Waves the height of a 10-story building regularly propagate into the north Pacific from the mouth of the Columbia River, but one won’t find big-wave surfers riding them. These waves propagate beneath the ocean surface, carrying near-surface organisms and chemicals halfway to the ocean floor. Oregon State University scientists who identified and documented how these waves emerge from the edge of a river plume reported their findings recently in the journal Nature.
Satellite imagery clearly shows the plumes of the Columbia River and other large rivers around the world as a major influence on the near-shore waters. The satellite image showed the influence of the Columbia River, which forces fresh water into the Pacific Ocean on the outgoing tide. The interface between the fresher, surface waters originating from the Columbia and saltier, deeper waters, forms a system that creates large-amplitude waves. The large waves are generally not seen at the surface, but their signature is – visible slicks and changes in surface roughness and color that scientists, sailors and commercial fishers have known about for years.
On the northern Oregon coast, these waves emerge when fresh water is forced from the mouth of the Columbia River with the outgoing tide, the researchers say. Since the fresh water is also lighter, it spreads over the surface of the coastal waters; its signature can be seen over tens of miles from aircraft or satellite. The interface between the fresher, surface waters and saltier deep waters forms a wave guide upon which large-amplitude waves propagate. Some of these internal waves propagate back toward the Oregon coast where they may break as they shoal and mix with near-shore water. Scientists don’t yet know all of the impacts of these waves.