Berkeley Pit slough

On February 8, 2013 material from the southeast wall of the Berkeley Pit collapsed into the Pit water in what is known as a rotational slump or slough. Such sloughs are relatively common in open pit mines. For example, a similar slough occurred at the Berkeley Pit in 1998.

This photo from July 2013 shows the rim of the Berkeley Pit were a slough deposited surface material into the Pit lake in Feb. 2013. Photo by Fritz Daily.

This photo from July 2013 shows the rim of the Berkeley Pit were a slough deposited surface material into the Pit lake in Feb. 2013. Photo by Fritz Daily.

The recent slough was about 550 feet wide and caused an estimated 820,000 tons of material to collapse into the Pit. Montana Bureau of Mines & Geology (MBMG) monitoring showed that the water level in the Pit lake rose about 0.6 feet as a result of the slough. For comparison, over the past several years the water in the Berkeley Pit has risen about 0.65 feet per month.

Current projections still estimate that water levels at one of the surrounding monitoring compliance points for the Berkeley Pit system will reach the Critical Level (5,410 feet) around 2023.

Pumping and treating of Berkeley Pit water will be required when water levels at any of these compliance points reach the Critical Water Level. Currently, the highest water level is in the Pilot Butte shaft to the north of the Pit. As of June 2013, the Berkeley Pit water level was 5,310.89 feet above sea level, and the water level in the Pilot Butte shaft was 5,335.72 feet above sea level, or about 75 feet below the critical level.

Click here for more information about the Critical Water Level.

5 Responses so far.

  1. Jim Larson says:

    Was there any prior indication that the slough was imminent?

    Jim Larson

    • PitWatch says:

      We don’t think so, but passed your question on to Montana Resources, the Montana Bureau of Mines, and the Montana Department of Environmental Quality to double-check.

      • Len Hoar says:

        wow ,,, looks to B very interesting to undeniably serious . Hopefully everything half mile semi circle into the concentrator area is survey pin pointed and Constantly monitored for movement into the direction of the pit,,,,,,,,,,,,no room for error or surprise now ……Instant involement now … By alot of responsiblity.

        • PitWatch says:

          Thank you for your comment. We hope everyone finds the Pit interesting at the least! Ground and surface water around the Pit are extensively and regularly monitored. You can learn more from the article How is the Pit monitored? and the other articles in the Monitoring section of our website. Additionally, Montana Resources monitors any land movement, such as the slough that occurred earlier this year, as part of their active mining operation adjacent to the Berkeley, and the Montana Bureau of Mines & Geology monitors seismic activity through its Earthquake Studies Office. In other words, a lot of people are directly involved in keeping an eye on the Berkeley Pit and surrounding area. It is certainly a lot of responsibility, not just for the professionals involved and the Butte community, but also for all of us who enjoy the many benefits of copper mining, like electricity and products too numerous to mention.

  2. John says:

    ARCO created this mess.

    Guess who owns ARCO, BP.

    Ring any bells?

    BP, the same BP that destroyed the Gulf of Mexico.

    I would eminent domain any remaining corporation’s property in the State and claim it for the citizens who have been irreparably damaged by ARCO.

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