Dam type and lake location characterize ice-marginal lake area change in Alaska and NW Canada between 1984 and 2019

Abstract

Abstract. 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 ∼5-year time periods between 1984 and 2019 in Alaska and northwest Canada. Overall, ice-marginal lakes in the region have grown in total number (+183 lakes, 38 % increase) and area (+483 km2, 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 (−51 km2, 40 % decrease), while moraine-dammed lakes increased (56 more, 26 % and +479 km2, 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 (<19 % 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.

Trends, Breaks, and Biases in the Frequency of Reported Glacier Lake Outburst Floods

“…Artificial drainages of moraine‐dammed lakes may also have helped to maintain a constant GLOF rate in past decades (Emmer et al., 2018; Haeberli et al., 2001). Ice‐dammed lakes, in contrast, are more short‐lived, and their formation is tied to thick glaciers that can impound lakes at their margins, a common situation along glaciers descending from ice fields in Alaska (Field et al., 2021; Rick et al., 2022) and Patagonia (Wilson et al., 2018). With climate‐enhanced melting, ice‐dammed lakes can enter cycles of outbursts such as lakes dammed by Tulsequah or Kennicott Glaciers that produced multiple GLOFs per year during the 20th century (Geertsema & Clague, 2005; Rickman & Rosenkrans, 1997).…”

“…Hence the regional increases in ice‐dammed failures (Figure 2) are tied to fewer lakes that burst more frequently. Despite some current positive trends, we may thus see declining trends in ice‐dam failures sometime in the future, when ongoing ice loss impedes the formation of such dams (Rick et al., 2022).…”

“…In Alaska, for example, the total number and area of ice‐dammed lakes decreased by 13% and 43%, respectively, between 1984 and 2019. Only 16 new ice‐dammed lakes have reformed in this period, possibly at higher elevations in recently deglaciated tributary valleys (Rick et al., 2022). Hence the regional increases in ice‐dammed failures (Figure 2) are tied to fewer lakes that burst more frequently.…”

“…Globally, the size and abundance of glacier lakes has doubled between 1990 and 2017 (Shugar et al., 2020). Most of the growth in glacier lake area has been tied to moraine‐dammed lakes (Buckel et al., 2018; Emmer et al., 2020; Rick et al., 2022; Wilson et al., 2018; Zheng, Allen, et al., 2021), motivating numerous GLOF hazard and risk appraisals (Emmer, 2018). However, our assessment is consistent with other regional assessments that noted a lack of any long‐term, continuous increase in the frequency of moraine‐dam failures (Emmer et al., 2020; Veh et al., 2019).…”

“…Yet several hundreds of ice-dammed lakes have disappeared in our study regions as a consequence of downwasting and retreat of glacier dams in past decades (Geertsema & Clague, 2005;Tweed & Russell, 1999;Wolfe et al, 2014). In Alaska, for example, the total number and area of ice-dammed lakes decreased by 13% and 43%, respectively, between 1984 and 2019. Only 16 new ice-dammed lakes have reformed in this period, possibly at higher elevations in recently deglaciated tributary valleys (Rick et al, 2022). Hence the regional increases in ice-dammed failures (Figure 2) are tied to fewer lakes that burst more frequently.…”