A cleaver, in descriptive geology, and in mountaineering on and near glaciers, is a ridge of rock that separates a unified flow of glacial ice from its uphill side into two glaciers flanking, and flowing parallel to, the ridge. (As a meat cleaver separates meat into smaller pieces, such a cleaver divides or cleaves the continuous flow from above into two distinct flows.) A cleaver may be thought of as analogous to an island in a river. (However, a common situation has the two flanking glaciers melting to their respective ends before their courses can bring them back together; the exceedingly rare analogy is a situation of the two branches of a river drying up, before the downstream tip of the island, by evaporation or absorption into the ground.)

The location of a cleaver is often an important factor in the choice among routes for glacier travel. For example, following a cleaver up or down a mountain may avoid travelling on or under an unstable glacial, snow, or rock area. This is usually the case on those summer routes to the summit whose lower portions are on the south face of Mount Rainier: climbers traverse the "flats" of Ingraham Glacier, but ascend Disappointment Cleaver and follow its ridgeline rather than ascending the headwall either of that glacier or (on the other side of the cleaver) of Emmons Glacier.