A billboard-size slab of sandstone slid off the face of Landscape Arch this week.
"I estimated the fallen section to be about 20 to 30 feet in length, about 4 feet across and a couple of feet thick," said Noel Poe, superintendent of Arches National Park."It came off the front, viewpoint side of the arch, toward the east end, not off the bottom, so the arch did not get any thinner in depth," he said.
Monday's fall was the second major rockfall from Landscape in the past four years. It lost a 60-foot-long, 10-foot-wide and 4 1/2-foot thick sheaf from its underside in September 1991.
About 2 dozen visitors witnessed the Monday event.
Brigham Young University geology professor Dale Stevens, an arch expert who has spearheaded the cataloging of more than 2,000 natural-stone arches and bridges inside the park, said the rockfall was due to natural weathering of the sandstone.
At 306 feet in length, Landscape Arch vies with Kolob Arch in Zion National Park as the longest natural-stone arch in the world.