Ripple Rock

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Coordinates: 50°08.2′N, 125°21.2′W Ripple Rock was an underwater, twin-peaked mountain in the Seymour Narrows of the Discovery Passage in British Columbia, Canada, a part of the marine trade route from Vancouver and coastal points north. The nearest town was Campbell River. Only 9 feet (3 meters) underwater at low tide, it was a marine hazard, described by the explorer George Vancouver as "one of vilest stretches of water in the world." It was destroyed by a planned explosion on April 5, 1958.

The first known large ship to fall prey to Ripple Rock was the sidewheel steamer USS Saranac in 1875, as it was heading north to Alaska. At least 20 large and 100 smaller vessels were badly damaged or sunk between then and 1958. At least 110 people drowned in these accidents.

As early as 1931, a Marine Commission recommended removing Ripple Rock, but it wasn't until 1942 that the government authorized attempts to remove it. There as political opposition to the destruction of Ripple Rock, as some felt it would serve well as a bridge support to connect Vancouver Island and the mainland.

The first attempts at planting explosive charges on Ripple Rock were made with floating drilling barges with the goal of blasting away the rock in pieces. The first, in 1943, was secured with six 3.8 cm steel cables attached to anchors that altogether weighed 998 metric tons. This approach was abandoned when one cable broke on average every 48 hours. Another attempt in 1945, involving two large overhead steel lines was similarly abandoned after only 93 (out of 1500 planned) controlled explosions were successful.

In 1953, the National Research Council of Canada commissioned a feasibility study on the idea of planting a large explosive charge underneath the peaks by drilling vertical and horizontal shafts from Maud Island in the sound. Based on the study, this approach was recommended. Dolmage and Mason Consulting Engineers were retained to plan the project, and three firms: Northern Construction Company, J.W. Stewart Limited, and Boyles Brothers Drilling Company were granted the contract, which ended up costing in excess of 3 million Canadian dollars.

Between November 1955, and April 1958, a three-shift operation involving an average of 75 men worked to build a 174 meter vertical shaft from Maud Island, a 762 meter horizontal shaft to the base of Ripple Rock, and two main 91-meter vertical shafts into the twin peaks, from which "coyote" shafts were drilled for the explosives. 1,270 metric tons of Nitramex 2H explosives were placed in these shafts, estimated at 10 times the amount needed for a similar explosion above water.

The explosion took place at 9:31:02 am on April 5, 1958. 635,000 metric tons of rock and water was displaced by the explosion, resulting in debris at least 300 meters in the air, falling on land on either side of the narrows. The blast increased the clearing at low tide to about 45 feet.

The Royal Canadian Mounted Police cleared the area of within 3 miles of the explosion, and the engineers and TV crew that witnessed the explosion were housed in a bunker.

The explosion was noted as one of the largest non-nuclear planned explosions on record, though Soviet authorities reported larger explosion in the Ural Mountains to carve a new channel for the Kolonga River and in China to open a copper mine.