A swamp or bog occurring in depressions in poorly drained alluvial or glacial terrain in northern Canada or the United States. The depression usually accumulates a saturated, highly compressible mixture of mineral particles and decaying vegetal matter, topped by a hummocky surface of sphagnum moss, and incapable of supporting heavy loads or traffic. In the colder and wetter parts of Alaska, these accumulations spread widely over low-amplitude terrain and are not confined to depressions.