Search

While glacial remnants in the form of viscous flow features in the mid-latitudes of Mars are considered to be cold-based in the present-day, an increasing amount of geomorphic evidence suggests that at least some flow features were previously wet-based or had a mixed thermal state (polythermal) at during their evolution. Many of the viscous flow features known as glacier-like forms have been observed to emerge from alcoves that appear similar to cirques on Earth. Terrestrial cirques are typically characterized by a concave basin connected to a steep backwall. Cirques are expected to form from depressions in mountainsides that fill with snow/ice and over time support active glaciers that deepen the depressions by wet-based glacial erosion. To assess which alcoves on Mars are most "cirque-like", we mapped a population of ~2000 alcoves in Deuteronilus Mensae, a region in the mid-latitudes of Mars characterized by mesas encompassed by glacial remnants. Based on visual characteristics and morphometrics, we refined our dataset to 386 "cirque-like alcoves", which is five times the amount of glacier-like forms in the region, and used this to assess the past extent and style of glaciation on Mars. Using high resolution imagery, we find geomorphic evidence for glacial occupation associated with the cirque-like alcoves, including crevasse-like features, surface lineations, polygonal terrain, and moraine-like ridges. We propose that the cirque-like alcoves with icy remnants similar to rock glaciers on Earth represent a late stage of glacier-like form evolution. We also outline stages of cirque-like alcove evolution, linking a potential early stage of cirque-like alcoves to gully activity. On a population-wide scale, the cirque-like alcoves have a south to southeastward aspect bias, which may indicate a requirement for increased insolation for melting to occur and a connection to gullies on Mars. While the alcoves also have similarities to other features such as landslide scarps and amphitheater-headed valleys, the cirque-like alcoves have unique morphologies and morphometrics that differentiate their origin. Assuming warm-based erosion rates, the cirque-like alcoves have timescales consistent with both glacier-like forms and other viscous flow features like lobate debris aprons, whereas cold-based erosion rates would only allow the older timescales of lobate debris aprons. We propose that based on the geomorphic features and southward aspect, cirque-like alcove formation is more consistent with warm-based glaciation. [ABSTRACT FROM AUTHOR]

Sediments deposited by glacial meltwaters (for example, ice‐contact delta deposits) form permeable packages in the subsurface that can act as reservoirs for both water and hydrocarbons. They are also an important source of aggregate for the construction industry. As reservoirs they are challenging to characterize in terms of their structure, flow and storage properties due to their complex depositional history. In this study, ice‐contact deltas of Salpausselkä I and II end moraines in Southern Finland are studied using a combination of geomorphological mapping, sedimentological studies and near surface geophysical methods. Sedimentary logs from isolated outcrops were correlated to ground penetrating radar (GPR) profiles to unravel the internal structure and depositional history of these ice‐contact deltas. Subsequently, electrical resistivity tomography (ERT) and gravity data were analysed to estimate the depth to bedrock and to model porosity distribution within the sediments. Results of the study suggest that the delta deposits have a broad range of porosities (10 to 42%) with lowest values found in the bottomset beds. The most variable porosities are in the subaqueous ice‐contact–fan zone, and consistently high porosities occur in delta foreset/topset facies. Detailed sedimentary logging linked to the GPR data shows heterogeneities such as mud drapes on foresets and kettle holes which are below the resolution of ERT and gravity methods but significantly affect reservoir properties of the deltas. Moreover, oscillation of the ice‐margin may have introduced larger heterogeneities (for example, buried ice marginal ridges, or eskers) into the sedimentary sequence which are atypical for other Gilbert‐type deltas. Finally, subglacially sculpted, highly variable bedrock topography exerts a major control on sediment distribution within the delta making reservoir volume and quality less predictable. This work has implications for present‐day freshwater aquifers and low enthalpy geothermal energy in southern Finland and other deglaciated regions, as well as hydrocarbon exploration of analogous deposits in the subsurface from Pleistocene and pre‐Pleistocene glaciogenic sequences. [ABSTRACT FROM AUTHOR]

Glacial cirques are widely used palaeoenvironmental indicators, and are key to understanding the role of glaciers in shaping mountain topography. However, notable uncertainty persists regarding the rate and timing of cirque erosion. In order to address this uncertainty, we analyse the dimensions of 2208 cirques in Britain and Ireland and model ice accumulation to investigate the degree of coupling between glacier occupation times and cirque growth. Results indicate that during the last ~120 ka, cirques were glacier‐free for an average of 52.0 ± 21.2 ka (43 ± 18%); occupied by small (largely cirque‐confined) glaciers for 16.2 ± 9.9 ka (14 ± 8%); and occupied by large glaciers, including ice sheets, for 51.8 ± 18.6 ka (43 ± 16%). Over the entire Quaternary (i.e. 2.6 Ma), we estimate that cirques were glacier‐free for 1.1 ± 0.5 Ma; occupied by small glaciers for 0.3 ± 0.2 Ma; and occupied by large glaciers for 1.1 ± 0.4 Ma. Comparing occupation times to cirque depths, and calculating required erosion rates, reveals that continuous cirque growth during glacier occupation is unlikely. Instead, we propose that cirques attained much of their size during the first occupation of a non‐glacially sculpted landscape (perhaps during the timeframe of a single glacial cycle). During subsequent glacier occupations, cirque growth may have slowed considerably, with the highest rates of subglacial erosion focused during periods of marginal (small glacier) glaciation. We propose comparatively slow rates of growth following initial cirque development because a 'least resistance' shape is formed, and as cirques deepen, sediment becomes trapped subglacially, partly protecting the bedrock from subsequent erosion. In support of the idea of rapid cirque growth, we present evidence from northern British Columbia, where cirques of comparable size to those in Britain and Ireland developed in less than 140 ka. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Drumlins are subglacial bedforms streamlined in the direction of ice flow. Common in deglaciated landscapes, they have been widely studied providing rich information on their internal geology, size, shape, and spacing. In contrast with bedform investigations elsewhere in geomorphology (aeolian and fluvial dunes and ripples for example) most drumlin studies derive observations from relict, and thus static features. This has made it difficult to gain information and insights about their evolution over time, which likely hampers our understanding of the process(es) of drumlin formation. Here we take a morphological approach, studying drumlin size and spacing metrics. Unlike previous studies which have focussed on databases derived from entire ice sheet beds, we adopt a space‐for‐time substitution approach using individual drumlin flow‐sets distributed in space as proxies for different development times/periods. Framed and assisted by insights from aeolian and fluvial geomorphology, we use our metric data to explore possible scenarios of drumlin growth, evolution and interaction. We study the metrics of the size and spacing of 36 222 drumlins, distributed amongst 71 flow‐sets, left behind by the former British‐Irish Ice Sheet, and ask whether behaviour common to other bedform phenomena can be derived through statistical analysis. Through characterizing and analysing the shape of the probability distribution functions of size and spacing metrics for each flow‐set we argue that drumlins grow, and potentially migrate, as they evolve leading to pattern coarsening. Furthermore, our findings add support to the notion that no upper limit to drumlin size exists, and to the idea that perpetual coarsening could occur if given sufficient time. We propose that the framework of process and patterning commonly applied to non‐glacial bedforms is potentially powerful for understanding drumlin formation and for deciphering glacial landscapes. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Ice‐sheets flowing over soft sediments produce undulations in the bed, typically of metres in relief, of which drumlins are the most abundant and widely investigated. Consensus regarding their mechanism of formation has yet to be achieved. In this paper we examine the spatial organization of drumlins in order to provide an improved description of the phenomenon and to guide hypotheses of their formation. We review the literature highlighting contradictory findings regarding drumlin spatial organization and then use this to motivate our study based on a large sample (42 488) of drumlins from Canada, Britain and Norway. Are there typical arrangements in drumlin positioning and are they organized in a regular spatial manner (patterned) or are they distributed randomly? We recognize that drumlin fields are inherently patchy and therefore apply inhomogeneous spatial statistics in order to study their distribution. This shows that whilst drumlins are occasionally randomly placed, their main state is non‐ random. They exhibit a strong and statistically significant signal of regularity across lengths scales of 100 to 1200 m. We conclude that patterning is a near ubiquitous property of drumlins. This finding of regularity demonstrates spatial self‐organization in the bedforming process with drumlins as an emergent manifestation of sub‐glacial sediment mobility. Kilometre‐scale interactions between drumlins must occur as they evolve, or interactions may arise as a consequence of growth or migration. Hypotheses or models are required that can explain the regular spacing of drumlins. We highlight three suggestions for such self‐organization: instability in the coupling of ice flow–sediment flux–bed shape; local feedback between sediment mobility and relief; and coarsening by growth or migration. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Investigation of drumlins is significant to both glaciology and palaeoglaciology but the sheer diversity of their composition and internal structure is often cited as a major obstacle towards a satisfactory (unifying?) explanation of their formation. This paper presents the first systematic survey of the vast literature on this subject, with the aim of concisely summarising observations and identifying any emergent patterns or commonality that theories of drumlin formation should be able to explain. Results confirm that investigations are often limited by availability of suitable sediment exposures (40% of studies report data from <5 drumlins and 44% do not specify sample size), although borehole data and geophysical techniques can alleviate this problem. However, it is clear that the constituents of drumlins are incredibly diverse in terms of their composition (e.g. a range of lithologies, clast shapes, sizes and fabrics); structure (e.g. sediments that are sorted, homogeneous, surface conformable, unconformable); and evidence of deformation (e.g. ranging from pervasive, to non-pervasive/limited, to absent). Despite this diversity, our review leads us to suggest that drumlin composition can be simplified to five basic types: (i), mainly bedrock, (ii), part bedrock/part till; (iii), mainly till; (iv), part till/part sorted sediments; and (v), mainly sorted sediments. This is a potentially significant step, in that it reduces the oft-cited complexity of drumlin composition and provides a more realistic goal for theories or numerical models of drumlin formation to target. The various types can occur within the same drumlin field, which leaves us with two possible implications for drumlin formation. (1) Different types of drumlin are formed/seeded by different processes, despite being morphologically similar (equifinality?) — investigation of drumlin composition may, therefore, reveal diagnostic processes/explanations for these different types of drumlin and we argue that bedrock ‘drumlins’ are an example. (2) A single process occurs across large parts of the ice-bed interface to create drumlinised terrain in a variety of sediments — investigation of drumlin composition may, in this case, simply reflect pre-existing sediments but, importantly, the way in which the drumlin-forming mechanism modifies/is modified by them. We argue that the latter, simpler, explanation applies to all other types of drumlin (excluding purely bedrock forms) and conclude that the diversity in drumlin composition is no obstacle to a single unifying theory. [Copyright &y& Elsevier]

The literature on drumlins is pervaded by the notion that their longitudinal profile is usually highly asymmetric with a stoss steeper end and a lee gentler end, and that this can be used to infer the palaeo ice flow direction. The idea is built up in many papers covering more than a century of research. However, most of the early published papers were qualitative in nature and more recent quantitative papers appear to challenge the ubiquity of the classical stoss-lee shape. Here the shape of the drumlin longitudinal profile of 29,238 drumlins in the British Isles has been analysed. Drumlins were grouped into flowsets for which a palaeo ice flow direction was inferred independently of the drumlin shape. Given such ice flow directions it was then possible to identify the upflow and downflow ends of each drumlin and to trace and extract its longitudinal profile. Results indicate that the highest point of the drumlin is usually found around half way along the profile. The mean slope angles at the stoss and lee ends were found to be very similar. Finally, the average profile built from all mapped drumlins appears almost symmetric. In conclusion, drumlin longitudinal profile is far from being the classically asymmetric shape widely reported in text-book descriptions. Drumlins are mostly symmetrical in shape with a very slight tendency towards the classical shape. Highly asymmetric drumlins do exist but are rare and with an almost equal numbers of drumlins that are the reverse of this. These findings are verified both at the entire population level and the flowset level. This demonstrates that the idealized stoss-lee shape of classically-asymmetric drumlins is not representative of the population and should be replaced with that of mostly symmetric bumps. Drumlin shape is not a good indicator of the palaeo ice flow direction. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The availability of a bathymetric database that covers about 80% of the Icelandic shelf has made it possible to produce a geomorphological map of the glacial landforms. The digital elevation model of the bathymetry was analyzed as a series of shaded relief images. Trough edges, bulging trough mouths, moraines, eskers, melt water channels, streamlined bedrock and streamlined drift, mostly hitherto unmapped, distributed all around the island have been identified. Moraines are found on the shelf, within troughs and inside fjords. Streamlined landforms are always confined to the bottom of troughs. Troughs appear to have been cut by ice streams draining an ice sheet that likely covered the entire shelf. At the shelf break, most troughs terminate with contours that bulge in a convex-outwards fashion. This suggests that an ice stream eroded, transported and finally deposited large amounts of sediment at the trough mouth. Overall, the glacial morphology of the shelf highlights a radial pattern that indicates a main ice divide near the centre of Iceland. [ABSTRACT FROM AUTHOR]

Four boulder samples from the Piano del Praiet frontal moraine in the Gesso della Barra Valley (Maritime Alps) have been 10Be dated. The results give a weighted mean age of 11 340±370 (870) yr, constraining the frontal moraine to the Egesen glacial stadial, during the Younger Dryas cold phase. By applying the same 10Be production rate to other Egesen moraines previously dated in the Alps, we obtain similar ages for all of them. This suggests a synchroneity of the Egesen deglaciation in the European Alps at the end of the Younger Dryas. From the palaeoshape of the Egesen glacier, reconstructed by means of geomorphological mapping, an Equilibrium Line Altitude depression (δELA) of −520 to −530 m, with respect to the present-day ELA, and of −260 to −320 m, with respect to the Little Ice Age ELA, has been calculated. Comparison with other Alpine sector δELAs indicates that the Maritime Alps experienced humid climatic conditions during the Younger Dryas. [ABSTRACT FROM AUTHOR]

Marine-based ice streams are responsible for a significant proportion of the ice mass loss from the present-day Greenland Ice Sheet, East Antarctic Ice Sheet (EAIS) and West Antarctic Ice Sheet (WAIS) but the processes controlling their initiation, evolution and shutdown remain elusive, hindering our understanding of how existing ice masses will respond to predicted future warming. The exposed beds of palaeo-ice streams offer a unique opportunity to study subglacial processes, which are largely inaccessible in contemporary settings. We use high resolution multibeam swath bathymetry data from the Barents Sea to map the geomorphology of a palaeo-ice stream bed, located in Olgastretet (Olga Trough), approximately 75 km southeast of Kong Karls Land and 200 km east of central Svalbard. This reveals evidence for shut down of a marine-based ice stream, followed by a phase of passive retreat or lift-off of the ice stream facilitating preservation of crevasse-squeeze ridges (CSRs). Subsequently, active retreat of the ice margin was re-established and is marked by recessional moraine ridges located upstream of the CSRs. Previously, CSRs have been mainly associated with surging land-terminating ice margins, however our work adds to recent observations of CSRs on the beds of marine-based ice streams, implying that they may be more common than previously thought. It also indicates that marine-based ice streams may switch on- and off in a surge-like manner which has important implications for our understanding of ice stream life cycles and the modelling of ice sheets. • Preservation of crevasse-squeeze ridges on the seabed, under an ice stream only possible following an ice stream shutdown. • Ice stagnated and either deglaciated passively or lifted-off of the seabed (or a combination thereof). • Renewed active retreat of the ice margin is recorded by recessional, saw-toot moraines up-flow. • Direct, geomorphological evidence for surge-stagnation-reactivation cycles of a marine ice stream. • Presence of an extensive ice shelf/ice melange can be a possible explanation for marine ice stream shut down. [ABSTRACT FROM AUTHOR]

• The Monte Cavallo hosted an isolated glacial system (ca. 37 km2) during the LGM. • LGM ELAs in the south-eastern Alps were between 1100 and 1700 m. • Reconstructed palaeoprecipitation is similar to the modern-day climate. • Mediterranean moisture advection was key for glacier development. • Lake sediments in the Caltea Valley relate to a pre-LGM interstadial (>45 ka BP) Glacier-based reconstructions of Equilibrium Line Altitudes (ELAs) are important to understand changes of temperature and precipitation over longer time scales and may help to validate regional palaeoclimate models. Here, we present new insights into the ELA in the south-eastern part of the European Alps during the Last Glacial Maximum (LGM, 26.5 to 19 ka), based on the geomorphological record of the Monte Cavallo Group (Venetian Prealps, NE-Italy). This mountain range hosted a glacial system that remained isolated from larger valley glaciers in its vicinity and therefore likely responded very dynamically to changes in climatic boundary conditions. Through detailed mapping of glacial sediments and landforms, we were able to constrain the extent of these palaeoglaciers and model their surface geometry and ELA via semi-automated toolboxes in a geographic information system. In the absence of numerical datings, these landforms were related to an LGM advance through geomorphological and stratigraphical means. In a next step, ELAs were also recalculated for other LGM glaciers in the south-eastern Alps, allowing wider palaeoclimatic conclusions to be drawn. These ELAs are in the range of 1100 to almost 1700 m and show a strong E-W gradient with particular low values in the Julian and eastern Carnic Prealps. This pattern indicates that during the LGM a precipitation gradient existed along the south-eastern fringe of the Alps, with moisture being preferentially advected to these mountain ranges while the Venetian Prealps in the West received less precipitation. Based on the reconstructed ELAs, annual precipitation sums during the regional LGM glacier culmination (ca. 25.5 to 23.5 ka) are estimated between 1820 and 2920 ± 750 mm/yr. Those values are largely compatible with data from modern weather stations and indicate no or little reduction in LGM precipitation as it is reported from other parts of the Alps. [ABSTRACT FROM AUTHOR]

Glacier reconstructions are widely used in palaeoclimatic studies and this paper presents a new semi-automated method for generating glacier reconstructions: GlaRe, is a toolbox coded in Python and operating in ArcGIS. This toolbox provides tools to generate the ice thickness from the bed topography along a palaeoglacier flowline applying the standard flow law for ice, and generates the 3D surface of the palaeoglacier using multiple interpolation methods. The toolbox performance has been evaluated using two extant glaciers, an icefield and a cirque/valley glacier from which the subglacial topography is known, using the basic reconstruction routine in GlaRe. Results in terms of ice surface, ice extent and equilibrium line altitude show excellent agreement that confirms the robustness of this procedure in the reconstruction of palaeoglaciers from glacial landforms such as frontal moraines. [ABSTRACT FROM AUTHOR]

Glaciogenic sediments are present in many hydrocarbon-producing basins across the globe but their complex nature makes it difficult to characterise the reservoir-quality sedimentary units. Despite this, Ordovician glacial deposits in North Africa, and Carboniferous-Permian glaciogenic sequences in the Middle East, have been proven to host significant, economical, hydrocarbon accumulations. Additionally, discoveries have been made in the shallow (<1000 m below seabed), glacial, Pleistocene sedimentary succession of the North Sea (e.g. Peon and Aviat). This paper provides a predictive exploration framework in the form of a conceptual model of glaciogenic sediment-landform distributions. The model is based on the extensive onshore glacial sedimentary record integrated with available offshore data. It synthesises the published knowledge, drawing heavily on glacial landsystem models, glacial geomorphology and sedimentology of glaciogenic deposits to provide a novel conceptual model allowing for the efficient description and interpretation of glacial sediments and landforms in the subsurface. Subsequently, land-terminating and water-terminating ice sheet depositional systems are described and discussed, with respect to ice advance and retreat cycles. This detailed description focuses on the macro-scale stratigraphic organisation of glacial sediments with relation to the ice margin, aiding the prediction of glaciogenic sediment distributions, and their likely geometry, architecture and connectivity as reservoirs. • A novel conceptual model for the distribution of glaciogenic reservoirs. • First-pass interpretation tool for complex glaciogenic sequences. • Ice margin position controlling reservoir quality. • Identification of landforms and sediments crucial to reservoir predictability. [ABSTRACT FROM AUTHOR]

Two large "moraine" ridges (Salpausselka I and Salpausselka II), extending to over 600 km in length, delineate two major stillstand/readvance positions of the Fennoscandian ice sheet during the last deglaciation, inferred to be chronologically related to the cool climate event known as the Younger Dryas (age). During this time the Baltic ice lobe and the Finnish Lake District ice lobe, constituting a part of the southern marigin of the Fennoscandian ice sheet, were grounded in a large proglacial lake, the Baltic ice lake, a predecessor to the modern-day Baltic Sea. Most of the sediments were delivered to the ice margin by meltwater and deposited in the form of ice-contact deltas, over a very short period (230 and 250 years respectively for Salpausselka I and II). As a result, the "moraine" ridge is mostly composed of glaciofluvial sands, gravels and boulders rather than diamicton which is more typical of moraine sedimentology. In this study, high resolution LIDAR data (2m horizontal, 0.3m vertical), provided courtesy of the National Land Survey of Finland and processed by the Geological Survey of Finland, ground penetrating radar profiles and outcrops were analyzed and interpreted. These provide a record of rapid sedimentation from high-magnitude meltwater discharge, through subglacial channels, resulting in rapid buildup of ice contact fans to the water surface and subsequent progradation of deltaic forests. Renewed retreat of the ice margin lead to abandonment of the Salpausselka I and deposition of the Salpausselka II ridge, 25 km to the north. In the Lahti region, where the two ice lobes were confluent, the largest deltaic complex developed. Sediments of Salpausselkas in Finland are a world class example of a sedimentary environment which records, with great detail, the processes of the formation of ice-contact, Gilbert-type, deltas marking stillstand positions of the southern margin of the Fennoscandian Ice Sheet during the Younger Dryas. [ABSTRACT FROM AUTHOR]

A glacial geomorphological analysis of three valleys on Mt. Mavrovouni (North Pindus Mountains, Greece) is presented alongside a pilot study using cosmogenic 36Cl to obtain surface exposure ages from iron-rich ophiolite glacial and periglacial boulders. At least three distinct morphostratigraphic units of glacial (moraines) and periglacial (relict pronival ramparts) origin have been identified. Four 36Cl surface exposure ages were obtained from the stratigraphically youngest glacial and periglacial deposits. Although this limited dataset with relatively large uncertainties cannot support a robust geochronology, the ages are consistent with the 36Cl-based chronologies of limestone-derived moraines on Mt. Tymphi (NW Greece) and Mt. Chelmos (S Greece), confirming that the last glaciers on this massif formed during the Last Glacial Maximum as also indicated by other studies in the Pindus mountains. At the same time it provides confidence in the suitability of 36Cl dating for iron-rich samples, such as ophiolites, using an updated 36Cl model that incorporates improved production rates for iron spallation. The presented preliminary chronology of moraines and pronival ramparts is based on those ages as well as on local and regional morphostratigraphic correlations. The stabilisation of the most extensive Late Pleistocene glaciers took place during the Last Glacial Maximum, at 27.0 ± 6.5 ka whereas the presence of pronival ramparts dated at 20.2 ± 4.8 ka suggests persisting cold and arid conditions. Older, still undated glacial deposits exist lower in the valleys which can be attributed to the Middle Pleistocene major glaciation phases (MIS 12/MIS 6), based on their relative morphostratigraphic position within the glacial sedimentary sequence. • Benefits of ophiolite for dating glacial landforms compared with limestone • Pilot study of 36Cl surface exposure dating on ophiolites with high iron content • Preliminary glacial chronology using 36Cl ages and morphostratigraphic correlations • Two distinct glaciations ascribed to the Late and Middle Pleistocene respectively. • Last glaciation on Mt. Mavrovouni in NW Greece occurred around the global LGM. [ABSTRACT FROM AUTHOR]

Mapping of glacial landforms has long been a cornerstone of glacial geomorphology, but it was not until the advent of remote sensing and GIS that widespread detailed mapping could be achieved. Using the examples of subglacial bedforms and the BRITICE project, I highlight how large databases of glacial geomorphological mapping can be used to: i) understand landform genesis; ii) reconstruct palaeo-ice sheets; and iii) validate ice sheet models. Arguably, glacial geomorphology has never been more useful. However, there is still room for improvement. Automated mapping techniques remain in their infancy. Yet, detailed remote sensing data at continental scales is becoming available, the scale of which is a daunting challenge for lone-manual mapping. Could machine learning hold an answer? Furthermore, completed work is often disparately stored and non-standardised. This leads to duplication of research and limits the utility of the collected datasets for future researchers. Here, I call upon the glacial geomorphological community to launch an open-access database of glacial geomorphological mapping on a global scale. [ABSTRACT FROM AUTHOR]