Surface Lowering Rates Research Articles

Thinning and dynamics of the glacier terminus at the Pasterze Glacier (Austria), 2016–2021

As a result of global warming, glaciers worldwide recede and lose mass. Glacier ablation is influenced by surface characteristics, in particular the existence of debris cover. The evolution of glaciers may also be influenced by the existence of proglacial lakes, which are worldwide increasing in number and size. We examine the recent changes of the terminus of Pasterze Glacier by discussing the thinning and dynamics of the glacier terminus along with the changes of the glacial-proglacial transition zone between September 2016 and September 2021. By considering land cover in the interpretation, we find that glacier surface characteristics show different rates of elevation changes and surface movement. We mainly use orthophotos and digital elevation models (DEMs) resulting from airborne surveys of 12 different acquisition dates, but also draw on ablation stake measurements, lake water level data, water temperature data, as well as thermal infrared (TIR) imagery. While debris-covered ice lowered typically −5.0 m a−1 ± 4.6 m a−1 (mean ± standard deviation), debris-free ice was affected by ablation in the range of −7.0 m a−1 ± 2.7 m a−1, thus demonstrating that melt rates in similar elevations are related to surface characteristics. The elevation change rates were, in most cases, in a similar range throughout the observed periods of time. The horizontal displacement close to glacier-marginal crevasses amounted to up to ∼8 m a−1, but was mostly in the range of ∼1–4 m a−1. Considering both horizontal displacement and elevation changes, we find that clean and dirty ice surfaces show larger thickness losses and are moving faster compared to debris-covered glacier surfaces. Diurnal and seasonal fluctuations of lake water levels in the range of decimeters and lake water temperatures mostly clearly exceeding 0 °C are indicative of the potential influence of the proglacial lake on the glacier terminus. Given the decelerating and decaying behavior of the Pasterze Glacier in recent decades, we interpret the change rates of surface lowering and horizontal displacement 2016–2021 to be influenced by other factors such as the recently formed proglacial lake. This is also supported by direct ablation measurements that mostly show lesser ice melt differences compared to DEM-based surface elevation changes, suggesting that other factors such as thermally-induced melting contributed to an increased elevation difference.

Glacier thinning, recession and advance, and the associated evolution of a glacial lake between 1966 and 2021 atAusterdalsbreen, westernNorway

AbstractThe Jostedalsbreen is the largest ice cap in Norway and mainland Europe. Rapid retreat of many of its outlet glaciers since the 2000s has led to the formation of several glacial lakes. Processes causing the formation and expansion of glacial lakes and their interaction with a glacier and terminal moraine have not been widely addressed yet. In this study, we investigate the degradation of the front of the southeast‐facing outlet glacier Austerdalsbreen. Based on a variety of remotely sensed data (UAV‐based and airborne orthophotos and DEMs, satellite images), we analyze the coincident glacial and proglacial changes of Austerdalsbreen and quantify the evolution of this transition zone during the last decades. In particular, we focus on the short‐term evolution of the glacial lake since 2010, we examine the context of a glacier advance in the 1990s, and we report long‐term changes by utilizing 1960s imagery. We discuss the evolution and conditions of Austerdalsbreen compared to other outlet glaciers of Jostedalsbreen. Overall, the glacier terminus has experienced a recession in the last decades. The 1990s terminus advance was more restricted than at other nearby outlet glaciers due to glacier surface debris cover, which is a critical factor for the glacier and lake evolution. However, in the most recent period, since 2012, a distinct expansion of a glacial lake is quantifiable. Since the rates of glacier surface lowering also considerably increased since approximately 2017 and the glacier retreated since the beginning of the 2000s with a clear maximum length decrease in 2015, we interpret the recently formed glacial lake as a contributory factor of glacial changes.

The paraglacial adjustment of an Alpine lateral moraine, Bas Glacier d’Arolla, Switzerland

ABSTRACT Within Alpine catchments, glacial landforms are subject to post-depositional reworking during and following deglaciation. Ice-marginal moraines are thought to rapidly stabilise within ~200 years in this topographic context, although ice-proximal slopes are particularly prone to alteration by debris flows and solifluction. This study investigates landform transformation, documenting geomorphological change at the Bas Glacier d’Arolla, Switzerland. Gully development on a moraine slope was assessed using archive image sets obtained in 1977, 1988 and 2009 to derive historical elevation models. Raster differencing suggests that the mean rate of surface lowering on the upper moraine slope was 7.15 ± 1.83 m (± minimum level of detection) over the observation period (1977–2009), a rate of 0.22 m yr−1. The erosion of the landform resulted in an incontiguous moraine crestline. Whilst some landforms may undergo limited transformation upon deglaciation, selected sites are subject to rapid geomorphologic change, involving crestline retreat via the initial dissection by gullies, followed by the removal of inter-gully slopes.

Weakening of the pinning point buttressing Thwaites Glacier, West Antarctica

Abstract. The Thwaites Eastern Ice Shelf buttresses a significant portion of Thwaites Glacier through contact with a pinning point 40 km offshore of the present grounding line. Predicting future rates of Thwaites Glacier’s contribution to sea-level rise depends on the evolution of this pinning point and the resultant change in the ice-shelf stress field since the breakup of the Thwaites Western Glacier Tongue in 2009. Here we use Landsat-8 feature tracking of ice velocity in combination with ice-sheet model perturbation experiments to show how past changes in flow velocity have been governed in large part by changes in lateral shear and pinning point interactions with the Thwaites Western Glacier Tongue. We then use recent satellite altimetry data from ICESat-2 to show that Thwaites Glacier’s grounding line has continued to retreat rapidly; in particular, the grounded area of the pinning point is greatly reduced from earlier mappings in 2014, and grounded ice elevations are continuing to decrease. This loss has created two pinned areas with ice flow now funneled between them. If current rates of surface lowering persist, the Thwaites Eastern Ice Shelf will unpin from the seafloor in less than a decade, despite our finding from airborne radar data that the seafloor underneath the pinning point is about 200 m shallower than previously reported. Advection of relatively thin and mechanically damaged ice onto the remaining portions of the pinning point and feedback mechanisms involving basal melting may further accelerate the unpinning. As a result, ice discharge will likely increase up to 10 % along a 45 km stretch of the grounding line that is currently buttressed by the Thwaites Eastern Ice Shelf.

Two decades of dynamic change and progressive destabilization on the Thwaites Eastern Ice Shelf

Abstract. The Thwaites Eastern Ice Shelf (TEIS) buttresses the eastern grounded portion of Thwaites Glacier through contact with a pinning point at its seaward limit. Loss of this ice shelf will promote further acceleration of Thwaites Glacier. Understanding the dynamic controls and structural integrity of the TEIS is therefore important to estimating Thwaites' future sea-level contribution. We present a ∼ 20-year record of change on the TEIS that reveals the dynamic controls governing the ice shelf's past behaviour and ongoing evolution. We derived ice velocities from MODIS and Sentinel-1 image data using feature tracking and speckle tracking, respectively, and we combined these records with ITS_LIVE and GOLIVE velocity products from Landsat-7 and Landsat-8. In addition, we estimated surface lowering and basal melt rates using the Reference Elevation Model of Antarctica (REMA) DEM in comparison to ICESat and ICESat-2 altimetry. Early in the record, TEIS flow dynamics were strongly controlled by the neighbouring Thwaites Western Ice Tongue (TWIT). Flow patterns on the TEIS changed following the disintegration of the TWIT around 2008, with a new divergence in ice flow developing around the pinning point at its seaward limit. Simultaneously, the TEIS developed new rifting that extends from the shear zone upstream of the ice rise and increased strain concentration within this shear zone. As these horizontal changes occurred, sustained thinning driven by basal melt reduced ice thickness, particularly near the grounding line and in the shear zone area upstream of the pinning point. This evidence of weakening at a rapid pace suggests that the TEIS is likely to fully destabilize in the next few decades, leading to further acceleration of Thwaites Glacier.

Recessional pattern and surface elevation change of the Parvati Glacier, North-Western Himalaya (1965-2018) using remote sensing

ABSTRACT We present a long-term assessment (1965–2018) of recessional and area change patterns as well as the recent decade surface velocity (, 2000–2001 and 2017–2018) and elevation change (, 2003–2016) of the Parvati Glacier, north-western Himalaya. Multi-temporal high (Corona, Hexagon, and PlanetScope) to medium (Land Remote-Sensing Satellite (System, Landsat) Thematic Mapper (TM)/Enhanced Thematic Mapper+ (ETM+)/Operational Land Imager (OLI), Sentinel 2A- Multispectral Instrument (MSI), and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)) resolution images from 1965 to 2018 were analysed to evaluate multi-parameters of glacier dynamics. We estimated an average annual recessional rate of 37.5 ± 0.5 m and total area loss of 2.2 ± 0.01 km2 for the Parvati Glacier over the past half-century (i.e. 1965–2018). During 1973–1989, the Parvati Glacier experienced a significant recession (70.9 ± 3.1 m a−1) that resultant into disintegrated of the glacier in two separate glaciers between 1981 and 1989. We observed a higher average recession rate (28.4 ± 1.6 m a−1) of the detached glacier after its disintegrated from the Parvati Glacier (18.7 ± 1.6 m a−1) between 1989 and 2018. However, the debris-covered ice area of the Parvati Glacier (about 12%) increased twice that of the detached glacier (about 6.1%) during 1994–2018. The estimated reveals a substantial slowdown by about 27.7% and about 20% for the Parvati and detached glacier, respectively, during 2000–2001 and 2017–2018. Overall the annual average surface lowering rate (−0.7 ± 0.5 m a−1) for both the glacier has been almost similar during 2003–2016 but varied significantly at altitudinal. Our study shows inconsistency in previously reported recessional rate and observed advance phases in 1976–1989 and 2009–2013 for the Parvati Glacier during almost the same duration of the study. It is mainly ascribed to the misinterpretation of glacier boundaries using the Survey of India (SoI) topographic map of 1962 where glacier boundaries more generalized and by using coarser resolution of Landsat Multispectral Scanner (MSS) images (1970s), particularly for the debris-covered area. Overall, the Parvati Glacier shows a significant recession and frontal area change; and in the recent decades, extensive surface lowering, along with an observable slowdown in glacier and appearance of ice-cliffs in the ablation area collectively point towards substantial glacier degeneration over the period of our analysis.

A multidisciplinary approach for physical landscape analysis: scientific value and risk of degradation of outstanding landforms in the glacial plateau of the Loana Valley (Central-Western Italian Alps)

Landforms characterized by high scientific value (i.e. geomorphosites) might undergo modifications due to intrinsic and extrinsic factors (natural and human-induced processes). In the framework of geoheritage analyses, the assessment of the value (scientific or additional) of geomorphosites should be performed side by side with the analysis on the risk of degradation (fragility and vulnerability). A multidisciplinary method is proposed for the analysis of landforms that are potentially fragile but outstanding for their scientific value related to geological, geomorphological and ecological values. A geomorphological map was produced for the glacial plateaux of the Loana Valley (Central-Western Italian Alps), where an outstanding geomorphosite was detected: the Cortenuovo Calcareous Ridge. The site is herein analysed in terms of the representativeness of geological and (paleo)geomorphological features as well as for its support role to the ecosystem. For dissemination purposes, a simplified version of the geomorphological map (i.e., geomorphological box) was prepared for the site. Specific morphometric and dendrogeomorphological analyses were then performed to investigate more in detail the risk of degradation of the site. It resulted to be a spatially restricted hotspot of geodiversity, characterized by an average surface lowering rate (0.44 cm/y on average) comparable to that achieved in similar geomorphologic contexts in the Alpine environment. The obtained results testify to a potential vulnerability to natural processes of this highly scientific valued site, which will surely benefit from a legal recognition as a component of geoheritage, with a specific regulation for its protection, that could prove to be strategic.

The sensitivity of cosmogenic radionuclide analysis to soil bulk density: Implications for soil formation rates

AbstractImproving our knowledge of soil formation is critical so that we can better understand the first‐order controls on soil thickness and more effectively inform land‐management decisions. Cosmogenic radionuclide analysis has allowed soil scientists to more accurately constrain the rates at which soils form from bedrock. In such analysis, the concentration of an isotope, such as Beryllium‐10, is measured from a sample of bedrock. Because this concentration is partly governed by the lowering of the bedrock‐soil interface, a cosmogenic depth‐profile model can be fitted to infer the bedrock and surface lowering rates compatible with the measured concentrations. Given that the bedrock‐soil interface is shielded by soil, the cosmic rays responsible for the in‐situ production of the radionuclide are attenuated, with attenuation rates dependent on the density profile of this soil. Many studies have assumed that soil bulk density is either equal to that of the bedrock or constant with depth. The failure to acknowledge the variations in soil bulk density means that cosmogenically derived soil formation rates previously published may be under‐ or overestimates. Here, we deploy a new model called “CoSOILcal” to a global compilation of cosmogenic analyses of soil formation and, by making use of estimated bulk density profiles, recalculate rates of soil formation to assess the sensitivity to this important parameter. We found that where a soil mantle >0.25 m overlies the soil‐bedrock interface, accounting for the soil bulk density profile brings about a significantly slower rate of soil formation than that previously published. Moreover, the impact of using bulk density profiles on cosmogenically derived soil formation rates increases as soil thickens. These findings call into question the accuracy of our existing soil formation knowledge and we suggest that future cosmogenic radionuclide analysis must consider the bulk density profile of the overlying soil.Highlights The effect of heterogeneities in soil bulk density on cosmogenically derived soil formation rates is unknown. Soil formation rates are recalculated using a new model to analyse the effect of density variations. Accounting for density in soils >0.25 m thickness brings about significantly slower soil formation rates. Measuring soil bulk density is essential when cosmogenically deriving soil formation rates.

Erosion of rocky shore platforms by block detachment from layered stratigraphy

AbstractThe majority of shore platforms form in rocks that are characterised by layered stratigraphy and pervasive jointing. Plucking of weathered, joint and bed bounded blocks is an important erosion process that existing models of platform development do not represent. Globally, measuring platform erosion rates have focused on microscale (< 1 mm) surface lowering rather than mesoscale (0.1‐1 m) block detachment, yet the latter appears to dominate the morphological development of discontinuity rich platforms. Given the sporadic nature of block detachment on platforms, observations of erosion from storm event to multi‐decadal timescales (and beyond) are required to quantify shore platform erosion rates. To this end, we collected aerial photography using an unmanned aerial vehicle to produce structure‐from‐motion‐derived digital elevation models and orthophotos. These were combined with historical aerial photographs to characterise and quantify the erosion of two actively eroding stratigraphic layers on a shore platform in Glamorgan, south Wales, UK, over 78‐years. We find that volumetric erosion rates vary over two orders of magnitude (0.1‐10 m3 yr‐1) and do not scale with the length of the record. Average rates over the full 78‐year record are 2‐5 m3 yr‐1. These rates are equivalent to 1.2‐5.3 mm yr‐1 surface lowering rates, an order of magnitude faster than previously published, both at our site and around the world in similar rock types. We show that meso‐scale platform erosion via block detachment processes is a dominant erosion process on shore platforms across seasonal to multi‐decadal timescales that have been hitherto under‐investigated. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Subglacial controls on dynamic thinning at Trinity-Wykeham Glacier, Prince of Wales Ice Field, Canadian Arctic

ABSTRACTMass loss from glaciers and ice caps represents the largest terrestrial component of current sea level rise. However, our understanding of how the processes governing mass loss will respond to climate warming remains incomplete. This study explores the relationship between surface elevation changes (dh/dt), glacier velocity changes (du/dt), and bedrock topography at the Trinity-Wykeham Glacier system (TWG), Canadian High Arctic, using a range of satellite and airborne datasets. We use measurements of dh/dt from ICESat (2003–2009) and CryoSat-2 (2010–2016) repeat observations to show that rates of surface lowering increased from 4 m yr−1 to 6 m yr−1 across the lowermost 10 km of the TWG. We show that surface flow rates at both Trinity Glacier and Wykeham Glacier doubled over 16 years, during which time the ice front retreated 4.45 km. The combination of thinning, acceleration and retreat of the TWG suggests that a dynamic thinning mechanism is responsible for the observed changes, and we suggest that both glaciers have transitioned from fully grounded to partially floating. Furthermore, by comparing the separate glacier troughs we suggest that the dynamic changes are modulated by both lateral friction from the valley sides and the complex geometry of the bed. Further, the presence of bedrock ridges induces crevassing on the surface and provides a direct link for surface meltwater to reach the bed. We observe supraglacial lakes that drain at the end of summer and are concurrent with a reduction in glacier velocity, suggesting hydrological connections between the surface and the bed significantly impact ice flow. The bedrock topography thus has a primary influence on the nature of the changes in ice dynamics observed over the last decade.

Forty three years of micro-erosion meter monitoring of erosion rates on shore platforms at Kaikōura Peninsula, South Island, New Zealand

Using micro-erosion meters (MEM) and traversing micro-erosion meters (TMEM), surface lowering rates of shore platforms on Kaikōura Peninsula, South Island, New Zealand have been measured over a total of 43 years. This record is the longest monitored network of this type. Since 1973, erosion rates have been calculated over two, two year periods 1973–1975, (n = 31) and 1993–1996, (n = 55) and at decadal scales; 1973–1993 (n = 15), 1973–2004 (n = 12), 1993–2004 (n = 46), 1993–2008 (n = 34), 1993–2016, (n = 18), 1973–2016 (n = 6). After 43 years, surface lowering rates remain similar to previously published rates at an average of 0.525 to 1.181 mm. a−1. Statistical analysis shows that erosion rates over all measurement periods are derived from the same population. Thus, short term rates derived from two years of monitoring remain indicative of decadal rates of erosion. Variations between measurement periods are best explained by the loss of the more rapidly eroding bolt sites. These losses point to the difficulty of maintaining monitoring over longer time scales. A means of statistical manipulation (previously published) allows for these losses to be accounted for in determining long term rates of platform lowering. In November 2016 a Mw 7.8 earthquake raised the Kaikōura Peninsula approximately 0.8–1 m, elevating much of the shore platforms above the tide range. This earthquake has reset the MEM record ending this long running erosion monitoring site of shore platform surface lowering. However the MEM network is now being used to monitor post-earthquake response of the uplift shore platforms and new marine terraces.

The episodic rise, net growing rate and kinematics of radial faults of the Salinas de Oro diapir using paleoseismological techniques (NE Spain). Salt upwelling versus karstic subsidence

This paper explores the use of trenching and paleoseismological techniques to determine salt flow rates into a salt diapir for the first time in the literature. The Salinas de Oro diapir, located in the northern Spanish Pyrenees, is an oval-shaped Triassic-salt stock that extends vertically for ≫7 km down to the Paleozoic basement. Salt dissolution subsidence and diapir growth are coeval active processes. Karstification is responsible for the development of large sinkholes, a thick caprock and the monocline folding and ring faulting of the Cretaceous and Early Tertiary limestone rim. The evaporite karstic aquifer discharges high-concentration water of up to 137 g/l of total dissolved solids and a conductivity over 200 mS/cm into the Salado Creek, which drains the diapir top. The salinity monitoring of this drainage provides a maximum karstic surface lowering rate of around 2.8 mm/yr. Salt upwelling has caused the 150 m uplift of the annular limestone escarpment and the development of ≫3000 m long radial grabens with up to 90 m of vertical offset that disrupt drainages, displace Quaternary deposits and overprint concentric faults. The 260 cm drag folding of lacustrine facies exposed in a 42 m long and 6.5 m deep trench due to the creep motion of the western radial fault of Azanza Graben yielded a minimum short-term uplift slip rate of 1.75 mm/yr for the last 1485 years and provides a minimum salt supply rate of over 5 mm/yr considering karstification lowering. This value that is several hundred times higher than average, evidence the discontinuous growth of Salinas de Oro diapir.

Stranded landscapes in the humid tropics: Earth's oldest land surfaces

Defying common expectations, some of the oldest landscapes on Earth are found in the humid tropics. 40Ar/39Ar dating shows that Fe-rich regolith that armors the ∼700–1000 m elevation banded iron-formation plateaus at Urucum, Mato Grosso do Sul, Brazil, results from chemical weathering that began at least 70 million years ago. Cosmogenic 3He concentrations in residual hematite clasts and the underlying saprolite on one plateau imply an extraordinarily slow surface lowering rate of 0.07–0.10 mMa−1 maintained over the last ∼17–70 Ma. Cosmogenic 10Be and 26Al concentrations in a quartz vein in the same plateau suggest a similarly low surface erosion rate of ∼0.11–0.18 mMa−1 over the past few million years. Cosmogenic 3He concentrations in goethite cementing a ∼200 m elevation indurated pediment ∼3 km northwest of the plateau escarpment yields a minimum exposure age of ∼2.6 Ma, revealing that some of the low-lying areas had already been incised and locally stabilized by goethite cementation by then. In contrast, 36Cl measurements on limestone outcrops at ∼170 m elevation and ∼6.5 km northwest of the Urucum plateau reveal short-term erosion rates of 7.1 ± 0.4 and 10.1 ± 0.5 mMa−1, showing that areas not stabilized by goethite cementation are undergoing erosion at a relatively fast pace. The ∼700 m of relief at Urucum is consistent with differential denudation over ∼70 Ma controlled by lithological differences in chemical and physical rates of weathering and erosion. Effective chemical weathering and protracted low rates of erosion for the high-elevation surface result in armoring by a resilient residue of hematite blocks that are relatively insoluble and too heavy to transport. Armoring by the surface lag of large chemically resilient hematite blocks and bedded hematite saprolite focuses meteoric water flow into the subsurface and along faults. Preferential subsurface flow along the permeable pathways between insoluble hematite blocks, combined with segmentation of the Urucum Surface into isolated catchments too small to host active drainage systems, brings physical erosion to a stand-still. The only effective erosive processes on the Urucum plateau are subsurface chemical erosion and scarp retreat. Non-steady-state landscapes in which elevation differences result from prolonged differential denudation are a common feature of Earth's southern hemisphere cratons, and they inherit their present form from underlying lithologies coupled with geomorphic processes active since the Mesozoic.

Sediment supply from lateral moraines to a debris-covered glacier in the Himalaya

Abstract. Debris-covered glaciers in the Himalaya play an important role in the high-altitude water cycle. The thickness of the debris layer is a key control of the melt rate of those glaciers, yet little is known about the relative importance of the three potential sources of debris supply: the rockwalls, the glacier bed and the lateral moraines. In this study, we hypothesize that mass movement from the lateral moraines is a significant debris supply to debris-covered glaciers, in particular when the glacier is disconnected from the rockwall due to downwasting. To test this hypothesis, eight high-resolution and accurate digital elevation models from the lateral moraines of the debris-covered Lirung Glacier in Nepal are used. These are created using structure from motion (SfM), based on images captured using an unmanned aerial vehicle between May 2013 and April 2018. The analysis shows that mass transport results in an elevation change on the lateral moraines with an average rate of -0.31±0.26 m year−1 during this period, partly related to sub-moraine ice melt. There is a higher elevation change rate observed in the monsoon (-0.39±0.74 m year−1) than in the dry season (-0.23±0.68 m year−1). The lower debris aprons of the lateral moraines decrease in elevation at a faster rate during both seasons, probably due to the melt of ice below. The surface lowering rates of the upper gullied moraine, with no ice core below, translate into an annual increase in debris thickness of 0.08 m year−1 along a narrow margin of the glacier surface, with an observed absolute thickness of approximately 1 m, reducing melt rates of underlying glacier ice. Further research should focus on how large this negative feedback is in controlling melt and how debris is redistributed on the glacier surface.

Weighted linear combination method versus grid based overlay operation method – A study for potential soil erosion susceptibility analysis of Malda district (West Bengal) in India

Soil erosion is a natural process. The factors which are responsible for soil erosion are rainfall, flowing water, ice, temperature changes, gravity i.e. mostly the physical agents of erosion along with the anthropogenic agents. The present paper focuses on the delineation of soil erosion susceptible areas in Malda district (west Bengal) using weighted linear combination method and grid based overlay operation method and their effectiveness. The Arc GIS 9.3 software were used to complete the process of Geo-referencing, digitization of drainage network, and the generation of various maps like; Rainfall, Soil texture, Slope, Land use/cover, Vegetation and distance from river maps etc, of Malda district. The surface lowering rate map and the determination of rate of soil erosion of fifteen blocks in Malda district has been prepared and determined using field based empirical pegging operation data for the years 2015 and 2016 through Arc GIS 9.3 software. Potential soil erosion susceptibility zonation map has been prepared based on weighted linear combination (WLC) method and grid based overlay operation method with selected eight soil erosion parameters in ARC-GIS 9.3 software and ERDAS environment. The validation of the both methods has been done based on accuracy assessment and ROC curve.

Rapid Surface Lowering of Benito Glacier, Northern Patagonian Icefield

The Patagonian Icefields, which straddle the Andes below 46°S, are one of the most sensitive ice masses to climate change. However, recent mass loss from the icefields, along with its spatial and temporal variability, is not well constrained. Here we determine surface elevation changes of Benito Glacier, a 163 km2 outlet glacier draining the western flank of the North Patagonian Icefield, using a combination of field and satellite-derived elevation data acquired between 1973 and 2017. Our results demonstrate that, just below the equilibrium line, the glacier dramatically thinned by 139 m in the past 44 years, equivalent to a mean rate of 3.2 ± 0.2 m a-1. However, surface lowering was temporally variable, characterized by a hiatus between 2000 and 2013, and a subsequent increase up to 7.7 ± 3.0 m a-1 between 2013 and 2017. Analysis of Benito Glacier’s flow regime throughout the period indicates that the observed surface lowering was caused by negative surface mass balance, rather than dynamic thinning. The high rate of surface lowering observed over the past half a decade highlights the extreme sensitivity of mid-latitude glaciers to recent atmospheric forcing.

Evolution of high-Arctic glacial landforms during deglaciation

Glacial landsystems in the high-Arctic have been reported to undergo geomorphological transformation during deglaciation. This research evaluates moraine evolution over a decadal timescale at Midtre Lovénbreen, Svalbard. This work is of interest because glacial landforms developed in Svalbard have been used as an analogue for landforms developed during Pleistocene mid-latitude glaciation. Ground penetrating radar was used to investigate the subsurface characteristics of moraines. To determine surface change, a LiDAR topographic data set (obtained 2003) and a UAV-derived (obtained 2014) digital surface model processed using structure-from-motion (SfM) are also compared. Evaluation of these data sets together enables subsurface character and landform response to climatic amelioration to be linked. Ground penetrating radar evidence shows that the moraine substrate at Midtre Lovénbreen includes ice-rich (radar velocities of 0.17 m ns−1) and debris-rich (radar velocities of 0.1–0.13 m ns−1) zones. The ice-rich zones are demonstrated to exhibit relatively high rates of surface change (mean thresholded rate of −4.39 m over the 11-year observation period). However, the debris-rich zones show a relatively low rate of surface change (mean thresholded rate of −0.98 m over the 11-year observation period), and the morphology of the debris-rich landforms appear stable over the observation period. A complex response of proglacial landforms to climatic warming is shown to occur within and between glacier forelands as indicated by spatially variable surface lowering rates. Landform response is controlled by the ice-debris balance of the moraine substrate, along with the topographic context (such as the influence of meltwater). Site-specific characteristics such as surface debris thickness and glaciofluvial drainage are, therefore, argued to be a highly important control on surface evolution in ice-cored terrain, resulting in a diverse response of high-Arctic glacial landsystems to climatic amelioration. These results highlight that care is needed when assessing the long-term preservation potential of contemporary landforms at high-Arctic glaciers. A better understanding of ice-cored terrain facilitates the development of appropriate age and climatic interpretations that can be obtained from palaeo ice-marginal landsystems.

Dynamic Response of Sjögren Inlet Glaciers, Antarctic Peninsula, to Ice Shelf Breakup Derived from Multi-Mission Remote Sensing Time Series

The substantial retreat or disintegration of numerous ice shelves has been observed on the Antarctic Peninsula. The ice shelf in the Prince Gustav Channel has retreated gradually since the late 1980s and broke up in 1995. Tributary glaciers reacted with speed-up, surface lowering and increased ice discharge, consequently contributing to sea level rise. We present a detailed long-term study (1993-2014) of the dynamic response of Sjogren Inlet glaciers to the disintegration of the Prince Gustav Ice Shelf. We analyzed various remote sensing datasets to identify the reactions of the glaciers to the loss of the buttressing ice shelf. A strong increase in ice surface velocities was observed, with maximum flow speeds reaching 2.82±0.48 m d-1 in 2007 and 1.50±0.32 m d-1 in 2004 at Sjogren and Boydell glaciers respectively. Subsequently, the flow velocities decelerated, however in late 2014, we still measured approximately twice the values of our first observations in 1996. The Sjogren Inlet glaciers retreated 61.7±3.1 km² behind the former grounding line in 1996. For the glacier area below 1000 m a.s.l. and above the 2014 grounding (399 km²), a mean surface lowering of -68±10 m (-3.1 m a-1) was observed in the period 1993-2014. The lowering rate decreased to -2.2 m a-1 in the period 2012-2014. Based on the surface lowering rates, geodetic mass balances of the glaciers were derived for different time periods. A strongly negative mass change rate of -1.16±0.38 Gt a-1 was found for the area of all Sjogren Inlet glaciers (including the area above 1000 m a.s.l.) above the 2014 grounding line (559km2) for the earliest period (1993-2001). Due to the dynamic adjustments of the glaciers to the new boundary conditions the rate changed to -0.54±0.13 Gt a-1 in the period 2012-2014, resulting in an average mass change rate of -0.84±0.18 Gt a-1 (1993-2014) for the same domain. Including the retreat of the ice front and grounding line, a total mass change of -37.5±8.2 Gt (-1.79±0.39 Gt a-1) and a contribution to sea level rise of 20.9±5.2 Gt (-0.99±0.25 Gt a-1) were computed for the period 1993-2014. Analysis of the ice flux revealed that

Climate and hillslope degradation vary in concert; 85 ka to present, eastern Sierra Nevada, CA, USA

Degradation in the landscape results when the interactions of climate, substrate, and biota dislodge and transport sediment that is mantling landforms. Rates of degradation through time control landform stability and resiliency. Therefore, records of past degradation rates can be used to inform us on how a given landscape responded to significant changes in past climates. For example, climate has varied at many temporal scales, and some of the largest recent shifts enabled the glacial advances and retreats in time scales of 20–100ka. Therefore, it is reasonable to expect that the rate of landscape degradation has also varied at similar time scales. However, the general hillslope diffusion equation that is commonly used to model cross-profiles of hillslopes on time scales of thousands to tens of thousands of years typically relies on a constant and optimized rate parameter to generate a model cross-profile approximating the current observed landform cross-profile. Using a time-varying diffusivity parameter, we generated three separate degradation scenarios for the Mono Basin moraine in the eastern Sierra Nevada, CA, USA, in order to assess the potential impact of varying past climates on sediment transport. We used published paleoclimate records in the study area and modern rates of surface degradation from climates that correspond broadly to those paleoclimates. The results indicate that, in this case, the climate driven and, therefore, time-dependent degradation model produces a good fit between the modeled and observed landform profiles. Results showed that, when the surface elevations of the reference case (constant optimized diffusivity) were compared through time to the surface elevations of the time-dependent model, the differences were relatively small. The largest deviation was found to occur during the Last Glacial Maximum (LGM). We found that for investigations into the geological effects of climate change in glacial and polar regions, the use of time-varying diffusivity offers improved estimates of landform degradation through time. The rates of surface lowering that change through time are important for analyses of the depths of past exposures, exposure dating, and renewal or preservation of surfaces, all of which are relevant in landscape dating, in interpretation of paleoecology, and in modeling landscape evolution.

Ice-cored moraine degradation mapped and quantified using an unmanned aerial vehicle: A case study from a polythermal glacier in Svalbard

Ice-cored lateral–frontal moraines are common at the margins of receding high-Arctic valley glaciers, but the preservation potential of these features within the landform record is unclear. Recent climatic amelioration provides an opportunity to study the morphological evolution of these landforms as they de-ice. This is important because high-Arctic glacial landsystems have been used as analogues for formerly glaciated areas in the mid-latitudes. This study uses SfM (Structure-from-Motion) photogrammetry and a combination of archive aerial and UAV (unmanned aerial vehicle) derived imagery to investigate the degradation of an ice-cored lateral–frontal moraine at Austre Lovénbreen, Svalbard. Across the study area as a whole, over an 11-year period, the average depth of surface lowering was −1.75±0.89m. The frontal sections of the moraine showed low or undetectable rates of change. Spatially variable rates of surface lowering are associated with differences in the quantity of buried ice within the structure of the moraine. Morphological change was dominated by surface lowering, with limited field evidence of degradation via back-wastage. This permits the moraine a greater degree of stability than previously observed at other sites in Svalbard. It is unclear whether the end point will be a fully stabilised ice-cored moraine, in equilibrium with its environment, or an ice-free lateral–frontal moraine complex. Controls on geomorphological change (e.g. topography and climate) and the preservation potential of the lateral–frontal moraine are discussed. The methods used by this research also demonstrate the potential value of SfM photogrammetry and unmanned aerial vehicles for monitoring environmental change and are likely to have wider applications in other geoscientific sub-disciplines.