One of the earliest reliable maps of the Merrimack River mouth, from an 1827 Army Corps of Engineers survey, shows a 1-mile-long section of Plum Island and Salisbury Beach that no longer exists.
That change was set in motion over a two-week period, when "The Three Hurricanes" hit in mid- to late December, 1839.
The story is breathlessly told in a book called "Awful Calamities," or "The Shipwrecks of December 1839," published shortly after the storms. Dozens of ships were lost and 150 people drowned along the Massachusetts coast.
In Newburyport, two of the storms came on a high tide that produced a surge larger than anything that had been seen in at least 30 years. Water rose well above the tops of Newburyport docks and spilled onto downtown streets. One ship tied to docks was pulled under. Almost a third of the 130 ships in Newburyport harbor were damaged.
The high water severely damaged the beach dunes, eventually ripping a new channel through Salisbury Beach. It split the river mouth in half and created a new channel to the sea that is now Plum Island Basin. An island had formed in the middle of the mouth, and over the course of the next decade it attached itself to Plum Island. An Army Corps of Engineers survey in 1851 shows it as a long narrow finger called "New Point." Over the years it has broadened to become the northern end of the island, now occupied by about 500 homes.
Erosion problems and property damage were evident as early as the 1700s, when a Revolutionary War-era fort at the river mouth washed away. But erosion caused scant public concern because there were very few homes on Plum Island.
In an 1854 history of Newburyport, Euphemia Blake describes the southern end of the 9-mile-long island as having a few farms, and the wild, unoccupied northern end as "entirely composed of sand, which is thrown by the wind into hillocks of various heights and forms, and on the eastern shore is continually the sport of Atlantic billows, which change its outline from year to year, making its shore a new study, to the lover of nature, who might here revel in one of her wildest and most fantastic forms."