text: The Superstack was built by Inco Limited (and later purchased by Vale) at an estimated cost of 25 million dollars. Construction on the structure was underway during the Sudbury tornado of August 20, 1970; the structure swayed heavily in the wind, but remained standing and suffered only minor damage. Six workers were on top of the construction platform when the storm hit, and all survived. The same day was the final day of construction on the stack, with the construction fully completed by the evening of August 21, 1970.
  The stack entered into full operation in 1972. From the date of its completion until the Ekibastuz GRES-2 chimney was constructed in 1987, it was the world's tallest smokestack. Between the years 1972–75 it was the tallest freestanding structure in Canada.
  Prior to the construction of the Superstack, the waste gases contributed to severe local ecological damage. The Copper Cliff smelter was already home to some of the world's tallest stacks, including two  chimneys constructed in 1928-29 and 1936. However, these proved to be insufficient and compounded by open coke beds in the early to mid-20th century and logging for fuel, an inevitable near-total loss of native vegetation occurred. Of particular interest to geologists are the now exposed rocky outcrops, which have been permanently stained charcoal black, first by the pollution wafting over the decades from the roasting yards, then by the acid rain in a layer which penetrates up to three inches into the once pink-grey granite.
  The Superstack was built to disperse sulphur gases and other byproducts of the smelting process away from the city of Sudbury. It did this by placing the gases high in the air, where they normally blew right past the city on the prevailing winds. As a result, these gases can be detected in the atmosphere around Greater Sudbury in a  radius of the Inco plant. During the 1970s and 80s, the sulphur dioxide plume formed a permanent, opaque, cloud-like formation running across the entire horizon as seen from a distance. Periodic inversions would cause the plume to fall into the city.
  Construction of the Superstack was followed by an environmental reclamation project which has included rehabilitation of existing landscapes and selected water bodies such as Lake Ramsey. An ambitious regreening plan has seen over three million new trees planted within the Greater Sudbury area. In 1992, Inco and the city were given an award by the United Nations in honour of their environmental rehabilitation programmes.
  On November 3, 2014, Vale announced that they may decide to stop using the stack, following a $1 billion project to reduce emissions by 85% that negates the need for the stack. If no other use for it is found, Vale may decommission the superstack, demolish it, and replace it with a much smaller chimney. In 2017, Vale announced plans to decommission the Superstack upon the construction of two smaller, more energy efficient stacks. On July 28, 2020, Vale updated that news, stating that the stack at its Copper Cliff Complex had been taken out of service. It would remain on "hot standby" for about two months while the replacement flue connections were tested but the stack would then be demolished over the years.