(CNN) — A group of 18 kayakers paddling on Lake Superior on Monday had stopped to take in the scenic view along the Pictured Rocks National Lakeshore when, suddenly, sections of the sandstone cliff wall collapsed into the water just yards in front of them.

Maxim Rigaux was in the kayak closest to the rockfall. “We noticed it first when some little rocks fell down just next to one of our guides who was just under the cliff,” he said.

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The guide paddled away, and even bigger rocks began raining down.

Rigaux started recording and captured video of the massive rockfall as entire swath of the cliff cascaded into the lake, raising a plume of water and dust.

“We had no idea if there would be even more rockfall,” he said. “We were kind of in shock and awe at the same time.”

The colored sandstone cliffs rise up to 200 feet high. They’re notable for the vertical mineral streaks that make them look like naturally painted abstract murals in some places.

The power of Lake Superior shapes the coastline on the the Pictured Rocks National Lakeshore, the National Park Service says.

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“The slope has been over-steepened by waves pounding away at the bottom of the slope,” Richard Ziegler, a geology professor at Northern Michigan University, told CNN affiliate WLUC.

“The slopes becomes too steep, gravity takes over, and rocks start to fall,” Ziegler said.

Although it makes geological sense, it’s still an unusual sight if you’re setting off for a relaxing day on the water.

“The tour leaders were as surprised as we were,” Rigaux said. “They had never experienced this before.”

Van Ouellette-Ballas, the kayaking group’s guide, told WLUC, “I’m definitely not getting near these rocks again. That’s for sure.”

Rigaux said the group “all realized how unique the experience was but also how narrowly we escaped a more tragic accident.”

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