Kiirunavaara (Kiruna) iron ore mine owned by LKAB (Sweden) is one of the largest underground mines. Mining started in 1898 as an open pit mine. In mid-1950, the mine started a transition to underground mining and passed to only underground mining in 1962. More substantial problems with seismicity started in 2007-2008 when the deepest mining level was 907 m (ca. 670 m below surface). By 2016, th...