tsunami risk - especially low on the Virginia coast
Source: National Oceanic and Atmospheric Administration (NOAA), National Geophysical Data Center - Natural Hazards Viewer
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.
The threat is small, but real. In 2000, a scientific study of cracks at the edge of the coastal shelf suggested how a 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.3
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.4
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.5 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.6
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.7 To the north, Newfoundland was affected by a tsunami in 1929.8
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..."9
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 damage at Willoughby Spit after 1933 hurricane Source: National Oceanic and Atmospheric Administration (NOAA) Photo Library |