Earthshots: Satellite Images of Environmental Change

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» Mesabi Range, Minnesota, USA

The boom times of iron ore mining in northern Minnesota are long gone, but mining operations continue and are even expanding, as seen in these Landsat images.

The Mesabi Range, which stretches 80–100 miles from Grand Rapids to Babbitt, contributed about 60% of the total iron ore output in the United States throughout most of the 20th century. The soft ore was close to the surface, and it could be scooped from open-pit mines and shipped by rail to Lake Superior and eventually to steel mills.

Iron ore production peaked in the 1940s when more than 600,000 tons were shipped during World War II. Production remained high in the postwar years and then declined. The high-grade ore was soon nearly depleted. Mining activity on the Mesabi Range now involves digging out lower grade ore for processing.

The iron ore open-pit mines on the Range are among the biggest in the world. But the footprints of the mines’ tailings ponds are even bigger. Both are readily visible in these Landsat images.

Map of the featured area.

The mines on the Mesabi Range historically extracted hematite, a rusty-red gravel-like ore. Hematite contained 50–70% iron and could be dug out of the ground and shipped right out to be made into steel. From 1890 to about 1980, 2.5 billion tons of this ore was mined here, but these “natural ores” were largely depleted by the 1980s.

Landsat images acquired after 1984, however, show continued expansion of the open-pit mines. The rock being mined now is a lower grade ore called taconite, which has about 25–30% iron content. Taconite is a hard, dense rock containing a mixture of silicates and magnetite and is abundant on the Mesabi Range.

New processing methods developed in the mid-20th century made taconite mining profitable. After it’s mined, the taconite is crushed into a fine powder. The magnetite is separated with magnets and agglomerated into marble-sized pellets. The finished pellets contain over 65% iron. These pellets are shipped to steel mills.

Because only about one-third of the magnetite is used in the taconite production process, large amounts of tailings are generated. While the open-pit mines are visible in Landsat images, it’s the large pink/purple areas—the tailings basins—that really stand out because they take up more area.

Tailings flow as slurry into these basins, which are bounded by earthen dikes. Taconite tailings particles range from the size of clay to sand. Some of the tailings may be mined again as technology develops to remove any remaining iron.

The USGS aerial photo from 1953 includes a portion of the area shown in this Landsat series. The urban areas are the towns of Virginia and Eveleth. The historical aerial photos extend the imagery record back at least two decades further than the Landsat scenes. Using these photos from the collection at EROS, we can see the mining activity and associated land changes even earlier than the Landsat record.

Other mines also continue to expand, even in the Landsat era. The Hull-Rust-Mahoning Mine near Hibbing is one of the biggest mines in the world. Some call it the “Grand Canyon of the North.”

Rather than a natural wonder, the 535-foot-deep mine is another huge open pit gouged into the Mesabi Range and expanded over the decades. In the Landsat images, it’s still the tailings basin that stands out and takes up more land area. The mine itself is between the tailings basin and the city of Hibbing. Both the basin and the mine expand during this time series of Landsat images.

Another tailings pond expands farther to the south. This is the Keetac mine and tailings basin.

Another USGS aerial photo shows part of this area pre-Landsat. The Hull-Rust-Mahoning open-pit mine is just north of Hibbing in 1953, but the current tailings basin had not been established yet.

At the western end of the Mesabi Range is another consequence of the mining industry. Once mining operations halted in some parts of the Range, the deep open pits that were created were left to fill with rainwater and groundwater inflow. One of these lakes is the Canisteo pit lake.

At about 4.8 miles long and 0.5 mile wide, it’s about the same size as Trout Lake to the south, a natural lake. The Canisteo pit is actually a complex of 19 inactive mine pits. The lake is now an average of 100 feet deep, with its deepest point a remarkable 300 feet. (For comparison, the deepest point in Mille Lacs Lake, Minnesota’s second largest lake, is about 40 feet.)

The filling of this pit lake concerns residents of the adjacent small towns. Without some kind of intervention, these towns could eventually flood. The current temporary solution is a drain tile system to carry groundwater leaving the pit toward Trout Lake.

The Hill Annex Mine pit lake is also in this scene, just east of Canisteo pit lake. This lake is also very deep. Hill Annex Mine State Park is located on the lake’s shores.

The USGS aerial image shows the open pit mines that are now Canisteo pit lake. The towns of Coleraine and Bovey sit between these mines and Trout Lake.


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