Abstract Active layer increase may contribute to greenhouse gas emissions, ecosystem change, and increased hazards. Here, we show the results of field measurements of active-layer thickness from 156 monitoring sites in Arctic, Antarctic and mountain permafrost regions. Active layer thickness increased significantly at 55% and 38% of sites in the Arctic and Antarctic regions, at more than 90% European mountain and high elevation Asian sites, and at sites in South America, demonstrating worldwide permafrost degradation during the first quarter of this century (2000–2024). The largest changes were observed in mountain regions where active layer doubled at several sites. The smallest changes were observed at sites with thick surficial organic horizons and high ground ice content. In continuous permafrost, sites generally exhibited smaller increases compared to sites in discontinuous permafrost. Regression analysis indicates Arctic active layer changes are attributable to increasing thawing degree-days, followed by increases in total rainfall. Other permafrost regions require more sites and longer time-series to draw conclusions regarding active layer change attribution.

Cryopanation terraces and cryopediments are large erosional periglacial features found in unglaciated mountains in periglacial (cold, nonglacial) environments. These landforms occur primarily in regions not previously glaciated. Cryoplanation terraces occur in the upper reaches of mountainous terrain and resemble giant staircases composed of alternating steep risers and gently sloping treads. Cryopediments are sloping rectilinear or concave-up surfaces of transportation extending downslope from the residual uplands in which cryoplanation terraces are formed, often approaching valley bottoms. These landforms function as an integrated system, producing and transporting sediment through the action of periglacial processes. Cryopediments also occur in lowland environments outside the borders of continental glaciations. Several extensive European cryopediments are discussed in detail.

Despite strong terrain influences on the climate of the Appalachian Highlands in the eastern USA, few attempts have been made to systematically collect air and soil temperature data from summits and other high-elevation sites in this region. This paper reports on the Appalachian Highlands Environmental Monitoring (AHEM) mesoscale climate network, a series of 20 high-elevation sites recording temperature at hourly intervals from 1996 to 2008 on Appalachian summits along a 1500 km transect extending from Maine to North Carolina. Observations included air temperature, ground surface temperature, and soil temperature at 25 cm depth. Data were analyzed with respect to four issues: (1) accuracy of air temperature estimates and comparisons with previous studies; (2) relations between the altitude of the 0 °C mean annual air temperature and latitudinal position; (3) variations in frequency distributions of freeze–thaw days with latitude; and (4) the accuracy of an existing soil temperature classification scheme in the Appalachians. Analytic results include: (1) topographically informed interpolation techniques provide more accurate temperature estimates than traditional methods; (2) the elevation of the 0 °C mean annual air temperature decreases systematically with increasing latitude; (3) the frequency distributions of freeze–thaw days are related directly to latitudinal position; (4) classifications of mean annual soil temperature based on data from the 25 cm level are in general agreement with an existing U.S. Department of Agriculture soil-temperature map suggesting permafrost underlying high-elevation locations in the northern Appalachian Highlands..

Traditional Inupiaq sigluaq are cellars excavated into permafrost for storage of large quantities of game, fish, and other foodstuffs harvested for subsistence. Permafrost provides both a cultural and regulatory ecosystem service to Arctic peoples. A cellar thermal monitoring program in Utqiagvik (formerly Barrow), Alaska, documented catastrophic flooding, collapses, and other issues in these cellars related to warming climatic conditions, community functions, and development. This paper provides an update on the Utqiagvik monitoring program, which was operational from 2005 to 2019. All five monitored cellars exhibited stable to warming mean annual internal temperatures over the period of observation. Two cellars flooded, another was abandoned because of sloughing walls, and two were functioning until the COVID-19 pandemic. Based on experiences gained from the 14-year Utqiagvik monitoring program, we conduct a vulnerability assessment using the source-pathway-receptor-consequence (SPRC) model and identify several vulnerability reduction measures. We recommend the SPRC model to aid evaluation of specific vulnerabilities of cellars and other traditional frozen infrastructure, and to improve future monitoring methods and products through increased community participation. Any attempt to provide data for community-resilience decisions should start with identifying and communicating process components, thereby bridging stakeholder learning and responses (their "heuristics" in the SPRC model) and science-based knowledge.

Altiplanation (cryoplanation) terraces are conspicuous and widespread elements of upland landscapes in Alaska's interior. They occur in staircase-like series, primarily along divides in ridge-crest positions, and as summit platforms. Hanks (side slopes) consist of a steep upper section composed of coarse clastic debris and amorphous solifluction forms, grading through a break in slope (the 'solischrund') to a gentler lower section (cryopediment) dominated by well-defined solifluction lobes and low-order hillslope hydrological networks. An individual terrace unit consists of a steep scarp (riser) and a subjacent gently inclined tread (platform). A sequential group or series of adjacent terrace units, descending from a summit platform along ridge crests, are referred to collectively as an altiplanorium. Altiplanation terraces are a prominent feature of the attitudinal zonal arrangement of landscape phenomena in interior Alaska, and are confined to the upland periglacial zone between 915 and 1675 m.a.s.l. They are positioned below the contemporary snowline. Three study areas are given detailed verbal, cartographic, and photographic description. These areas (Mount Fairplay, High Valley/Denali Mountain, and Goodpaster Uplands) could serve as type localities for altiplanation landform assemblages. An appendix identifies the locations of many other areas in the Alaskan interior containing well-developed altiplanation landforms, and demonstrates the widespread geographic distribution of these landforms.

General geomorphometry is concerned with the geometric form of the continuous land surface and can be useful for identifying topographic "signatures." Hypsometry has found numerous applications in several subfields of geomorphology, but has not been used extensively in published periglacial work. Hypsometric analysis was applied in this study to several unglaciated and glaciated locales in Alaska's Yukon-Tanana Upland and Indian River Upland physiographic sections, extensive areas of eastern Beringia in which cryoplanation landforms are ubiquitous. Never-glaciated terrain in this region has a hypsometric signature distinctly different from that of glaciated areas within sample areas ranging in size from 0.25 to 100 km(2). Cryoplanated terrain exhibits a distinctive convex-upward hypsometric signature, a reflection of a greater proportion of the reference solid (land mass) remaining intact than in typical mature fluvial or glaciated terrain. Because the elevational position of cryoplanation terraces is slightly below and parallel with snowline position it is, in effect, climatically determined from above, and localized planar surfaces develop near that level. Comparison with terrain in the southwestern USA demonstrates that substantial differences also exist between the hypsometry of upland periglacial terrain in eastern Beringia and that of inselbergs and pediments in warm-desert geomorphic landscapes, casting doubt on a suggestion that cryoplanation terraces and cryopediments in high-latitude mountains could be inherited from past intervals of subtropical desert conditions We conclude that characteristic periglacial erosional topography exists in unglaciated areas of Beringia and can be detected and described quantitatively through objective methods.

Stephen Taber's early work on ice segregation and frost heaving was far ahead of its time. His laboratory experiments regarding ice segregation led to our current understanding of frost heave by civil and geotechnical engineers building roads and other structures in cold regions. It also laid the foundation for later process‐oriented field studies of cold‐climate geomorphic processes. Taber's 1943 regional monograph on the origin and history of perennially frozen ground in Alaska, published by the Geological Society of America, was the earliest example of regional cryostratigraphy, and pioneered the regional permafrost and Quaternary studies undertaken later by Katasonov, Popov, Mackay, Péwé, Hopkins, and others. An important dimension of Taber's Alaska work was his application of knowledge gained through laboratory experimentation to the interpretation of ground‐ice exposures in the field. While S. W. Muller is widely regarded as the “father” of permafrost studies in North America, Taber is properly viewed as the “progenitor” of cryostratigraphic studies, although he is not yet widely regarded as such. This study uses archival resources to provide historical context regarding the development of Taber's monograph, to investigate details about the review and publication process it underwent, and to explore the question of why it remains undervalued.

Automated recognition and delineation of specific landforms and their constituent elements ranks among the most active areas of contemporary geomorphological research. This study contributes to that literature by applying semi‐ and fully automated recognition procedures to upland periglacial geomorphic landscapes. The Cryoplanation Terrace semi‐Automated Recognition (CTAR) algorithm utilizes basic terrain parameters to identify locations of cryoplanation terraces (CTs) from the high‐resolution ArcticDEM. Using a multistep process, candidate areas are identified based on morphometric characteristics. CTAR uses terrain derivatives to search ridges, hills, and mountains for flat areas bounded by abrupt breaks in slope. Because CTs are found exclusively in upland periglacial environments, some locations require that low‐lying areas be filtered out. To assess accuracy, CTAR was tested at five local study sites distributed across eastern Beringia, each containing multiple CTs delimited manually in a previous study. CTAR performed well, with an overall accuracy of 90%. A strong linear relationship exists between the size of CTAR‐delimited terraces and those identified in a previous study through air‐photo interpretation. In addition to identifying nearly all of the CTs in the five study areas, a fully automated version of the algorithm (GEE‐CTAR), implemented in Google Earth Engine, identified nearly 8,000 previously unmapped potential CTs in the Seward Peninsula region of western Alaska. The ability to identify CTs from digital elevation models provides a useful tool for recognizing and delineating upland periglacial topography. Objective recognition of large erosional landform elements created by periglacial processes is a critical step in developing the field of periglacial geomorphometry.

Russian permafrost regions are unparalleled in extent, history of development, population presence, and the scale of economic activities. This special issue, «Permafrost Regions in Transition», provides a timely opportunity to (a) examine major issues associated with changing permafrost conditions in natural environments and areas of economic development; (b) present insights into new methods of permafrost investigations; and (c) describe new opportunities and risks threatening sustainable development of Arctic populations and industrial centers in Russia. The issue begins with papers focused on methods of permafrost research, followed by papers focused on examining changes in permafrost under natural conditions, and in Arctic settlements. The last two papers examine potential impacts of permafrost degradation on the Russian economy and potential health implications.

The Circumpolar Active Layer Monitoring (CALM) network is an ongoing international effort to collect and disseminate standardized measurements of active-layer dynamics to monitor the response of near-surface permafrost parameters to climate change. This work presents a distillation of 25 years (1995-2019) of observations from three north-south transects of CALM sites in tundra environments of Alaska. Transects examined in this work bisect tundra regions of discontinuous permafrost on the Seward Peninsula, and the continuous permafrost zone on the western and eastern sections of the Arctic Foothills and Arctic Coastal Plain. These transects represent regional climatic gradients, several physiographic provinces, and regionally characteristic landcover associations. Total active-layer thickening at observed sites ranged from 7 to 26 cm; more significant thaw occurred in the foothills despite less pronounced warming air temperature trends. This summary highlights several regional active layer responses to climate warming, complicated by distinct thermal landscape sensitivities, landscape variability, and documented thaw subsidence. Data summarized in this report are publicly available and represent an important validation resource for earth-system models that include regions in the continuous and discontinuous permafrost zones of northern and western Alaska.

ABSTRACT Nivation, the suite of weathering and transportation processes attributed to late-lying snowpatches, is linked to the formation of cryoplanation terraces (CTs). CTs resemble giant staircases arranged in repeating sequences of low-gradient treads and steep scarps that extend over hundreds of meters. The nivation hypothesis of CT development has been supported in recent literature examining weathering and erosion trends, but the mechanisms involved in transporting sediment across CT treads remain underinvestigated. Sorted stripes, a type of patterned ground encountered on CT treads, have been linked to efficient snow meltwater flow across low gradients, indicating that these features could be an important component of CT formation. In this study, we use short-term soil thermal and moisture records, particle-size analysis, and apparent thermal diffusivity calculations to examine periglacial processes operating on two incipient CTs. Initial results indicate that: (1) the coarse (boulder and cobble size) portions of sorted stripes function as subsurface channels for sediment transportation across gently sloping CT treads (generally < 12°) by flowing water; (2) hillslope hydrology is an important component of the erosion processes sculpting upland periglacial environments; and (3) late-lying snowbank environments are highly dynamic during warm weather, with large amounts of sediment transported over short periods.

The Circumpolar Active Layer Monitoring (CALM) program is the primary global-change monitoring program concerned with the seasonally frozen active layer above permafrost. The active layer has been designated by the Global Climate Observing System and the Global Terrestrial Observing Network as an 'Essential Climate Variable'. CALM was launched in 1991 on a volunteer basis in cooperation with the International Tundra Experiment. CALM observatories in Russia and Alaska have been supported since 1998 by the U.S. National Science Foundation through five consecutive five-year funding cycles. In its current configuration, the CALM network includes observation sites throughout the circum-Arctic region and a substantial number of sites in Antarctica. Open access to data and data harmonization are hallmarks of the program. In addition to its ongoing emphasis on field observations of active-layer thickness, temperature, soil moisture, and thaw subsidence are currently being monitored at many sites. Increased emphasis is being placed on observing the dynamics of other landscape and ecosystem parameters, including vegetation, landscape patterns, and soils. Other developing features of the program include expanded education and outreach activities, close cooperation with other international programs, and provision of quality-controlled, standardized data products that meet the needs of the wider scientific community.

Cryoplanation terraces (CTs) are large (3000–800 000 m2) erosional landforms found in upland periglacial environments. Two hypotheses for the formation of CTs are supported in contemporary literature: (1) CT formation is controlled primarily by geologic structure; and (2) CTs are climatically controlled through nivation, a suite of erosional processes associated with late-lying snowbanks. A persistent question in periglacial geomorphology is whether nivation can produce CT-scale landforms. This paper examines the unusual deglaciation history of “Frost Ridge” on the Cathedral Massif, northwestern British Columbia, to estimate long-term denudation attributable to nivation processes active since the last glacial maximum. Frost Ridge forms one flank of an east–west-oriented glacial valley. During deglaciation, marginal drainage created V-shaped erosional notches on both valley walls. Minimization of solar radiation on the steep north-facing wall (Frost Ridge) allowed snowbanks to accumulate and persist in the marginal drainage features and nivation processes to erode the slope. Today, several large nivation hollows (incipient CTs) are present near the summit of Frost Ridge, while the V-shaped marginal drainage features are preserved at lower elevations and on the opposite, south-facing valley wall. A high-resolution survey using an unmanned aerial vehicle (UAV) allowed volumes of marginal drainage and incipient terrace features to be compared. Based on this volumetric comparison, denudation rates are estimated to range from 4.2 to 125.8 mm/kyr, which are comparable with relatively short-term nivation rates reported from Antarctica and mid-latitude alpine periglacial areas.

ABSTRACTCryoplanation terraces are prominent but enigmatic landforms found in present and past periglacial environments. Geomorphologists have debated for more than a century over processes involved in the formation of these elevated, step-like, bedrock features. Presented here are the first numerical surface exposure ages and scarp retreat rates from cryoplanation terraces in the Yukon-Tanana Upland (YTU) in Alaska, part of unglaciated eastern Beringia, obtained from terrestrial cosmogenic nuclides (TCN) in surface boulders. Ages comprise six10Be TCN ages from two terrace treads near Eagle Summit and six36Cl ages from two treads on Mt. Fairplay. Based on these exposure ages, scarps at both locations were last actively eroding from 49 to 22.4 ka. Both locations exhibit time-transgressive development, particularly near scarp-tread junctions. Boulder exposure ages and distances between sampled boulder locations were used to estimate scarp retreat rates of 0.11 to 0.56 cm/yr. These numerical exposure ages presented here demonstrate that the cryoplanation terraces in the YTU are diachronous surfaces actively eroding during multiple cold intervals. With these results, hypotheses for cryoplanation terrace formation are discussed and evaluated for the YTU, including those based on geologic structure, nivation, and the influence of permafrost.

Cryoplanation terraces are elevated bedrock features resembling giant staircases, with alternating steep scarps and shallow sloping treads. These landscape-scale features have long been associated with periglacial environments, but the processes involved in their formation remain vaguely specified and contentious. The two leading hypotheses for the formation of cryoplanation terraces are centered on: (1) geologic structure; and (2) nivation-driven scarp retreat. The nivation-formation hypothesis invokes scarp retreat under erosion processes associated with late-lying snowbanks. To test whether cryoplanation terraces develop through scarp retreat, six relative weathering indices (fracture counts, Cailleux roundness, Cailleux flatness, Krumbein sphericity, rebound, and weathering rind thickness) were measured across well-developed terraces in unglaciated eastern Beringia (central and western Alaska) at Mt Fairplay, Eagle Summit, and Skookum Pass. Statistically significant differences in relative weathering indices detected through chi-square and multiple-comparison procedures indicate that material is less weathered closer to scarps, i.e. that these areas were more recently exposed than those distant from the scarp. Based on these findings, a refined model of time-transgressive cryoplanation terrace development through nivation-driven scarp retreat is proposed. This new qualitative model addresses the removal of weathered material from terrace treads down side slopes through piping and gravity-driven mass-wasting processes. (c) 2019 John Wiley & Sons, Ltd.

Quaternary Research is an international journal devoted to the advancement of the interdisciplinary understanding of the Quaternary Period.We aim to publish articles of broad interest with relevance to more than one discipline,

Ongoing climate change is causing fundamental changes in the Arctic, some of which can be hazardous to nature and human activity. In the context of Earth surface systems, warming climate may lead to rising ground temperatures and thaw of permafrost. This Data Descriptor presents circumpolar permafrost maps and geohazard indices depicting zones of varying potential for development of hazards related to near-surface permafrost degradation, such as ground subsidence. Statistical models were used to predict ground temperature and the thickness of the seasonally thawed (active) layer using geospatial data on environmental conditions at 30 arc-second resolution. These predictions, together with data on factors (ground ice content, soil grain size and slope gradient) affecting permafrost stability, were used to formulate geohazard indices. Using climate-forcing scenarios (Representative Concentration Pathways 2.6, 4.5 and 8.5), permafrost extent and hazard potential were projected for the 2041–2060 and 2061–2080 time periods. The resulting data (seven permafrost and 24 geohazard maps) are relevant to near-future infrastructure risk assessments and for targeting localized geohazard analyses.

Six hundred sixty-one rock glaciers in the northern Absaroka and Beartooth Ranges of south-central Montana were digitized and evaluated using geographic information systems technology and an array of topographic and environmental parameters. Beartooth rock glaciers are larger, occur at higher elevations, receive more precipitation, and are subject to lower temperatures than northern Absaroka rock glaciers. Elevation is strongly correlated with rock glacier activity. Comparative analysis of these adjacent mountain ranges indicates that Beartooth geomorphic landscapes are shifting from predominantly glacial to periglacial regimes, and that the northern Absarokas have largely completed this transition. Because glaciers are declining in response to climate warming, rock glaciers could soon become the most important source of ice in the region.