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Chicken Little: Don't Look Up! Look Down!

Jan. 20, 2024
CLARK'S REMARKS: Nope, the sky isn't falling. Vertical land motion is really what many of us need to worry about.

Turns out Chicken Little was wrong. The sky isn’t falling. The earth is sinking!

Just about two years ago in this space, I noted the nexus between sea level rise and the rate at which many coastal cities are sinking. Sea level rise, a frequent topic here, is a result of thermal expansion due to the warming sea water and the volume of water added by melting glaciers and ice sheets.

At the same time, there is also impact from vertical land motion (uplift and subsidence) on sea level rise. According to a study by a team of researchers from NASA’s Jet Propulsion Laboratory (JPL) and Rutgers University, published last September in Science Advances, the NYC metropolitan area subsided at an average rate of 0.06 in. (1.5 mm) per year, between 2016 and 2023. Some areas had even higher rates of vertical land motion, including the southern portion of Governors Island and sites near Coney Island and Arverne by the Sea in Queens, all areas built on various types of fill.

Significant subsidence was also noted in the Bayonne area of New Jersey – an area I previously noted as being at significant risk – and Riker’s Island, which has undergone landfilling.

Now a recent study by researchers at Virginia Tech’s Earth Observation & Innovation (EOI) Lab and a research geologist with the U.S. Geological Survey, published in January 2024 issue of PNAS Nexus, finds that more than 50% of infrastructures in major cities like New York, Baltimore, and Norfolk may have subsidence rates as high as 0.08 in. (2 mm) per year. The study also identified an additional nine metro areas affected by spatially variable land subsidence: Boston, MA; Providence, RI; New Haven, CT; Atlantic City, NJ; Wilmington, NC; Charleston, SC; Jacksonville, FL; and Miami, FL. Several areas in Atlantic City, Savannah, and Charleston were reported to be subsiding at rates faster than 0.16 in. (4 mm) per year!

Since, as the study notes, “the railway network density on the U.S. east coast is among the highest in the country, particularly in New England,” their railway system exposure analysis was notable. It showed “sinking on 81% to 99% of the railway systems (7,452 to 9,221 km out of 9,247 km) and 42% (11 out of 26) of train stations, with subsidence rates of >3 mm per year observed along 41 to 846 km stretch of railways on the U.S. east coast. The high density of underground railways (subways) in New York City increases the risk associated with the observed subsidence hazard in this region.”

The threats to infrastructure posed by vertical land motion, coupled with NOAA predicting sea level rise on the U.S. east coast of 10 to 12 in. (0.25 to 0.30 meters) by 2050, are stark reminders of the urgent need to accelerate our efforts at both adapting to, and mitigating the effects of, climate change. Are we up to the challenge?

A regular contributor to HPAC Engineering and a member of its editorial advisory board, the author is a principal at Sustainable Performance Solutions LLC, a south Florida-based engineering firm focusing on energy and sustainability. He can be reached at [email protected].