In 1851, the U.S. Army Corps of Engineers began to clear obstacles from the strait Hell Gate with explosives; the process would last 70 years. On September 24, 1876, the Corps used 50,000 pounds (23,000 kg) of explosives to blast the dangerous rocks, which was followed by further blasting work. On October 10, 1885, the Corps carried out the largest explosion in this process, annihilating Flood Rock with 300,000 pounds (140,000 kg) of explosives. The blast was felt as far away as Princeton, New Jersey and sent a geyser of water 250 feet (76 m) in the air. The blast has been described as "the largest planned explosion before testing began for the atomic bomb", although the detonation at the Battle of Messines in 1917 was larger. Rubble from the detonation was used in 1890 to fill the gap bet