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Distributed Acoustic Sensing (DAS) is increasingly recognised as a valuable tool for glaciological seismic applications, although analysing the large data volumes generated in acquisitions poses computational challenges. We show the potential of active-source DAS to image and characterise subglacial sediment beneath a fast-flowing Greenlandic outlet glacier, estimating the thickness of sediment layers to be 20–30 m. However, the lack of subglacial velocity constraint limits the accuracy of this estimate. Constraint could be provided by analysing cryoseismic events in a counterpart 3-day record of passive seismicity through, for example, seismic tomography, but locating them within the 9 TB data volume is computationally inefficient. We describe experiments with data compression using the frequency-wavenumber (f-k) transform ahead of training a convolutional neural network, that provides a ~300-fold improvement in efficiency. In combining active and passive-source and our machine learning framework, the potential of large DAS datasets could be unlocked for a range of future applications. [ABSTRACT FROM AUTHOR]

Tidewater glaciers are an important and difficult part of the cryosphere to study owing to their complex nature and often inaccessible and physically challenging environments. The interaction of glacier and fjord processes furthermore presents particular observational challenges. Modelling provides a possible solution to these issues, but, at the glacier scale, the processual complexities require a 3-D full-Stokes approach that is computationally expensive. Additionally, the lack of data for model validation or constraints imposes further obstacles. Despite this, progress on modelling such glaciers with explicit inclusion of all relevant processes is being made. The key remaining challenges are including more realistic representations of calving and coupling 3-D glacier modelling with 3-D fjord circulation modelling to allow inclusion of the effect of cross-fjord circulation. We are confident, however, that these issues can be resolved and will be resolved over the next decade. [ABSTRACT FROM AUTHOR]

Distributed Acoustic Sensing (DAS) is increasingly recognised as a valuable tool for glaciological seismic applications, although analysing the large data volumes generated in acquisitions poses computational challenges. We show the potential of active-source DAS to image and characterise subglacial sediment beneath a fast-flowing Greenlandic outlet glacier, estimating the thickness of sediment layers to be 20–30 m. However, the lack of subglacial velocity constraint limits the accuracy of this estimate. Constraint could be provided by analysing cryoseismic events in a counterpart 3-day record of passive seismicity through, for example, seismic tomography, but locating them within the 9 TB data volume is computationally inefficient. We describe experiments with data compression using the frequency-wavenumber (f-k) transform ahead of training a convolutional neural network, that provides a ~300-fold improvement in efficiency. In combining active and passive-source and our machine learning framework, the potential of large DAS datasets could be unlocked for a range of future applications. [ABSTRACT FROM AUTHOR]

Tidewater glaciers are an important and difficult part of the cryosphere to study owing to their complex nature and often inaccessible and physically challenging environments. The interaction of glacier and fjord processes furthermore presents particular observational challenges. Modelling provides a possible solution to these issues, but, at the glacier scale, the processual complexities require a 3-D full-Stokes approach that is computationally expensive. Additionally, the lack of data for model validation or constraints imposes further obstacles. Despite this, progress on modelling such glaciers with explicit inclusion of all relevant processes is being made. The key remaining challenges are including more realistic representations of calving and coupling 3-D glacier modelling with 3-D fjord circulation modelling to allow inclusion of the effect of cross-fjord circulation. We are confident, however, that these issues can be resolved and will be resolved over the next decade. [ABSTRACT FROM AUTHOR]

Subglacial hydrology modulates basal motion but remains poorly constrained, particularly for soft-bedded Greenlandic outlet glaciers. Here, we report detailed measurements of the response of subglacial water pressure to the connection and drainage of adjacent water-filled boreholes drilled through kilometre-thick ice on Sermeq Kujalleq (Store Glacier). These measurements provide evidence for gap opening at the ice-sediment interface, Darcian flow through the sediment layer, and the forcing of water pressure in hydraulically-isolated cavities by stress transfer. We observed a small pressure drop followed by a large pressure rise in response to the connection of an adjacent borehole, consistent with the propagation of a flexural wave within the ice and underlying deformable sediment. We interpret the delayed pressure rise as evidence of no pre-existing conduit and the progressive decrease in hydraulic transmissivity as the closure of a narrow (< 1.5 mm) gap opened at the ice-sediment interface, and a reversion to Darcian flow through the sediment layer with a hydraulic conductivity of ≤ 10−6 m s−1. We suggest that gap opening at the ice-sediment interface deserves further attention as it will occur naturally in response to the rapid pressurisation of water at the bed. [ABSTRACT FROM AUTHOR]

We present the first fully coupled 3D full-Stokes model of a tidewater glacier, incorporating ice flow, subglacial hydrology, plume-induced frontal melting and calving. We apply the model to Store Glacier (Sermeq Kujalleq) in west Greenland to simulate a year of high melt (2012) and one of low melt (2017). In terms of modelled hydrology, we find perennial channels extending 5 km inland from the terminus and up to 41 and 29 km inland in summer 2012 and 2017, respectively. We also report a hydrodynamic feedback that suppresses channel growth under thicker ice inland and allows water to be stored in the distributed system. At the terminus, we find hydrodynamic feedbacks exert a major control on calving through their impact on velocity. We show that 2012 marked a year in which Store Glacier developed a fully channelised drainage system, unlike 2017, where it remained only partially developed. This contrast in modelled behaviour indicates that tidewater glaciers can experience a strong hydrological, as well as oceanic, control, which is consistent with observations showing glaciers switching between types of behaviour. The fully coupled nature of the model allows us to demonstrate the likely lack of any hydrological or ice-dynamic memory at Store Glacier. [ABSTRACT FROM AUTHOR]

Distributed Acoustic Sensing (DAS) is a new technology in which seismic energy is detected, at high spatial and temporal resolution, using the propagation of laser pulses in a fiber‐optic cable. We show analyses from the first glaciological borehole DAS deployment to measure the englacial and subglacial seismic properties of Store Glacier, a fast‐flowing outlet of the Greenland Ice Sheet. We record compressional and shear waves in 1,043 m‐deep vertical seismic profiles, sampled at 10 m vertical resolution, and detect a transition from isotropic to anisotropic ice at 84% of ice thickness, consistent with the Holocene‐Wisconsin transition. We identify subglacial reflections originating from the base of a 20 m‐thick layer of consolidated sediment and, from attenuation measurements, interpret temperate ice in the lowermost 100 m of the glacier. Our findings highlight the promising potential of DAS technology to constrain the seismic properties of glaciers and ice sheets. Plain Language Summary: Distributed Acoustic Sensing (DAS) is a new technology for seismic surveying in which the transmission of light through fiber‐optic cables is used to record seismic energy, with unprecedented spatial resolution compared to traditional techniques. Our paper presents data from the first borehole‐glaciological deployment of DAS, in which fiber‐optic cable was installed in a 1,043 m‐deep vertical borehole on Store Glacier, a fast‐flowing outlet of the Greenland Ice Sheet. The detailed seismic anatomy of the glacier that our survey provides—an independent measurement of the seismic response every 10 m—gives new insights about its internal flow regime and temperature and even allows us to detect layers of sediment underlying it. We predict that DAS surveying will play an increasingly large role in future glaciological investigations as the recognition of its promising potential grows. Key Points: Distributed Acoustic Sensing (DAS) is a new technology for recording seismic data using laser pulses propagating in a fiber‐optic cableWe present the first borehole‐glaciological application of DAS, installing cable in a 1,043 m‐deep borehole on Greenland's Store GlacierWe evidence, at 10 m vertical resolution, anisotropic and temperate ice beyond ~880 m depth and ~20 m of consolidated subglacial sediment [ABSTRACT FROM AUTHOR]

Supraglacial lake drainage events influence Greenland Ice Sheet dynamics on hourly to interannual timescales. However, direct observations are rare, and, to date, no in situ studies exist from fast-flowing sectors of the ice sheet. Here, we present observations of a rapid lake drainage event at Store Glacier, west Greenland, in 2018. The drainage event transported 4.8 x 106 m³ of meltwater to the glacier bed in ~5 h, reducing the lake to a third of its original volume. During drainage, the local ice surface rose by 0.55 m, and surface velocity increased from 2.0 m⋅d-1 to 5.3 m⋅d-1. Dynamic responses were greatest ~4 km downstream from the lake, which we interpret as an area of transient water storage constrained by basal topography. Drainage initiated, without any precursory trigger, when the lake expanded and reactivated a preexisting fracture that had been responsible for a drainage event 1 y earlier. Since formation, this fracture had advected ~500 m from the lake's deepest point, meaning the lake did not fully drain. Partial drainage events have previously been assumed to occur slowly via lake overtopping, with a comparatively small dynamic influence. In contrast, our findings show that partial drainage events can be caused by hydrofracture, producing new hydrological connections that continue to concentrate the supply of surface meltwater to the bed of the ice sheet throughout the melt season. Our findings therefore indicate that the quantity and resultant dynamic influence of rapid lake drainages are likely being underestimated. [ABSTRACT FROM AUTHOR]

Iceberg calving accounts for between 30 % and 60 % of net mass loss from the Greenland Ice Sheet, which has intensified and is now the single largest contributor to global sea level rise in the cryosphere. Changes to calving rates and the dynamics of calving glaciers represent a significant uncertainty in projections of future sea level rise. A growing body of observational evidence suggests that calving glaciers respond rapidly to regional environmental change, but predictive capacity is limited by the lack of suitable models capable of simulating calving mechanisms realistically. Here, we use a 3-D full-Stokes calving model to investigate the environmental sensitivity of Store Glacier, a large outlet glacier in West Greenland. We focus on two environmental processes: undercutting by submarine melting and buttressing by ice mélange, and our results indicate that Store Glacier is likely to be able to withstand moderate warming perturbations in which the former is increased by 50 % and the latter reduced by 50 %. However, severe perturbation with a doubling of submarine melt rates or a complete loss of ice mélange destabilises the calving front in our model runs. Furthermore, our analysis reveals that stress and fracture patterns at Store's terminus are complex and varied, primarily due to the influence of basal topography. Calving style and environmental sensitivity vary greatly, with propagation of surface crevasses significantly influencing iceberg production in the northern side, whereas basal crevasses dominate in the south. Any future retreat is likely to be initiated in the southern side by a combination of increased submarine melt rates in summer and reduced mélange strength in winter. The lateral variability, as well as the importance of rotational and bending forces at the terminus, underlines the importance of using the 3-D full-Stokes stress solution when modelling Greenland's calving glaciers. [ABSTRACT FROM AUTHOR]

Intense rainfall events significantly affect Alpine and Alaskan glaciers through enhanced melting, ice-flow acceleration and subglacial sediment erosion, yet their impact on the Greenland ice sheet has not been assessed. Here we present measurements of ice velocity, subglacial water pressure and meteorological variables from the western margin of the Greenland ice sheet during a week of warm, wet cyclonic weather in late August and early September 2011. We find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice-sheet interior. We suggest that the late-season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less-efficient winter mode. Reanalysis data reveal that similar cyclonic weather conditions prevailed across southern and western Greenland during this time, and we observe a corresponding ice-flow response at all land- and marine-terminating glaciers in these regions for which data are available. Given that the advection of warm, moist air masses and rainfall over Greenland is expected to become more frequent in the coming decades, our findings portend a previously unforeseen vulnerability of the Greenland ice sheet to climate change. [ABSTRACT FROM AUTHOR]

Abstract: Geologic studies of sediment deposited by glaciers can provide crucial insights into the subglacial environment. We studied muddy diamictites in the ANtarctic geological DRILLing (ANDRILL) AND-1B drill core, acquired from beneath the Ross Ice Shelf in McMurdo Sound, with the aim of identifying paleo-ice stream activity in the Plio–Pleistocene. Glacial advances were identified from glacial surfaces of erosion (GSEs) and subglacial diamictites within three complete sequences were investigated using lithofacies associations, micromorphology, and quartz sand grain microtextures. Whereas conditions in the Late Pliocene resemble the modern Greenland Ice Sheet where fast flowing glaciers lubricated by surface meltwater terminate directly in the sea (interval 201–212mbsl) conditions in the Late Pleistocene are similar to modern West Antarctic Ice Sheet (WAIS) ice streams (38–49mbsl). We identify the latter from ductile deformation and high pore-water pressure, which resulted in pervasive rotation and formation of till pellets and low relief, rounded sand grains dominated by abrasion. In the transitional period during the Mid-Pleistocene (55–68mbsf), a slow moving inland ice sheet deposited tills with brittle deformation, producing lineations and bi-masepic and unistrial plasma fabric, along with high relief, conchoidally fractured quartz grains. Changes in the provenance of gravel to cobble-size clasts support a distant source area of Byrd Glacier for fast-flowing paleo-ice streams and a proximal area between Darwin and Skelton Glaciers for the slow-moving inland ice sheet. This difference in till provenance documents a shift in direction of glacial flow at the core site, which indirectly reflects changes in the size and thickness of the WAIS. Hence, we found that fast ice streaming motion is a consequence of a thicker WAIS pushing flow lines to the west and introducing clasts from the Byrd Glacier source area to the drill site. The detailed analysis of diamictites in AND-1B demonstrates that Pliocene glacial intervals were warmer than in the Pleistocene when polar ice sheets grew from local inland ice to regional ice streams. [Copyright &y& Elsevier]

Subglacial lakes identified beneath the Antarctic Ice Sheet belong to a rare category of unexplored environments on Earth's surface. The key to understanding the origin and longevity of subglacial lakes is likely contained in their sedimentary sequences. Here we explore the nature of a sedimentary succession in a deep tectonic trough identified as a prime candidate for a large subglacial paleolake. The trough is the 100-km-long, 620-m-deep Christie Bay, located in the east arm of the Great Slave Lake, Canada. High-resolution seismic reflection data and short sediment cores collected in the deep trough show a 150-m-thick sequence of fine-grained sedimentary lake fill separating glacial ice-contact deposits from draped Holocene lake sediments. We interpret this sequence to consist of sediments that accumulated in a subglacial lake that covered an area larger than 130 km2. The inferred presence of a subglacial paleolake is supported by results from hydrologic modeling of drainage pathways beneath the Laurentide Ice Sheet during the last glacial maximum. Our data point toward the existence of a dynamic subglacial lake environment where sediments were delivered by discharge of meltwater from a subglacial water system. A core sample of the sedimentary lake fill in Christie Bay may elucidate whether living organisms exist in subglacial lakes. [ABSTRACT FROM AUTHOR]

The Greenland Ice Sheet is thinning at an accelerating pace and the ice sheet's contribution to sea-level rise has doubled in less than a decade. New data show rapid and widespread changes in the behaviour of the ice sheet, particularly along the coastal margin. These changes coincide with a decade of sustained Arctic warming of up to 3 °C. Decay of the Greenland Ice Sheet in response to global warming will not only be governed by increased surface melting during longer and warmer summers but also by a speed-up of coastal glaciers that drain the interior ice sheet. A precise estimate of sea-level rise in the twenty-first century relies on improved theoretical treatment of these glaciers in computer models. [ABSTRACT FROM AUTHOR]

Abstract: The foreground of Elisebreen, a retreating valley glacier in West Svalbard, exhibits a well-preserved assemblage of subglacial landforms including ice-flow parallel ridges (flutings), ice-flow oblique ridges (crevasse-fill features), and meandering ridges (infill of basal meltwater conduits). Other landforms are thrust-block moraine, hummocky terrain, and drumlinoid hills. We argue in agreement with geomorphological models that this landform assemblage was generated by ice-flow instability, possibly a surge, which took place in the past when the ice was thicker and the bed warmer. The surge likely occurred due to elevated pore-water pressure in a thin layer of thawed and water-saturated till that separated glacier ice from a frozen substratum. Termination may have been caused by a combination of water drainage and loss of lubricating sediment. Sedimentological investigations indicate that key landforms may be formed by weak till oozing into basal cavities and crevasses, opening in response to accelerated ice flow, and into water conduits abandoned during rearrangement of the basal water system. Today, Elisebreen may no longer have surge potential due to its diminished size. The ability to identify ice-flow instability from geomorphological criteria is important in deglaciated terrain as well as in regions where ice dynamics are adapting to climate change. [Copyright &y& Elsevier]

Surface crevassing is common on most of Earth's glaciers and particularly prevalent on fast-moving outlet glaciers characterised by high surface strain rates. As well as having implications for the mechanics of ice deformation and net strength, crevasses represent a means of transferring surface-generated meltwater and associated heat into the interior, and ultimately possibly to the base, of ice masses. Theoretically, surface crevasses are restricted to the uppermost tens of metres of an ice mass, but this can be extended by hydrofracturing where crevasses are water-filled. However, details - such as the locations of hydrofracturing both within a crevasse field and more locally within individual crevasses - are poorly understood such that vertical crevasse extent remains largely unconstrained. This knowledge gap mainly reflects the challenges associated with obtaining measurements of crevasse depth at glaciers, in terms of both obtaining direct access and geophysical imaging, especially of water-filled crevasses.Borehole optical televiewing (OPTV) records a high-resolution, geometrically-accurate image of the complete wall of any logged borehole, revealing the visible ice types and structures intercepted by that borehole. The technique therefore represents one means of investigating deep crevasses at ice masses, noting that such crevasses need to be inclined sufficiently to intersect an approximately vertical borehole. Here, we report evidence from a 325 m-long OPTV log of a borehole drilled ~30 km upglacier of the terminus of Store Glacier, a fast-moving tidewater glacier in west Greenland. While most structural features in the OPTV log are low-angle alternating decimetre-scale layers of clear ice and bubble-rich ice, interpreted as stratification, several high-angle features were also imaged. These were present to a depth of ~275 m and were typically centimetres to decimetres thick and composed of predominantly bubble-free ice. In one case, parallel crystal edges indicative of a directional freezing front were evident. Close inspection of the OPTV log also reveals that most of the high-angle layers enclosed one or more (and exceptionally, 11) structurally concordant millimetre-thick bubbly layers. We interpret the steeply-dipping layers as crevasses containing refrozen meltwater, and the fine bubbly layers as individual episodes of crevasse re-opening, refilling and refreezing – each expelling a new layer of gas as freezing completes. Implications for the transfer of mass and heat from the glacier's surface to its interior are explored by (i) comparing measured borehole temperatures with modelled englacial temperatures, and (ii) a spatial analysis of local surface crevassing. [ABSTRACT FROM AUTHOR]

As part of the research project RESPONDER, we performed two combined radar-seismic surveys to identify the bed conditions and suitable drilling locations at Store Glacier, a marine-terminating glacier in West Greenland. The two sites at 30 (Low Site) and 60 km (High Site) upstream of the snout of the glacier are thought to be part of the same subglacial drainage system but have different conditions both at the surface and at the base. As the ice-bed contact in the seismic data was sometimes difficult to identify we used the radar (Ground Penetrating Radar) data for confirmation.At the Low Site in the ablation zone, the surface is icy and crevassed. The five 2 to 3 km long seismic profiles show a large subglacial trench (width 2 km, depth 350 m) orientated in flow direction. The basal conditions vary with patches water, whether or not present in saturated sediments or exclusively at the base, both at the along-flow and across-flow profiles but they appear mainly at the sloping sides of the trench. The NE side of the trench contains a 100 to 150 m thick stratified sequence of softer, less consolidated sediments. At the High Site at equilibrium line, the surface is snowy with two frozen supra-glacial lakes. The two seismic profiles show less topography but have a similar patchy character. Despite thicker ice the ice-bed contact is much clearer visible in the seismic data which we contribute to a better coupled snowstreamer. The 5 km along-flow profile has a flat base consisting of sediments. A clear single englacial reflection following the shape of the base can be seen at 85% depth of the ice column, possibly the Holocene-Wisconsin transition. At the 1.7 km across-flow profile there is a 130 m rise of the bed from S to N. Judging by the strength of the basal reflection the sediments at the northern side are softer then at the southern side. [ABSTRACT FROM AUTHOR]

Ice loss from the Greenland Ice Sheet is currently the single largest cryospheric contributor to global sea level rise. The two most significant factors influencing ice loss are the acceleration of fast-flowing, marine-terminating glaciers, and surface run-off, which has increased steadily over the last several decades. Since almost all water from the surface is routed to the bed, hydrological systems at the base of the glacier are inherently conditioned by surface processes. Unpicking the relationships between surface (melt)water input, basal hydrology, and ice velocity is therefore key to understanding the effects of global warming on the contribution of marine-terminating glaciers to global sea level rise.Passive seismology enables the continuous observation of a range of phenomena occurring within and underneath glaciers, such as icequakes, crevassing, and tremors associated with water transport. This technique is therefore ideally suited to studying the effects of variations in surface water input over the duration of a melt season. Over the course of two field campaigns in May and June–July 2018, a network of 12 near-surface and 3 deep borehole geophones was deployed on Store Glacier, a large marine-terminating glacier in West Greenland, as part of the multidisciplinary RESPONDER project. The stations have recorded continuously since early May, capturing a wide range of phenomena including the onset and duration of the surface melting season, regional earthquakes, impulsive microseismic activity, and the drainage of a supraglacial lake. Here, we present findings in the form of spectrograms and the locations of microseismic events recorded by the network. The spectrograms show a clear and sudden transition between relative seismic quiescence and increased mid–high frequency activity on 5 June, corresponding to the onset of significant surface melting. The seismic signatures of meteorological events such as prolonged rainfall are also captured in the spectrograms. This dataset is therefore uniquely suited to investigating links between the input of surface water, microseismicity and basal hydrology. [ABSTRACT FROM AUTHOR]

The structure of subglacial hydrological drainage systems beneath large Greenlandic tidewater glaciers influences ice velocity due to its effect on basal traction, and it may also influence calving by its control on melting at the ice-ocean interface. Understanding these systems is critical to being able to accurately predict the evolution of the Greenland Ice Sheet and the resulting sea-level rise, as the fifteen largest Greenland outlet glaciers are responsible for 77% of the additional mass loss from the ice sheet due to acceleration since 2000. In this study, we use numerical modelling and observations of Store Glacier in West Greenland to constrain the form of the subglacial drainage system and melt rates from the resulting plumes, both of which are poorly known.We investigate the evolution of Store Glacier's subglacial hydrology using the open-source, full-Stokes model Elmer/Ice in a novel 3D application, the GlaDS hydrological module, which includes a distributed sheet and the ability to form concentrated channels when the sheet locally reaches sufficient thickness to initiate melting in cavities. At first, we produce a baseline winter scenario in which the hydrological system contains only basally derived meltwater produced primarily from friction at the bed. We then investigate the hydrological system during summer, focussing specifically on 2012 and 2017, which provide examples of high and low inputs of surface meltwater, respectively. When the model is forced with constant average runoff from summer (Jun-Aug) 2012, outputs show a hydrological system with significant sheet activity extending 55km inland and channels with a cross-sectional area higher than 1 m2 forming up to 45 km from the margin. However, we also find the hydrological system to be active in winter, when significant sheet flux is evident up to 35 km inland, and channels form as far as 25 km inland. The discharge of meltwater into the fjord produces convective plumes throughout the year, and these drive average submarine ice-front melt rates of up to 0.15 m d-1 in summer and 0.12 m d-1 in winter, rising to 1.6 m d-1 and 1.07 m d-1, respectively, for average temporal maximum melt rates. When the model is forced with daily time-series of summer runoff, we find a higher intensity of plume melting, reaching 0.16 m d-1 on average (rising to 2.21 m d-1 for the average temporal maximum). Our study shows that plume-induced ice-front melting is substantial even in winter, and we hypothesise that the high spatial variability and intensity during summer may drive calving through plume-induced notches cutting into the ice front as well as by undercutting of the terminus as a whole. [ABSTRACT FROM AUTHOR]

Abstract: Elisebreen, a retreating valley glacier in NW Svalbard, experienced a surge in the past, possibly during the Little Ice Age when ice was thicker and the bed warmer. The surge produced an assemblage of subglacial landforms and sediments now appearing in front of the downwasting ice margin. We have analysed an array of sedimentary properties of basal till from glacial flutings, ploughing marks, an interflute ground moraine, and meandering ridges in order to infer processes of till formation and deformation during the unrecorded surge. Till in flutings and ploughing marks reveals higher mechanical abrasion than in other landforms, but grain size distribution and mineralogy are largely the same everywhere. Micromorphological characteristics are also very similar and comprise ductile and brittle deformation structures, indicating fluctuating porewater pressures. Frequent micrograin fracturing suggests stress concentration along grain bridges during the surge. Till was formed by a combination of lodgement and deformation, caused mainly by clast ploughing. Meandering ridges containing till with water escape structures indicate that surge termination was facilitated by rapid water evacuation from the ice-bed interface through R-type channels. Micromorphological similarity of till found in flutings, ploughing marks, and interflute areas suggests that the resolution of the micromorphological signature is insufficient to constrain the different processes that led to the formation of those landforms. [Copyright &y& Elsevier]