The ocean's vastness holds many mysteries, and among the most awe-inspiring are the colossal waves that can suddenly appear, posing significant threats to maritime navigation. These giant waves can be classified into several categories, each with its unique origin and characteristics.
Giant waves may be classified in basically five categories:
- ‘Big Splashes’: the result of a landslide, volcanic eruption, or calving of a glacier.
- ‘Tsunamis’: the result of an undersea earthquake.
- ‘Storm Surges’: the result of a tropical storm or very powerful cyclone.
- ‘Big Surf’: huge shoreline waves generated by large cyclonic storm systems.
- ‘Rogue or Freak Waves’: mysterious storm-generated waves that tower two to four times higher than other waves in the vicinity. On very rare occasions the wave occurs without a storm present.
Big Splashes
The biggest splash of all (that scientists are aware of) was that in Lituya Bay, Alaska on July 9, 1958. Lituya Bay is an arm of the much larger Glacier Bay in Southeastern Alaska and was carved by retreating glaciers from the Brady Icefield. A 7.3 earthquake caused a massive landslip on the south shore of the bay creating a gigantic wave some 1,740-feet high that swept across the opposite shoreline and Cenotaph Island. Two people camping and fishing in the bay died.
Aerial view of a hillside inundated by a 1,700-foot wave in Lituya Bay, Alaska, following an earthquake-caused landslide in July 1958. (Coast and Geodetic Survey)
Map of Lituya Bay showing estimated wave run-up levels during the event. (Illustration from geology.com)
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Tsunamis
Earthquake-generated tsunamis are, like ‘Big Splashes’, of geologic- rather than meteorologic-origin. The Boxing Day earthquake off the coast of Sumatra (9.3 on the Richter scale) on December 26, 2004 generated what is likely the largest tsunami in modern history. An extensive section of shoreline south of Banda Aceh, on the northern tip of Sumatra was struck by a tsunami averaging 80 feet in height with a maximum height of 115 feet estimated to have come ashore between Labuhan and Leupung. The run-up was measured some 170 feet in the hills in this region. One city alone, Meulaboh, suffered the worst casualties of all: 40,000 of the 120,000 residents perished. However, tsunamis, like storm surges, are not so much waves as they are walls of water with no ‘back trough’ behind them.
Storm Surges
The deadliest storm surge in modern records occurred in the Brahmaputra River Delta of Bangladesh on November 12-13, 1970. The surge was some 40 feet high and drowned 300,000-500,000 people. The Great Boha Cyclone remains the deadliest tropical storm in human history. Storm surges like tsunamis, are walls of water not waves.
Storm surge during the Great Boha Cyclone of November 12, 1970. (Graph from WMO ‘Climate into the 21st Century’)
Even higher storm surges have been reported. The famous Bathurst Bay Cyclone of March 5, 1899 apparently crushed Australia’s Queensland State with a 42-foot storm surge according to survivors. This is the record highest storm surge we have corroborated by eyewitnesses.
Big Surf
The largest surf in the world occurs along the northern and eastern shores of the Hawaiian Islands and select locations along the California and Baja of Mexico coast. The biggest waves occur when powerful winter storms in the Alaskan Aleutian Islands and Gulf of Alaska generate a sort of ripple effect that streams across the North Pacific and spawn the waves that occasionally crash ashore in the above referenced regions. Of course, the biggest waves don’t actually come ashore but are confined to the reefs and shoals some miles from the actual coastline. Big-wave surfers ride 70 and 80-foot monsters and wait for the day that a 100-footer will test their skills. According to Casey’s book the site that has the best potential to produce 100-foot plus big surf is the Cortez Bank, a submerged chain of mountains about 115 miles west of Point Loma, San Diego County, California.
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Surfing The Ocean's Biggest Waves | BBC Earth Science
Rogue or Freak Waves
Rogue waves, also known as freak waves, are disproportionately large and unexpected waves that can appear in the open ocean. A rogue wave is usually defined as a wave that is two times the significant wave height of the area. The significant wave height is the average of the highest one-third of waves that occur over a given period. Therefore, a rogue wave is a lot bigger than the other waves that are happening in its vicinity around the same time.
On February 8, 2000, the British research ship Discovery accurately measured a gigantic 98-foot high wave while on a scientific expedition 155 miles west of the coast of Scotland. The wind had been blowing at 50mph or greater for over 12 continuous hours in the vicinity of the observed wave. This is the highest ‘officially’ measured wave at sea. Ramapo recorded a 112-foot wave near the Philippines during a typhoon in February 1933 and the report seems legitimate. It has become apparent that such monsters are not as rare as previously thought.
Many large vessels have simply vanished after encountering what one presumes were rogue or freak waves. Cruse ships face a serious threat as well: in February 1995 the Queen Elizabeth 2 encountered a rogue wave of some 100 feet (estimated) in The North Atlantic that almost foundered the iconic vessel. In fact, so many large ships have been lost that it begs the question why nobody seems to care aside from Lloyd’s of London, the premier marine insurance agency.
One of the places rogue waves appear to happen most frequently is off the southeast coast of South Africa. A professor of applied mathematics at the University of Colorado at Boulder, Dr. Bengt Fornberg, studied this phenomenon with Marius Gerber of the University of Stellenbosch, South Africa. Fornberg believes there is a particular reason extremely large waves occur there.
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“It’s the interaction of wave swell with the current,” he says.
Specifically, it’s when a large ocean swell hits the fast-moving Agulhas current. When this happens, the curved current narrowly focuses the wave’s energy, like an optical lens can powerfully focus light into a single beam.
Dr. Libe Washburn, a geography professor at the University of California, Santa Barbara, explains what occurs to waves interacting with a current like the Agulhas.
“It shortens their wavelength and makes them steeper,” he says.
Rogue wave infographic. (NOAA)
The supertanker ‘World Glory’ split in half and sank after a 70-foot rogue wave crushed her off the coast of South Africa in 1968.
Tim Janssen, a research scientist who studies physical oceanography in Half Moon Bay, California, says one of the best examples of a rogue wave is the so-called New Year’s Wave of 1995. On Jan. 1, a 26-meter (85-foot) wave struck the Draupner oil rig in the North Sea off Norway.
“It was one of the first observations [of a rogue wave] with a digital instrument,” Janssen says.
Danger at Sea
Obviously, these huge waves are able to inflict damage on oceangoing vessels.
“The waves are pretty dangerous, especially for bigger ships because they can crack their hulls,” Washburn says.
Fornberg, the mathematician, says rogue waves may also form from eddies, currents that flow in a different direction than the main current.
“Eddies are often generated along the edges of currents, but they can survive for long times and are able to drift across oceans, forming very extensive eddy fields,” he says. “These eddy fields in fact contain far more kinetic energy than the currents do. Within, and in the immediate vicinity of currents, rogue waves tend to be somewhat predictable-and they are confined to relatively small areas. On the other hand, energy focusing due to the chaotic, irregular and widely distributed eddies is somewhat less likely, and is essentially unpredictable, as these can occur almost everywhere.”
While there are many oceanographers and other scientists who forecast rogue waves, there is a lot more to be learned.
“These waves occur everywhere, all the time,” Janssen says.
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