A portion of a glacier that travels much more quickly than adjacent portions of the glacier.
Part of an ice sheet in which the ice flows more rapidly and not necessarily in the same direction as the surrounding ice. The margins are sometimes clearly marked by a change in direction of the surface slope, but maybe indistinct.
A zone of high velocity within an ice cap or ice sheet. By analogy with flood waters, which have high velocities within their channels but low velocities in the flood plain, ice streams are often (but not necessarily) associated with a subglacial trough.