After thousands of years in one seemingly precarious position, the hanging boulder at the Polar Caves in Rumney finally gave in to gravity, falling to the ground on the last day of the park’s season earlier this month. The boulder has been an attraction in the park since it opened more than 100 years ago.
The park said no one was injured by the Oct. 18 crash.
“During the off-season, Polar Caves will assess the site to determine appropriate next steps. The safety of our guests and employees continues to be our highest priority,” the park said in a statement.
The so-called “Mysterious Hanging Boulder” looked like it defied the laws of gravity: Despite its more than 80-ton weight, it jutted out from a wall of granite, allowing visitors to walk underneath it, with more than 75% of the formation’s weight suspended above their heads. According to a sign at the site, the boulder rested on the rock face at three points.
What the park refers to as “caves” are more like passageways between large granite boulders, left over as the Laurentide Ice Sheet — which once covered most of modern day Canada and all of New England – receded more than 10,000 years ago. Joseph Licciardi, a glacial geologist at the University of New Hampshire, said this glacier helped shape the present day landscape, including the formations at the park.
“Those boulders were probably moved last about maybe 14-something-thousand years ago,” he said.
Licciardi said he hasn’t been to the park to examine the fallen boulder, but he guessed it finally reached a “tipping point” after the cumulative effect of thousands of years of exposure to wind, rain and changing temperatures. He said its fall reminded him of the Old Man of the Mountain, both in terms of why it fell and the emotional reaction many Granite Staters might have had to those rock formations crashing to earth.
“In both cases, we're looking at probably very gradual weakening of the rock over time through weathering,” Licciardi said. Processes like frost wedging, in which water seeps into cracks and then expands as it freezes, can lead to structural weakening over time, he said.
“It was probably more of a gradual build up of instability versus anything that would have been a dramatic cause for pushing it over the edge,” he said.
But when these formations do finally collapse after thousands of years in one place, the moments can be dramatic. A video published on Instagram by a visitor showed smashed railings and a hiking trail obstructed by the fallen rock.
And it can be hard for people to notice that the earth’s surface is constantly changing, especially since geological events unfold on timescales far longer than a human lifetime, Licciardi said.
“We live on such a dynamic planet. And that includes the rocks,” he said.
