Stone Walls Reveal History of Earth’s Magnetic Wanderings

Growing up in southern New Hampshire, geochemist John Delano explored the stone walls around his family home on what was once farmland. Decades later, he stumbled upon similar pilings of stone while walking through the woods in rural New York.

The two were connected. By the late 1800s, nearly 170,000 farming families had built an estimated 246,000 miles of stone walls across the Northeast to mark boundaries and clear their land of the granite that had been deposited throughout the region about 10,000 years ago. During the Industrial Revolution, most of the sites were abandoned and overgrown by forests within a few decades.

Delano, a distinguished teaching professor emeritus of Atmospheric and Environmental Sciences (DAES) at UAlbany, was not only intrigued by the historical significance of these walls, but also discovered their locations could help reconstruct Earth’s shifting north magnetic pole.

Delano reviewed hundreds of publicly available original land surveys. (Photo courtesy of The Conversation)

Using hundreds of publicly available original land surveys, along with airborne LIDAR images, Delano mapped 726 of miles of stone walls built between 1685 and 1910, that were often used as property boundaries. He then compared compass measurements of the boundary lines recorded by early surveyors in the 18th and 19th centuries to current day magnetic north.

He wrote an article on March 12 in The Conversation, an online journal of news and opinion by academics, to describe the project.

“I knew that the location of magnetic north drifts over time due to changes in the Earth’s core. Could I determine its drift using stone walls and the old land surveys? My preliminary map of stone walls and a few historical surveys showed that the approach had potential,” said Delano, who retired in late 2016.

His model was consistent with other reconstructions of the Earth’s magnetic shifts in the past 300 years. For example, the current direction of stone walls built along New Hampshire’s Stoddard township indicate that magnetic north has moved about 6.6 degrees further west since 1768.

 “Data from these stone walls strengthen the current geophysical model about the Earth’s magnetic field,” he said.

Delano’s findings were published last month in the American Geophysical Union’s Journal of Geophysical Research.