It survived for thousands of years, then suddenly fell: The mystery behind New Hampshire's 80-ton boulder

A massive granite rock which used to loom over visitors on a walking track for over a century has now come crashing down at one of the famous tourist spots in New Hampshire. The 80-ton rock called Mysterious Hanging Boulder fell on October 18 at Polar Caves Park in Rumney, marking the last day of the year 2026 for the attraction. Fortunately, no harm has been done as nobody was in the vicinity of the falling rock, The Boston Globe reports. It has been for many generations that the attraction is well-known for such unique features that can only be found there. One of those has been the hanging granite rock, which looks like it will fall down at any moment, but has been standing firm since the inception of the park 104 years ago.

The event has led to increased attention being given to the origin of such large-scale rock formations, what causes them to be stable, and why even seemingly stable formations ultimately fail.

Geologists have said that erosion, gravity, and freeze-thaw cycles could have played a part in the failure, but the exact cause remains unknown.

A famous New Hampshire landmark loses its precarious position

The Mysterious Hanging Boulder was a unique site at Polar Caves Park, where people could visit and walk around granite rock formations through tunnels. The site was established in 1922, and the rock was always in place.

Its unique positioning made it even more fascinating. As noted by The Boston Globe, there was a sign next to the rock indicating that it weighed 80 tons, with 75% of the weight hanging above people's heads.

This is what made the boulder unique, but its stability depended on a balance between its weight and the granite rock beneath it.

On the day when the rock fell (October 18), part of the wooden bridge got damaged. In the video taken after the fall, broken parts of the railing and an upright stone could be seen. There was no access to the trail beyond the damaged area.

The timing of the event means that it happened when the season at the park was coming to an end. Officials are relieved that no one was injured, and stated that the site would be assessed for its safety before any decision is taken.

No final cause of the collapse has been stated by the park yet. Their primary goal is to assess the area and ensure its safe operation in the future.

How glaciers created the landscape — and why the rock may have fallen

Despite the boulder having been in its place for over a hundred years, the geological past of the boulder goes way back.

According to Professor Joe Licciardi of the Department of Glacial Geology at the University of New Hampshire, interviewed by The Boston Globe, it is likely that the granite boulder was placed in its hanging position by a glacier many thousands of years ago.

Glacial activity also formed the scenery in Polar Caves, where giant granite boulders create gaps and tunnels in which people can walk.

It seems that the fall of the granite boulder may be caused by a number of factors acting upon it over time rather than one particular event.

According to geologist Jan Earle, who has worked with both the US Geological Survey and the state parks, erosion may gradually undermine the base of a balanced boulder. Weather conditions may erode the rock, while accumulation of water and debris around a rock formation may change the forces acting on it.

Gravity plays an important role when the supporting structure fails to hold the stone in place.

The freeze could have been a factor. According to Licciardi, water can get into the cracks in granite and cause expansion upon freezing. The repeated freeze-thaw process causes widening of cracks in rocks and their weakening.

Both factors are possible explanations rather than a proven description of what actually took place at Polar Caves. The Park did not comment on the cause any further, reports The Globe. The determination of what happened exactly would require more data than just the fact of the fall of the rock.

What the collapse means for Polar Caves Park's future

This situation leaves Polar Caves Park in an actual predicament: how to handle the park, which is famous for its attractions, once one of the geological elements of the area has become ruined?

Nine granite caves can be found throughout the park; in addition, there are some unique passages and rock structures.

Among other elements that are located along the trails, there are sections known as the Lemon Squeeze, Devil's Turnpike and Fat Man's Misery. This means that this boulder's absence cannot be interpreted as the end of the attraction, although the ruined part needs proper handling.

The evaluation during the off-season will help to determine how to use this part of the trail and what changes should be made to make sure that the visitors and staff members of the park are safe.

According to the Boston Globe, the management of the park stated that safety was their first concern.

This case reminds us of the previous experience of the state of New Hampshire, where another geological element, the Old Man of the Mountain, which had the shape of a human face, fell from Cannon Mountain in May 2003.

This situation leaves Polar Caves Park in an actual predicament: how to handle the park, which is famous for its attractions, once one of the geological elements of the area has become ruined?

Nine granite caves can be found throughout the park; in addition, there are some unique passages and rock structures. Among other elements that are located along the trails, there are sections known as the Lemon Squeeze, Devil's Turnpike and Fat Man's Misery. This means that this boulder's absence cannot be interpreted as the end of the attraction, although the ruined part needs proper handling.

The evaluation during the off-season will help to determine how to use this part of the trail and what changes should be made to make sure that the visitors and staff members of the park are safe. According to the Boston Globe, the management of the park stated that safety was their first concern.

This case reminds us of the previous experience of the state of New Hampshire, where another geological element, the Old Man of the Mountain, which had the shape of a human face, fell from Cannon Mountain in May 2003.