel, 2010; PERMOS, 2016). Destabilization, including plummet and rapid dispatch, has been documented (Delaloye et al., 2010; Buchli et al., 2013; Bodin et al., 2017). One particularly long fourth dimension series shows velocities around 1960 but slightly lower than during recent years (Hartl et al., 2016). In contrast to nearby glaciers, no clear alter in rock glacier velocity or height was detected at a site in the Andes between 1955 and 1996 (Bodin et al., 2010). The majority of similar landforms investigated in the Alaska Brooks Range increased their velocity since the 1950s, while few others slowed down (Darrow et al., 2016).

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Physics of Terrestrial Planets and Moons

J. Helbert , ... D. Reiss , in Treatise on Geophysics (Second Edition), 2015

10.xi.iii.5.2.1 Lobate debris aprons, lineated valley make full, and concentric crater fill up

Mass wasting phenomena that display similarities to terrestrial stone glaciers were beginning described in detail by Squyres (1978) and Squyres (1979). He subdivided them on the basis of their morphology into lobate droppings aprons ( Figure 9 ), lineated valley fill up, and concentric crater fill. Lobate droppings aprons are characterized by a convex-upwardly topography and a steep and distinct menses forepart, strongly suggesting plastic deformation and flow. They can also show lineations on their surfaces, which can be both parallel and perpendicular to the menses direction. Where lobate debris aprons are bars by valley walls, their surfaces are deformed into contractional lineations parallel to the circumscribed walls. Material with this specific surface texture is called lineated valley fill ( Effigy 10(a) and 10(b) ). Lobate debris aprons and lineated valley fill are best adult where mesas and valleys with steep walls are plant, in particular at the steep scarps of the dichotomy boundary. Concentric crater fill is found in the interior of many craters, where ridges and troughs show a concentric blueprint that tin also show lobate flow fronts toward the crater center. All these types of landforms show evidence for plastic deformation and resemble terrestrial rock glaciers (Lucchitta, 1984; Squyres, 1978, 1979, 1989), which are mixtures of rock and ice (Barsch, 1996; Wahrhaftig and Cox, 1959). Whalley and Azizi (2003) gave a comprehensive review on the terminology and problems related to the identification of rock glaciers on Mars.

Figure 9. Lobate debris apron surrounding a mount in the southern midlatitudes (∼   41°   S, 103°   Due east) on Mars. The morphology of the apron suggests viscid period. Such deposits have been compared to terrestrial rock glaciers. Perspective fake-color view of HRSC epitome 0451. The diameter of the droppings apron is about 50   km (north is down, toward the viewer). copyright: ESA/DLR/FU Berlin.

Figure ten. Comparisons between cold-climate landforms on Globe (left) and Mars (right). (a) Glaciers fusing together in the Yukon region (Canada; image courtesy Marli Miller, Academy of Oregon; image source: Earth Scientific discipline Globe Image Bank). (b) Convergent menstruation features on Mars, probably the result of the flow of stone glacier-like material (MOC prototype SP245006). (c) Water ice-wedge polygons in terrestrial permafrost terrain (Yukon, Canada; epitome courtesy Agriculture and Agri-Food Canada). (d) Patterned ground (polygons) on Mars. The diameter of the smaller polygons is <   10   yard and comparable to the size of ice-wedge polygons on Globe (HiRISE image TRA_000856_2265).

 Image credit NASA/JPL/University of Arizona.

Several hypotheses try to explain the origin of the ice in these debris flows. H2o water ice could accept formed by straight condensation of ice from the atmosphere (Squyres, 1978) or by snow precipitation (Squyres, 1989). It could likewise accrue by water vapor diffusion down into the regolith and subsequent condensation (Mellon and Jakosky, 1995). Finally, groundwater may seep into droppings and create interstitial ice (Lucchitta, 1984; Mangold and Allemand, 2001; Squyres, 1989). The elastic particles in the lobate droppings aprons might come from rock falls that accumulated at the base of scarps (Colaprete and Jakosky, 1998; Squyres, 1978) or, alternatively, from landslides (Lucchitta, 1984; Mangold and Allemand, 2001).

It has been demonstrated by Squyres (1978) on the basis of photoclinometry and by Mangold and Allemand (2001) and Li et al. (2005) on the basis of MOLA topographic profiles that the cross-exclusive shape of lobate droppings aprons can exist approximated past the period law of polycrystalline ice (Glen, 1955) and the menstruation relation of water ice (Paterson, 1994; Vialov, 1958). Colaprete and Jakosky (1998) modeled flow of ice nether Martian weather and establish that menstruum rates are very depression. To create lobate droppings aprons of the observed size, they showed that temperatures 20 to 40 Yard college than present average midlatitude temperatures (∼   210   M), ice contents exceeding eighty%, and cyberspace accumulation rates of ≥   1   cm per year are required.

Lobate droppings aprons, lineated valley fill, and concentric crater make full are young landforms. Crater counts yield low crater densities, and accented ages of <   100   Ma have been derived (due east.1000., Berman et al., 2003; Caput et al., 2005; Li et al., 2005; Mangold, 2003; Squyres, 1978). Withal, morphometric evidence for former lobate debris that were flooded past lava flows or droppings flows (east.g., lahars) more than 1   Ga ago suggests that much older stone glaciers existed equatorward of xxx°, indicating a paleoclimate allowing ground water ice to be stable at that latitudes (Hauber et al., 2008). Indeed, a contempo study concluded that widespread glaciation on the northern midlatitudes spanned a range of at least 600   Ma and ended roughly 100   Ma (Fassett et al., 2014).

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Principles and Criteria of Landslides Identification and Discrimination From the Features Formed by Other Mass-Wasting Phenomena

Alexander Strom , Kanatbek Abdrakhmatov , in Rockslides and Rock Avalanches of Central Asia, 2018

4.iii Rock Avalanches Versus Rock Glaciers

Some other natural miracle typical of loftier mountainous regions that tin exist misinterpreted equally rock avalanche is a rock glacier—gradual and relative ho-hum movement of debris enriched past the interstitial ice ( Whalley, 1974; Barsch, 1977, 1988 Barsch, 1977 Barsch, 1988 ; Haeberli, 1985; Owen and England 1998). In general, debris transported past rock glaciers moves like a crawler belt and so that boulders laying on acme of the body move faster and gradually vicious from its forepart existence overlaid by the inner office of the rock glacier [ibid], which is totally different from rock avalanches that, as can be derived from the internal structure of the deposits (Heim, 1932; Strom, 1994, 2006 Strom, 1994a Strom, 1994b Strom, 2006 ), movement entirely as a laminar flow. Debris is supplied to stone glaciers either by real glaciers upstream or (and) by the numerous small rock falls and snow avalanches from the steep valley walls. The frontal and lateral slopes of these accumulations are inclined at an angle of placidity typical of the clast-supported mixture of angular boulders and fines.

Rock glaciers are widespread in the Central Asian region, usually above 3000   one thousand a.southward.l. (Gorbunov and Titkov, 1989; Titkov, 1979; Gorbunov et al., 1992; Schröder, 1992; Schröder et al., 2005) and sometimes really look very similar to rock avalanches (Fig. 4.29). They often dam pocket-size river valleys.

Figure 4.29. Rock glaciers in the Chong-Aksu River valley (Northern Tien Shan, Kyrgyzstan) in the epicentral zone of the 1911 M8.2 Kemin convulsion. (A) (42.85° North, 77.263° Eastward), fed by the nowadays-day small glaciers in the upper reaches of the catchment mainly; (B) (42.853° N, 77.283° East), fed by rock falls and snow avalanched from the valley walls. Both stone glaciers dammed the river partially. It tin exist hypothesized that some acceleration of their movement could be acquired by the 1911 earthquake, which surface rupture passed ane.0–1.five   km s of the river.

Audio bigotry between rock glaciers and rock avalanches is based on the absence of the headscarp somewhere above the rock glacier comparable in volume with the deposits, which is essential for rock avalanches. Another discriminating feature is the run-up over the opposite valley slope or whatever other meaning obstacle, which is impossible for rather slowly moving rock glaciers but is common for stone avalanches that move by inertia releasing enormous momentum gained during initial downslope acceleration.

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