The ranger made it clear: “Erosion never sleeps.”
At St. Anthony Falls, this is particularly true as millions of gallons of turbulent water churn through the heart of Minneapolis, eroding rocks, shoreline, and infrastructure. During a trip to the Falls Lock & Dam Visitors Center yesterday, students in The Power of Water class learned just how destructive that water can be.
“We learned about erosion from cavitation,” said Grace.
“Cavitation is when the pressure is so low that water starts to boil on its own when it goes really fast,” explained Hailey. “When the water cools down, it implodes and contracts.” That process, confirmed the ranger, creates erosion, leaving rocks, turbines, and other water structures pocked with rough, damaged surfaces.
The ranger encouraged students to explore an old turbine mounted at the Visitors Center so they could experience the effects of cavitation erosion. Small hands touched the rough blades impacted by years of seething water.
The ranger took students up to the observation deck overlooking the lock, and then across the lock to get a better view of the falls. But getting to the other side created a dilemma for a few students. “Do I have to do that?” asked Devin, looking with big eyes at the narrow catwalk hundreds of feet above the lock. “It’s so unstable!”
Jocelyn assured Devin that it was perfectly safe. “The architecture is stable,” she said, doing a quick engineering analysis of the walkway.
“I studied architecture a couple of years ago at Summer Academy and just by looking at it, I can tell it has a strong hold.” She identified a familiar zigzag pattern in the bridge construction that she knew created stability in a structure.
Hailey also felt it was safe. “I saw that it said ‘maximum capacity 3.5 tons’. All of us couldn’t take that bridge down,” she laughed. Despite their assurances, Devin made sure to “just kinda run” across.
Once on the other side of the lock, Sammy was struck by the differences between the two sections of water. “I think it’s kinda funny that over here is all calm,” he motioned to the water in the lock, “and here it’s all crazy!” The “crazy” falls raged over the ramps put in place to slow the water down and minimize cavitation erosion.
In the end, the ranger challenged the students to continue learning about and preserving the beautiful river and falls that have made the Twin Cities what they are.