Topographic controls on ice flow and recession for Juneau Icefield (Alaska/British Columbia)

Globally, glaciers are losing dramatic volumes of ice, especially in Alaska, which dominates sea-level rise from glaciers. Plateau icefields may be especially sensitive to climate change due to the non-linear controls their topography imparts on their response to climate change. However, Alaskan plateau icefields have been subject to little structural glaciological or regional geomorphological assessment, which makes the controls on their present and former mass balance difficult to ascertain.

We inventoried 1050 glaciers and 401 lakes of the Juneau Icefield region for the year 2019. We found that 63 glaciers had disappeared since the 2005 inventory, with a reduction of glacier area of 422 km². We also present the first structural glaciological and geomorphological map for an entire plateau icefield in Alaska. Glaciological mapping of nearly 20,000 features included crevasses, debris cover, foliation, ogives, medial moraines and, importantly, areas of glacier fragmentation, where glaciers either separated from tributaries via lateral recession (n=59), and disconnected within areas of former icefalls (n=281). Geomorphological mapping of >10,000 landforms included glacial moraines, glacial lakes, trimlines, flutes and cirques. These landforms were generated by a temperate icefield during the “Little Ice Age” neoglaciation. These data demonstrate that the present-day outlet glaciers, which have a similar thermal and ice-flow regime, have undergone largely continuous recession since the “Little Ice Age”.

These data document the interactions between topography and glacier change. Importantly, disconnections are occurring within glaciers can separate accumulation and ablation zones, increasing rates of glacier mass loss. We show that glacier disconnections are widespread across the icefield and should be critically taken into consideration when icefield vulnerability to climate change is considered.