Tsunamis in Virginia
The tide on the Virginia coast rises and falls about 1-3 feet, twice a day, at the NOAA reference stations.1 Development along the shoreline is based on those predicted tides, including potential high water and waves from floods that have a 1% chance of occuring each year (the "100-year floods").
In theory, however, an earthquake could generate a tsunami (formerly called a "tidal wave"), displacing water in the ocean and creating a sudden surge as much as 10-25 feet high on Virginia's eastern coastline. The risk of Virginia being affected is considered very low, because very few earthquakes occur near the passive margin of the eastern United States. No one paid much attention to the tsunami threat - until the disastrous tsunami in the Indian Ocean in December, 2004.
Norfolk became the first "Tsunami Ready" Virginia city (in January 2006). Norfolk's assistant director of Emergency Preparedness and Response was not worried about a tsunami, and thought that he would win the Mega Millions lottery before a tsunami affected Hampton Roads - but said "I went after it because of the potential there would be some federal funds available."2 After all, the risk to Norfolk is greater than zero.
tsunami risk - especially low on the Virginia coast
Source: National Oceanic and Atmospheric Administration (NOAA), National Geophysical Data Center - Natural Hazards Viewer
The threat is small, but real. On June 13, 2013, a storm (derecho) off the coast of New Jersey or an underwater landslide triggered a minor tsunami on the East Coast. On the Jersey shoreline, the tsunami was clearly observed. A breakwater that is normally 3-4 feet underwater was exposed, and three people were swept into the ocean from rocks that were 5-6 feet above sea level. In Virginia, six hours later a tsunami was recorded by equipment. The water level gauge at Kiptopeke on the Eastern Shore recorded a maximum rise of 10 inches, occuring 12 minutes after the gauge at Chesapeake Bay Bridge-Tunnel recorded a 3-inch rise. Such a change, well within the normal 1-3 feet tidal change each 12 hours or so, caused no damage.3
In 2000, a scientific study of cracks at the edge of the coastal shelf suggested how a damaging tsunami could be generated near the Virginia coast, despite the small number of earthquakes in the region. Landslides occur along the continental slope, initiated by those rare eathquakes or excessive accumulation of sediments on the continental slope. Potentially, warming of methane hydrates (natural gas) now buried in ice crystals in coastal shelf sediments could "bubble up" if warm ocean currebnts shift location, causing a landslide and displacing enough of the Atlantic Ocean water to cause a tsunami.4
If an earthquake did occur in the Atlantic Ocean, it would need to be near the Virginia coastline to trigger a tsunami that could flood Virginia Beach, Norfolk, or the Eastern Shore. Research that indicates even a 7.5 magnitude quake "must be located offshore and within 100 km of the continental slope to induce a catastrophic slope failure" has reduced fears that earthquakes in the seismically-active Caribbean might pose a risk to Virginia.5
Another unlikely-but-possible-so-be-Tsunami-Ready risk is that the Cumbre Vieja volcano in the Canary Islands could collapse. Such a landslide, even though on the other side of the Atlantic Ocean, could generate a 10-25 foot high tsunami on the Virginia coast.6 An earthquake in Lisbon, Portugal in 1755 generated a tsunami across the Atlantic Ocean; it could happen again - though research published in 2006 suggested that it might require 10,000 more years before Cumbre Vieja became unstable enough to threaten the East Coast of the United States.7
Canary Islands, far across the Atlantic Ocean from Virginia...
Source: National Oceanic and Atmospheric Administration (NOAA), National Geophysical Data Center - ETOPO1 1 Arc-Minute Global Relief Model
Tsunamis have already struck on the western edge of the Atlantic Ocean, though far north and south of Norfolk/Virginia Beach. Port Royal in Jamaica was hit by tsunamis after a 1692 earthquake. The Palisadoes sandspit sank, killing one-third of the residents - an indication of the potential impact to residents on the shoreline of Virginia Beach and especially Willoughby Spit in Norfolk.8 To the north, Newfoundland was affected by a tsunami in 1929.9
A hurricane may have generated a tsunami that devastated Assateague and Chincoteague islands in 1821:10
- Residents reported that as the storm approached the coast from the southeast, the sea receded and exposed miles of ocean bottom. Soon afterward, a deep roar could be heard moments before a "monstrous wall of inky waters rushed with the speed of lightning toward the island." The wall of water struck Assateague first, decimating trees and anything else in its path, and then struck Chincoteague, carrying away men and ponies "like insects." One man with his grandson clinging to his neck was reportedly swept far up on to the mainland six miles to the west and another was found the next morning hanging in a pine tree by his waistband twenty feet from the ground (Scribner's Monthly, April 1877). Modern interpretations of the cause of the tsunami of 1821 include an offshore hurricane, whose wave action generated an underwater landslide.
A worst-case scenario involving a tsunami in Virginia has occurred - but it was 35 million years ago. A bolide (comet/meteorite) hit the earth near what is today the Eastern Shore, and the impact sent waves as far as the foothills of the Blue Ridge. "A train of giant waves traveled across Virginia to the mountains, perhaps overlapping them..."11
- (In the Hollywood movie Deep Impact, a comet slammed into the Atlantic Ocean and the waves washed up to the base of the Blue Ridge. The scene at the end of the movie, of a traffic jam getting swamped by waves as key characters race up the mountain slopes, was filmed on the Route 234 bypass in Prince William County - but don't look in Virginia for those mountains. Those hills were covered by ponderosa pines that grow in the western United States; the movie's final scenes were not filmed in Virginia.)
bathymetric-topographic digital elevation model (DEM) of Virginia Beach area, used to calculate tsunami inundation risk
Source: National Oceanic and Atmospheric Administration (NOAA), National Geophysical Data Center - Virginia Beach, VA 1/3 arc-second MHW DEM
damage at Willoughby Spit after 1933 hurricane
Source: National Oceanic and Atmospheric Administration (NOAA) Photo Library
1. National Oceanic and Atmospheric Administration (NOAA) - Center for Operational Oceanographic Products and Services, Reference Stations (last checked August 20, 2011)
2. "Norfolk is tsunami-ready and has a sign to prove it," The Virginia-Pilot, January 10, 2006, http://hamptonroads.com/2006/01/norfolk-tsunamiready-and-has-sign-prove-it (last checked August 20, 2011)
3. "TSUNAMI of 13 June, 2013 (Northwestern Atlantic Ocean)," West Coast/Alaska Tsunami Warning Center, National Oceanic and Atmospheric Administration/National Weather Service, http://oldwcatwc.arh.noaa.gov/previous.events/06-13-13/index.php (last checked July 3, 2013)
4. "News Release : Undersea Cracks along Continental Shelf Could Trigger Tsunamis along U.S. East Coast," Woods Hole Oceanographic Institution, April 28, 2000, http://www.whoi.edu/page.do?pid=9779&tid=282&cid=985&ct=162 and Neal W. Driscoll, Jeffrey K.Weissel, and John A. Goff, "Potential for large-scale submarine slope failure and tsunami generation along the U.S. mid-Atlantic coast," Geology, pp. 407-410, May 2000, http://www.earthinstitute.columbia.edu/news/aboutStory/pdf/28-407.pdf (last checked August 20, 2011)
5. Uri S. ten Brink, Homa J. Lee, Eric L. Geist, David Twichell, "Assessment of tsunami hazard to the U.S. East Coast using relationships between submarine landslides and earthquakes," in Marine Geology vol. 264, pp.65–73 (2009), http://www.sciencedirect.com/science/article/pii/S0025322708001710 (last checked August 20, 2011)
6. Steven N. Ward, Simon Day, "Cumbre Vieja Volcano -- Potential collapse and tsunami at La Palma, Canary Islands," Geophysical Research Letters, Vol. 28, No. 17, pp.3397-3400, September 1, 2001, http://www.agu.org/pubs/crossref/2001/2001GL013110.shtml (last checked August 20, 2011)
7. "New research puts 'killer La Palma tsunami' at distant future," PhysOrg.com, September 20, 2006, http://www.physorg.com/news77977989.html (last checked August 20, 2011)
8. "Historical Events - Port Royal, Jamaica, 1692," The Tsunami Risks Project, http://www.nerc-bas.ac.uk/tsunami-risks/html/HJamaica.htm (last checked August 20, 2011)
9. "1929 Grand Banks Tsunami," Tsunami, http://www.ess.washington.edu/tsunami/general/historic/grandbanks29.html (last checked August 20, 2011)
10. "Hazard Mitigation Plan," Eastern Shore Hazard Mitigation Planning Committee, Accomack-Northampton Planning District Commission, 2011, p.30, http://www.a-npdc.org/hazardplan.pdf (last checked August 31, 2012)
11. "A Virginia tsunami? It already happened," Richmond Times-Dispatch, January 2, 2005, Page B1
Rocks and Ridges
The Chesapeake Bay "Bolide" That Shaped the Groundwater in Southeastern Virginia
Will Norfolk (and the Rest of Hampton Roads) Drown?