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Across the northern European Alps, a long tradition of Quaternary studies has constrained post-LGM (Last Glacial Maximum) landscape history. The same picture remains largely unknown for the southern portion of the orogen. In this work, starting from existing10Be exposure dating of three boulders in Val Viola, Central Italian Alps, we present the first detailed, post-LGM reconstruction of landscape (i.e., glacial, periglacial and paraglacial) response south of the Alpine divide. We pursue this task through Schmidt-hammer exposure-age dating (SHD) at 34 sites including moraines, rock glaciers, protalus ramparts, rock avalanche deposits and talus cones. In addition, based on the mapping of preserved moraines and on the numerical SHD ages, we reconstruct the glacier extent of four different stadials, including Egesen I (13.1 ± 1.1 ka), Egesen II (12.3 ± 0.6 ka), Kartell (11.0 ± 1.4 ka) and Kromer (9.7 ± 1.4 ka), whose chronologies agree with available counterparts from north of the Alpine divide. Results show that Equilibrium Line Altitude depressions (ΔELAs) associated to Younger Dryas and Early Holocene stadials are smaller than documented at most available sites in the northern Alps. These findings not only support the hypothesis of a dominant north westerly atmospheric circulation during the Younger Dryas, but also suggest that this pattern could have lasted until the Early Holocene. SHD ages on rock glaciers and protalus ramparts indicate that favourable conditions to periglacial landform development occurred during the Younger Dryas (12.7 ± 1.1 ka), on the valley slopes above the glacier, as well as in newly de-glaciated areas, during the Early Holocene (10.7 ± 1.3 and 8.8 ± 1.8 ka). The currently active rock glacier started to develop before 3.7 ± 0.8 ka and can be associated to the Löbben oscillation. Four of the five rock avalanches dated in Val Viola cluster within the Early Holocene, in correspondence of an atmospheric warming phase. By co

Rock avalanches are large flow-like movements of fragmented rock that can cause extensive and rapid topographic changes, for which very few quantitative data are available. This paper analyses the geomorphological and hydrological impact of the 3 million m3 Thurwieser rock avalanche (2004, Italian Central Alps) by using Terrestrial Laser Scanner, airborne Lidar and GNSS data collected from 2005 to 2014. Sediment yield with respect to the normal valley regime, the dynamic and mass balance of affected glaciers, and the reorganization of superficial and groundwater flow networks are quantified. In the middle portion of the avalanche deposit, a natural sediment trap collected sediments from a new stream channel developed along the upper portion of the deposit and from a lateral drainage basin. This made possible to assess the 10-year impact of the rock avalanche on the sediment yield, which increased from about 120 to about 400 t km-2·a-1.The rock avalanche partially covered a glacier with a shallow debris layer that acted as a thermal insulator, limiting ice ablation and producing a 10-m high scarp between the free surface of the glacier and the debris-covered portion. A reduction of 75% of ice ablation was observed due to thermal insulation. The rock avalanche filled a tributary valley, splitting the original drainage basin in two. Under ordinary flows, seepage occurs within the avalanche deposit along the old valley axis. During high flow conditions, a new stream channel is activated along the middle and lower margin of the deposit, which has produced a new alluvial fan on the main valley floor. The fan evolution is described up to the present volume of about 2000 m3.

We monitor bedload transport and water discharge at six stations in two forested headwater streams of the Columbia Mountains, Canada. The nested monitoring network is designed to examine the effects of channel bed texture, and the influence of alluvial (i.e.step pools and riffle pools) and semialluvial morphologies (i.e.boulder cascades and forced step pools) on bedload entrainment and transport. Results indicate that dynamics of bedload entrainment are influenced by differences in flow resistance attributable to morphology. Scaled fractional analysis shows that in reaches with high form resistance most bedload transport occurs in partial mobility fashion relative to the available bed material, while calibers finer than 16mm attain full mobility during bankfull flows. Equal mobility transport for a wider range of grain sizes is achieved in reaches exhibiting reduced form resistance. Our findings confirm that the Shields value for mobilization of the median surface grain size depends on channel gradient and relative submergence; however, we also find that these relations vary considerably for cobble and gravel bed channels due to proportionality between dimensionless shear stress and grain size. Exponents of bedload rating curves across sites correlate most with the D90s of the mobile bed, however, where grain effects are controlled (i.e.along individual streams), differences in form resistance across morphologies exert a primary control on bedload transport dynamics. Application of empirical formulae developed for use in steep alpine channels present variable success in predicting transport rates in forested snowmelt streams. Formulae that explicitly account for reductions in mobile bed area and high morphological resistance associated with woody debris provide the best approximation to observed empirical data.

The variability of glacier response to atmospheric temperature rise in different topo-climatic settings is still a matter of debate. To address this question in the Central Italian Alps, we compile a post-LIA (Little Ice Age) multitemporal glacier inventory (1860-1954-1990-2003-2007) along a latitudinal transect that originates north of the continental divide in the Livigno Mountains and extends south through the Disgrazia and Orobie ranges, encompassing continental-to-maritime climatic settings. In these sub-regions, we examine the area change of 111 glaciers. Overall, the total glacierized area has declined from 34.1 to 10.1 km2, with a substantial increase in the number of small glaciers due to fragmentation. The average annual decrease (AAD) in glacier area has risen by about 1 order of magnitude from 1860-1990 (Livigno: 0.45; Orobie: 0.42; and Disgrazia: 0.39%a-1) to 1990-2007 (Livigno: 3.08; Orobie: 2.44; and Disgrazia: 2.27%a-1). This ranking changes when considering glaciers smaller than 0.5 km2 only (i.e., we remove the confounding caused by large glaciers in Disgrazia), so that post-1990 AAD follows the latitudinal gradient and Orobie glaciers stand out (Livigno: 4.07; Disgrazia: 3.57; and Orobie: 2.47%a-1). More recent (2007-2013) field-based mass balances in three selected small glaciers confirm post-1990 trends showing the consistently highest retreat in continental Livigno and minimal area loss in maritime Orobie, with Disgrazia displaying transitional behavior. We argue that the recent resilience of glaciers in Orobie is a consequence of their decoupling from synoptic atmospheric temperature trends, a decoupling that arises from the combination of local topographic configuration (i.e., deep, northfacing cirques) and high winter precipitation, which ensures high snow-avalanche supply, as well as high summer shading and sheltering. Our hypothesis is further supported by the lack of correlations between glacier change and glacier attributes in Orobie, as

Debris-flow monitoring in instrumented areas is an invaluable way to gather field data that may improve the understanding of these hazardous phenomena. A new experimental site has been equipped in the Autonomous Province of Bozen-Bolzano (Eastern Alps, Italy) for both monitoring purposes and testing early warning systems. The study site (Gadria basin) is a 6.3 km2 catchment subjected to frequent debris flows. The monitoring system in the Gadria basin consists of rain gauges, radar sensors, geophones, video cameras, piezometers and soil moisture probes. Transmission of data and alerts from the instruments exploits in part radio technology. The paper presents the data gathered during the first three years of activity, with two debris-flow events recorded at the station varying in magnitude and characteristics, and discusses the perspectives of debris-flow monitoring and related research. © 2014 Springer Science+Business Media Dordrecht.

In this paper we quantify the sediment dynamics in the formerly glaciated Zielbach catchment in the Italian Alps from the end of the Last Glacial Maximum (LGM) until today. As a basis for our quantification, we use the stratigraphic record offered by a 3.5 km2 large fan that we explore with a seismic survey, stratigraphic analyses of drillhole material, and 14C ages measured on organic matter encountered in these drillings. In addition, we calculate past denudation rate variability in the fan deposits using concentrations of cosmogenic 10Be. We merge this information into a scenario of how the sediment flux has changed through time and how this variability can be related to climatic variations, framed within well-known paraglacial models. The results document a highly complex natural system. From the LGM to the very early Holocene, ice-melted discharge and climate variability promoted a high sediment flux (sedimentation rate up to 40 mm/yr). This flux then dramatically decreased toward interglacial values (0.8 mm/yr at 5-4 calibrated kyr B.P.). However, in contrast to the trend of classic paraglacial models, the flux recorded at Zielbach shows secondary peaks at 6.5 ka and 2.5 ka, with values of 13 mm/yr and 1.5 mm/yr, respectively. Paleo-denudation rates also decrease from ̃33 mm/yr at the beginning of the Holo cene to 0.42 mm/yr at 5 ka, with peaks of ̃6 mm/yr and 1.1 mm/yr at 6.5 ka and 2.5 ka. High-amplitude climate change is the most likely cause of the secondary peaks, but anthro pogenic activities may have contributed as well. The good correlation between paleo-sedimentation and paleo-denudation rates suggests that the majority of the deglaciated material destocked from the Zielbach catchment is stored in the alluvial fan. © 2014 Geological Society of America.

We examine preliminary data from a landslide inventory that combines the mapping of landslides and deep-seated gravitational slope deformations (DSGSDs) in Val di Sole, eastern Central Alps, Italy. Landslide identification and classification was conducted via interpretation of sequential airphotos (API), LiDAR shaded-relief rasters. Landslide geometries were measured in the field for a sample of events. Seeking to evaluate landslide-driven sediment flux, we consider landslides as sediment sources and we classify them into rapid, full-mobility failures and slow, partial-mobility ones. The corresponding sediment flux, solely associated with rapid failures, exhibits clear lithologic controls, with metamorphic rocks displaying markedly higher landslide activity. DSGSDs occur exclusively in metamorphic terrain and landslides tend to cluster around them. Accordingly, these large-scale slope deformations could play a prominent role in modulating the contemporary landslide sediment flux. In the compilation of the inventory, the use of LiDAR and airphotos did not prove to be mutually exclusive. We recommend the two methodologies be employed in an integrated framework.

This study examines channel-reach morphology and bedload yield dynamics in relation to landscape structure and snowmelt hydrology in headwater streams of the Columbia Mountains, Canada. Data collection relies on field surveys and geographic information systems analysis in conjunction with a nested monitoring network of water discharge and bedload transfer. The landscape is characterized by subdued, formerlyglaciated upland topography in which the geomorphic significance of landslides and debris flows is negligible and fluvial processes prevail. While the spatial organization of channel morphology is chiefly controlled by glacially imposed local slope in conjunction with wood abundance and availability of glacigenic deposits, downstream patterns of the coarse grain-size fraction, bankfull width, bankfull depth, and stream power are all insensitive to systematic changes of local slope along the typically stepped long profiles. This is an indication that these alluvial systems have adjusted to the contemporary snowmelt-driven water and sediment transport regimes, and as such are able to compensate for the glacially-imposed boundary conditions. Bedload specific yield increases with drainage area suggesting that fluvial re-mobilization of glacial and paraglacial deposits dominate the sedimentary dynamics of basins as small as 2 km2. Stepwise multiple regression analysis shows that annual rates of sediment transfer aremainly controlled by the number of peak events over threshold discharge. During such events, repeated destabilization of channel bed armoring and re-mobilization of sediment temporarily stored behind LWD structures can generate bedload transport across the entire snowmelt season. In particular, channel morphology controls the variability of bedload response to hydrologic forcing. In the present case studies, we show that the observed spatial variability in annual bedload yield appears to be modulated by inter-basin differences in morphometric characteristics

Basin-wide erosion rates can be determined through the analysis of in situ-produced cosmogenic nuclides. In transient landscapes, and particularly in mountain catchments, erosion and transport processes are often highly variable and consequently the calculated erosion rates can be biased. This can be due to sediment pulses and poor mixing of sediment in the stream channels. The mixing of alluvial sediment is one of the principle conditions that need to be verified in order to have reliable results. In this paper we perform a field-based test of the extent of sediment mixing for a w42 km2 catchment in the Alps using concentrations of river-born 10Be. We use this technique to assess the mechanisms and the spatiotemporal scales for the mixing of sediment derived from hillslopes and tributary channels. The results show that sediment provenance and transport, and mixing processes have a substantial impact on the 10Be concentrations downstream of the confluence between streams and tributary channels. We also illustrate that the extent of mixing significantly depends on: the sizes of the catchments involved, the magnitude of the sediment delivery processes, the downstream distance of a sample site after a confluence, and the time since the event occurred. In particular, continuous soil creep and shallow landsliding supply high 10Be concentration material from the hillslope, congruently increasing the 10Be concentrations in the alluvial sediment. Contrariwise, a high frequency of mass-wasting processes or the occurrence of sporadic but large-magnitude events results in the supply of low-concentration sediment that lowers the cosmogenic nuclide concentration in the channels. The predominance of mass-wasting processes in a catchment can cause a strong bias in detrital cosmogenic nuclide concentrations, and therefore calculated erosion rates may be significantly over- or underestimated. Accordingly, it is important to sample as close as possible to the return-period of large-s

Wepresent a regional inventory of rock glaciers (n=1514) and protalus ramparts (228) for the Lombardy region, central Italian Alps. To identify and classify the landformswe inspect three sequential air-orthophoto mosaics and a 2 m-DSM, and conduct confirmatory field work. The inventory forms an empirical basis to analyze: (i) the relative contribution of hillslope (i.e., talus slopes) and glacial (i.e., moraines) sediment stores to rock glacier sediment supply; (ii) linkages between the landforms inventoried and local topographic attributes; (iii) the spatial variability of periglacial activity in relation to a parsimonious set of environmental variables (i.e., elevation, precipitation, and lithology); and (iv) the effects of the Pleistocene–Holocene climatic transition on the distribution of intact and relict landforms. This analysis reveals that the elevation of rock glacier termini can vary over 200 m as a function of slope aspect. In turn, the distribution of rock glaciers among aspect categories is controlled by the structure of the valley network that promotes NWand SE exposures. Talus rock glaciers prevail numerically over the glacier-related typology, even though the latter population appears to have increased during the Holocene. Relict and intact rock glaciers have distinct spatial patterns in that the former display, on average, a 400-melevation drop and a less clustered distribution towards northern aspects, suggesting that they have developed in more “permafrost-prone” climatic conditions. Analyzing the study region through a 27.5 km-grid has been instrumental for showing that the rock glacier specific area and terminus elevation are: (i) positively correlatedwith terrain elevation; and (ii) negatively correlated with mean annual precipitation. As a consequence, in relation to Holocene generalized atmospheric temperature rise, intact rock glaciers have progressively disappeared fromthewetter and milder portions of the central Italian Alps. Analysis of r

To characterize channel-network morphodynamics and response potential in the Gadria-Strimm basin (14.8 km^2) we conduct a concerted effort entailing: (i) high-resolution mapping of landforms, channel reaches, and sediment sources; and (ii) historical evolution of colluvial channel disturbance through sequential aerial photosets (1945-59-69-82-90-00-06-11). The mapping was carried out via stereographic inspection of aerial photographs, examination of 2.5-m gridded DTM and DSM, and extensive field work. The study area is a formerly glaciated basin characterized by peculiar landform assemblages imposed by a combination of tectonic and glacial first-order structures. The most striking feature in Strimm Creek is a structurally-controlled valley step separating an upper hanging valley, dominated by periglacial and fluvial processes, and a V-notched lower part in which lateral colluvial channels are directly connected to Strimm’s main stem. In Gadria Creek, massive kame terraces located in proximity of the headwaters provide virtually unlimited sediment supply to frequent debris-flow activity, making this sub-catchment an ideal site for monitoring, hence studying the mechanics of these processes. Preliminary results point to a high spatial variability of the colluvial channel network, in which sub-sectors have remained consistently active during the study period while others have become progressively dormant with notable forest re-growth. In an attempt to link sediment flux to topography and substrate type, future work will involve photogrammetric analysis across the sequential aerial photosets as well as a morphometric/geomechanical characterization of the surficial materials.

Basin-wide erosion rates can be determined through the analysis of in situ-produced cosmogenic nuclides based on the idea that samples taken at the outlet of a catchment are representative of the entire upstream basin. However, this is only true when a certain number of assumptions are verified. Among the most important assumptions is that denudation rates are uniform through space and time; i.e. the catchment is in cosmogenic steady-state. If this is the case, then the in-going nuclide flux through production is equal to the out-going flux through decay and erosion, and the system is in isotopic equilibrium. When this condition is not matched, the calculation of basin-wide erosion rates through cosmogenic nuclides is subject to the well-mixing conditions of the alluvial sediment in the rivers. Here, we bring a new contribution towards the understanding of sediment mixing effects on in-situ cosmogenic nuclide concentrations in alluvial sediment. We proceed by following the methodology proposed by Binnie et al. (2006), and present the results from a sediment mixing model for a small ( 42 km2) catchment in the Alps. The model results show the importance of the sampling location and of the catchment’s size to have reliable erosion rates. However, the models also highlight the importance of knowing the sediment transfer mechanisms and the processes magnitude. When the transport of sediment mainly occurs through soil creep and shallow landslides, high concentration material is supplied into the fluvial system, increasing the 10Be concentration in the alluvial sediment. Likewise, the high-frequency of mass-wasting processes or the occurrence of sporadic but large-magnitude events, allow the supply of low-concentration sediment that result in a lower cosmogenic nuclide signal in the channels. A strong bias arises for the calculation of basin-wide erosion rates if mass-wasting processes dominate the mechanisms of sediment transfer in the catchment. In this situation the use

To evaluate landslide response of mountain drainage basins to forest management we examine a historical inventory in northeastern Vancouver Island. The study area is underlain by extrusive (upper Triassic Karmutsen Formation) and intrusive rocks (Jurassic Island Intrusions). The dataset, compiled via interpretation of sequential aerial photosets, helicopter traverses, and extensive fieldwork, comprises a total of 1961 sediment sources, including 798 field-measured events. Field- and photo-based data cover a time window of approximately 70 years. The effects of forest management on landslide activity are assessed in terms of landslide density, sediment production, landslide geometry, landslide magnitude-frequency relations, topographic conditions of landslide initiation and deposition, and sediment redistribution across landscape components. Results indicate that forest management alters natural landslide dynamics in many respects. Logging-related debris avalanches are typically smaller. Consequently, the magnitude-frequency relation in logged terrain occupies the small-medium magnitude spectrum (< 6000 m3), with frequencies increasing by over an order of magnitude. Lithologic effects on sediment production appear amplified, in that terrain underlain by extrusive rocks become increasingly more unstable than intrusive ones. Analysis of landslide initiation and deposition zones reveals that forest management promotes colluvial aggradation on mid and lower hillslopes and in gullies. This pattern, which accelerates sediment recharge of gully systems, has the potential of increasing the frequency of channelized debris-flows, hence cause an extended period of disturbance, before sediment dynamics recover to pre-logging conditions. The effects of forest clearing on hillslope-channel coupling are composite: in cutblocks the percentage of sediment delivered to streams is reduced by 20-60% whereas road-related landslides are associated with highestconnectivity to streams.

Debris flow is an efficient process of sediment transfer from slope base to piedmont depositional fans in mountain drainage basins. To advance understanding of debris-flow sediment dynamics at the regional scale, we analyze a historical (1998-2009) database of debris flows from 77 basins of Alto Adige Province, northeastern Italy. By combining information on event volumetric deposition, high-resolution digital topography, and Quaternary sediment mapping we are able to link debris-flow sediment flux to morphometry, lithologic variability, and sediment availability. We show that basin-wide specific sediment yield (SSY) scales as an inverse power function of basin area. This function is strongly controlled by the way rock type and abundance of Quaternary deposits affect the rate of downstream sediment recruitment. When sediment flux associated with each debris-flow event is subsumed across discrete spatial increments of the entire region, a complex sedimentary signature in the area-SSY space is apparent. That is, SSY increases downstream up to areas as large as 1 km2, and starts to decline beyond this scale, regardless of sediment availability. We propose that this area-SSY relation is characteristic of debris flow-dominated settings.

Debris flows are one of the most relevant natural hazards in mountain regions. A combination of structural (e.g. check-dams) and non structural (e.g. warning systems) measures is needed in most cases to reduce debris flow risks, and both benefit from experimental data on debris-flow characteristics. A new experimental site is being equipped in the Autonomous Province of Bolzano (Italy) for both monitoring purposes and testing warning systems. The study site (Gadria basin) is a small channel subjected to frequent debris flows. The overall system includes the following components: 4 rain gauges located at different elevations, 5 radar sensors and 5 geophones, and 3 video cameras and flash lights to record the propagation and the deposition of the debris flow. Transmission of data and alerts from the instruments will use radio technology because GSM coverage is not available in the basin.

Landslides exert prominent controls on the morphology of mountain drainage basins and drive the overall sediment flux across landscape components. In this context, historical landslide inventories are critical for quantifying landslide sediment dynamics through time and assessing relevant contributions to regional sediment budgets. We present an historical inventory that combines the mapping of deep-seated gravitational slope deformations (DSGSD) and shallow landslides in Val di Sole (707 km2), eastern Central Alps, Italy. The study area was selected for two reasons: (i) the composite geological setting including intrusive, metamorphic, and sedimentary formations, which provides the opportunity to evaluate lithological effects on landslide sediment transfer; and (ii) the homogeneous distribution of forest cover, which warrants higher reliability of landslide identification through time. In so doing we avoid areas dominated by large rock walls and sedimentary linkages (e.g., unvegetated talus slopes and screes), typically associated to a chronic flux of colluvial sediment. In these conditions, owing to the subtle contrast between parent material and freshly eroded debris, the identification of fresh landslide scars in sequential photosets is difficult and unreliable. For the same reason, evaluation of the visibility time window for clusters of landslides would become highly uncertain. Data collection involved interpretation of seven sequential photosets (1959, 1969, 1973, 1983, 1996, 2000, 2006) and LiDAR-derived hillshade rasters in conjunction with field measurements. Fieldwork served to measure landslide depths and obtain a volumetric transformation factor for remotely-sensed landslide areas. Inspection of LiDAR hillshades allowed to identify and delineate the perimeter of large slope deformations, otherwise masked by a number of environmental conditions during aerial photo interpretation (e.g., forest cover, shadow, and snow). In the compilation of the inventory

Debris flows are the most efficient processes of sediment transfer from slope base to alluvial fan terminus in mountain drainage basins. To advance current understanding of debris-flow sediment dynamics at the regional scale we analyze historical debris-flow events in 82 basins of the Alto Adige Province, north-eastern Italy. By combining historical information on event-based debris-flow volumetric deposition and high-resolution (LiDARderived) digital topography we (i) identify seasonal trends in debris-flow activity; (ii) characterize the principal topographic conditions at which debris-flow initiation, transportation, and deposition occur; (iii) detail debris-flow sediment transfer at the basin and the regional scales; and (iv) identify lithologic dependences on debris-flow activity. For the first time, we show that basin-wide specific sediment yield describes a negative scaling relation with basin area, which in turn, is modulated by dominant bedrock geology and chiefly by the abundance of glacial and paraglacial surficial materials.

Landscape evolution in mountainous catchments is the result of multiple factors acting at different scales in time and space. The main components affecting basin morphologies are: uplift, glacial cycles, erosion (long timescale), mass movements and cycles of freeze-thaw (short timescale). In this study, we quantify the rates of sediment production and transfer from an alpine catchment in which debris flows are a dominant geomorphic agent. We use cosmogenic nuclides to determine the connectivity between source areas and sinks and to estimate the timescale of sediment production and the fluxes of sediment through the basin. The Zielbach basin consists of a ca. 30 km2-large central basin where cascade and step-pool channels have eroded into the highly fractured and foliated metamorphic bedrock, and a ca. 10 km2-large eastern tributary basin where a network of debris flow channels are perched on a deep-seated sackung. Whereas the central basin shows a poor connectivity between hillslopes and the channel network, the debris flow channels of the eastern tributary basin are closely connected with the bordering hillslopes. In the central basin, the geometry of the channel network is strongly affected by the litho-tectonic fabric as channels parallel the major faults and foliations. In the headwaters, rock glaciers and rock fall deposits tens of meters thick form transverse topographic ridges which retain the sediment in a semi-closed sedimentary traps. Moreover field work and GIS analysis reveal a strong relationship between structural setting and sediments production in which sediment production is high in weakened shear and fault zones. The eastern tributary basin has highly fractured bedrock, partially related to ice retreat after the LGM age. The whole catchment is characterize by a high production of sediments related both to tectonic structure present in the area and to the steep slopes left by the glacial retreat. The geomorphology shows a clear difference between th

Debris flows are one of the most relevant natural hazards in mountain regions. A combination of structural (e.g. check dams) and non structural (e.g. warning systems) measures is needed in most cases to reduce debris flow risks, and both benefit from experimental characteristics. A new experimental site is being equipped in the Autonomous Province of Bolzano (Italy) for both monitoring purposes and testing warning systems. The study site (Gadria basin) is a small channel subjected to frequent debris flows. The overall system includes the following components: 4 rain gauges located at different elevations, 5 radar sensors and 5 geophones, and 3 video cameras and flash lights to record the propagation and the deposition of the debris flow. Transmission of data and alerts from the instruments will use radio technology because GSM coverage is not available in the basin.

In coastal British Columbia, Canada, the glacial palimpsest profoundly affects the geomorphic structure of mountain drainage basins. In this context, by combining remotely sensed, field- and GIS-based data, we examine the scaling behavior of bankfull width and depth with contributing area in a process-based framework. We propose a novel approach that, by detailing interactions between colluvial and fluvial processes, provides new insights on the geomorphic functioning of mountain channels. This approach evaluates the controls exerted by a parsimonious set of governing factors on channel size. Results indicate that systematic deviations from simple power-law trends in bankfull width and depth are common. Deviations are modulated by interactions between the inherited glacial and paraglacial topography (imposed slope), coarse grain-size fraction, and chiefly the rate of colluvial sediment delivery to streams. Cumulatively, departures produce distal cross-sections that are typically narrower and shallower than expected. These outcomes, while reinforcing the notion that mountain drainage basins in formerly glaciated systems are out of balance with current environmental conditions, show that cross-sectional scaling relations are useful metrics for understanding colluvial-alluvial interactions.

Mountain drainage basins are complex systems due to the variety of active geomorphic processes,their interactions at different spatial/temporal scales, and the history of the landscape in terms of climate and tectonic activity. geomorphic coupling. These systems encompass hillslopes dominated by diffusive surface erosion and/or landsliding, steep confined channels dominated by debris flows, and purely alluvial channels flowing along major valley floors where fluvial transport prevails. In this context, the overall process of sediment transfer across landscape components and the associated disturbance-cascade are poorly understood, including the relative importance of one geomorphic process over the others at the watershed scale. In places where hillslopes and channels are well-connected, transport processes overlap, hence strongly interact via geomorphic coupling. The term coupling is used in geomorphology (e.g.,Brunsden and Thornes, 1979; Caine and Swanson, 1989) to indicate the degree of connectivity between hillslope and fluvial processes. Coupled systems exhibit direct colluvial-alluvial interaction, as opposed to decoupled (or buffered) systems, where colluvial sediment inputs do not reach the channel network. Evaluation of degree of coupling is critical to drainage basin sediment dynamics as it controls (i) sediment and process-disturbance cascades, and (ii) in what proportion hillslope denudation rate contributes to drainage basin sediment storage and fluvial sediment yield respectively (e.g., Roberts and Church, 1986; Reid and Dunne, 1996). In geomorphology, the importance of coupling between channels and adjacent hillslopes has been long acknowledged (e.g., Korup, 2005; Fryirs et al., 2007). However, relatively little work has attempted to assess its role in a systematic way. Partly because only very few empirical studies (both field-based and remotely-sensed) have tried to combine hillslopes and channelized landscape components (Benda et al., 1998). In thi

We examine basin-wide colluvial sediment dynamics in the Tsitika and Eve Rivers(about 600 km2), coastal British Columbia, Canada. The colluvial sediment cascade is documented by classifying landslide types, characterizing the dominant sediment sources, and identifying preferential sites of colluvial delivery across the landscape. The study is based on the compilation and analysis of a 70-year landslide inventory. This analysis reveals that open-slope landslides delivering material to seasonal or perennial channels and fluvial terraces are the dominant source-to-sink pathways. This finding indicates high instability of the headwaters drainage network and its ongoing adjustment after generalized sediment recharge occurred in the Last Glacial Maximum (LGM). To quantify interactions between colluvial and fluvial processes the landscape has been subdivided into geomorphic domains, which include planar slopes, unchannelled valleys, erosional (source) and depositional (sink) colluvial channels, as well as fluvial channels. In the study period, landslide activity across landscape components has generated net sediment degradation on planar slopes and source colluvial channels, whereas unchannelled valleys, sink colluvial channels and fluvially-dominated channels have been accumulating material. The newly-developed scaling relation of the landslide sediment yield appears to be controlled by the spatial organization of relict glacial structures. It follows that landslide yield is highest in unchannelled topography, decreases at the scale of channel initiation(drainage area (Ad) about 0.002 km2), and remains constant for scales where source colluvial and hanging fluvial domains overlap (0.002 < Ad< 0.06). Landslide sediment injections start declining consistently beyond areas larger than 0.6 km2 (the scale of relict trough initiation), where fluvial environments are still partially connected to adjacent hillslopes. Cumulative daily yield indicates that landslide sediment redist

Colluvial sediment dynamics are examined using a 70-year landslide inventory in formerly glaciated mountain drainage basins of coastal British Columbia, Canada. Landslide sediment transfer is documented by identifying landslide types, and by characterizing preferential sites of landslide initiation, delivery, and storage across spatial scales. Data analysis reveals that open-slope landslides delivering material to seasonal or perennial channels and fluvial terraces are the dominant mechanisms of sediment transfer. This finding suggests high instability of the low-order channel network and its ongoing re-organization (degradation) after generalized sediment recharge occurred in the last glacial maximum. In the study period, landslide activity across the landscape has generated net degradation on planar slopes and first-order colluvial channels, whereas unchannelled valleys, higher-order colluvial channels and alluvial channels have accumulated material. The scaling relation of the landslide sediment yield appears to be controlled by the spatial arrangement of the relict glacial macro-forms. Landslide yield is highest in unchannelled topography, decreases at the scale of channel initiation (Ad~0.002 km2), and remains constant for drainage areas where length scales of cirque/valley walls and hanging valley floors overlap (0.002bAdb0.06). Injections of landslide material start declining consistently beyond areas larger than 0.6 km2 (the scale of relict glacial trough initiation), where fluvial environments become increasingly disconnected from landslide inputs. Cumulative yield indicates that colluvial sediment redistribution is limited to small basins; specifically, 90% of the colluvial load is released at scales smaller than about 0.6 km2

We examine basin-wide colluvial sediment dynamics through the compilation of a 70-year landslide inventory in mountain environments of coastal British Columbia. In particular, we document the colluvial sediment cascade by characterizing the dominant sediment sources, and by identifying preferential sites of colluvial delivery and storage across landscape scales. Results reveal that open-slope landslides evacuating material to ephemeral or permanent streams and fluvial terraces are the preferential source-to-sink pathways. This pattern suggests high instability of the headmost channel network and its ongoing re-organization after generalized sediment recharge occurred during the last glacial maximum. In the study period, the colluvial sediment budget calculated across geomorphic process domains indicates net volume loss on planar slopes and source colluvial channels, whereas unchannelled valleys, sink colluvial channels and fluvially-dominated channels have been aggrading. In this context, we propose a novel approach to represent colluvial sediment yield as a function of drainage area. This scaling relation appears to be controlled by the spatial organization of geomorphic process domains, as imposed by the morphometry of the glacial palimpsest. It follows that colluvial yield is highest in unchannelled topography, decreases at the scale of channel initiation, and remains constant for drainage areas where source colluvial and hanging fluvial domains overlap. Colluvial sediment injections start declining consistently beyond areas larger than 0.6 km2, where fluvial environments are still partially coupled. Evaluation of the colluvial scaling trend in conjunction with British Columbia fluvial sediment yield, allows us to identify landscape scales of sediment aggradation and degradation, hence to infer preferential scales of contemporary sediment storage.