For a century, up until it crumbled 20 years ago, the Old Man of the Mountain could be viewed because it was held together by chains, spikes and geologists scrambling over the face of Cannon Mountain.

Now it can be viewed again, but this time because of drones, old photos and the power of high-end gaming computers.

“The underlying technique that we’re using – photogrammetry – is when you have images of an object or landscape from different perspectives you can use parallax, the same way our eyes give us perspective, to reconstruct the three dimensions of an object from two-dimensional pictures,” said Matthew Maclay, a graduate student in earth sciences at Dartmouth’s Guarini School of Graduate and Advanced Studies, who has created a 3-D model of the Old Man that gives an eerily accurate look at the iconic Great Stone Face.

The technology is well established to make digital images of historical and archeological objects and geology. You can learn more about it along with the history, geology and culture of the Great Stone Face, at a virtual event beginning 11 a.m. on Wednesday, May 3 – the 20th anniversary of the day the stone formation finally succumbed to gravity. For more information check the Old Man of the Mountain Legacy Fund website.

Maclay’s graduate research involves understanding the geology of Cannon Cliff, which was crumbling long before the Old Man fell and is crumbling still. “People think of it as a fossil, a remnant of where the Old Man used to be, but what we hope to convey is that Cannon Cliff is one of the most dynamic places in the White Mountains,” said Maclay.

As part of the ongoing project, the researchers installed 24 sensors that record the bedrock temperature at Cannon Cliff. They will also be conducting laboratory analyses of rock samples from the area to investigate chemical changes in minerals due to mildly acidic rainwater and snowmelt. The connection to the Old Man was obvious.

“What we’re studying at the cliff are those exact weathering processes that caused it to (fall). … The very mild acidity is enough, with enough time, to start to degrade the feldspar in Conway granite,” Maclay said.

Combined with annual stress from the freeze-thaw cycle, the expansion and contraction that creates New Hampshire potholes every winter, the overlapping rock ledges that combined to make a profile when seen from the north were doomed to fall eventually.

Through the model, Maclay was able to estimate the volume and mass of rock that was lost when the Old Man of the Mountain fell. According to his measurements, around 750 cubic meters of granite fell.

“The Old Man of the Mountain may have weighed nearly 2,000 tons when it collapsed,” Maclay said. Efforts to keep the profile intact beginning in 1958, when the state first started spending money on it, included straps held by three-inch bolts drilled into the granite. Some of the stone holding those bolts eventually weakened, contributing to the 2003 collapse.

That 1958 work is part of the reason the 3D model was possible, Maclay said. Helicopters flew around the Old Man as work began, taking photographs from angles other than the typical tourist photo looking southward.

“It captured the Old Man, mostly from above but also orbiting around … Those pictures, looking up at the chin block or looking north, those are really important,” he said, because they provided the information needed to fill in the side of the Old Man that wasn’t easily visible.

Maclay and collaborators Jesse Casana and Carolin Ferwerda at Dartmouth’s Spatial Archaeometry Lab were already modeling Cannon Cliff, including aerial surveys using a drone. It wasn’t much of a reach to include digitized versions of those old pictures from film negatives taken between 1958 and 1976 to re-create the Old Man. Maclay processed the imagery in the Planetary Surface Processes Computing Lab led by Marisa Palucis, an assistant professor of earth sciences at Dartmouth.

Maclay, who was 7 years old when the Old Man fell, grew up in Wisconsin but says his years in New Hampshire have led him to see how important that iconic structure remains to the state. And he has come to appreciate our cliffs even though he’s not a rock climber.

“I might be the only grad student in the earth sciences department at Dartmouth who doesn’t climb,” he said.

Also on Wednesday, Governor Chris Sununu is expected to sign HB 96 at the Executive Council meeting, recognizing May 3 as Old Man of the Mountain Day.