July 30, 2010
When 16-year-old solo circumnavigator Abby Sunderland was reported lost at sea somewhere in the southern Indian Ocean in June and then found alive with her boat damaged, it was a reminder of the power of the ocean.
Her 40-foot sailboat was dismasted. The boat had five watertight compartments and was designed to be self-righting in case of a capsizing. She had a dry suit, survival bag and rubber raft. After the dismasting she activated an emergency beacon and was rescued by a French cargo ship.
All indications are that she was a very experienced sailor with a well designed and equipped sailboat and emergency plans. It is possible she was hit by a rogue wave.
Rogue waves have been found to be more common than originally thought, according to a newly published book called Introduction to California’s Beaches and Coast by Gary Griggs. Published by the University of California Press, it is part of the California Natural History Guides. It is not a guide to the beaches, but rather a fascinating book about why California has beaches and why they shrink and grow.
By far one of the revelations of the book is the section on rogue waves. Consider the following tidbits from the book:
* A German container ship the length of two and a half football fields left Germany for Savannah, Ga., in 1978. On Dec. 12 the unsinkable ship disappeared “with one unintelligible distress call.” All that was found was debris and an unlaunched lifeboat. It was assumed the ship was hit by a large wave.
* In February 1995 the Queen Elizabeth II ocean liner reported a 90-foot wall of water in the North Atlantic.
* Two Antarctic cruise ships, the Bremen and the Caledonian Star, encountered 100-foot waves within a week of each other. Both had their bridge windows broke, and the Bremen lost navigation and propulsion for two hours.
* In March 2007 the cruise ship MS Prinsendam was hit by a 70-foot wave while rounding the tip of South America.
* “In the 21 years between 1981 and 2001, 124 ships over 600 feet long were reported to have sunk, often by what is usually called ‘severe weather.'”
The European Space Agency in 2000 began a five-year project using twin radar satellites to study how common rogue waves were. They evaluated 30,000 images for a three-week period when the Bremen and Caledonian were hit by big waves. The scientists identified 10 individual waves from around the world that were more than 80 feet high. “This came as a big surprise and provided strong evidence that large rogue waves are far more common than was previously believed,” Griggs wrote. These rogue waves don’t occur on beaches but on the open ocean, usually where strong currents and winds combine.
Griggs, a professor at UC Santa Cruz, has the lowdown on beaches growing and shrinking, El Nino and the Pacific Decadal Oscillation. El Nino is also called the Southern Oscillation, giving it the acronym ENSO.
El Nino produced a real wakeup call for coastal residents. El Nino-related events in December 1977 and January 1978 damaged the California coasts, especially the Central and Southern coasts. A 50-year storm series associated with the El Nino of 1983 combined with high tides caused even worse damage. Coastal damage in 1977-78 amounted to $59 million in 2008 dollars but $218 million in 1983 in 2008 dollars.
Here in El Dorado County the 1983 El Nino produced 73 inches of annual rainfall, the second highest in 137 years of local rainfall records. It also caused a landslide that closed Highway 50 for 75 days and wiped out part of the flume, which PG&E replaced with a tunnel.
The other recently discovered event is the Pacific Decadal Oscillation, which is more like a several-decade-long event. It varies between warm and cool periods of ocean temperature. These ocean temperature variations affect air pressures, wind patterns and storm tracks, according to Griggs. When a warm PDO cycle combines with an El Nino, winter storms become more severe. El Ninos occur when the pool of warm water in the eastern Pacific moves westward when the westerly trade winds stop for unknown reasons and the winds blow to the east.
Most beach sands originate from rivers, which bring sediment down during winter storms. The ocean waves bring it to the beach in the summer. Beach sand can be blown back into the dunes, which actually buffer the land from the erosive action of the ocean. It can also sink out of sight into submarine canyons that are in some cases near the shore. Some beaches become sand starved because of dams, such as the San Clemente Dam on the Carmel River. That dam is 90 percent full of sediment, 2.5 million cubic yards, according to Griggs. Another dam full of sediment is the Matilija Dam on the Ventura River now 93 percent full of sediment — 6 million cubic yards.
Construction of jetties and harbors creates wider beaches nearby, but can result in beach loss farther down the coast from these facilities.
Beaches have a seasonal aspect to them, being shrunken by winter storms and then lengthened as regular summer wave action brings sand ashore.
This compendium of shoreline geography, weather and offshore information includes 183 color illustrations, 13 line drawings and 20 maps. The paperback version sells for $19.95.