# Rapid ice-marginal lake growth in Alaska driven by glacier retreat through bed overdeepenings

## TL;DR

Glacial lakes in Alaska are growing rapidly due to glacier retreat, especially in deep subglacial basins, which could lead to much larger lakes in the future.

## Contribution

The study quantifies recent ice-marginal lake growth and maps glacier-bed overdeepenings as predictors of future lake expansion in Alaska.

## Key findings

- Ice-marginal lakes in Alaska grew by 156 km2 between 2018 and 2024, with 80% of growth in overdeepenings.
- Glaciers with lakes thinned 23 to 54% more than those without, showing dynamic glacier-lake coupling.
- Approximately 4,250 km2 of overdeepenings are connected to lakes, suggesting potential for over fourfold lake growth.

## Abstract

Glacial lakes in the Alaska region expanded by >150 km2 between 2018 and 2024, representing a 50 to 120% faster rate of expansion than previous periods (1986–2018). This growth primarily occurred in mapped glacier-bed overdeepenings. There is approximately 4,250 km2 of glacier-bed overdeepenings connected to lakes today, indicating that future regional ice-marginal lake area could be more than four times larger than today. Glacier response to ice-marginal lakes varies substantially as some exhibit a dynamic response with positive feedbacks leading to glacier retreat and rapid lake growth, while others show a passive response, where lake growth is typically much slower. Understanding this response is critical for projecting individual glacier mass loss and lake growth.

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.