Scientists say basin storage up as glacier thins; 2025 outburst released about 51,000 acre‑feet

Juneau — University and federal scientists told the City and Borough of Juneau Assembly’s Committee of the Whole that ongoing drone surveys and river monitoring show Suicide Basin’s storage capacity has been increasing even as the Mendenhall ice dam thins, raising the potential for large outburst floods in some years.

Dr. Jason Edmondson, a glaciologist with the University of Alaska, said the 2025 outburst “released 51,000 acre feet of water,” and that figure is more than half the volume of Mendenhall Lake. He described three main drivers: ice‑dam thinning, melt of floating icebergs in the basin, and small shifts in the ice‑dam location that can add or subtract thousands of acre‑feet of storage.

Why it matters: storage capacity and basin shape are core inputs to river forecasts, and they have changed substantially since routine drone surveys began in 2018. Edmondson said drone‑derived digital elevation models (DEMs) and repeated surveys allow scientists to build elevation–volume curves used by forecasters to…