Glacial-Lake Outburst Floods and Cryospheric Hazards
Mapping and forecasting outburst floods from a changing cryosphere.
Installing GPS instruments on glacial ice in Patagonia
A fourth thread confronts the hazards posed by a rapidly changing cryosphere. As glaciers retreat, meltwater collects in ice-marginal and moraine-dammed lakes that can fail catastrophically, releasing glacial-lake outburst floods (GLOFs) that travel far downstream. We have mapped how these lakes are evolving across Alaska and High Mountain Asia, characterized how their outburst behavior is changing, and worked to build science-based systems for forecasting GLOF hazard. (Jacquet et al., 2017; Rick et al., 2022; Rick et al., 2023)
Recent work tracks the rapid growth of ice-marginal lakes driven by glacier retreat, and the seasonal-to-decadal dynamics of lakes perched on debris-covered glaciers. These observations anchor the forecasts communities will need as the cryosphere continues to change. (McGrath et al., 2026; Zeller et al., 2024)
References
2026
Rapid ice-marginal lake growth in Alaska driven by glacier retreat through bed overdeepenings
Daniel McGrath, Louis Sass, William H. Armstrong, and 2 more authors
Proceedings of the National Academy of Sciences, Mar 2026
The number and cumulative area of ice-marginal lakes have expanded globally in recent decades, with many lakes residing in glacier-bed overdeepenings, which are subglacial basins formed through preferential glacial erosion. However, current lake expansion rates, key drivers of expansion, and maximum future lake extents are poorly quantified. This is notable because glacial lakes pose hazards, alter hydrologic and ecological systems, and, in some cases, accelerate glacier flow and retreat. Here, we quantify recent ice-marginal lake growth and use existing ice thickness and topographic data to map glacier-bed overdeepenings in Alaska as a predictor of recent and future locations of lake growth. Ice-marginal lakes in the region grew by +156 km2 (26 km2 y−1) between 2018 and 2024, representing a 50% increase relative to the 2009–2018 rate. Eighty percent of lake growth since 2018 occurred in mapped glacier-bed overdeepenings. Approximately 4,250 km2 (2,966 to 5,503 km2 accounting for ± ice thickness uncertainty) of the overdeepened area is connected to an ice-marginal lake, indicating the potential for more than fourfold lake growth of existing lakes as glaciers retreat. An additional 14,500 km2 (12,469 to 17,134 km2) of remaining glacier area resides on glacier-bed overdeepenings not connected to existing lakes, highlighting the potential for substantial new lake development. Velocities from lake-terminating glaciers show clear passive and dynamic endmembers on a continuum of glacier–lake coupling. Glaciers with ice-marginal lakes thinned 23 to 54% more than glaciers of similar area without lakes, underscoring the critical importance of dynamic glacier–lake coupling on the evolution of glaciers in Alaska.
2024
Seasonal to decadal dynamics of supraglacial lakes on debris-covered glaciers in the Khumbu region, Nepal
Lucas Zeller, Daniel McGrath, Scott W. McCoy, and 1 more author
Supraglacial lakes (SGLs) play an important role in debris-covered glacier (DCG) systems by enabling efficient interactions between the supraglacial, englacial, and subglacial environments. Developing a better understanding of the short-term and long-term development of these features is needed to constrain DCG evolution and the hazards posed to downstream communities, ecosystems, and infrastructure from rapid drainage. In this study, we present an analysis of supraglacial lakes on eight DCGs in the Khumbu region of Nepal by automating SGL identification in PlanetScope, Sentinel-2, and Landsat 5–9 images. We identify a regular annual cycle in SGL area, with lakes covering approximately twice as much area during their maximum annual extent (in the pre-monsoon season) than their minimum annual extent (in the post-monsoon season). The high spatiotemporal resolution of PlanetScope imagery (∼ daily, 3 m) shows that this cycle is driven by the appearance and expansion of small lakes in the upper debris-covered regions of these glaciers throughout the winter. Decadal-scale expansion of large, near-terminus lakes was identified on four of the glaciers (Khumbu, Lhotse, Nuptse, and Ambulapcha), while the remaining four showed no significant increases over the study period. The seasonal variation in SGL area is of comparable or greater magnitude as decadal-scale changes, highlighting the importance of accounting for this seasonality when interpreting long-term records of SGL changes from sparse observations. The complex spatiotemporal patterns revealed in our analysis are not captured in existing regional-scale glacial lake databases, suggesting that more targeted efforts are needed to capture the true variability of SGLs on large scales.
2023
Unchanged frequency and decreasing magnitude of outbursts from ice-dammed lakes in Alaska
B. Rick, D. McGrath, S. W. McCoy, and 1 more author
Glacial lakes can form and grow due to glacial retreat, and rapid lake drainage can produce destructive floods. Outburst flood compilations show a temporal increase in frequency; however, recent studies highlight the role of observational bias, creating uncertainty about current and future glacial-lake hazards. Here, we focus on the Alaska region, which generated a third of previously documented outbursts globally. Using multitemporal satellite imagery, we documented 1150 drainages from 106 ice-dammed lakes between 1985 and 2020. Documented events became more frequent over time, however, accounting for increasing image availability reveals no significant increase occurred. Most lakes decreased in area and volume, suggesting a reduction in regional flood hazard. Our satellite-based approach documented 60% more events in a 35-year period than had previously been documented over 100 years. This suggests that outburst floods have historically been underreported and warrants systematic study of other regions.
2022
Dam type and lake location characterize ice-marginal lake area change in Alaska and NW Canada between 1984 and 2019
Brianna Rick, Daniel McGrath, William Armstrong, and 1 more author
\textlessp\textgreater\textlessstrong class="journal-contentHeaderColor"\textgreaterAbstract.\textless/strong\textgreater Ice-marginal lakes impact glacier mass balance, water resources, and ecosystem dynamics and can produce catastrophic glacial lake outburst floods (GLOFs) via sudden drainage. Multitemporal inventories of ice-marginal lakes are a critical first step in understanding the drivers of historic change, predicting future lake evolution, and assessing GLOF hazards. Here, we use Landsat-era satellite imagery and supervised classification to semi-automatically delineate lake outlines for four \textlessspan class="inline-formula"\textgreater∼5\textless/span\textgreater-year time periods between 1984 and 2019 in Alaska and northwest Canada. Overall, ice-marginal lakes in the region have grown in total number (\textlessspan class="inline-formula"\textgreater+183\textless/span\textgreater lakes, 38 % increase) and area (\textlessspan class="inline-formula"\textgreater+483\textless/span\textgreater km\textlessspan class="inline-formula"\textgreater^\textrm2\textless/span\textgreater, 59 % increase) between the time periods of 1984–1988 and 2016–2019. However, changes in lake numbers and area were notably unsteady and nonuniform. We demonstrate that lake area changes are connected to dam type (moraine, bedrock, ice, or supraglacial) and topological position (proglacial, detached, unconnected, ice, or supraglacial), with important differences in lake behavior between the sub-groups. In strong contrast to all other dam types, ice-dammed lakes decreased in number (six fewer, 9 % decrease) and area (\textlessspan class="inline-formula"\textgreater−51\textless/span\textgreater km\textlessspan class="inline-formula"\textgreater^\textrm2\textless/span\textgreater, 40 % decrease), while moraine-dammed lakes increased (56 more, 26 % and \textlessspan class="inline-formula"\textgreater+479\textless/span\textgreater km\textlessspan class="inline-formula"\textgreater^\textrm2\textless/span\textgreater, 87 % increase for number and area, respectively) at a faster rate than the average when considering all dam types together. Proglacial lakes experienced the largest area changes and rate of change out of any lake position throughout the period of study and moraine-dammed lakes which experienced the largest increases are associated with clean-ice glaciers (\textlessspan class="inline-formula"\textgreater<19\textless/span\textgreater % debris cover). By tracking individual lakes through time and categorizing lakes by dam type, subregion, and topological position, we are able to parse trends that would otherwise be aliased if these characteristics were not considered. This work highlights the importance of such lake characterization when performing ice-marginal lake inventories and provides insight into the physical processes driving recent ice-marginal lake evolution.\textless/p\textgreater
2017
Hydrologic and geomorphic changes resulting from episodic glacial lake outburst floods: Rio Colonia, Patagonia, Chile
J. Jacquet, S. W. McCoy, D. McGrath, and 5 more authors
Glacial lake outburst floods (GLOFs) are a prominent but poorly understood cryospheric hazard in a warming climate. We quantify the hydrologic and geomorphic response to 21 episodic GLOFs that began in April 2008 using multitemporal satellite imagery and field observations. Peak discharge exiting the source lake became progressively muted downstream. At ~40–60 km downstream, where the floods entered and traveled down the main stem Rio Baker, peak discharges were generally \textless 2000 m3 sÀ1, although these flows were still \textgreater1–2 times the peak annual discharge of this system, Chile’s largest river by volume. As such, caution must be applied to empirical relationships relating lake volume to peak discharge, as the latter is dependent on where this observation is made along the flood path. The GLOFs and subsequent periods of free drainage resulted in \textgreater 40 m of incision, the net removal of ~25 × 106 m3 of sediment from the source lake basin, and a nonsteady channel configuration downstream. These results demonstrate that GLOFs sourced from low-order tributaries can produce significant floods on major main stem rivers, in addition to significantly altering sediment dynamics.
