For part of 1966, Steele Glacier in the Icefield Ranges, Yukon Territory, Canada, made a spectacular advance at a rate exceeding 500 m per month. The main part of the surge continued for two years, but by early 1968 the advance had slowed to less than one tenth of the maximum rate. For most of the 35-km length of the main trunk the surface was a chaotic jumble of ice blocks, spires, and pinnacles, but large structures outlined by surface moraine were preserved. Most of these structures had been displaced 8 km by August 1967, irrespective of their original location. Preliminary measurements indicate structures were displaced similar distances down the length of the glacier and suggest that most of the glacier moved forward as a block. The surge has not been correlated with any local earthquake activity, and there is no evidence for a short-term climatic change. The movement is considered to result from critical dynamic conditions within the glacier, possibly facilitated by increased amounts of water along the ice-bedrock contact.