El Capitan rises over 3,000 feet above the floor of Yosemite National Park in California. Scaling this granite edifice is considered a rite of passage among elite climbers, who come from around the world to test themselves on its sheer face.

But this towering behemoth is the site of frequent rockfalls. Over 20 have occurred in the last decade, including one in 2017 that killed a climber. The majority of these falls have been linked to rock formations known as flakes, sheets of rock that are peeling off El Capitan like layers of onion skin.

With infrared imaging, scientists have now essentially peered behind two of the largest flakes, Boot Flake and Texas Flake, to determine how well they’re connected to El Capitan. The results, presented at a meeting of the European Geosciences Union in Vienna in April, suggest that the underlying structures linking each flake to the 100-million-year-old granite are surprisingly small. By visualizing these attachment points, scientists can monitor them to keep climbers safe.

“This is a beautiful study,” said Allen Glazner, a geologist at The University of North Carolina at Chapel Hill not involved in the research. It shows how much “glue” is holding these rocks up, he said.