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The Day the Piscataqua River Exploded


An engineer's dream

By 1904 the initial excavation was done. Engineers had already blasted and scooped out 500,000 tons of rock from the center of the point. The result was a horseshoe-shaped crater with sheer rock walls 60 feet high and 80 feet thick. Around the edge rose a great cofferdam, the biggest of its kind, designed to keep out the "terrible tide"  of seawater.  The inside of the hollowed-out Henderson's Point, with its manmade wooden stairways and walkways, looked more like a geological feature from the White Mountains than the seashore. Three hundred workers were on the job at once, including many brave divers. (Two workers were killed during the nine-year project.)

An on-site machine shop was needed to keep up with the experimental designs. Drill holes measuring 70 to 80 feet were more than twice the length ever attempted before. Special sticks of dynamite had to be manufactured to fit the holes. And because some of the dynamite would be underwater for as much as three weeks, the sticks were wrapped in two layers of paraffin, effectively making them waterproof. Two hundred tons of dynamite were used in all. Special electrical systems had to be designed to make sure that the final 50 tons of dynamite would go off simultaneously during the historic blast on July 22, 1905.

"This improvement makes almost a straight entrance into the harbor," the Granite Monthly reported with some trepidation in 1904, "and what changes in the extreme currents of the river from the increased flow of water it will make, is as yet problematical."

Henderson's Point explores in 1905


Watch us blow up

Archived photos of July 22 show great crowds climbing off Portsmouth trains and trolleys to witness the great explosion. The women are uniformly dressed in long skirts and white blouses, the men in dark sport coats with panama hats or derbies. They mug for the Kodak cameras and pose with Portsmouth policemen along the "combat zone" off Water Street.

 "This will be one of the most remarkable feats of engineering of its kind ever attempted," the Cambridge Times announced to its Boston readers on Saturday morning. "The wonderful explosion which blasted Hell Gate does not compare with this event." Newspapers from Massachusetts to Maine offered special travel rates that included tickets to wooden observations platforms along both sides of the Piscataqua.

Portsmouth ale maker Frank Jones had been a major advocate of the modernized naval shipyard. Federal projects meant more workers and more workers meant more beer. Although Jones had died three years earlier, his company was not shy about selling the event. They distributed thousands of  souvenir booklets entitled "A Day Long to be Remembered" that included the best spots to view the explosion and an invitation to tour "the largest brewery in the land."  

"The name of Frank Jones of Portsmouth will live as long as there is any place of being on this globe," the booklet read, as if composed by a drunken copywriter. "In Portsmouth itself there is so much to be seen that it is almost impossible to see it all."

Jones was so tied to local history, according to the souvenir booklet, "that the mere mention of Portsmouth to a stranger will invariably call forth the remark, 'Oh, yes, that is where they make the Frank Jones ale.'" 


Exactly on schedule, after an appropriate countdown, someone in the observation building shouted "FIRE!" Miss Edith Foster, daughter of the project superintendent from Worcester, Massachusetts, threw the switch and the electrical current set off 50 tons of dynamite in 200 expertly placed holes. Seconds later "the greatest engineering enterprise of its kind ever known" was over. The flooded area cushioned the explosion as predicted, shooting up the spout of water and debris, but creating surprisingly little seismic shock.  Bits of exposed rock did not fly off and injure spectators as some had predicted. The only mishap, according to later reports, was a man struck by a slow moving automobile as he fled the area. Within minutes a fleet of small boats filled with curious tourists were already headed toward ground zero to examine the results and collect floating mementos.

The U-shaped cofferdam shattered as planned, breaking up the rock below, followed by a small "tidal wave" that swamped bridges and washed onto the nearby shores. Fears that the earth might crack or be knocked off its axis by the explosion proved unfounded. In fact, the event went so smoothly that one Kittery resident wrote to the newspaper wondering if visitors who had traveled far, even camped out overnight, might have gone away disappointed.

With little danger and no accidents, the event was considered "a complete success" according to the media and to the proud corps of navy engineers. Even naval hero John Paul Jones would be pleased, one newspaper noted, since he too had been forced to navigate his warship Ranger around Henderson's Point in the Revolutionary War. Coincidentally, the body of Captain Jones was just then arriving back in the United States after being recently exhumed from beneath the streets of Paris where he was buried in 1792.  

The city's historic summer was just beginning. Days before the Henderson's Point explosion, the local papers announced that negotiations to end a bloody war between Japan and Russia would be held here. For 30 days in August, the events of the Treaty of Portsmouth kept the region in the spotlight of world news.  

Technically the project was not finished even six years later. In August of 1911 government engineers formally reported that the removal of Henderson's Point was "satisfactory." But cost overruns, according to the local newspaper, might lead to a $250,000 lawsuit. To be even more technical, Henderson's Point is still there. Although the 1905 explosion displaced 270,000 cubic yards of rock and soil, the rest of the geological formation is still underwater. A sonar test of Portsmouth Harbor made more than a decade ago shows the base of the formation resting comfortably some 11 meters below the surface at low tide.    


Copyright © 2013 by J. Dennis Robinson, all rights reserved. Robinson’s history column appears in the Portsmouth Herald every other Monday and exclusively online at his independent Web site He is the author of 11 books including UNDER THE ISLES OF SHOALS and AMERICA’S PRIVATEER, available on and in local stores. 



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