Borealis Glacier is in North Cascades National Park in the U.S. state of Washington and is on the north slopes of Primus Peak. Borealis Glacier flows generally northeast for a distance of approximately . Borealis Glacier descends from nearly , but is split into an upper and lower sections. The upper section is as much as wide, but ends abruptly in an icefall along some cliffs. The lower section has been retreating significantly, and between 1990 and 2009 lost almost in length, creating a proglacial lake at the terminus.