Winthrop Glacier, Alpine glacier on Mount Rainier, Washington State

Winthrop Glacier is an alpine glacier on the northeastern side of Mount Rainier, covering the slopes with thick ice and dense snow. Its surface displays deep crevasses and intricate ice formations shaped by constant glacial movement.

The Winthrop Glacier is named after Theodore Winthrop, the writer who travelled through the Pacific Northwest in the 1850s. It is one of four glaciers on Mount Rainier known to have released debris flows, alongside the Nisqually, Kautz and South Tahoma glaciers. Up to the Steamboat Prow it is joined to the Emmons Glacier, after which the two split, the Emmons turning east-northeast and the Winthrop continuing northeast.

The glacier serves as an educational site for researchers studying climate patterns and geological formations in the Cascade Mountain Range.

The glacier ends in forest at about 4,900 ft (1,500 m), and its meltwater feeds the White River. It is one of four Mount Rainier glaciers known to have released debris flows, alongside the Nisqually, Kautz and South Tahoma glaciers, so plan routes with that hazard in mind.

The Winthrop is one of four glaciers on Mount Rainier known to have released debris flows, alongside the Nisqually, Kautz and South Tahoma. Its meltwater drains into the White River, and at its lower end the ice is heavily covered with rock where it ends in forest at about 4,900 feet.