Properties of natural supraglacial debris in relation to modelling sub‐debris ice ablation

As debris‐covered glaciers become a more prominent feature of a shrinking mountain cryosphere, there is increasing need to successfully model the surface energy and mass balance of debris‐covered glaciers, yet measurements of the processes operating in natural supraglacial debris covers are sparse. We report measurements of vertical temperature profiles in debris on the Ngozumpa glacier in Nepal, that show: (i) conductive processes dominate during the ablation season in matrix‐supported diamict; (ii) ventilation may be possible in coarse surface layers; (iii) phase changes associated with seasonal change have a marked effect on the effective thermal diffusivity of the debris. Effective thermal conductivity determined from vertical temperature profiles in the debris is generally ~30% higher in summer than in winter, but values depend on the volume and phase of water in the debris. Surface albedo can vary widely over small spatial scales, as does the debris thickness. Measurements indicate that debris thickness is best represented as a probability density function with the peak debris thickness increasing down‐glacier. The findings from Ngozumpa glacier indicate that the probability distribution of debris thickness changes from positively skewed in the upper glacier towards a more normal distribution nearer the terminus. Although many of these effects remain to be quantified, our observations highlight aspects of spatial and temporal variability in supraglacial debris that may require consideration in annual or multi‐annual distributed modelling of debris‐covered glacier surface energy and mass balance. Copyright © 2012 John Wiley & Sons, Ltd.     

Complex spatial feedbacks of tephra redistribution,ice melt and surface roughness modulate ablation on tephra covered glaciers

Tephra fallout from the 2011 Grímsvötn eruption onto Svínafellsjökull, Iceland, created an ice‐ash landscape of a type that is rarely studied but is nevertheless common in glacio‐volcanic regions. We used terrestrial laser scanning (TLS) to measure ice surface topography and absorption at high spatial resolution, confirming ablation rates either reduce or increase under thick (insulating) and thin (reduced albedo) ash deposits, respectively. Fourier transform analysis of the TLS data identified that a three‐fold increase in aerodynamic roughness was attributable to an increase in larger (> 0·2 m) surface features. Moreover, TLS measurements revealed the importance of ash redistribution by meltwater in generating differential melting which modifies roughness and ash patchiness, such that the net effect of these spatial ash–ice feedbacks was to reduce ablation rates by up to 59%. The modulating effects of these previously undocumented feedbacks on ablation rates are, therefore, significant and must be correctly parameterized if ash‐covered glacier mass balances are to be predicted correctly. Copyright © 2012 John Wiley & Sons, Ltd.     

Interannual variability in glacier contribution to runoff from a high‐elevation Andean catchment: understanding the role of debris cover in glacier hydrology

We present a field‐data rich modelling analysis to reconstruct the climatic forcing, glacier response, and runoff generation from a high‐elevation catchment in central Chile over the period 2000–2015 to provide insights into the differing contributions of debris‐covered and debris‐free glaciers under current and future changing climatic conditions. Model simulations with the physically based glacio‐hydrological model TOPKAPI‐ETH reveal a period of neutral or slightly positive mass balance between 2000 and 2010, followed by a transition to increasingly large annual mass losses, associated with a recent mega drought. Mass losses commence earlier, and are more severe, for a heavily debris‐covered glacier, most likely due to its strong dependence on snow avalanche accumulation, which has declined in recent years. Catchment runoff shows a marked decreasing trend over the study period, but with high interannual variability directly linked to winter snow accumulation, and high contribution from ice melt in dry periods and drought conditions. The study demonstrates the importance of incorporating local‐scale processes such as snow avalanche accumulation and spatially variable debris thickness, in understanding the responses of different glacier types to climate change. We highlight the increased dependency of runoff from high Andean catchments on the diminishing resource of glacier ice during dry years.     

The influence of ground ice distribution on geomorphic dynamics since the Little Ice Age in proglacial areas of two cirque glacier systems

Holocene glaciers have contributed to an abundance of unstable sediments in mountainous environments. In permafrost environments, these sediments can contain ground ice and are subject to rapid geomorphic activity and evolution under condition of a warming climate. To understand the influence of ground ice distribution on this activity since the Little Ice Age (LIA), we have investigated the Pierre Ronde and Rognes proglacial areas, two cirque glacier systems located in the periglacial belt of the Mont Blanc massif. For the first time, electrical resistivity tomography, temperature data loggers and differential global positioning systems (dGPS) are combined with historical documents and glaciological data analysis to produce a complete study of evolution in time and space of these small landsystems since the LIA. This approach allows to explain spatial heterogeneity of current internal structure and dynamics. The studied sites are a complex assemblage of debris‐covered glacier, ice‐rich frozen debris and unfrozen debris. Ground ice distribution is related to former glacier thermal regime, isolating effect of debris cover, water supply to specific zones, and topography. In relation with this internal structure, present dynamics are dominated by rapid ice melt in the debris‐covered upper slopes, slow creep processes in marginal glacigenic rock glaciers, and weak, superficial reworking in deglaciated moraines. Since the LIA, geomorphic activity is mainly spatially restricted within the proglacial areas. Sediment exportation has occurred in a limited part of the former Rognes Glacier and through water pocket outburst flood and debris flows in Pierre Ronde. Both sites contributed little sediment supply to the downslope geomorphic system, rather by episodic events than by constant supply. In that way, during Holocene and even in a paraglacial context as the recent deglaciation, proglacial areas of cirque glaciers act mostly as sediment sinks, when active geomorphic processes are unable to evacuate sediment downslope, especially because of the slope angle weakness. Copyright © 2014 John Wiley & Sons, Ltd.     

Heterogeneous water storage and thermal regime of supraglacial ponds on debris‐covered glaciers

The water storage and energy transfer roles of supraglacial ponds are poorly constrained, yet they are thought to be important components of debris‐covered glacier ablation budgets. We used an unmanned surface vessel (USV) to collect sonar depth measurements for 24 ponds to derive the first empirical relationship between their area and volume applicable to the size distribution of ponds commonly encountered on debris‐covered glaciers. Additionally, we instrumented nine ponds with thermistors and three with pressure transducers, characterizing their thermal regime and capturing three pond drainage events. The deepest and most irregularly‐shaped ponds were those associated with ice cliffs, which were connected to the surface or englacial hydrology network (maximum depth = 45.6 m), whereas hydrologically‐isolated ponds without ice cliffs were both more circular and shallower (maximum depth = 9.9 m). The englacial drainage of three ponds had the potential to melt ~100 ± 20 × 10³ kg to ~470 ± 90 × 10³ kg of glacier ice owing to the large volumes of stored water. Our observations of seasonal pond growth and drainage with their associated calculations of stored thermal energy have implications for glacier ice flow, the progressive enlargement and sudden collapse of englacial conduits, and the location of glacier ablation hot‐spots where ponds and ice cliffs interact. Additionally, the evolutionary trajectory of these ponds controls large proglacial lake formation in deglaciating environments. Copyright © 2017 John Wiley & Sons, Ltd.     

Macro‐scale bed roughness of the siple coast ice streams in West Antarctica

Subglacial bed conditions are key to understanding ice stream behaviour and evolution, with bed roughness re?ecting substrate composition and ?ow resistance. Here we present an analysis of bed roughness in the Siple Coast region of West Antarctica from airborne radio‐echo sounding data. The ice streams are associated generally with low bed roughness values, which decrease downstream. The bed of the slow‐?owing Ice Stream C (～10 000 km²) is also characterized by being smooth at all scales (wavelengths ranging from 5 km to in excess of 40 km). Furthermore, the bed is smooth either side of Ice Stream C. This suggests the location of the ice stream is controlled by internal ice sheet dynamics rather than by bed morphology. If the ice stream were encouraged to migrate laterally, when active, there would be little resistance offered by the subglacial morphology. Other inter‐ice stream regions are rough, however, indicating a subglacial topographic in?uence on ice stream position. Bed roughness increases up‐?ow of ice streams, which, unless the bed is modi?ed, may limit the inland migration of these systems. Copyright © 2004 John Wiley & Sons, Ltd.     

The formation of supraglacial debris covers by primary dispersal from transverse englacial debris bands

Glaciological controls on debris cover formation are investigated from the perspective of primary dispersal of supraglacial debris across a melting ice surface. This involves the migration of angled debris septa outcrops across a melting, thinning glacier ablation zone. Three measures of a glacier's ability to evacuate supraglacial debris are outlined: (1) a concentration factor describing the focusing of englacial debris into specific supraglacial mass loads; (2) the rate of migration of a septum outcrop relative to the local ice surface; and (3) a downstream velocity differential between a slower septum outcrop and the faster ice surface velocity. Measures (1) and (2) are inversely related, while measure (3) increases down‐glacier to explain why slow‐moving, thinning ice rapidly becomes debris covered. Data from Glacier d'Estelette (Italian Alps) are used to illustrate these processes, and to explore the potential for debris cover formation and growth in different glaciological environments. The transition from a ‘clean’, transport‐dominated to a debris‐covered ablation‐dominated glacier is explained by the melting out of more closely‐spaced debris septa, in combination with the geometric interactions of angled septa and ice surface in a field of reducing flow and increasing ablation. The growth and shrinkage of debris covers are most sensitive to glaciological changes at glaciers with gently‐dipping debris‐bearing foliation, but less sensitive at high‐compression glaciers whose termini are constrained by moraine dams and other forms of obstruction. These findings show that a variety of debris‐covered glacier types will show a spectrum of response characteristics to negative mass balance. Copyright © 2013 John Wiley & Sons, Ltd.     

Detection and classification of surface roughness in an Arctic marginal sea ice zone

Sea ice dynamic and thermodynamic processes are important and highly variable elements of the marginal ice zone (MIZ). This study examines the detection and classification of statistically separable sea ice classes in the MIZ through a range of temporal and spatial scales. A helicopter‐based laser system was used to obtain large‐scale and a ship‐based laser profiler to identify small‐scale roughness types, respectively. The analysis of variance of surface height data from helicopter‐ and ship‐based laser systems, active microwave (AMW) C‐band backscattering data and passive microwave (PMW) (37 and 89 GHz) brightness temperature data reveal different classes that statistically differ from one another. We found significant statistical difference in variances in AMW data with six classes that differ in VV polarization, three classes in VH polarization, and five classes in HH polarization in the MIZ (e.g. snow‐covered first‐year ice, ice rubble, pancake ice, frost flowers, melt pond, flooded ice, and ice edge) of southeastern Beaufort Sea. The PMW emission was not as effective at discrimination, yielding only one statistically separable class. The results can potentially be extended to satellite‐based investigations of the MIZ at regional scales. Copyright © 2012 John Wiley & Sons, Ltd.     

Gravity profiling as a technique for determining the thickness of glacier ice

Summary Detailed gravity measurements recently carried out on the Gorner glacier, Switzerland, are used to determine the variation of thickness across the glacier ice. The Gorner glacier was chosen as a test site because seismic control was available. The glacier ice at a profile near the Monte Rosa massif is associated with a relative gravity low of about –23 mgal. Model oalculations yield a corresponding ice thickness of about 400 m at the central part of the profile. A comparison of the derived residual gravity anomaly with the calculated effect of the 3-D ice model based on seismic information is made. It is shown that the regional field determined for the Gorner glacier is appropriate and gives the correct residual anomaly associated with the glacier ice. Therefore, the proposed gravity technique for determining variations of the thickness of glacier ice appears to be a valuable and rather inexpensive method for surveying glaciers.Institut für Geophysik, ETH-Zürich, Contribution No 145.     

Modelling the hydrological response of debris‐free and debris‐covered glaciers to present climatic conditions in the semiarid Andes of central Chile

We apply the process‐based, distributed TOPKAPI‐ETH glacio‐hydrological model to a glacierized catchment (19% glacierized) in the semiarid Andes of central Chile. The semiarid Andes provides vital freshwater resources to valleys in Chile and Argentina, but only few glacio‐hydrological modelling studies have been conducted, and its dominant hydrological processes remain poorly understood. The catchment contains two debris‐free glaciers reaching down to 3900 m asl (Bello and Yeso glaciers) and one debris‐covered avalanche‐fed glacier reaching to 3200 m asl (Piramide Glacier). Our main objective is to compare the mass balance and runoff contributions of both glacier types under current climatic conditions. We use a unique dataset of field measurements collected over two ablation seasons combined with the distributed TOPKAPI‐ETH model that includes physically oriented parameterizations of snow and ice ablation, gravitational distribution of snow, snow albedo evolution and the ablation of debris‐covered ice. Model outputs indicate that while the mass balance of Bello and Yeso glaciers is mostly explained by temperature gradients, the Piramide Glacier mass balance is governed by debris thickness and avalanches and has a clear non‐linear profile with elevation as a result. Despite the thermal insulation effect of the debris cover, the mass balance and contribution to runoff from debris‐free and debris‐covered glaciers are similar in magnitude, mainly because of elevation differences. However, runoff contributions are distinct in time and seasonality with ice melt starting approximately four weeks earlier from the debris‐covered glacier, what is of relevance for water resources management. At the catchment scale, snowmelt is the dominant contributor to runoff during both years. However, during the driest year of our simulations, ice melt contributes 42 ± 8% and 67 ± 6% of the annual and summer runoff, respectively. Sensitivity analyses show that runoff is most sensitive to temperature and precipitation gradients, melt factors and debris cover thickness. Copyright © 2016 John Wiley & Sons, Ltd.     

Microtopography of bare peat: a conceptual model and objective classification from high‐resolution topographic survey data

Peatlands globally are at risk of degradation through increased susceptibility to erosion as a result of climate change. Quantification of peat erosion and an understanding of the processes responsible for their degradation is required if eroded peatlands are to be protected and restored. Owing to the unique material properties of peat, fine‐scale microtopographic expressions of surface processes are especially pronounced and present a potentially rich source of geomorphological information, providing valuable insights into the stability and dominant surface process regimes. We present a new process‐form conceptual framework to rigorously describe bare peat microtopography and use Structure‐from‐Motion (SfM) surveys to quantify roughness for different peat surfaces. Through the first geomorphological application of a survey‐grade structured‐light hand‐held 3D imager (HhI), which can represent sub‐millimetre topographic variability in field conditions, we demonstrate that SfM identifies roughness signatures reliably over bare peat plots (<1 m²), although some smoothing is observed. Across 55 plots, the roughness of microtopographic types is quantified using a suite of roughness metrics and an objective classification system derived from decision tree analysis with 98% success. This objective classification requires just five roughness metrics, each of which quantifies a different aspect of the surface morphology. We show that through a combination of roughness metrics, microtopographic types can be identified objectively from high resolution survey data, providing a much‐needed geomorphological process‐perspective to observations of eroded peat volumes and earth surface change. Copyright © 2018 John Wiley & Sons, Ltd.     

A conceptual model of supra‐glacial lake formation on debris‐covered glaciers based on GPR facies analysis

Supra‐glacial lakes and ponds can create hotspots of mass loss on debris‐covered glaciers. While much research has been directed at understanding lateral lake expansion, little is known about the rates or processes governing lake deepening. To a large degree, this knowledge gap persists due to sparse observations of lake beds. Here we report on the novel use of ground penetrating radar (GPR) surveys to simultaneously collect supra‐glacial lake bathymetry and bottom composition data from Spillway Lake (surface area of 2.4 × 10⁵ m²; volume of 9.5 × 10⁴ m³), which is located in the terminus region of the Ngozumpa Glacier in the Khumbu region of the Nepal Himalaya. We identified two GPR bottom signals corresponding to two sedimentary facies of (1) sub‐horizontal layered fine sediment drape and (2) coarse blocky diamict. We provide an understanding of the changes in subaqueous debris distribution that occur through stages of lake expansion by combining the GPR results with in situ observations of shoreline deposits matching the interpreted facies. From this, we present an updated conceptual model of supra‐glacial lake evolution, with the addition of data on the evolving debris environment, showing how dominant depositional processes can change as lakes evolve from perched lakes to multi‐basin base‐level lakes and finally onto large moraine‐dammed lakes. Throughout lake evolution, processes such as shoreline steepening, lakebed collapse into voids and conduit interception, subaerial and subaqueous calving and rapid areal expansion alter the spatial distribution and makeup of lakebed debris and sediments forcing a number of positive and negative feedbacks on lake expansion. Copyright © 2016 John Wiley & Sons, Ltd.     

Using structure‐from‐motion to create glacier DEMs and orthoimagery from historical terrestrial and oblique aerial imagery

Increased resolution and availability of remote sensing products, and advancements in small‐scale aerial drone systems, allows observations of glacial changes at unprecedented levels of detail. Software developments, such as structure‐from‐motion (SfM), now allow users an easy and efficient method to generate three‐dimensional (3D) models and orthoimages from aerial or terrestrial datasets. While these advancements show promise for current and future glacier monitoring, many regions still suffer a lack of observations from earlier time periods. We report on the use of SfM to extract spatial information from various historic imagery sources. We focus on three geographic regions, the European Alps, high Arctic Norway and the Nepal Himalayas. We used terrestrial field photographs from 1896, high oblique aerial photographs from 1936 and aerial handheld photographs from 1978 to generate digital elevation models (DEMs) and orthophotos of the Rhone glacier, Brøggerhalvøya and the lower Khumbu glacier, respectively. Our analysis shows that applying SfM to historic imagery can generate high quality models using only ground control points. Limited camera/orientation information was largely reproduced using self‐calibrated model data. Using these data, we calculated mean ground sampling distances across each site which demonstrates the high potential resolution of resulting models. Vertical errors for our models are ±5.4 m, ±5.2 m and ±3.3 m. Differencing shows similar patterns of thinning at lower Rhone (European Alps) and Brøggerhalvøya (Norway) glaciers, which have mean thinning rates of 0.31 m a^?1 (1896–2010) to 0.86 m a^?1 (1936–2010) respectively. On these clean ice glaciers thinning is highest in the terminus region and decreasing up‐glacier. In contrast to these glaciers, uneven topography, exposed ice‐cliffs and debris cover on the Khumbu glacier create a highly variable spatial distribution of thinning. The mean thinning rate for the Khumbu study area was found to be 0.54 ± 0.9 m a^?1 (1978–2015). Copyright © 2017 John Wiley & Sons, Ltd.     

Processes at the margins of supraglacial debris cover: Quantifying dirty ice ablation and debris redistribution

Current glacier ablation models have difficulty simulating the high-melt transition zone between clean and debris-covered ice. In this zone, thin debris cover is thought to increase ablation compared to clean ice, but often this cover is patchy rather than continuous. There is a need to understand ablation and debris dynamics in this transition zone to improve the accuracy of ablation models and the predictions of future debris cover extent. To quantify the ablation of partially debris-covered ice (or ‘dirty ice’), a high-resolution, spatially continuous ablation map was created from repeat unmanned aerial systems surveys, corrected for glacier flow in a novel way using on-glacier ablation stakes. Surprisingly, ablation is similar (range ~ 5 mm w.e. per day) across a wide range of percentage debris covers (~ 30–80%) due to the opposing effects of a positive correlation between percentage debris cover and clast size, countered by a negative correlation with albedo. Once debris cover becomes continuous, ablation is significantly reduced (by 61.6% compared to a partial debris cover), and there is some evidence that the cleanest ice (<~ 15% debris cover) has a lower ablation than dirty ice (by 3.7%). High-resolution feature tracking of clast movement revealed a strong modal clast velocity where debris was continuous, indicating that debris moves by creep down moraine slopes, in turn promoting debris cover growth at the slope toe. However, not all slope margins gain debris due to the removal of clasts by supraglacial streams. Clast velocities in the dirty ice area were twice as fast as clasts within the continuously debris-covered area, as clasts moved by sliding off their boulder tables. These new quantitative insights into the interplay between debris cover characteristics and ablation can be used to improve the treatment of dirty ice in ablation models, in turn improving estimates of glacial meltwater production. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

The retrieval of two-dimensional distribution of the earth''''s surface aerodynamic roughness using SAR image and TM thermal infrared image

The research for the land surface fluxes has madea quiet great progress for its breakthroughs in the fieldof regional or global interactions between land surfaceand atmosphere. However, many remote sensing mod-els for estimating the land surface fluxes need the pa-rameters of surface momentum, heat, resistance ofwater vapor at a referenced height, which are the func-tion of aerodynamic surface roughness zad. It hasbeen validated that the retrieval of the land surfacefluxes is very sensitive to…     

Subaerial gravel size measurement using topographic data derived from a UAV‐SfM approach

Accurate and reliable methods for quantifying grain size are important for river science, management and in various other sedimentological settings. Remote sensing offers methods of quantifying grain size, typically providing; (a) coarse outputs (c. 1 m) at the catchment scale where individual grains are at subpixel level, or; (b) fine resolution outputs (c. 1 mm) at the patch scale. Recently, approaches using unmanned aerial vehicles (UAVs) have started to fill the gap between these scales, providing hyperspatial resolution data (< 10 cm) over reaches a few hundred metres in length, where individual grains are at suprapixel level. This ‘mesoscale’ is critical to habitat assessments. Most existing UAV‐based approaches use two‐dimensional (2D) textural variables to predict grain size. Validation of results is largely absent however, despite significant differences in platform stability and image quality obtained by manned aircraft versus UAVs. Here, we provide the first quantitative assessment of the accuracy and precision of grain size estimates produced from a 2D image texture approach. Furthermore, we present a new method which predicts subaerial gravel size using three‐dimensional (3D) topographic data derived from UAV imagery. Data is collected from a small gravel‐bed river in Cumbria, UK. Results indicate that our new topographic method gives more accurate measures of grain size (mean residual error ‐0.0001 m). Better results for the image texture method may be precluded by our choice of texture measure, the scale of analysis or the effects of image blur resulting from an inadequate camera gimbal. We suggest that at our scale of assessment, grain size is more strongly related to 3D variation in elevation than to the 2D textural patterns expressed within the imagery. With on‐going improvements, our novel method has potential as the first grain size quantification approach where a trade‐off between coverage and resolution is not necessary or inherent. Copyright © 2017 John Wiley & Sons, Ltd.     

Evaluation of the snow‐covered area data product from MODIS

The Moderate Resolution Imaging Spectroradiometer (MODIS), flown on board the Terra Earth Observing System (EOS) platform launched in December 1999, produces a snow‐covered area (SCA) product. This product is expected to be of better quality than SCA products based on operational satellites (notably GOES and AVHRR), due both to improved spectral resolution and higher spatial resolution of the MODIS instrument. The gridded MODIS SCA product was compared with the SCA product produced and distributed by the National Weather Service National Operational Hydrologic Remote Sensing Center (NOHRSC) for 46 selected days over the Columbia River basin and 32 days over the Missouri River basin during winter and spring of 2000–01. Snow presence or absence was inferred from ground observations of snow depth at 1330 stations in the Missouri River basin and 762 stations in the Columbia River basin, and was compared with the presence/absence classification for the corresponding pixels in the MODIS and NOHRSC SCA products. On average, the MODIS SCA images classified fewer pixels as cloud than NOHRSC, the effect of which was that 15% more of the Columbia basin area could be classified as to presence–absence of snow, while overall there was a statistically insignificant difference over the Missouri basin. Of the pixels classified as cloud free, MODIS misclassified 4% and 5% fewer overall (for the Columbia and Missouri basins respectively) than did the NOHRSC product. When segregated by vegetation cover, forested areas had the greatest differences in fraction of cloud cover reported by the two SCA products, with MODIS classifying 13% and 17% less of the images as cloud for the Missouri and Columbia basins respectively. These differences are particularly important in the Columbia River basin, 39% of which is forested. The ability of MODIS to classify significantly greater amounts of snow in the presence of cloud in more topographically complex, forested, and snow‐dominated areas of these two basins provides valuable information for hydrologic prediction. Copyright © 2003 John Wiley & Sons, Ltd.     

Using UAV acquired photography and structure from motion techniques for studying glacier landforms: application to the glacial flutes at Isfallsglaciären

Glacier and ice sheet retreat exposes freshly deglaciated terrain which often contains small‐scale fragile geomorphological features which could provide insight into subglacial or submarginal processes. Subaerial exposure results in potentially rapid landscape modification or even disappearance of the minor‐relief landforms as wind, weather, water and vegetation impact on the newly exposed surface. Ongoing retreat of many ice masses means there is a growing opportunity to obtain high resolution geospatial data from glacier forelands to aid in the understanding of recent subglacial and submarginal processes. Here we used an unmanned aerial vehicle to capture close‐range aerial photography of the foreland of Isfallsglaciären, a small polythermal glacier situated in Swedish Lapland. An orthophoto and a digital elevation model with ~2 cm horizontal resolution were created from this photography using structure from motion software. These geospatial data was used to create a geomorphological map of the foreland, documenting moraines, fans, channels and flutes. The unprecedented resolution of the data enabled us to derive morphological metrics (length, width and relief) of the smallest flutes, which is not possible with other data products normally used for glacial landform metrics mapping. The map and flute metrics compare well with previous studies, highlighting the potential of this technique for rapidly documenting glacier foreland geomorphology at an unprecedented scale and resolution. The vast majority of flutes were found to have an associated stoss‐side boulder, with the remainder having a likely explanation for boulder absence (burial or erosion). Furthermore, the size of this boulder was found to strongly correlate with the width and relief of the lee‐side flute. This is consistent with the lee‐side cavity infill model of flute formation. Whether this model is applicable to all flutes, or multiple mechanisms are required, awaits further study. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

The role of the sediment budget in understanding debris flow susceptibility

This study proposes a sediment‐budget model to predict the temporal variation of debris volume stored in a debris‐flow prone watershed. The sediment‐budget is dominated by shallow landslides and debris outflow. The basin topography and the debris volume stored in the source area of the debris‐flow prone watershed help evaluating its debris‐flow susceptibility. The susceptibility model is applied to the Tungshih area of central western Taiwan. The importance of the debris volume in predicting debris‐flow susceptibility is reflected in the standardized coefficients of the proposed statistical discriminant model. The high prediction rate (0·874) for the occurrence of debris flows justifies the capability of the proposed susceptibility models to predict the occurrence of debris flows. This model is then used to evaluate the temporal evolution of the debris‐flow susceptibility index. The analysis results show that the numbers of watershed which are classified as a debris‐flow group correspond well to storage of sediment at different time periods. These numbers are 10 before the occurrence of Chi‐Chi earthquake, 13 after the occurrence of Chi‐Chi earthquake, 16 after the occurrence of landslides induced by Typhoon Mindulle (Typhoon M), and 14 after the occurrence of debris flows induced by Typhoon M. It indicates that the occurrence of 7·6 Chi‐Chi earthquake had significant impact on the debris flow occurrence during subsequent typhoons. Copyright © 2009 John Wiley & Sons, Ltd.