Hell Gate, the largest explosion recorded before the atomic age

«In the midst of them a terrifying explosion was heard that seemed to come from the bowels of the earth (…) Finally, the explosive force that had not yet been extinguished evidently reached the main deposit of dynamite that Adam had lowered into the hole where the worm hid. The result was terrifying. All the surrounding ground – and for a great distance – trembled and split into long, deep fissures, the edges of which trembled and collapsed, throwing up clouds of sand which fell again hissing on contact with the water. that came to the surface. The house, despite its robustness, was shaken to its foundations. Huge stones leapt up as if from a volcano, and some of them—huge massive blocks, carved and worked by human hands—disintegrated in the air as if touched by some infernal force. The trees that were next to the house – and therefore, presumably, above the hole – were uprooted and thrown into the air.”

This apocalyptic description corresponds to the end of The Lair of the White Worm, the last novel written by Bram Stoker, the author of dracula. [Atención, spoilers a partir de aquí] In it, the protagonist takes advantage of a large kite tied to the battlement of a castle (originally in order to scare off a plague of birds) to attract lightning from a storm and explode the dynamite that has previously accumulated in the well, ending with the gigantic and monstrous beast that gives the work its title [fin de spoilers].

The curious thing about all this is that, it is said, for that passage Stoker would have been inspired by a real event that occurred in 1883, although without a worm in between, of course: the blasting of the rocks of Hell Gate.

Hell Gate is a strait in the East River of New York, separating New York’s Ward Island from the west of the city and Astoria (Queens) from the east. Its name literally means Gate of Hell, although it is actually a deformation of its original name, the Dutch expression Hellgate (something like Clear Strait), since the navigator of that nationality Adriaen Block was the first to cross it in 1614. It was a dangerous passage due to the currents that existed in it, as well as the semi-submerged rocks, which it prevented ships from traveling between the New York port and the Atlantic Ocean; dozens of shipwrecks testified to this.

There was no solution to the currents, but the rocks could be removed, which is why a pharaonic plan began in the middle of the century to clear that route. The first studies were carried out by the Navy in 1848, eventually recommending that some points such as Pot Rock, Frying Pan and Way’s Reef be dynamited, in order to widen and deepen the pass, facilitating navigation and port defense. The mission was entrusted to the Army Corps of Engineers, whose technicians went to work in 1851.

The main obstacle was located in a place called Hallett’s Point, a promontory on Long Island where the East River not only narrowed but also had its bottom bristling with reefs, and where a stream that was named Whorl-Gate ran. alluding to the whirlpools it formed, although today the name has derived from Hurl-Gate; hurl it means to vomit, which is equally expressive. In fact, in 1832 the depth had already been increased by just over half a meter by dynamiting the rocky walls using a galvanic battery, but with limited results; now the idea was much more ambitious, so the works were going to be more complex, not only because of the dimensions but because the technique had evolved.

Public domain photo on Wikimedia Commons

In 1867, a report by General John Newton, the person in charge of the project, concluded that a drilling ship had to be used, equipped with twenty-one drills that would open small holes between 3 and 4 meters in the rocky bottom into which 13-meter charges would be introduced. to 15 kilos of nitroglycerin. The idea was successfully tested in 1869 at Diamond Reef and in 1871 at Coenties Reef, but work at Hallett’s Point began earlier, in the summer of 1869, with the construction of a wooden formwork dam to facilitate the opening of holes and galleries. , chipping by hand in some parts and with a diamond drill in others. There was a stoppage just a year later, when the funds ran out, but then work resumed until a total of more than 6,000 cubic meters of stone was removed.

In 1874, the bed of the East River was thus supported by a 6-kilometre network of timbered galleries, supported by hundreds of pillars and intended to house the explosives. Now, it was a huge company and the years went by as it became necessary to overcome obstacles of all kinds: natural, of course, but also budgetary and technical ones. The first ones were solved, as we have seen, the second ones interrupted the activity several times but in a country that was already thriving economically like the US they were solved quite quickly; the third, in this last stage, focused on the difficulty of exploding that without having too much impact on the Astoria neighborhood and the islands of Ward and Blackwell.

The challenge was to manage to destroy the rock but without the shock wave endangering human lives or property. It was decided that the best thing to do was to distribute the mines widely, adapting them to the elliptical shape of the reef so that each explosion contributed to the collapse of the rocky vault, instead of concentrating the charges and blowing it up. The chosen explosive was a combination of nitroglycerin and gunpowder, with a predominance of one or the other depending on the composition of the rock at each site; We tried to use the minimum necessary so, according to the calculations, one kilogram would be needed for each cubic meter approximately. To protect it from moisture, it was inside tin cans that had to be inserted into each hole; the number of these amounted to 4,427, each one 7 centimeters in diameter more or less and 2.7 meters deep, separated from each other 2 or 3 meters, so it took nine days to have everything ready.

The primer charges were also protected from marine corrosion with brass casings. Battery-operated fuses were used as detonators, grouped 20 by 20 -one battery for every 160 fuses- and connected with cables; unrolling these took a couple of days and a half, since the total length exceeded 45,000 meters, constituting a closed circuit. The detonation occurred at 2:50 p.m. on September 24, 1876 and was characterized by a cloud of steam, gases, and pulverized rock that was projected upwards but with hardly any shock wave, to the point that no glass breakage was recorded. in the windows of nearby buildings despite the fact that a slight tremor was noted in Brooklyn and all of New York; The biggest damage, apparently, was the paint falling off some houses.

The volume of rock removed is estimated at around 48,000 cubic meters, to which must be added another 34,770 from the work prior to the explosion, in which a total of 23,000 kilograms of explosive were used. However, the culminating chapter of that engineering odyssey was still missing because a few years later, on October 10, 1885, another larger explosion took place and, seeing that there was no danger, 50,000 spectators were allowed to attend. The objective this time was to demolish Flood Rock, for which 140,000 kilos of explosives were used.

The colossal detonation was felt in neighboring New Jersey and produced a spectacular column of water 76 meters high. It is disputed with that of the Battle of Messines, in Belgium (in 1917, during the First World War, when the British mined the German positions before assaulting them), the honor of being the largest in History before that of Trinity, the first atomic bomb tested in the New Mexico desert. The resulting debris served to merge the islands of Great Mill Rock and Little Mill Rock. No wonder it would inspire Bram Stoker.


The lair of the white worm (Bram Stoker)/The improvement of East River and Hell Gate (General John Newton in The Popular Science Monthly)/The modern high Explosives. Nitro-glycerine and dynamite: their manufacture, their use, and their application to mining and military engineering (Manuel Eissler)/Gunpowder, explosives and the state. A technological history (Brenda J. Buchanan)/The conquest of Hell Gate /Wikipedia

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