Nantucket, MA Coastal Erosion Rate
Is the coast eroding 8.1 miles north of Nantucket, MA?
USGS's shoreline-change data puts this stretch, 8.1 miles north of Nantucket, MA, at 1.95 feet of erosion a year on average, a long-term rate for this specific ~3.5-mile section, not one storm's damage. At that rate, the shoreline has lost roughly 19.5 feet over the last decade.
What this reading actually covers
USGS surveys the coast in transects spaced a few hundred feet apart; this page groups the nearest ones into a single ~3.5-mile reading for the stretch closest to Nantucket, MA, rather than showing one arbitrary line. Segment center: 41.38, -70.04. The survey behind it runs to 2007-2009, in USGS's New England / Mid-Atlantic assessment, using the LRR method. Shoreline surveys aren't repeated every year, so this is the most recent long-term measurement USGS has published for this coast, not a live reading.
What 1.95 ft/yr means over time
Run 8.1 miles north of Nantucket, MA's 1.95 ft/yr rate forward 25 years and it implies about 49 feet of further retreat, assuming nothing changes, which is exactly the assumption a seawall or nourishment project exists to break.
What backs this reading up
This reading comes from 45 individual transects averaged together, 100% of which measured erosion rather than growth. USGS's confidence interval here is ±0.76 ft/yr. Among the 1211 US coastal segments with a measurable trend, this one ranks 139 for erosion, 1 being the fastest-retreating coast in the dataset. Source: USGS Open-File Report 2010-1119. Rank 328 nationally for erosion belongs to Paia, HI, 5093 miles from this stretch, measured at 0.44 ft/yr, 0.2x this stretch's rate. 1.1 miles up the coast, Nantucket, MA shows 2 ft/yr of eroding.
Not this whole stretch, just Nantucket itself: the Coastal Change Hazards Portal is USGS's own live version of this data.