via Wikipedia:.
Ripple Rock is an underwater mountain that had two peaks (9 feet and 21 feet below the surface) in the Seymour Narrows of the Discovery Passage in British Columbia, Canada,[1] a part of the marine trade route from Vancouverand coastal points north. The nearest town is Campbell River. Only 2.7 metres (9 feet) underwater at low tide, it was a marine hazard in what the explorer George Vancouver described as “one of the vilest stretches of water in the world.”[2][3] The hazard was not only hitting the rock but also big, dangerous eddies caused by tidal currents round the rock.[4] Ships using the strait preferred to wait until slack tide.
Its top was removed by a planned explosion on 5 April 1958.[5] This is a National Historic Event in Canada. The Ripple Rock explosion was seen throughout Canada, live on CBC Television. It was one of the first live coast-to-coast television broadcasts of an event in Canada.[6]
It was so named in 1862 by Captain Richards, RN,[7] because its summits were about at sea level and made a prominent standing wave in the fast tidal current of the strait.