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Fact Check-Plymouth Rock cannot provide an accurate measure of sea level

Plymouth Rock, the place where William Bradford and other pilgrims are popularly believed to have made first landfall in what is now the United States, is not a benchmark of sea-level rise and does not prove that modern ocean-level rise driven by human-led climate change is a myth, despite a viral post shared online.

The Rock is a “nationally recognized symbol of America’s founding,” Donna D. Curtin, Executive Director of the Pilgrim Hall Museum in Plymouth, Massachusetts told Reuters, and “is significant for its role in shaping America’s founding mythologies.”

“A modest, solitary boulder of Dedham Granite located on the Plymouth, MA waterfront, the Rock has been popularly identified since the early 18th century as the landing place of the Mayflower Pilgrims in 1620,” she said.

A user on Twitter posted an image of Plymouth Rock with text burned onto the image that reads: “Here’s Plymouth Rock which has been at sea level since 1620. Certified by William Bradford” (here).

The individual shared the image on Twitter with a caption that reads: “This is Plymouth Rock. It has lain [sic] here for 400 years. 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 tweet has gathered more than 26,300 likes and 11,000 shares at the time of writing.

It was shared further by users on Facebook, with examples viewable (here), (here), (here), (here) and (here).

THE MOBILE HISTORY OF PLYMOUTH ROCK

The rock cannot provide an accurate measure of sea-level rise, nor has the rock been in the same location since 1620, as claimed in the viral post (here).

The tale that the Rock marks the landing place of the Pilgrims “has a basis in local oral tradition and gained widespread recognition in 19th and 20th century popular fiction and secondary accounts,” Curtin said, however, “there is no period documentation of the story.”

Curtin also told Reuters that the Rock has “unquestionably” been moved over the past few centuries, having been broken, split and relocated several times.

For example, the top portion was removed to Town Square in 1774 and later in 1834 to Pilgrim Hall Museum. The two halves of the Rock were reunited on the waterfront under a granite canopy in 1880, Curtin said, and later was entirely excavated and lowered onto the shoreline in 1920 with a new granite portico placed over it in 1921 (here).

Curtin also told Reuters that the Rock is regularly under water with high tide. Reuters found numerous images of such published by media outlets and photographers (here), (bit.ly/3yIahbz).

SEA LEVEL RISE IN MASSACHUSETTS

Meanwhile, sea level rise has been recorded in the state, Dr. Simon Engelhart, Department of Geography at Durham University confirmed to Reuters. The tide gauge at Boston has recorded an average rise of 2.89 mm/year since 1921 (28.9cm or 0.95 feet over that time), while to the south at Woods Hole, MA, a tide gauge records a rise of 2.98 mm/year on average since 1932 (26.5cm or 0.87 feet) (here).

It is also not possible to gauge sea level rise by one photograph at a location without knowing the position of the tides at that time, Engelhart said, with the great diurnal tidal range at Plymouth recording at 10.53 feet (here).

"In some areas of the world, people have made carvings into bedrock that record where sea level was and associated it with a date (for example the Celsius seal rock in Sweden) (here) but this relies on having immovable bedrock and a clear identifying mark for where sea level was (including either small tidal ranges or documentation of which tidal datum is being recorded). Clearly Plymouth Rock does not meet any of these requirements and is not a reliable indicator of sea level change since the 1620s,” he added.

Reuters previously addressed false claims that two images at the same location can be used to disprove today’s global mean sea level rise (here), (here), (here).

VERDICT

False. Plymouth Rock has a mobile history, having been placed in various locations since the 18th century. A mobile rock cannot be used as an accurate measure of sea level through the centuries, and the Rock has also been pictured covered by seawater in recent years at times of high tide.

This article was produced by the Reuters Fact Check team. Read more about our work to fact-check social media posts here .

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