Ice Disintegration Research Articles

Investigating the effect of deicing parameters using high-pressure water jet

Maritime operations are impacted by ice accretion on decks, bulkheads, and offshore structures during the winter or in extremely frigid climates. In most cases, the traditional method of deicing maritime vessels is human labor, which requires enormous effort and lengthy hours for unsatisfactory results, particularly when the ice adhesion strength is high. This study experimentally examined combined effects of operational parameters, including operating pump pressure, nozzle geometry, water jet temperature, standoff distance, and time of cut, on the depth and width of a cut through an ice block. In comparison to other parameters, the influence of nozzle geometry on both the width and depth of cut was found to be more significant, with R-squared values of 85% and 62% respectively. Increasing the depth and width of the cut facilitated the delamination and disintegration of ice from an aluminum mold. This indicates that water jet deicing on maritime vessels could be effective, therefore achieving the objective of this study. The optimization of operational parameters is used to develop a cuttability chart for various thicknesses of accumulated ice on marine vessels.

The effect of landfast sea ice buttressing on ice dynamic speedup in the Larsen B embayment, Antarctica

Abstract. We observe the evacuation of 11-year-old landfast sea ice in the Larsen B embayment on the East Antarctic Peninsula in January 2022, which was in part triggered by warm atmospheric conditions and strong offshore winds. This evacuation of sea ice was closely followed by major changes in the calving behaviour and dynamics of a subset of the ocean-terminating glaciers in the region. We show using satellite measurements that, following a decade of gradual slow-down, Hektoria, Green, and Crane glaciers sped up by approximately 20 %–50 % between February and the end of 2022, each increasing in speed by more than 100 m a−1. Circumstantially, this is attributable to their transition into tidewater glaciers following the loss of their ice shelves after the landfast sea ice evacuation. However, a question remains as to whether the landfast sea ice could have influenced the dynamics of these glaciers, or the stability of their ice shelves, through a buttressing effect akin to that of confined ice shelves on grounded ice streams. We show, with a series of diagnostic modelling experiments, that direct landfast sea ice buttressing had a negligible impact on the dynamics of the grounded ice streams. Furthermore, we suggest that the loss of landfast sea ice buttressing could have impacted the dynamics of the rheologically weak ice shelves, in turn diminishing their stability over time; however, the accompanying shifts in the distributions of resistive stress within the ice shelves would have been minor. This indicates that this loss of buttressing by landfast sea ice is likely to have been a secondary process in the ice shelf disaggregation compared to, for example, increased ocean swell or the drivers of the initial landfast sea ice disintegration.

The effect of pre-treatment and anaerobic digestion for pathogens reduction in agricultural utilization of sewage sludge

The aim of the research work was to explain the possibilities of application of waste activated sludge (WAS) pretreatment processes prior to anaerobic digestion (mesophilic fermentation). Hydrodynamic disintegration and freezing/thawing disintegration methods were used. Based on the microbiological and parasitological analyses, a significant decrease in pathogenic bacteria, coliphages, and parasite eggs was observed. The number of bacteria analyzed (Salmonella sp., Escherichia coli, Clostridium perfringens) and coliphages were reduced from 19.3to 42.3% after hydrodynamic cavitation. A similar effect was achieved for destruction by freezing/thawing with dry ice between 7.8 and 14.9%. The effectiveness of parasite eggs reduction (Ascaris sp., Trichuris sp., Toxocara sp.) for these disintegration methods ranged from 10.7 to 29.3%. The highest results were observed for the hybrid disintegration method (hydrodynamic cavitation + dry ice disintegration) caused by a synergistic effect. Salmonella sp. in 1 gd.w. decrease about 69.7%, E. coli by 70.0%, Clostridium perfringens by 38.4%, and coliphages by 48.2%. Disruption of WAS by a hybrid method led to a reduction in the number of helminth eggs Ascaris sp. (63.8%), Trichuris sp. (64.3%), and Toxocara sp. (66.4%). After anaerobic digestion under mesophilic conditions, an additional reduction of analyzed bacterial pathogens and helminth eggs were observed. The introduction of hybrid disintegrated WAS to the fermentation chamber resulted in higher efficiency in decrease (from 1 to 23%) in comparison to the control sample (70%WAS + 30%DS (inoculum-digested sludge)).

Vermicular Ridge Features on Dundas Harbour, Devon Island, Nunavut

Conspicuous ridges with a circular, sinuous and anastomosing morphology, termed Vermicular Ridge Features (VRFs), have been observed along the coast of Dundas Harbour, Devon Island, Nunavut, Canada. Periglacial and glacial processes can produce morphologically similar ridge landforms, such as stone circles or ice disintegration features. However, VRFs are both morphologically and morphometrically distinct. We utilize aerial drone imagery, digital elevation models, grain size analysis, and field observations of VRFs to compare morphology, morphometry, environmental conditions and substrate characteristics to documented periglacial and glacial features with a circular to anastomosing ridge pattern. We interpret VRFs to be formed by paraglacial processes produced from the passive ablation of stagnant “dead” ice and subsequent deposition of supra- and englacial debris as a hummocky “ring-ridge” moraine. If these features are, in fact, ring-ridge moraines, then this is the first documentation of a ring-ridge moraine in Nunavut, Canada.

Foehn Event Triggered by an Atmospheric River Underlies Record‐Setting Temperature Along Continental Antarctica

AbstractA record‐setting temperature of 17.5°C occurred on 24 March 2015 at the Esperanza station located near the northern tip of the Antarctic Peninsula (AP). We studied the event using surface station data, satellite imagery, reanalysis data, and numerical simulations. The Moderate Resolution Imaging Spectroradiometer Antarctic Ice Shelf Image Archive provides clear evidence for disintegration and advection of sea ice, as well as the formation of melt ponds on the ice sheet surface at the base of the AP mountain range. A deep low‐pressure center over the Amundsen‐Bellingshausen Sea and a blocking ridge over the southeast Pacific provided favorable conditions for the development of an atmospheric river with a northwest‐southeast orientation, directing warm and moist air toward the AP, and triggering a widespread foehn episode. A control simulation using a regional climate model shows the existence of local topographically induced warming along the northern tip of the AP (∼60% of the full temperature signal) and the central part of the eastern AP (>90% of the full temperature signal) with respect to a simulation without topography. These modeling results suggest that more than half of the warming experienced at Esperanza can be attributed to the foehn effect (a local process), rather than to the large‐scale advection of warm air from the midlatitudes. Nevertheless, the local foehn effect also has a large‐scale advection component, since the atmospheric river provides water vapor for orographic precipitation enhancement and latent heat release, which makes it difficult to completely disentangle the role of local versus large‐scale processes in explaining the extreme event.

UAS-Based Change Detection of the Glacial and Proglacial Transition Zone at Pasterze Glacier, Austria

Glacier-related applications of unmanned aircraft systems (UAS) in high mountain regions with steep topography are relatively rare. This study makes a contribution to the lack of UAS applications in studying alpine glaciers in the European Alps. We transferred an established workflow of UAS-based change detection procedures to Austria’s largest glacier, the Pasterze Glacier. We focused on a selected part of the glacier tongue and its proglacial vicinity to obtain detailed knowledge of (i) the behavior of a lateral crevasse field, (ii) the evolution of glacier surface structures and velocity fields, (iii) glacier ablation behavior and the current glacier margin, and (iv) proglacial dead ice conditions and dead ice ablation. Based on two UAS flight campaigns, accomplished in 2016 (51 days apart), we produced digital elevation models (DEMs) and orthophotos with a ground sampling distance (GSD) of 0.15 m using Structure-from-Motion (SfM) photogrammetry. Electrical resistivity tomography (ERT) profiling was additionally conducted in the proglacial area. Results indicate distinct changes in the crevasse field with massive ice collapses, rapid glacier recession, surface lowering (mean of −0.9 m), and ice disintegration at the margins, calculated degree day factors on the order of −7 to −11 mm d−1·°C−1 for clean ice parts, and minimal changes of the debris-covered dead ice in the proglacial area. With this contribution we highlight the benefit of UAS in comparison to commonly used terrestrial methods and satellite-related approaches.

Remote detection of cryoacoustic signals using noise interferometry of seafloor pressure data

We have observed a large number of 5-15 Hz hydroacoustic arrivals in seafloor pressure data collected in 2009-2010 by the Marine Observations of Anisotropy Near Aoteroa (MOANA) experiment offshore the South Island of New Zealand. Preliminary manual picking revealed that a small number (<10%) of these signals appeared to originate from Antarctica (potentially related to ice disintegration events). Automatic detection of Antarctic signals in MOANA data using frequency-wavenumber (f-k) analysis is precluded in the 5-15 Hz band by spatial aliasing. Instead we have developed a two-stage directional detection scheme based on ambient noise Green’s functions between MOANA stations, which reveal noise directivity in the amplitude asymmetry between forward and reverse lags. For each 20-minute time window of the continuous dataset, we cross-correlate all pressure data, and tabulate windows containing significant energy at the predicted acoustic arrival times between stations and originating from backazimuths consistent with Antarctica. We then beamform each candidate window to estimate signal approach angles. We find that our noise-based approach succeeds in detecting our initial manually-picked events. Back-projecting our detections indicates that many correlate with known iceberg locations from satellite remote sensing studies. We also observe that detection frequency is comparatively lowest in Austral winter, as expected.

Improving of anaerobic digestion by dry ice disintegration of activated sludge

Disintegration by dry ice has a positive effect on the degree and rate of surplus activated sludge anaerobic digestion. By applying thermal disintegration the lysis of cells occurs in minutes instead of days. The intracellular and extracellular components are set free and are immediately available for biological degradation which leads to an improvement of the subsequent anaerobic process. Thermal disintegration by dry ice of the surplus activated sludge results in organic matter and a polymer transfer from the solid phase to the liquid. During disintegration process soluble chemical oxygen demand (SCOD) value and proteins concentration increase about 583 and 265 mg/dm, respectively. In the same time concentration of carbohydrates increase about 53 mg/dm. In addition the degree of thermal disintegration changed from 13% for the volume ratio of dry ice to surplus activated sludge 0.25:1 to 49% for the volume ratio of dry ice to sludge 1:1. The addition of thermal disintegrated sludge (30% SASDI of volume) to the digestion process leads to increased biogas production about 49%.

Deglaciation landforms and C-14 chronology of the Lac Guillaume-Delisle area, eastern Hudson Bay: A report on field evidence

This paper presents new field data pertaining to the deglaciation of the Lac Guillaume-Delisle area, aiming to establish its emplacement in time and space between the breaching of the Laurentide Ice Sheet (LIS) over Hudson Bay and the final ice disintegration over Northern Québec and Labrador. The deglaciation of the east coast of Hudson Bay started at 8200cal BP in the south-western sector of the Lac Guillaume-Delisle estuary, when the marine limit was at 271m above sea level (asl). By 8000cal BP, frontal moraines and proximal glacio-marine sediments were deposited in the transverse valleys along the coastal cuesta ridges at a mean elevation of 250m asl. They are associated with a regional topographic pinning event of the western margin of the Quebec-Labrador Ice Sheet (QLIS) on the high coastal relief. At that time, the coastal relief encouraged a change in deglaciation mode from fast calving in the open and deep Tyrrell Sea to a tidewater ice-sheet controlled by the topography. The ice front thereafter retreated eastward under very large and fast crustal unloading where ice-contact deltas fed by short sandar and eskers were deposited between 7900 and 7400cal BP (between 240 and 195m asl), as the ice front was receding inland and lost contact with Tyrrell Sea. A series of deposits and landforms characterize this modification in the sedimentation regime when the ice-sheet margin changed from tidewater to terrestrial. Dating shows that the deglaciation of the western margin of QLIS on land was very fast, i.e. faster than when the front of the ice-sheet was in contact with the Tyrrell Sea. As the fall of the relative sea-level continued, a large volume of paraglacial sediments was deposited in the river valleys making up vast fluvial terraces and deltas between 6500 and 5800cal BP (between 125 and 100m asl). Since then, land emergence has continued at a rate of about 1.3m/century. Downcutting by rivers, post-glacial deltaic sedimentation and shoreline changes still continue today.

Coastal landfast sea ice decay and breakup in northern Alaska: Key processes and seasonal prediction

Seasonal breakup of landfast sea ice consists of movement and irreversible ice detachment in response to winds or oceanic forces in the late stages of ice decay. The breakup process of landfast sea ice in the Chukchi Sea at Barrow, Alaska, was analyzed for the years 2000 through 2010 on the basis of local observations of snow and ice conditions, weather records, image sequences obtained from cameras, coastal X band marine radar, and satellite imagery. We investigated the relation of breakup to winds, tides, and nearshore current measurements from a moored acoustic Doppler current profiler. Two breakup modes are distinguished at Barrow on the basis of the degree of ice decay. Mechanical breakup due to wind and oceanic forces follows ablation and weakening of the ice. Thermal breakup is the result of ice disintegration under melt ponds, requiring little force to induce dispersion. Grounded pressure ridges are pivotal in determining the breakup mode. The timing of thermal breakup of the nearshore ice cover was found to correlate with the measured downwelling solar radiation in June and July. This linkage allows for the development of an operational forecast of landfast ice breakup. Results from forecasts during 2 years demonstrate that thermal breakup can be predicted to within a couple of days 2 weeks in advance. The cumulative shortwave energy absorbed by the ice cover provides for a measure of the state of ice decay and potential for disintegration. Discriminating between the two modes of breakup bears the potential to greatly increase forecasting skill.

Seismic Arrays on Drifting Ice Floes: Experiences from Four Deployments in the Arctic Ocean

In the last three decades our knowledge about the seismic structure and the seismicity of the world's oceans has increased tremendously through the common availability of ocean bottom seismometers for active and passive seismic studies ( e.g. , Orcutt et al. 1976; Toomey et al. 1985; Tolstoy et al. 2008). The safe recovery of the instruments is essential to access the acquired data. Comparable studies of the polar oceans do not exist, because the perennial sea-ice cover in polar regions prevents a safe recovery of ocean bottom instruments. Hence, the seismic structure and the earthquake activity of large parts of the Arctic Ocean, including the Gakkel Ridge, one of the most prominent members of ultraslow-spreading mid-ocean ridges (< 20 mm/y full rate; Dick et al. 2003), are largely unknown. Mounting conventional land seismometers on drifting sea ice is the only way to acquire seismic data in the Arctic Ocean. The difficult access to the survey area, which requires icebreaking vessels and helicopters, and the cold temperatures and a constantly moving seismometer platform, represent highly unsuitable survey conditions. However, Kristoffersen et al. (1982) made first attempts at recording regional earthquakes in the Arctic by attaching a sonobuoy array to an ice floe. Jokat et al. (2003) demonstrated that the acquisition of refraction seismic data is possible with seismic stations mounted on drifting ice floes. Okal and MacAyeal (2006) report on a deployment of seismometers on icebergs in Antarctica recording a variety of ice-induced (cryogenic) signals (MacAyeal et al. 2009). We deployed seismic arrays on drifting sea ice during four expeditions in 2001, 2007, 2008, and 2009, recording local and regional earthquakes along Gakkel Ridge. In addition, the records contained many sorts of cryogenic signals (“icequakes”) stemming possibly from collisions between ice floes, crack formation, or disintegration of ice floes …

Ice sheet advance, dynamics, and decay configurations: evidence from west central Scotland

A 3700-km 2 area adjacent to the Firth of Clyde, Scotland, is examined to constrain the development and dynamics of the western central sector of the last British and Irish Ice Sheet. Results from geomorphological mapping, lithostratigraphic investigations, three-dimensional geological modelling and field observations are combined to produce an empirically constrained, five-stage conceptual model of ice sheet evolution. (A) Previously published dates on interstadial organic deposits and mammalian fossils suggest that the Main Late Devensian (MLD) (MIS 2) glaciation of central Scotland began after 35 ka cal BP. During build-up, ice advanced from the western Scottish Highlands into the Clyde and Ayrshire basins. Glaciomarine muds and shelly deposits scavenged from the Firth of Clyde were redeposited widely as shelly tills and glacial rafts. Ice advance against reverse slopes generated, and subsequently overtopped, ice-marginal sediment accumulations. We hypothesise that some of these formed pre-cursor ridges which were moulded into suites of ribbed moraine during the glacial cycle. (B) Sustained stadial conditions at the Last Glacial Maximum (LGM) (c 30–25 ka cal BP) resulted in development of a major dispersal centre over the Firth of Clyde and Southern Uplands. This dispersal centre locally preserved previously formed subglacial bedforms, and fed a wide corridor of fast-flowing ice east towards the Firth of Forth. (C) Initial deglaciation promoted a substantial re-configuration of the ice surface, with enhanced westward drawdown into the outer Firth of Clyde and eastward migration of an ice divide towards the Clyde-Forth watershed. (D) Renewed ice sheet thickening over the Firth of Clyde may have accompanied growth of the Irish Ice Sheet during the Killard Point Stadial (c 17.1–15.2 ka cal BP); it was associated with limited bed modification. Subsequent ice sheet retreat was characterised by substantial meltwater production, ponding and erosion. (E) Late stages of MLD ice sheet retreat were punctuated by one or more significant ice margin oscillations. Discovery of De Geer moraines at the site of a former proglacial lake in western Ayrshire allows glacier flow at the ice margin to be approximated as ≤290 m a −1 during one such oscillation. Such velocities were probably enabled by basal sliding and shallow sediment deformation. At this stage those parts of the MLD ice sheet margin that were grounded in the Firth of Clyde were extremely vulnerable to collapse. Final disintegration of glacier ice in the Clyde basin probably occurred early in the Lateglacial Interstadial (Greenland Interstadial-1), coinciding with marine incursion to c 40 m above present day sea level.

The Holocene history of George VI Ice Shelf, Antarctic Peninsula from clast-provenance analysis of epishelf lake sediments

The Antarctic Peninsula has experienced a dramatic increase in temperature and the loss of ca. 14,000 km 2 of ice-shelf area in recent years. During this time George VI Ice Shelf (GVIIS) has remained relatively intact, but it is now reaching its theoretical limit of viability. Epishelf lakes, formed when ice shelves dam the mouths of marine embayments, accumulate sediments that can be used to constrain past ice-shelf behaviour. They are stratified water bodies with an upper layer of fresh meltwater overlying a marine layer of water. Multi-proxy analysis of a sediment core from Moutonnée Lake, an epishelf lake dammed by GVIIS on the east coast of Alexander Island, has recently shown that it retreated to at least the Ablation Point area in the early Holocene, ca. 9600–7500 years BP, demonstrating its vulnerability to periods of atmospheric and oceanic warmth. This study tests this interpretation of ice-shelf collapse through detailed analyses of granulometric, geochemical and Sr and Nd isotope provenance data for > 8 mm clasts from the same cores. Clast data from Moutonnée Lake were compared with geological reference data from two further lakes on Alexander Island (Ablation Lake and Citadel Bastion Lake) and an extensive archive of rocks and isotope-geochemical provenance data from the Antarctic Peninsula region. Underpinning this provenance analysis is the contrast between the plutonic/igneous outcrops in Palmer Land on the western side and the predominantly sedimentary strata of Alexander Island on the eastern side of George VI Sound, and the different patterns in their deposition that would be expected at Moutonnée Lake during periods of ice-shelf presence and absence. Results show that changes in clast distribution and provenance reflect the early Holocene retreat and reformation of George VI Ice Shelf at Moutonnée Lake. The period of ice-shelf retreat was marked by the onset of marine conditions in the basin followed by a rapidly deposited zone of clasts whose provenance, distribution, varied lithology and larger than average clast size are indicative of a period of lake ice disintegration and ice-rafted debris deposition between ca. 9600–8450 years BP. Igneous clasts in the ice-rafted debris have a close affinity with the plutonic provinces of western Palmer Land suggesting transport to the site by icebergs or recycling through Alexander Island strata/moraines. When epishelf lake conditions returned after ca. 7500 years BP, the clasts were smaller, the number of lithologies more limited and the assemblage dominated by olive-green vitric tuff and pale-green rhyolitic clasts that isotope data link to Early Cretaceous volcanic activity in Palmer Land. Their dominance in the upper part of the core most likely relates to increased erosion of Palmer Land ash/tuffs from volcanic outcrops on the floor of Moutonnée Valley and implies a downturn in climate after ca. 7500 years BP and the reformation of George VI Ice Shelf.

Structurally-controlled fluvioglacial erosion features near Schefferville, Québec

The coincidence as to location of a late-Wisconsin ice disintegration centre, with an earlier ice dispersal centre, some 30 miles north-west of Schefferville, Québec, resulted in large scale englacial meltwater flow from north-north-west to south-south-east across the Schefferville area. The direction of flow was controlled by the englacial hydraulic gradient, controlled in turn by the ice surface gradient. The Schefferville area is underlain by Proterozoic metasediments, exhibiting a series of parallel folds and thrust-faults aligned NW-SE ; this structure is reflected in the marked parallelism of the ridges and valleys. When the englacial meltwater streams were let down on to this substrate, structurally controlled alignment of the meltwater channels resulted. Generally, this has resulted in remarkably straight channels aligned along the strike or along faults. In the Houston Mountain area, however, steeply pitching anticlinos in slates oroduced a striking series of subglacial arcuate channels. At several points in the Schefferville area, subglacial meltwater flow down a hillside at right angles to the strike, and in the opposite direction to the dip, in zones of steeply dipping, well-bedded sediments, has produced the features referred to in literature as vallons, and earlier explained as being largely periglacial in origin. These are a special type of structurally controlled subglacial chute, in which there has been only slight periglacial modification of the original fluvioglacial form.

La déglaciation de la région de Rimouski, Bas-Saint-Laurent (Québec) : indices d’une récurrence glaciaire dans la Mer de Goldthwait entre 12 400 et 12 000 BP

La distribution des dépôts de marge glaciaire de la région de Rimouski a été analysée en fonction du cadre morphostructural préglaciaire, caractérisé par un relief appalachien typique dont les barres et les sillons, orientés NE-SO, sont subparallèles à la vallée du Saint-Laurent. Cette étude met en lumière l'influence déterminante du contexte morphostructural sur le mode de déglaciation, tant à l'échelle régionale que locale. L'invasion de la Mer de Goldthwait le long du Saint-Laurent, à partir de 14 000 BP, isole progressivement une calotte glaciaire régionale dans les Appalaches. Vers 13 400 BP, la marge septentrionale de la calotte appalachienne suit le tracé de la limite marine, fixée à 140 m d'altitude entre Rimouski et Luceville. Elle s'est stabilisée le long des premières grandes barres appalachiennes qui représentaient la première ligne d'ancrage de la marge glaciaire après l'invasion marine. Durant la phase de retrait qui suit, entre 13 360 et 12 700 ans BP, des masses de glace résiduelles sont abandonnées dans la vallée de ligne de faille de la Neigette et les sillons appalachiens de Saint-Fabien qui s'encombrent de formes de décrépitude (kames et kettles). Entre 12 400 BP et environ 12 000 BP, la marge glaciaire se stabilise sur le rebord du plateau de Sainte-Blandine, à moins de 13 km du littoral actuel. Cette période se signale par une récurrence glaciaire mise en évidence dans trois sites différents. Les modalités et la chronologie de la déglaciation au-delà de la limite marine ne sont pas connues.

Late Quaternary sea level change in Southern Beringia: postglacial emergence of the Western Alaska Peninsula

Postglacial sea level trends have varied dramatically across the Bering Platform because of differences in coastal and shelf geologic settings. Emergent shorelines and basal peats along the western Alaska Peninsula indicate that relative sea level has fallen since regional deglaciation occurred ca. 13,000 cal. yr BP. Age/elevation determinations on four shorelines (25 m :>10 ka, 16 m : 9.6–6 ka, 6 m : 2.1 ka, and 2–3 m : 1.8–0.6 ka) in the vicinity of Cold and Morzhovoi bays provide an estimate of the pace and timing of of sea level change since the last glacial maximum (LGM, 22–17 ka). Isostatic recovery and shoreline regression following the disintegration of continental and alpine ice has been interrupted by transgressive conditions at least twice since deglaciation. Changes in the balance between eustatic sea level rise and isostatic uplift resulted in the reactivation of marine scarps during the early to middle Holocene, but terrace cutting and a gap in the archaeological record about 2.1 ka suggest that sudden tectonic displacements also influence the record. Reconstructions of coastal paleogeography constrain the timing and distribution of regional archaeological settlement. Periods of shoreline erosion during stillstands or transgressions, and the episodic reorganization of intertidal environments that accompanies tectonic displacements, have conditioned site preservation potential and long-term adaptive strategies.

Climatic trend and the retreat and disintegration of ice shelves on the Antarctic Peninsula: an overview

Observation of the retreat and disintegration of ice shelves around the Antarctic Peninsula during the last three decades and associated changes in air temperature, measured at various meteorological stations on the Antarctic Peninsula, are reviewed. The climatically induced retreat of the northern Larsen Ice Shelf on the east coast and of the Wordie, George VI, and Wilkins ice shelves on the west coast amounted to about 10 000 km2 since the mid-1960s. A summary is presented on the recession history of the Larsen Ice Shelf and on the collapse of those sections north of Robertson Island in early 1995. The area changes were derived from images of various satellites, dating back to a late 1963 image from the recently declassified US Argon space missions. This photograph reveals a previously unknown, minor advance of the northern Larsen Ice Shelf before 1975. During the period of retreat a consistent and pronounced warming trend was observed at the stations on both east and west coasts of the Antarctic Peninsula, but a major cause of the fast retreat and final collapse of the northernmost sections of the Larsen Ice Shelf were several unusually warm summers. Temperature records from the nearby station Marambio show that a positive mean summer temperature was reached for the first time in 1992-93. Recent observations indicate that the process of ice shelf disintegration is proceeding further south on both sides of the Antarctic Peninsula.

Disintegration of ice under fast compressive loading

During the interaction of ice with ships or other offshore structures, a compressive zone develops in the ice. This is the focus of the present work. An interpretation of field measurements shows that the compressive ice load is far from uniform; indeed, most of the load is transmitted through small areas of intense pressure characterized by a highly damaged layer. The processes leading to the formation of these zones include fractures, and in particular spalls near the edges of the zones, as well as a separate process of damage and microstructural change within the layer itself. In order to capture the essential points for deducing design requirements, we have formulated a probabilistic model of high-pressure zones. The mechanics of failure of ice in these zones is explored. Triaxial tests have been conducted. Mechanisms discussed include microcracking (shear banding), recrystallization and grain boundary melting. As pressures increase, the microcracking and recrystallization are suppressed and the strain rates decrease. At even higher pressures, the results show pressure softening with enhanced strain rates. Two state variables are used to model the ice deformation, corresponding to the hardening at lower pressures, and to the softening at higher pressures. Finite element analyses of the ice response incorporating these variables, corresponding to a medium scale indentation test have yielded promising results, showing the decline in load and the layer formation.

The Late Wisconsinan deglacial history of the east-central Taseko Lakes area, British Columbia

Late Wisconsinan Fraser Glaciation retreat-phase deposits and landforms in the east-central Taseko Lakes area, British Columbia, are used to demonstrate a four-phase model of deglaciation. During phase I, at the onset of ice retreat, the Cordilleran Ice Sheet occupied much of the study area, blocking southward drainage of Fraser River. Phase II was marked by the deglaciation of uplands and plateaux. Meltwater drainage patterns were controlled by stagnating glaciers confined to valleys. Phase III commenced as remnant ice in the Fraser Valley downwasted to between 850 and 760 m elevation. At this time, interlobate glacial lakes formed in hanging valleys east of Fraser River. Drainage of glacial lakes occurred subglacially, and was accompanied by disintegration of remnant ice and an increase in mass movements in valleys. These events were followed by decreased sedimentation rates, reflecting lower meltwater volumes and exhaustion of unstable glacial debris during phase IV. Postglaciation valley fill was subject to fluvial degradation and terracing as modern drainage patterns became established.

Erosional origin of hummocky terrain in south-central Alberta, Canada

We propose that hummocky terrain in south-central Alberta is the product of subglacial erosion rather than supraglacial letdown during ice disintegration (a common view of hummock formation). Extensive exposures in hummocks contain sediments marking the history of Laurentide ice advance and deglaciation in the region. Regardless of the genesis of those sediments, units are abruptly truncated at the surface that represents the hummock and trough morphology, indicating that the hummocks are the product of differential erosion. Subglacial sediments predating the erosion and subglacial eskers overlying the erosion surface suggest that the erosion was also subglacial. Hummock morphology, lithostratigraphy correlated from hummock to hummock, truncation at the land surface, and widespread coarse boulder lags support a glaciofluvial origin for hummocky terrain in this region.