Investigators say St. Paul officials could not have predicted rockslide that killed 2 children

A rockslide that killed two children during a school field trip at a St. Paul park was the result of natural causes, and city officials could not have prevented or predicted it, according to findings of two investigations released Thursday.

Mayor Chris Coleman hired two independent investigators to examine the incident at Lilydale Regional Park. One investigation looked at what the city knew and whether the rockslide could have been prevented. The other examined the geotechnical aspects of the slide and what caused it.

The investigators found the collapse was an "unpredictable, natural occurrence," the city said in a statement. The city said it will continue to suspend permits for fossil hunting in the park while it creates a plan to keep park users informed of potential risks going forward.

Lilydale Regional Park runs along the Mississippi River. It's a popular destination for fossil hunting, which requires a permit from the city.

Fourth-graders from Peter Hobart Elementary School in St. Louis Park were on a fossil-hunting field trip in the park on May 22 when a mass of sand and broken shale fell from a bluff overlooking the fossil beds near the East Clay Pit. Two students — 10-year-old Mohamed Fofana and 9-year-old Haysem Sani — were killed. Two others were injured.

"My heart goes out to the parents and families of Mohamed and Haysem and others hurt or impacted by the May 22nd landslide," Coleman said in a statement.

One investigation led by Don Lewis, the dean at Hamline University's School of Law, found that the slope failure was apparently due to natural soil erosion common along the Mississippi River bluffs, aggravated by a rainy spring and foot traffic along unmarked trails. The other investigation, led by Ryan Benson of Northern Technologies Incorporated, found the rockslide was a result of natural changes in the environment, combined with weathered shale.

Benson's team said that due to many variables in the region, it is hard to predict when, where, or how big the next rockslide would be. However, the team's report said: "The only variable that is predictable with a high level of certainty is that slopes of this nature, although apparently stable to a non-professional, are inherently unstable, will undergo additional weathering, and are highly likely to undergo failures of varying degrees in the future."

Lewis's investigation looked at what the city knew before the slide. His team conducted more than 30 interviews, gathered 90,000 emails and 22,203 paper files. He said the city was aware that slope failures had occurred within the park and along the bluffs before. In May 2011, there was one slope failure north of the East Clay Pit, but it did not damage people or property. Nine months later, a Parks and Recreation forestry supervisor saw erosion while ice climbing in the Fossil Ground, and reported that the hillside was at risk.

Lewis' team found that while there was knowledge of soil erosion, there was no evidence of actual knowledge of unstable bluffs that posed a safety risk.

"The city did not know soil erosion posed a threat," Lewis said.

Current phone listings for families of the victims were not immediately available.