A surge of Mittie Glacier, a 50 km-long tidewater outlet glacier of Manson Icefield, occurred between approximately 1992 and 2007. Velocities increased slowly at first, but then increased rapidly to reach a peak of 4800 m a−1 in early 1996, the highest ever reported for a glacier in the Canadian Arctic. The surge initiated at the terminus and propagated up-glacier, with a maximum terminus advance of 7.3 km between 1994 and 1999. The surge was almost entirely restricted to the lower ~30 km of the glacier, in a region which radio-echo sounding shows to be grounded below sea level. A 3 km-wide crevasse with a 150 m opening occurred at the separation between faster moving ice downstream and slower moving ice upstream. Surge initiation appears to have been triggered by flotation of the lower terminus, caused by long-term thinning of this region during quiescence.

This paper presents geomorphological and historical records of the surge-type behaviour of Hansbreen, one of the most studied tidewater glaciers in Svalbard. The surge-type behaviour of the glacier has not been considered before due to the lack of evidence of this phenomenon. We integrate geomorphological mapping of the terrestrial and submarine forefields with historical data from the 19th and 20th centuries to reconstruct the glacier dynamics and identify the possible timing of surging. Landform assemblages are representative of the surging glacier landsystem, including crevasse-squeeze ridges (CSRs) and submarine streamlined glacial lineations. Abundant CSRs in the outer part of the terrestrial forefield were also documented in the 1980s, but most have been obliterated since then. We suggest the identified surge landsystem was produced during a surge of Hansbreen detected from photographs taken during the Austro-Hungarian expedition in 1872. Historical photogrammetric photos from the Norwegian expedition in 1918 revealed surge-diagnostic features in the glacier surface, including a folded medial moraine and a dense, complex network of crevasses. A potential next surge remains questionable in the following decades due to the low-lying accumulation area of the main stream hindering the mass build-up, but potential surges of the tributary glaciers should not be excluded.

Glacier surges are opportunities to study large amplitude changes in ice velocities and accompanying links to subglacial hydrology. Although the surge phase is generally explained as a disruption in the glacier's ability to drain water from the bed, the extent and duration of this disruption remain difficult to observe. Here we present a combination of in situ and remotely sensed observations of subglacial water discharge and evacuation during the latter half of an active surge and subsequent quiescent period. Our data reveal intermittently efficient subglacial drainage prior to surge termination, showing that glacier surges can persist in the presence of channel-like subglacial drainage and that successive changes in subglacial drainage efficiency can modulate active phase ice dynamics at timescales shorter than the surge cycle. Our observations favor an explanation of fast ice flow sustained through an out-of-equilibrium drainage system and a basal water surplus rather than binary switching between states in drainage efficiency.

We demonstrate that a ~20 km long valley glacier in the St. Elias Mountains, Yukon, can experience both partial and full surges, likely controlled by the presence of a topographic constriction and the formation and drainage of supraglacial lakes. Based on analysis of air photos, satellite images and field observations since the 1940s, we identify a full surge of ‘Little Kluane Glacier’ from 2013 to 2018, and a partial surge of just the upper north arm between 1963 and 1972. Repeat digital elevation models and velocity profiles indicate that the recent surge initiated from the upper north arm in 2013, which developed into a full surge of the main trunk from 2017 to 2018 with peak velocities of ~3600 m a−1 and frontal advance of ~1.7 km from May to September 2018. In 2016, a mass movement from the north arm to the main trunk generated a surface depression in a region immediately downstream of a topographic constriction, which promoted the formation and rapid drainage of supraglacial lakes to the glacier bed, and likely established the conditions to propel the initial partial surge into a full surge. Our results underscore the complex interplay between glacier geometry, surface hydrology and topography required to drive full surges of this glacier.

We use satellite image processing techniques to measure surface elevation and velocity changes on a temperate surging glacier, Sít’ Kusá, throughout its entire 2013–2021 surge cycle. We present detailed records of its dynamic changes during quiescence (2013–2019) and its surge progression (2020–2021). Throughout quiescence, we observe order-of-magnitude speedups that propagate down-glacier seasonally from the glacier's upper northern tributary, above a steep icefall, into the reservoir zone for the surging portion of the glacier. The speedups initiate in fall and gradually accelerate through winter until they peak in late spring, ~1 − 2 months after the onset of melt. Propagation distance of the speedups controls the distribution of mass accumulation in the reservoir zone prior to the surge. Furthermore, the intensity and propagation distance of each year's speedup is correlated with the positive degree day sum from the preceding melt season, suggesting that winter melt storage drives the seasonal speedups. We demonstrate that the speedups are kinematically similar to the 2020–2021 surge, differing mainly in that the surge propagates past the dynamic balance line at the lower limit of the reservoir zone, likely triggered by the exceedance of a tipping point in mass accumulation and basal enthalpy in the reservoir zone.

Glaciers in the Russian High Arctic have undergone accelerated mass loss due to atmospheric and oceanic warming in the Barents–Kara Sea region. Most studies have concentrated on the western Barents–Kara sector, despite evidence of accelerating mass loss as far east as Severnaya Zemlya. However, long-term trends in glacier change on Severnaya Zemlya are largely unknown and this record may be complicated by surge-type glaciers. Here, we present a long-term assessment of glacier change (1965–2021) on Severnaya Zemlya and a new inventory of surge-type glaciers using declassified spy-satellite photography (KH-7/9 Hexagon) and optical satellite imagery (ASTER, Sentinel-2A, Landsat-4/5 TM and 8 OLI). Glacier area reduced from 17 053 km2 in 1965 to 16 275 in 2021 (−5%; mean: −18%, max: −100%), with areal shrinkage most pronounced at land-terminating glaciers on southern Severnaya Zemlya, where there is a recent (post-2010s) increase in summer atmospheric temperatures. We find that surging may be more widespread than previously thought, with three glaciers classified confirmed as surge-type, eight as likely to have surged and nine as possible, comprising 11% of Severnaya Zemlya's 190 glaciers (37% by area). Under continued warming, we anticipate accelerated retreat and increased likelihood of surging as basal thermal regimes shift.

Using global Sentinel-1 radar backscatter data, we systematically map the locations of glaciers with surge-type activity during 2017–22. Patterns of pronounced increases or decreases in the strongest backscatter between two winter seasons often indicate large changes in glacier crevassing, which we treat here as a sign of surge-type activity. Validations against velocity time series, terminus advances and crevassing found in optical satellite images confirm the robustness of this approach. We find 115 surge-type events globally between 2017 and 2022, around 100 of which on glaciers already know as surge-type. Our data reveal a pronounced spatial clustering in three regions, (i) Karakoram, Pamirs and Western Kunlun Shan (~50 surges), (ii) Svalbard (~25) and (iii) Yukon/Alaska (~9), with only a few other scattered surges elsewhere. This spatial clustering is significantly more pronounced than the overall global clustering of known surge-type glaciers. The 2017–22 clustering may point to climatic forcing of surge initiation.

It is commonly asserted that there are two distinct classes of glacier surges: slow, long-duration ‘Svalbard-type’ surges, triggered by a transition from cold- to warm-based conditions (thermal switching), and fast, shorter-duration ‘Alaska-type’ surges triggered by a reorganisation of the basal drainage system (hydraulic switching). This classification, however, reflects neither the diversity of surges in Svalbard and Alaska (and other regions), nor the fundamental dynamic processes underlying all surges. We argue that enthalpy balance theory offers a framework for understanding the spectrum of glacier surging behaviours while emphasising their essential dynamic unity. In this paper, we summarise enthalpy balance theory, illustrate its potential to explain so-called ‘Svalbard-type’ and ‘Alaska-type’ surges using a single set of principles, and show examples of a much wider range of glacier surge behaviour than previously observed. We then identify some future directions for research, including strategies for testing predictions of the theory against field and remote sensing data, and priorities for numerical model development.

This study provides the first comprehensive reconstruction of the dynamics of Iceberg Glacier, located on western Axel Heiberg Island, and reveals detailed observations of a complete surge for the first time in the Canadian Arctic. Historical aerial photographs, declassified intelligence satellite photographs, optical satellite imagery and synthetic aperture radar data were used to quantify changes in terminus position, ice velocity and glacier thickness since the 1950s. A surge initiated at the terminus in 1981 and terminated in 2003, suggesting a 22-year active phase. High surface velocities, reaching ~2300 m a−1 in 1991, were accompanied by a maximum terminus advance of >7 km and a large transfer of mass down-glacier, causing significant median trunk-wide surface elevation changes attaining >3 ± 1 m a−1. We suggest that the retreat from a pinning point, flotation of the terminus, the removal of sea-ice from the ice front, and an increase in subglacial meltwater availability from relatively high air temperatures in 1981 likely contributed to surge initiation. The ensuing quiescent period has seen a continual decrease in surface flow rates to an average centreline velocity of 11.5 m a−1 in 2020–21, a gradual steepening of the glacier surface and a > 2.5 km terminus retreat.

Theory and observation show that glacier-flow regimes characterized by high basal slip enhance the projection of topographic detail to the surface, motivating this investigation into the efficacy of using glacier surges to improve bed estimation. Here we adapt a Bayesian inversion scheme and apply it to real and synthetic data as a proof of concept. Synthetic tests show a reduction in mean RMSE between true and inferred beds by more than half, and an increase in the mean correlation coefficient of ~0.5, when data from slip- versus deformation-dominated regimes are used. Multi-epoch inversions, which partition slip- and deformation-dominated regimes, are shown to outperform inversions that average over these flow regimes thereby squandering information. Tests with real data from a surging glacier in Yukon, Canada, corroborate these results, while highlighting the challenges of limited or inconsistent data. With the growing torrent of satellite-based observations, fast-flow events such as glacier surges offer potential to improve bed estimation for some of the world's most dynamic glaciers.

Basal conditions play an essential role in the dynamics of outlet glaciers, but direct observations at the bed of glaciers are challenging to obtain. Instead, inverse methods can be used to infer basal parameters from surface observations. Here, we use a simple ice-flow model as a forward model in an inversion scheme to retrieve the spatio-temporally variable basal stress parameter for Hagen Bræ, North Greenland, from 1990 to 2020. Hagen Bræ is a surge-type glacier with up to an order of magnitude variability of winter velocities near the grounding line. We find that downstream changes in the basal stress parameter can explain most of the variation of flow velocity, and we further identify a region of high resistance ~20–40 km from the grounding line. We hypothesise that this region of high resistance plays an important role in controlling glacier discharge.

Glacier surges are periodic episodes of mass redistribution characterized by dramatic increases in ice flow velocity and, sometimes, terminus advance. We use optical satellite imagery to document five previously unexamined surge events of Sít’ Kusá (Turner Glacier) in the St. Elias Mountains of Alaska from 1983 to 2013. Surge events had an average recurrence interval of ~5 years, making it the shortest known regular recurrence interval in the world. Surge events appear to initiate in the winter, with speeds reaching up to ~25 m d−1. The surges propagate down-glacier over ~2 years, resulting in maximum thinning of ~100 m in the reservoir zone and comparable thickening at the terminus. Collectively, the rapid recurrence interval, winter initiation and down-glacier propagation suggest Sít’ Kusá's surges are driven by periodic changes in subglacial hydrology and glacier sliding. Elevation change observations from the northern tributary show a kinematic disconnect above and below an icefall located 23 km from the terminus. We suggest the kinematic disconnect inhibits drawdown from the accumulation zone above the icefall, which leads to a steady flux of ice into the reservoir zone, and contributes to the glacier's exceptionally short recurrence interval.

We present a theoretical framework that integrates the dynamics of glaciers with and without the topographic confinement. This Part 1 paper concerns the former, which may exhibit surge cycles when subjected to thermal switches associated with the bed condition. With the topographic trough setting the glacier width and curbing the lateral drainage of the meltwater, the problem falls under the purview of the undrained plastic bed (UPB) formalism. Employing the UPB, we shall examine the external controls of the glacial behavior and test them against observations. Through our non-dimensionalization scheme, we construct a 2-D regime diagram, which allows a ready prognosis of the glacial properties over the full range of the external conditions, both climate- and size-related. We first discern the boundaries separating the glacial regimes of steady-creep, cyclic-surging and steady-sliding. We then apply the regime diagram to observed glaciers for quantitative comparisons. These include the Svalbard glaciers of both normal and surge types, Northeast Greenland Ice Stream characterized by steady-sliding, and Hudson Strait Ice Stream exhibiting cyclic surges. The quantitative validation of our model containing no free parameters suggests that the thermal switch may unify the dynamics of these diverse glaciers.

Negribreen, a tidewater glacier located in central eastern Svalbard, began actively surging after it experienced an initial collapse in summer 2016. The surge resulted in horizontal surface velocities of more than 25 m d−1, making it one of the fastest-flowing glaciers in the archipelago. The last surge of Negribreen likely occurred in the 1930s, but due to a long quiescent phase, investigations of this glacier have been limited. As Negribreen is part of the Negribreen Glacier System, one of the largest glacier systems in Svalbard, investigating its current surge event provides important information on surge behaviour among tidewater glaciers within the region. Here, we demonstrate the surge development and discuss triggering mechanisms using time series of digital elevation models (1969–2018), surface velocities (1995–2018), crevasse patterns and glacier extents from various data sources. We find that the active surge results from a four-stage process. Stage 1 (quiescent phase) involves a long-term, gradual geometry change due to high subglacial friction towards the terminus. These changes allow the onset of Stage 2, an accelerating frontal destabilization, which ultimately results in the collapse (Stage 3) and active surge (Stage 4).

Analysis of a recent surge of Morsnevbreen, Svalbard, is used to test predictions of the enthalpy balance theory of surging. High-resolution time series of velocities, ice thickness and crevasse distribution allow key elements of the enthalpy (internal energy) budget to be quantified for different stages of the surge cycle. During quiescence (1936–1990), velocities were very low, and geothermal heat slowly built-up enthalpy at the bed. Measurable mass transfer and frictional heating began in 1990–2010, then positive frictional heating-velocity feedbacks caused gradual acceleration from 2010 to 2015. Rapid acceleration occurred in summer 2016, when extensive crevassing and positive air temperatures allowed significant surface to bed drainage. The surge front reached the terminus in October 2016, coincident with a drop in velocities. Ice plumes in the fjord are interpreted as discharge of large volumes of supercooled water from the bed. Surge termination was prolonged, however, indicating persistence of an inefficient drainage system. The observations closely match predictions of the theory, particularly build-up of enthalpy from geothermal and frictional heat, and surface meltwater, and the concomitant changes in ice-surface elevation and velocity. Additional characteristics of the surge reflect spatial processes not represented in the model, but can be explained with respect to enthalpy gradients.

Donjek Glacier has an unusually short and regular surge cycle, with eight surges identified since 1935 from aerial photographs and satellite imagery with a ~12 year repeat interval and ~2 year active phase. Recent surges occurred during a period of long-term negative mass balance and cumulative terminus retreat of 2.5 km since 1874. In contrast to previous work, we find that the constriction where the valley narrows and bedrock lithology changes, 21 km from the terminus, represents the upper limit of surging, with negligible surface speed or elevation change up-glacier from this location. This positions the entire surge-type portion of the glacier in the ablation zone. The constriction geometry does not act as the dynamic balance line, which we consistently find at 8 km from the glacier terminus. During the 2012–2014 surge event, the average lowering rate in the lowest 21 km of the glacier was 9.6 m a−1, while during quiescence it was 1.0 m a−1. Due to reservoir zone refilling, the ablation zone has a positive geodetic balance in years immediately following a surge event. An active surge phase can result in a strongly negative geodetic mass balance over the surge-type portion of the glacier.

Karakoram glaciers experienced balanced or slightly positive mass budgets since at least the 1970s. Here, we provide an update on the state of balance of Central and Eastern Karakoram glaciers (12 000 km2) between 2008 and 2016 by differencing DEMs derived from satellite optical images. The mass budget of Central Karakoram glaciers was slightly positive (0.12 ± 0.14 m w.e. a−1) while eastern Karakoram glaciers lost mass (−0.24 ± 0.12 m w.e. a−1). The glacier-wide mass balances of surge-type and nonsurge-type glaciers were not statistically different. Our elevation change data also depict the effect of a > 100 Mm3 rock avalanche on Siachen Glacier ablation area in September 2010. It covered a 4 km2 area with a thick debris layer that unexpectedly, led to locally enhanced glacier mass loss during the following years. Enhanced melt opened a > 100 m deep 2 km2 depression and contributed to 6% of the mass loss of Siachen Glacier from 2010 to 2016 (−0.39 m w.e. a−1). We hypothesize that sub- or englacial melt may be responsible for this intriguing behaviour. This study contributes to a better knowledge of the regional pattern of the Karakoram anomaly and of the influence of rock avalanches on glacier mass changes.

Previous studies reported that Good Friday Glacier had been actively surging in the 1950–60s, 1990s and again in 2000–15. Based on observations of terminus position change from air photos and satellite imagery, we fill the gaps between previous studies and conclude that the glacier has been advancing continuously since 1959. Ice surface velocities extracted from optical and synthetic aperture radar satellite images show higher flow rates than on most other marine-terminating glaciers in the region. This behaviour contrasts with the regional trend of glacier retreat over this period. Possible explanations involve a delayed response to positive mass-balance conditions of the Little Ice Age, or a dynamic instability. There is, however, insufficient evidence to attribute this behaviour to classical glacier surging as suggested in previous studies. Based on present-day ice velocity and glacier geometry patterns in the terminus region, we reconstruct the evolution of ice motion throughout the advance, and suggest that what has previously been interpreted as a surge, may instead have been a localised response to small-scale perturbations in bedrock topography.

The West Kunlun Shan lie close to, or are perhaps part of, two significant glaciological phenomena – the High Mountain Asia surge ‘supercluster’ and the Karakoram Anomaly. However, glaciological studies, and particularly surge studies, in the range are limited. Here, we extend the database of known surges in the region using Landsat imagery and cross-correlation feature tracking. We examine 88 glaciers larger than 1 km2 in the Hotan Prefecture of Xinjiang, China, and find evidence of nine surges occurring between 1972 and 2017. Glaciers display low active phase velocities (~0.2–1.5 km a−1) that show seasonal acceleration in the summer, active phase periods as short as 2 years, and build-up and deceleration phases of months--years. Although these observations display characteristics indicative of both the classic hydrological and thermal switch mechanisms, the surging observed displays a close resemblance to that in the adjacent Karakoram ranges. Furthermore, the majority of the surges occur clustered at the end of a decadal-scale warming period, corroborating previously proposed causal links between climate and surging in the Karakoram. We suggest that the two regions should be considered part of one larger system when considering surge dynamics in High Mountain Asia.

Twin glaciers collapsed in 2016 near Aru Co, western Tibet and caused extreme loss to human beings. In this study, we attempted to track the dynamics of glaciers in the region, for example the glacier area and mass changes in Aru Co for the period 1971–2016, which were determined using topographic maps and Landsat images and ASTER-derived DEMs (2011–16), the Shuttle Radar Terrain Mission DEM (2000) and topographic maps (1971). Our results showed that the glacier area of Aru Co decreased by −0.4 ± 4.1% during 1971–2016. The geodetic mass-balance results showed that the glaciers in Aru Co lost mass at a rate of −0.15 ± 0.30 m w.e. a−1 during 1971–99, while they gained mass at a rate of 0.33 ± 0.61 m w.e. a−1 for the period 1999–2016. The twin glaciers experienced a larger negative mass budget than the others in the region before 1999. This process produced large amounts of meltwater, followed by a sustained increase in the meltwater on the pressure melting point, possibly in response to a period of positive mass balance (1999–2016) and then, transferred to the glacier bed until the glaciers collapsed.