Inco Superstack, Flue-gas stack in Greater Sudbury, Canada

The Inco Superstack is a tapered concrete chimney at Vale's Copper Cliff smelting complex in Greater Sudbury, Ontario. Completed in 1970 and in full operation from 1972, it rose 381 metres, widening to about 35 metres near its base. Dismantling began in September 2025, and by October 2025 its height had been cut by roughly 35 metres to about 345 metres.

Inco Limited built the Superstack at an estimated cost of 25 million dollars, with construction delayed by a 13-week labour dispute. Work was underway during the Sudbury tornado of August 20, 1970; the structure swayed heavily but suffered only minor damage, and the six workers on the construction platform survived. Construction was completed by the evening of August 21, 1970, and the stack entered full operation in 1972. Until the Ekibastuz GRES-2 chimney was built in 1987, it was the world's tallest smokestack.

The stack's name comes from Inco Limited, the company that built it and ran the Copper Cliff smelter before Vale took over. Its plume was a familiar sight on the horizon in the 1970s and 80s, and the regreening that followed earned Inco and the city a 1992 United Nations award.

The structure sits on Vale's facility grounds and can be viewed from several points across the city, especially on clear days. Best views often come from a distance or from elevated spots in town where you can take in its full height.

The Sudbury tornado of 20 August 1970 hit while the stack was still being built; the unfinished structure swayed heavily but held, with only minor damage. Six workers were on the construction platform at the top and all survived. That same day was the last day of construction, finished by the evening of 21 August 1970.