Altura Minnesota lagoon collapses

Abstract

In April 1976, a series of karst sinkholes opened in the holding lagoon of the Altura, Minnesota Waste Treatment Facility. This major failure was preceded by minor sinkhole formation during the construction of the facility in 1974. Subsequent detailed field mapping of the region around the community revealed at least 23 sinkholes not shown on existing maps. The distribution of the sinkholes as well as post-failure investigations of the lagoon indicate that catastrophic collapse is related to the presence of a thin, poorly indurated, jointed sandstone overlying a thick carbonate unit. The sandstone served to collect solutionally aggressive vadose water and to concentrate that water onto specific areas of the underlying carbonate. The resulting differential solution produced voids into which the overlying materials collapsed.