Mobilization of metal-contaminated sediment by ice-jam floods

 A large river ice jam and associated flooding in February 1996 on the Blackfoot and Clark Fork Rivers of western Montana mobilized large amounts of fine-grained sediment. Metal concentrations in sediment downstream from a reservoir containing large amounts of contaminated sediment were enriched in metals after the ice jam, while open reaches above the reservoir were diluted by ice-jam processes. This varied response shows the importance of understanding ice jam events to sediment and metal transport and suggests that ice jams must be considered as important agents affecting sediment metal concentrations in rivers. Received: 4 December 1997 · Accepted: 23 February 1998