The biggest wave on record occurred in Lituya Bay on the southern coast of Alaska in 1958. An earthquake measuring 8.3 on the Richter scale hit the area and shook loose an estimated 40 million cubic yards of dirt and glacier from a mountainside at the head of the bay. When the debris hit the water, a massive 1,720-foot wave was created and washed over the headland.
Technically this wave is described as a “Splash Wave” The photo above shows the headland beside the Lituya Glacier that was swept clean of soil and trees to a height of 1740 feet by the giant splash wave. The icebergs seen in the water of Lituya Bay, foreground, were knocked off the glacier by the landslide falling into the bay from a slope to the right of the photograph.
| Headland beside Lituya Glacier that was swept the giant 1740 ft wave
Photo by Byron Hale.
Rogue Waves &/or Freak Waves:
Rogue waves — giant walls of water that dwarf run-of-the-mill storm swells are distinct from the 33-foot-high, earthquake-generated tsunami waves we came to know in 2004. For ages, mariners have told of much bigger midocean waves, rising more than 200 feet to hammer the ships caught in their sights.
Rogue waves, also known as freak waves, have been the subject of more studies in recent years, due to the availability of ocean-monitoring satellites. The European Space Agency says its MaxWave satellite radar project detected more than 10 rogue waves measuring higher than 82 feet (25 meters) over a three-week period in 2001 — perhaps including the 100-foot whoppers that smashed the windows of the cruise ships Caledonia and Bremen.
A 70-footer washed over the Norwegian Dawn cruise ship in 2005, a nearly-100-footer was reported in 2004 during Hurricane Ivan, and there have been reliable measurements of a 112-foot (34-meter) wave that rose over the USS Ramapo in 1933. Could there have been bigger waves that people didn’t survive to tell about? Maybe so: In “The Bird in the Waterfall,” Jerry Dennis and Glenn Wolff report that computer models can produce theoretical waves as high as 219 feet (67 meters).
The big mystery has to do with the mechanism that causes the waves. A variety of studies, including the MaxWave observations, have shown that cross currents can “focus” the energy of wind-driven waves through constructive interference. “At some point, the waves all march in lockstep together, and then again they go their own way,” Vijay Panchang, a maritime engineering expert at Texas A&M University in Galveston said.
Sometimes freak waves can arise without those cross currents. “Sustained winds from long-lived storms exceeding 12 hours may enlarge waves moving at an optimum speed in sync with the wind,” (ESA). Seabed topography may play a role as well, Panchang said. A “bump” on the seafloor, for example, could give an extra boost to a wave at just the wrong time.
British research team observed some of the biggest sea swells ever measured.
In February 2000 those onboard a British oceanographic research vessel near Rockall, west of Scotland experienced the largest waves ever recorded by scientific instruments in the open ocean. Under severe gale force conditions with wind speeds averaging 21 ms−1 a shipborne wave recorder measured individual waves up to 29.1 m from crest to trough, and a maximum significant wave height of 18.5 m.
How often and what size?
In the book Oceanography and Seamanship, William G. Van Dorn provided an example of what the wave heights would be if a steady 33 mph (30 knot) wind blew for 24 hours over a fetch of 340 miles.
The most frequent wave height will be 8½ ft (2½ m).
The average wave height will be 11 ft (3 m).
10% of all waves will be higher than 18 ft (5 m).
The average wave height of the highest 10% of all waves will be 22 ft (7 m).
A 5% chance of encountering a single wave higher than 35 ft (11 m) among every 200 waves that pass in about 30 minutes. A 5% chance of encountering a single wave higher than 40 ft (12 m) among every 2,600 waves that pass in about five hours.
Please note these measurements aply to open ocean swells and waves.
One of Panchang’s biggest contributions to the science of big waves is to develop a forecasting model for coastal waves. Currently, the model is being applied to waves off the coast of Maine as well as the Gulf of Mexico and the Gulf of Alaska. You can check out the predictions here. “Our predictions are reasonable,” Panchang said — They catch the attention of mariners and oil-platform operators.
For more on the science of freak waves, check out archived articles from Science News and Discover magazine — as well as this tutorial from the National Oceanic and Atmospheric Administration and this “Savage Seas” Web site from WNET. You can even play around with a virtual wave generator.