Periglacial Landforms Research Articles

Chapter 3 Geomorphological framework: glacial and periglacial sediments, structures and landforms

Abstract The development of the conceptual ground model (CGM) is a critical component of any desk study or ground engineering project planning process. A key task of the engineering geologist is to develop the CGM in order to predict the occurrence of known terrain units, elements and facets within a given landsystem, and to communicate the lateral and vertical variability of engineering rocks and soils found within that system. This chapter details the significant ground components of glacial and periglacial landsystems within a geomorphological framework describing the sediments, structures and landforms that could reasonably be expected to be encountered in these terrains. Examples are provided of both modern and relict glacial and periglacial landforms, their mode of formation and their field recognition. Glaciogenic and periglacial sediments are described both in terms of their sedimentological and formal engineering description. The chapter provides a suggested naming nomenclature for these sediments that can be used within a BS 5930 description. An extensive photoglossary is presented as a field aide memoir, enabling the engineering geologist to identify these features once on site.

Chapter 5 Periglacial and permafrost ground models for Great Britain

Abstract Periglacial environments are characterized by cold-climate non-glacial conditions and ground freezing. The coldest periglacial environments in Pleistocene Britain were underlain by permafrost (ground that remains at or below 0°C for two years or more), while many glaciated areas experienced paraglacial modification as the landscape adjusted to non-glacial conditions. The growth and melt of ground ice, supplemented by temperature-induced ground deformation, leads to periglacial disturbance and drives the periglacial debris system. Ice segregation can fracture porous bedrock and sediment, and produce an ice-rich brecciated layer in the upper metres of permafrost. This layer is vulnerable to melting and thaw consolidation, which can release debris into the active layer and, in undrained conditions, result in elevated porewater pressures and sediment deformation. Thus, an important difference arises between ground that is frost-susceptible, and hence prone to ice segregation, and ground that is not. Mass-movement, fluvial and aeolian processes operating under periglacial conditions have also contributed to reworking sediment under cold-climate conditions and the evolution of periglacial landscapes. A fundamental distinction exists between lowland landscapes, which have evolved under periglacial conditions throughout much of the Quaternary, and upland periglacial landscapes, which have largely evolved over the past c. 19 ka following retreat and downwastage of the last British–Irish Ice Sheet. Periglacial landsystems provide a conceptual framework to interpret the imprint of periglacial processes on the British landscape, and to predict the engineering properties of the ground. Landsystems are distinguished according to topography, relief and the presence or absence of a sediment mantle. Four landsystems characterize both lowland and upland periglacial terrains: plateau landsystems, sediment-mantled hillslope landsystems, rock-slope landsystems, and slope-foot landsystems. Two additional landsystems are also identified in lowland terrains, where thick sequences of periglacial deposits are common: valley landsystems and buried landsystems. Finally, submerged landsystems (which may contain more than one of the above) exist on the continental shelf offshore of Great Britain. Individual landsystems contain a rich variety of periglacial, permafrost and paraglacial landforms, sediments and sedimentary structures. Key periglacial lowland landsystems are summarized using ground models for limestone plateau-clay-vale terrain and caprock-mudstone valley terrain. Upland periglacial landsystems are synthesized through ground models of relict and active periglacial landforms, supplemented by maps of upland periglacial features developed on bedrock of differing lithology.

Progress in Understanding the Dynamics, Internal Structure and Palaeoenvironmental Potential of Ice Wedges and Sand Wedges

AbstractA review of recent progress in understanding the dynamics, internal structure and palaeoenvironmental potential of ice wedges and sand wedges is presented, based on literature published between 2008 and 2015. Ice wedges constitute the most ice‐rich and widespread periglacial landform in permafrost lowlands. Thus, progress in understanding the processes associated with them, using a large variety of direct and indirect field and remote sensing methods, is important, particularly in a changing climate with increased potential for ice‐wedge degradation. Ice‐wedge polygons have been found to control microclimate, hydrology and greenhouse gas fluxes from permafrost. New technologies have allowed the identification of more fossil polygons, increasing their role in reconstructing periglacial conditions. Study of ice‐wedge casts, sand wedges and ice wedges has improved palaeoenvironmental reconstruction, particularly from the last glacial period and the Holocene, of changes to these landforms in both present and former permafrost areas. Polygons on Mars have recently attracted considerable attention, primarily due to increased remote sensing capabilities and even on‐site investigations, which identify ice in these landforms. Copyright © 2016 John Wiley & Sons, Ltd.

Surface dynamic of a protalus lobe in the temperate high mountain. Western Maladeta, Pyrenees

The Maladeta protalus lobe is located in the Maladetas massif (Central Pyrenees). A detailed geomorphologic map, RTK-GPS techniques, bottom temperature of the winter snowcover (BTS) technique and datalogger to monitor the ground thermal regime were used to reveal the present-day activity of the protalus lobe and its location in a mountain permafrost environment. Systematic monitoring using differential GPS at eight fixed points throughout the surface of the protalus lobe shows vertical and horizontal displacements during the field surveys of 2008, 2009, 2010, 2011, 2012 and 2013. The recorded dynamic defines a periglacial landform with low activity and rapid interannual variations in a thermal imbalance state. The location of protalus lobe in marginal periglacial environments of the temperate high mountain makes it an effective morphoclimatic geoindicator.

Geomorphology and landforms distribution in selected ice-free areas in the South Shetland Islands, Antarctic Northern Peninsula region

Ice-free areas cover a small percentage of the land in the South Shetland Islands. However, they are significant as they contain ecosystems highly sensitive to environmental changes and are located within a region affected by global warming. These areas are dominated by periglacial, glacial, fluvial, and coastal processes and landforms, where permafrost is often present. Soil development is observed although vegetation cover is sparse and closely related to the geomorphology. The mapping and monitoring of ice-free areas is important as they are highly sensitive to climate change. The objective of this study was to characterize and map surface landforms in ice-free areas using traditional mapping methods as well as advanced remote sensing techniques. Geomorphological and topographical maps were initially obtained through field measurements and observations, and complemented with existing aerial photography at scales between 1:2000 and 1:25000. Thereafter, satellite-borne data became available and were included in the methodology to further determine the distribution of the landforms. In the Antarctic environment, Synthetic Aperture Radar (SAR) provides the most reliable images as data can be obtained in any weather conditions as well as during the day and night. Fully polarimetric SAR RADARSAT-2 were used to determine seven different terrain classes representing surface landforms in ice-free areas around Maxwell Bay (King George Island). The SAR remote sensing techniques were successfully applied to identify different periglacial, fluvial, glacial, coastal, as well as lithological landforms. Field data from Fildes Peninsula were used to train a supervised classifier to map further areas around Maxwell Bay. In this case, the ice-free areas around Maxwell Bay clearly show the dominance of periglacial landforms and processes. Therefore, these techniques can be used to compare past and future results and to monitor areas affected by changing environmental factors and increasing human activities.

THE GEOMORPHOLOGIC FEATURES OF INTRUSIVE MAGMATIC STRUCTURES FROM BÂRGĂU MOUNTAINS (EASTERN CARPATHIANS, ROMANIA)

Igneous intrusive structures from Bârgau Mountains belong to the group of central Neogene volcanic chain of the Eastern Carpathians of Romania. The evolution of the relief developed on these structures are three main stages: the stage of injection of structures (Pannonian), the stage of uncovering of igneous intrusive bodies from Oligo-Miocene sedimentary cover (Pliocene), and the stage of subaerial modeling of magmatic bodies (Pliocene-current).In those circumstances, the geodiversity of intrusive magmatic structures from Bârgau Mountains is represented by several types of landforms such as: polycyclic landforms (erosional levels), structural landforms (the configuration of igneous intrusive structures), petrographic landforms (andesites, lithological contact), fluvial landforms (valleys, slopes, ridges), periglacial landforms (cryogenic and crionival landforms), biogenic and anthropogenic landforms. This study highlights certain features of the landforms modeled on igneous intrusive bodies with the aim of developing some strategy for tourism recovery by local and county authorities.

Evidence of paraglacial and paraperiglacial crisis in Alpine sediment transfer since the last glaciation (Ticino, Switzerland)

The “paraglacial” and “paraperiglacial” concepts were introduced in the second half of 20th Century for describe processes, landforms and deposits directly conditioned by deglaciation (paraglacial), respectively by permafrost degradation (paraperiglacial). They represents theoretical models describing the transition from glacial to periglacial, or more generally non glacial conditions (paraglacial model), and from periglacial to temperate conditions (paraperiglacial model). Evidences of sediment transfer conditioned by these processes were described in particular in the Arctic and Subarctic domains. These evidences are less generalised in the Alps and they consider rarely both concepts, integrating periglacial landforms and deposits in source to sink sediment transfer in a single catchment. Here we present evidences of para(peri)glacial sedimentary crises by quantifying sediment transfer from the periglacial zone to the delta in Lake Maggiore for the Ticino River catchment (southern Swiss Alps). Compilation and revision of chronological data, the assessment of sedimentation rates in the Ticino Valley, of progradation rates of the Ticino River delta and of rockwall erosion rates in the periglacial zone, allowed empirical models of sediment transfer to be produced. These models highlights significant high sedimentation rates in the valley floor during the beginning of the deglaciation, and significant rates of rockwall erosion during periods of intense temperature warming and intense permafrost degradation (such as at the beginning of Bølling and during the Preboreal), showing a very good correspondence with paraglacial and paraperiglacial theoretical models. Sediment transfer evolution during the entire Lateglacial and the first half of Holocene in the southern Swiss Alps may then be explained by a combination of a paraglacial erosion phase related to the deglaciation and of two paraperiglacial erosion phases related with significant periods of temperature warming during the Bølling/Allerød and the first part of the Holocene.

Amazonian-aged fluvial system and associated ice-related features in Terra Cimmeria, Mars

The Martian climate throughout the Amazonian is widely believed to have been cold and hyper-arid, very similar to the current conditions. However, ubiquitous evidence of aqueous and glacial activity has been recently reported, including channels that can be tens to hundreds of kilometres long, alluvial and fluvial deposits, ice-rich mantles, and glacial and periglacial landforms. Here we study a ∼340km-long fluvial system located in the Terra Cimmeria region, in the southern mid-latitudes of Mars. The fluvial system is composed of an upstream catchment system with narrow glaciofluvial valleys and remnants of ice-rich deposits. We observe depositional features including fan-shaped deposits, and erosional features such as scour marks and streamlined islands. At the downstream section of this fluvial system is an outflow channel named Kārūn Valles, which displays a unique braided alluvial fan and terminates on the floor of the Ariadnes Colles basin. Our observations point to surface runoff of ice/snow melt as the water source for this fluvial activity. According to our crater size–frequency distribution analysis the entire fluvial system formed during early to middle Amazonian, between ∼1.8−0.2+0.2Ga to 510−40+40Ma. Hydraulic modelling indicates that the Kārūn Valles and consequently the alluvial fan formation took place in geologically short-term event(s). We conclude that liquid water was present in Terra Cimmeria during the early to middle Amazonian, and that Mars during that time may have undergone several episodic glacial-related events.

Relative Paleoenvironmental Adjustments Following Deglaciation of the Byers Peninsula (Livingston Island, Antarctica)

ABSTRACTIn the present context of fast warming in the Antarctic Peninsula (AP), understanding past and recent environmental dynamics is crucial to better assess future environmental responses in this region. Very detailed geomorphological maps can help to interpret the interaction between glacial, periglacial, and paraglacial systems. The Holocene environmental sequence on Byers Peninsula, an ice-free area in the westernmost part of Livingston Island (Maritime Antarctica), is still poorly understood. This paper focuses on the geomorphology of the Cerro Negro, a volcanic plug located on the southeast fringe of this peninsula. The distribution of landforms and deposits generated by different geomorphological processes provides insights into the Holocene environmental dynamics on Byers Peninsula. During the fieldwork campaign in January 2014, an accurate geomorphological map of Cerro Negro and its surroundings was generated. Four geomorphological environments were identified: hill, north slope, southern escarpment, and marine terraces and present-day beach. Periglacial landforms are abundant, especially patterned ground features (blockstreams, sorted stone circles, stone stripes). All these cryoturbation landforms, except blockstreams, are active under present-day climate conditions. In addition to a sequence of Holocene marine terraces and slope deposits, such as talus cones and rockfalls, there is a glacial moraine adjoining the northern slope of the hill. From the morphostratigraphic correlation between the active and inactive landforms, we infer three main phases describing the paleoenvironmental evolution in this area: (1) maximum glacial expansion; (2) Holocene glacial retreat, lake formation, and intense periglacial dynamics; and (3) deglaciation of the Byers Peninsula and widespread periglacial processes. The Cerro Negro has been a nunatak for most of the Holocene; the lake located near the summit of this hill appeared when most of the Byers Peninsula was still covered by glacial ice. This study constitutes an example of how an accurate geomorphological characterization of a small area can complement other approaches to generate a better understanding of the paleoenvironmental evolution in the region.

Landscapes at the Periphery of Glacierization – Retrospect and Prospect

This paper reviews the evolution of palaeoglaciological reconstructions in regions at the periphery of glacierization, where an improved understanding of the role of glacial thermal regime has helped refine the delimitation of ice sheet maxima. Also significant has been the recognition in numerical models that some areas, especially ice sheet marginal zones, are subject to short periods of ice occupancy and hence that glacial landsystem signatures can be extremely subtle. This is compounded wherever cold-based conditions dominate during early stages of ice sheet recession, giving rise to a landform imprint typical of peripheral regions and hence often misinterpreted as unglaciated or glaciated only by older glaciations. Subtle landform imprints include meltwater channels, thin glacigenic veneers or scattered erratics and modified tors. More substantial glacigenic landform-sediment assemblages (‘drift belts’) do not always represent ice sheet maxima but instead may record significant changes in thermal regime, possibly linked to periods of ice-marginal stabilization. Some upland areas that lie beyond the traditionally demarcated limits of glaciation (e.g. Dartmoor in SW England) may contain subtle evidence of satellite ice cap development which has been overlooked due to the strong periglacial landform signature.

Geomorphological processes and frozen ground conditions in Elephant Point (Livingston Island, South Shetland Islands, Antarctica)

Elephant Point is an ice-free area in the SW corner of Livingston Island (Maritime Antarctica). The retreat of Rotch Dome glacier during the Holocene has exposed a land area of 1.16km2. Up to 17.3% of this surface has become ice-free between 1956 and 2010. A detailed geomorphological mapping of this ice-free environment was conducted in late January 2014. A wide range of active periglacial landforms show that periglacial processes are widespread. From the glacier to the coast four different geomorphological areas are identified: proglacial environment, moraine complex, bedrock plateaus and marine terraces. In situ measurements of the thawed soil depth show evidence of the widespread frozen ground conditions in the area. Field observations of permafrost exposures suggest that these frost conditions may be related to a soil permafrost regime, almost down to sea level. The activity of penguin colonies and elephant seals has created minor geomorphological features in the raised marine terraces. Here, several archaeological sites related to early human colonization of Antarctica were also found in natural shelters.

Modern and past periglacial features in Central Asia and their implication for paleoclimate reconstructions

In the continental areas of Central and High Asia, periglacial landform assemblages, sediment structures and processes are mainly influenced and determined by of soil humidity during freeze–thaw cycles. These cryogenic processes result in periglacial landforms such as solifluction, earth hummocks or patterned ground. The distribution of rock glaciers as clear indicators of permafrost is additionally determined by rock fall or moraine debris composed of large boulders (e.g. of granite). Periglacial features were used to reconstruct past climatic conditions, e.g. relict involutions and ice-wedge casts provide evidence for the distribution of former permafrost, say, for the Last Glacial Maximum (LGM). Past temperatures, e.g. mean annual air temperatures, can be estimated from these periglacial features and can be compared with other proxy data, such as glacier fluctuations. Examples from late Holocene solifluction activity in the Altai, Khangai and north-eastern Tibetan Plateau show a different intensity of solifluction processes during the late Holocene and Little Ice Age due to a decrease in temperature and higher soil humidity. The distribution of past permafrost in some regions is still a matter of debate because of different interpretations of sediment structures: sometimes features described as ice-wedge casts may be caused by roots or desiccation cracks due to drying of clay rich sediments. Seismically deformed unconsolidated deposits (seismites) can also be misinterpreted as periglacial involutions. The lack of certain landform assemblages and sediment structures does not necessarily mean that the area had no permafrost. Moisture conditions can also determine the periglacial landform generation to a large degree. They can be ordered in Central Asia as follows (from highest moisture availability to lowest): solifluction; rock glacier; permafrost involutions; ice-wedge casts; sand-wedge casts.

Reconstructing Periglacial Geomorphology: The Contribution of J. Ross Mackay

AbstractRoss Mackay's contributions to periglacial geomorphology are commonly regarded as the fruit of solo inspiration. In fact, his work is an exemplary product of its time. At the outset of his career, geomorphology was entering a radical transformation from interpretive study of landscape history towards quantitative study of landscape‐forming processes. Early periglacial geomorphology was concerned mainly with attempting to infer historical environmental conditions on the periphery of the great Pleistocene ice sheets and Mackay's earliest works are historically oriented accounts of regional geography. From 1960, however, his work, following the new perspective, was based on quantitative measurement of landforms and land‐forming processes, both in the field and on maps, and application of physical theory to interpret his observations. He focused attention on individual periglacial landforms that had hitherto been only superficially described. Outstanding aspects of Mackay's contributions are his genius for making critical field observations and his ability to use them to test geophysical theory. He was one of a very small number of pioneers who reconstructed periglacial geomorphology. Copyright © 2015 John Wiley & Sons, Ltd.

The distribution and climatic implications of periglacial landforms in eastern Australia

ABSTRACTMapping of over 4000 block deposits and scree slopes in eastern Australia is used to determine the extent of past strong freeze–thaw activity. Freeze–thaw landforms are common in the high country as far north as 30°S. There is a clear association between the locations of relict periglacial landforms and areas that receive more than 50 modern frost days. We infer about 10.5 °C cooling north of 35°S in the Diving Range, about 9 °C in the Australian Alps and about 5 °C in Tasmania during the phases when the lowest block deposits were active. An unexpected observation is the importance of precipitation in the distribution of block deposits north of 35°S. Here, the majority of block deposits have a southerly or westerly aspect, and lie in a narrow modern precipitation band of ca. 900–1050 mm. To the east, high‐elevation areas appear to have weaker diurnal oscillations limiting freeze–thaw activity. To the west, block deposits are absent, probably due to insufficient moisture to drive freeze–thaw processes. We cannot define specific last glaciation precipitation but the maintenance of a strong east–west precipitation gradient during glacial times is consistent with the maintenance of onshore easterlies during cold periods.

From valley to marginal glaciation in alpine-type relief: Lateglacial glacier advances in the Pięć Stawów Polskich/Roztoka Valley, High Tatra Mountains, Poland

The Pięć Stawów Polskich-Roztoka Valley in the High Tatras (Western Carpathians) features typical alpine-type relief with a deeply incised glacial trough and large, compound trough head cirque. The prominent hypsographic maximum in the valley (1680–2000m) along with a broad cirque bottom had provided a vast space for recording glacial and periglacial landforms, specifically the most recent Lateglacial advances. The valley has been intensively studied before in the context of glacial chronology. In this paper, we re-establish the post-Last Glacial Maximum (LGM) glacial chronology of the valley via detailed geomorphologic mapping, equilibrium line altitude (ELA) reconstruction, and Schmidt hammer (SH) dating, along with a critical review of previously published cosmogenic exposure age data (36Cl) and lacustrine sediment chronology.Our results indicate that the first four of the five distinguished Lateglacial stages (Roztoka I–III, Pusta I) occurred before the Bølling/Allerød (B/A) interstadial; thus, virtually the entire valley became deglaciated in course of the Oldest Dryas cold phase. A distinct reorganization of deglacial patterns from valley-type to marginal-type occurred before B/A warming when the ELA increased above the valley hypsographic maximum concentrated at the cirque bottom elevation. It shows that noticeable deglaciation step can be caused due to topographic reason with a minimal climate forcing. This points also to an important role of glaciated valley hypsography in regulating the distribution of moraines which is rarely taken into account in paleoglaciological reconstructions. We infer that glaciers vanished in the Tatra Mountains during the B/A interstadial. Later, a renewed advance during the Younger Dryas (Pusta II) formed a nearly continuous, festoon shaped pattern of moraines and rock glaciers in close distance to cirque backwalls. Furthermore, we discus some paleoenvironmental significance of the geomorphological record in the valley, as well, the applicability of SH dating in constructing glacial chronology.

Glacial and periglacial geomorphology and its paleoclimatological significance in three North Ethiopian Mountains, including a detailed geomorphological map

Geomorphological investigations and detailed mapping of past and present (peri)glacial landforms are required in order to understand the impact of climatic anomalies. The Ethiopian Highlands show a great variety in past and contemporary climate, and therefore, in the occurrence of glacial and periglacial landforms. However, only a few mountain areas have been studied, and detailed geomorphological understanding is lacking. In order to allow a fine reconstruction of the impact of the past glacial cycle on the geomorphology, vegetation complexes, and temperature anomalies, a detailed geomorphological map of three mountain areas (Mt. Ferrah Amba, 12°51′N 39°29′E; Mt. Lib Amba, 12°04′N 39°22′; and Mt. Abuna Yosef, 12°08′N 39°11′E) was produced. In all three study areas, inactive solifluction lobes, presumably from the Last Glacial Maximum (LGM), were found. In the highest study area of Abuna Yosef, three sites were discovered bearing morainic material from small late Pleistocene glaciers. These marginal glaciers occurred below the modeled snowline and existed because of local topo-climatic conditions. Evidence of such Pleistocene avalanche-fed glaciers in Ethiopia (and Africa) has not been produced earlier. Current frost action is limited to frost cracks and small-scale patterned ground phenomena. The depression of the altitudinal belts of periglacial and glacial processes during the last cold period was assessed through periglacial and glacial landform mapping and comparisons with data from other mountain areas taking latitude into account. The depression of glacial and periglacial belts of approximately 600m implies a temperature drop around 6°C in the last cold period. This cooling is in line with temperature depressions elsewhere in East Africa during the LGM. This study serves as a case study for all the intermediate mountains (3500–4200m) of the North Ethiopian highlands.

Little Ice Age debris lobes and nivation hollows inside Ubehebe Crater, Death Valley, California: Analog for Mars craters?

The 250m-deep, Ubehebe Crater is the youngest (<1000years) and largest (800m-wide) phreatomagmatic crater of the Ubehebe maar field of northern Death Valley, California, USA. The crater is blanketed by loose, unconsolidated ejecta debris and prominent tongue-shaped, steep-fronted debris lobes up to 200m long occur at the base of the crater's steep northeast-facing interior slope. Geomorphological observations, sedimentological analysis of outcrops and a ground penetrating radar survey, show the largest lobe to be composed of downslope-dipping progradational beds of ejecta resulting from repeated downslope avalanching (‘grain flow’) and cohesive debris flow inconsistent with an origin of the lobe as a singular coherent slump or flow. Large oval depressions on the upper surface of lobes are interpreted as relict nivation hollows occupied by former seasonal snow patches during recent Little Ice Age cooling (c. ~700year BP) when numerous rock glaciers and other periglacial landforms formed at high elevations in surrounding mountains. Lobes are interpreted as protalus ramparts formed when loose, non-cohesive ejecta from the steep unstable backwall of the crater moved downslope across snow patches and accumulated around their outer margins. Snow patch and lobe formation is considered to be a function of the local aspect-related meteorology of the crater's interior involving shading of northeast-facing interior slopes, radiative cooling and ponding of cold air, enhanced snow accumulation in the lee of the steep backwall combined with the availability of large volumes of loose ejecta. Ubehebe Crater and its lobes expand the geomorphic record of cool climate processes in Death Valley, the most well-known being the winter-ice facilitated ‘sliding boulders’ of Racetrack Playa. Having formed in an extreme environment, lobes offer an accessible terrestrial analog for poorly-understood debris lobes within Martian impact craters.

Quaternary glacial and periglacial processes in the Ethiopian Highlands in relation to the current afro-alpine vegetation

Summary. The highlands of Ethiopia show a great variety in present and past climate. The environments differ in altitude, latitude and local conditions. This has an influence on vegetation and geomorphologic processes. Present knowledge of past glacial and periglacial landforms concentrates around the highest mountain ranges of Ethiopia, the Semien Mountains, the Bale Mountains and the Arsi Mountains. Many intermediate mountains stay unexplored or just briefly discussed. No present glaciated mountains exist in Ethiopia but current periglacial processes occur on the highest peaks. The climate change sensitivity of the mountain environment can be assessed which can contribute to the study of the temperature sensitive treeline and land cover changes. Afro-alpine vegetation can be influenced by the presence of relict (peri)glacial landforms, which change the growing conditions by different soil properties. Further research will need to complement the existing observations by unexplored mountains and to establish altitudinal north-south trajects in Ethiopia regarding vegetation, geomorphological processes and landforms.

Origin and geographical characteristics of ponds in a high mountain region of central Japan

This study examines the role of landforms in pond formation in alpine and subalpine regions of central Japan. Mountain ponds larger than ca. 50 m2 were detected by interpretation of stereo-paired aerial photographs, and mapped in areas over 2000 m (above sea level). The mapped ponds totaled 304 in the 1347 km2 study area. Mass movement landforms are the major sites of pond basins, comprising 66.5 % of the total number; 65 ponds occur in depressions in displaced masses downslope of ridges, and 137 occur in linear depressions along main ridges. These ponds occur frequently in the snowiest parts of the study area, although geological setting also affects pond formation. The second and third major types of landforms with ponds are of volcanic and glacial origins, accounting for 16.8 and 15.8 % of all ponds, respectively. Nearly 90 % of these mapped ponds have an area smaller than 1000 m2. The size distribution of ponds varies with origin type. Mass movement landforms have a greater range of pond sizes, including both small (<1000 m2) and medium (1000–6000 m2), than do glacial and periglacial landforms. Volcanic landforms have the largest ponds, which exceed 10,000 m2 in some cases. Ponds on glacial landforms are at higher elevations and may be of uniform age post-glaciation, while other landform types can occur at any elevation and may span a wide range of ages. Landslide ponds may provide better habitats for aquatic species than those originating from other landforms, because they are not subject to the strong acid conditions of volcanic ponds or the longer snow-covered period of ponds on glacial landforms.

Current transition from glacial to periglacial processes in the Dolomites (South-Eastern Alps)

A close relationship between glacial and periglacial landforms is frequently observed in alpine environments, where a transition from glacial to periglacial processes often took place after the end of the Little Ice Age (LIA). Understanding the origin of these landforms is challenging, and assessing the current spatial domain of glacial and periglacial processes may be a difficult task in high-relief areas, where thick and widespread debris cover often characterize rapidly decaying glaciers. Here we present a comprehensive study of a composite landform located in the Dolomites (South-Eastern Alps), combining geomorphological, geophysical and topographic surveys with ground surface temperature measurements. Results indicate that a debris-covered glacier persists in the upper part, rather large compared to the LIA extent, but currently inactive and rapidly losing mass. An active rock glacier exists in the lower part, surrounded by discontinuous permafrost. A frozen body about 10m thick was detected in the rock glacier and geomorphological evidence suggests that this ice mass is completely detached from the debris-covered glacier. Our findings suggest that the lower part of the composite landform is probably a remnant of the ancient glacier tongue and is currently evolving under periglacial conditions. Periglacial processes are therefore replacing glacial processes which dominated in this site during the LIA.