Fact check: Plymouth Rock has been moved, not an accurate gauge of sea level rise since 1620

Kate S. Petersen, USA TODAY
·5 min read
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The claim: Water level at Plymouth Rock proves sea level rise minimal since 1620

Some social media users are claiming the sea level at Plymouth Rock, a Massachusetts monument and fabled 1620 landing place of the Pilgrims, proves that sea-level rise is minimal or non-existent.

"This is Plymouth Rock. It has lain here for 400 years," reads a July 4 Facebook post. "It was exposed to the oceans in 1620 & is in the exact same spot today. Oceans have failed to rise the few centimetres need (sic) to cover the rock with seawater. This is a clear message about how little earth's oceans are rising."

The post features a photo of Plymouth Rock, partially submerged by seawater at its current waterfront location at Pilgrim Memorial State Park in Plymouth, Massachusetts.

The post was shared more than 1,000 times in four days.

But the post is wrong. Plymouth Rock cannot be used as an accurate gauge of area sea-level rise since 1620 because it was only placed in its current position in 1920, according to historical records. Further, the rock does become completely submerged under seawater during some very high tides.

And the broader point about the sea not rising is also wrong. Plymouth Harbor sea levels are estimated to have risen roughly 1.5 feet since 1620, according to a state agency spokesperson.

USA TODAY reached out to social media users who shared the post for comment.

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Plymouth Rock has been moved

While it is often thought to be the landing place of the Pilgrims in 1620, the rock is not mentioned in the Pilgrim's written accounts of the landing, according to Donna Curtin, the executive director of Pilgrim Hall Museum in Plymouth, Massachusetts.

Regardless, the rock has not been "in the exact same spot" since that time, she told USA TODAY. It has been broken and moved.

The top part of the rock was broken off in 1774 and put on display in the town square and then outside Pilgrim Hall Museum. That piece wasn't reunited with the base of the rock until 1880. Both pieces were moved to their current location when the Plymouth waterfront was renovated in 1920, Curtin said.

The rock sits on a concrete foundation and was partially covered by sand when it was repositioned in 1920, Carolyn Assa, a spokesperson for the Commonwealth of Massachusetts, told USA TODAY in an email.

A photograph provided to USA TODAY by Pilgrim Hall Museum curator, Connor Gaudet, shows the large white pillared monument that currently houses Plymouth Rock, without the rock inside of it.

"So you can't draw ... conclusions based on the assumption that the rock is where it's been for 400 years," Curtin said. "It has been excavated. It has been moved."

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Area sea levels have risen, Plymouth Rock gets submerged

While the post claims sea levels haven't risen the "few centimeters" needed to cover the rock in 400 years, sea levels have risen more than a few centimeters since that time.

"Using the combination of radiocarbon dating of local landscape features and tide gauge records, it is reasonable to say that waters have risen approximately 1.5 feet in Plymouth Harbor since 1620," a spokesperson for the Massachusetts Office of Coastal Zone Management told USA TODAY in an email.

The post also claims that sea levels are not high enough to submerge Plymouth Rock, but Assa said it sometimes becomes fully submerged during very high tides.

Plymouth Rock can be seen mostly or fully submerged in seawater in multiple videos and photos posted to YouTube, Twitter, Facebook and local media.

Sea-level rise is primarily caused by the global warming-induced melting of ice sheets and glaciers, as well as the physical expansion of warming seawater.

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Our rating: False

Based on our research, we rate FALSE the claim that the water level at Plymouth Rock proves sea level rise has been minimal since 1620. The rock cannot be used as a gauge of sea level rise since 1620 because it has been moved, broken and altered, only arriving at its current location in 1920. Radiocarbon dating and tide gauges suggest the area sea level has risen around 1.5 feet since 1620, according to an agency official. The rock also does get completely covered with seawater during very high tides.

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This article originally appeared on USA TODAY: Fact check: Plymouth Rock not an accurate gauge of sea level rise