Natural Wonders: The Smoking Hills

In 1850, the Irish explorer Robert McClure saw smoke rising from the eastern shoreline of Cape Bathurst, in Canada’s Northwest Territories. He and his crew aboard HMS Investigator were elated. They hoped that this was a smoke signal from John Franklin and his lost expedition, which had disappeared while seeking the Northwest Passage five years earlier.

To their dismay, Franklin was nowhere in sight. Rather, they trudged up the multicolored escarped shoreline to find a hellish scene of sulfuric ponds and smoking rocks. It is said that McClure brought a rock on his ship as a souvenir. It burned a hole in his mahogany desk.

Smoking Hills from the Arctic Ocean. Photo: Ray Muzyka/Flickr


It was actually Sir John Franklin who first discovered and named the Smoking Hills during his earlier Mackenzie River Expedition (1825-1827). They were mapping Horton River when they saw smoke rising from the 100m hills.

The naturalist on that Mackenzie River Expedition, John Richardson, hypothesized that oxidation of sulfuric minerals and organic matter in the shale was to blame. He was right. Most originally thought that volcanic or hydrothermal activity caused the smoke. However, the unique site is home to subterranean oil shales, which spontaneously combust as the rock weathers and erodes.


Clouds of smoke from lignite deposits. Photo: Michael D. Turnbull


These deposits are made of lignite (brown coal) and high concentrations of sulfuric substances, which ignite when they come into contact with oxygen. Oxygen consumes the electrons in the pyrite and organic material in the shale. This releases a great amount of heat and hundreds of grams of sulfur dioxide every second. The rocks that undergo this process are called “bocannes”. The varied hot temperatures turn the rocks red, black, brown, yellow, and white. 

In addition to this, one-metre deep toxic ponds dot the one-hectare area. These caustic ponds contain high concentrations of minerals like aluminum, manganese, zinc, iron, cadmium, and nickel and host 14 species of acid-tolerant algae. From written records and oral tradition, it seems that the hills have burned for centuries. Occasionally, however, the exothermic reactions dissipate when oxygen levels die as the shale burns further into the cliff.

The Paulatuk people, who live almost 100km away, have always called the hills “the place of soot” or “the place of coal”. 

An eroding mud face. Photo: Michael D. Turnbull


The Smoking Hills is considered one of the seven wonders of the Northwest Territories. No roads are nearby; they’re accessible only by boat or helicopter. Visitors rarely set foot on the smoky shore, which is highly toxic and polluting.

The hills have impacted their surroundings, especially the tundra further inland. Sulfur dioxide has acidified the soil. The closer to the sea you go, the more desolate the land, as plant life struggles to withstand the acidity. 

It seems like this is one of those rare examples of natural pollution.