Tsunamis in Virginia

Tsunami Ready
The tide on the Virginia coast rises and falls about 1-3 feet twice a day at the NOAA reference stations. Development along the shoreline is based on those predicted tides, plus potential high water and waves from a flood that has a 1% chance of occurring each year (the "100-year flood") or from storm surges from major hurricanes.1

In theory, a very rare event 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 by a tsunami is considered very low, but the disastrous December 2004 tsunami in the Indian Ocean caused people to pay closer attention to the threat.

In 2006, Norfolk became the first East Coast city to earn recognition by the National Oceanic and Atmospheric Administration (NOAA) as "TsunamiReady/Storm Ready." According to the local paper, assistant director of Emergency Preparedness and Response was not worried about a tsunami, but:2

...decided to pursue the federal TsunamiReady certification, even though he admits the odds are better for him to hit the Mega Millions lottery than for a tsunami to strike Hampton Roads. "I went after it because of the potential there would be some federal funds available," he said. Then again, in his business, he said, you can't be too careful.

"Norfolk applying for the TsunamiReady program might sound a little farfetched," Talbot said, "but if something would happen, we have procedures in effect and know what to do."

tsunami risk - especially low on the Virginia coast
tsunami risk - especially low on the Virginia coast
Source: National Oceanic and Atmospheric Administration (NOAA), National Geophysical Data Center - Natural Hazards Viewer

Preparing for unexpected tsunamis would help prepare for storm surges associated with expected hurricanes. In addition, the risk to Norfolk is greater than zero. Tsunamis have struck the western edge of the Atlantic Ocean, north and south of Norfolk/Virginia Beach.

It is possible that the meteor impact 65 million years ago, which created the Chicxulub crater and led to the extiction of the dinosaurs, triggered landslides on the continental shelf and tsunamis along the Virginia shoreline.3

Such a worst-case scenario involving an impact and tsunami has occurred in what is now Virginia. A bolide (comet/meteorite) hit the Atlantic Ocean 35 million years ago, and instantly created a massive crater near what today is Cape Charles on the Eastern Shore. It triggered a wall of water that raced across the Coastal Plain and Piedmont, causing massive devastation to forests and wildlife.

The impact sent waves perhaps as far as the foothills of the Blue Ridge, possibly even washing over the mountains. According to the US Geological Survey:4

It is likely that the tsunamis reached and possibly overran the Blue Ridge Mountains.

The makers of the Hollywood movie Deep Impact created a climactic final scene comparable to the bolide's impact 35 million years ago. Hollywood altered geographic reality to enhance the dramatic scene at the end of the movie, where people trapped in a traffic jam were swamped by waves as key characters raced up the mountain slopes.

The scene was filmed on the Route 234 bypass in Prince William County, then under construction. There are no such mountains near Virginia's coastline, and the closest hill is a former landfill in Virginia Beach known as Mount Trashmore. The "movie mountains" in Deep Impact were covered by ponderosa pines. That species grows only west of the Mississippi River, so the scene where characters raced away from a tsunami was not filmed anywhere in Virginia.

only in Hollywood are there mountains within 6 miles of Virginia Beach
only in Hollywood are there mountains within 6 miles of Virginia Beach
Source: The Rellim Zone, Movie Review – Deep Impact (1998)

Bolide impacts are very rare events, with no predictable pattern for re-occurence. The Chicxulub event 65 million years ago and the Chesapeake Bay impact 35 million years ago created dramatic impacts, but the Tsunami Ready program anticipates a tsunami created by an earthquake and/or underwater landslide has a higher statistical probability.

Port Royal in Jamaica was hit by tsunamis after a 1692 earthquake. The Palisadoes sandspit sank, killing one-third of the residents. That provides an indication of the potential worst-case impact to residents on Willoughby Spit in Norfolk.5

damage at Willoughby Spit after 1933 hurricane
damage at Willoughby Spit after 1933 hurricane
Source: National Oceanic and Atmospheric Administration (NOAA) Photo Library

An 8.5–9.0 magnitude earthquake in Lisbon, Portugal in 1755 generated a tsunami all the way across the Atlantic Ocean in the Caribbean. Reports from the island of Martinique indicated that water rose as much as 30 feet high, in four separate cycles.6

To the north, Newfoundland was affected by a tsunami in 1929. It was noticed as far south as South Carolina, so Virginia was also affected.7

On June 13, 2013, a storm (derecho) off the coast of New Jersey or an underwater landslide triggered a minor tsunami that was clearly observed on the Atlantic Ocean shoreline. 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, a tsunami with a minor rise in water level was recorded six hours later. The gauge at Chesapeake Bay Bridge-Tunnel recorded a 3-inch rise, and 12 minutes later the gauge at Kiptopeke recorded a maximum rise of 10 inches. That change was well within the normal 1-3 feet tidal range that occurs roughly every 12 hours, and caused no damage.8

change in water height at Kiptopeke during June 13, 2013 tsunami
change in water height at Kiptopeke during June 13, 2013 tsunami
Source: National Oceanic and Atmospheric Administration (NOAA) - TSUNAMI of 13 June, 2013 (Northwestern Atlantic Ocean)

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 earthquakes and "mass wasting" of excessive accumulation of sediments on the continental slope.

The Cape Fear Slide, on the Outer Continental Shelf off the North Carolina coast, is one of the largest underwater landslides documented on the eastern edge of North America. It was triggered when a layer of salt rose up under pressure from overlying sediments, forming a dome with steeper and steeper slopes until the sediments broke free. A comparable slide today could generate a wave over 6 feet high on the Outer Banks of North Carolina.9

a 6-foot high tsunami would devastate much of Hampton Roads
a 6-foot high tsunami would devastate much of Hampton Roads
Source: National Oceanic and Atmospheric Administration (NOAA), NOAA/CIRES Scientists Help Prepare Virginia Beach For Tsunami, Storm-Driven Flooding

Sonar has documented numerous underwater landslides off the East Coast, along the edge of ravines that rivers carved into the shelf when water levels were lower. Massive slides include the Albemarle-Currituck Slide, Cape Lookout Slide and Cape Fear slide.

there is clear vidence of numerous underwater landslides (terrigenous debris-flow deposits) on the Outer Continental Shelf along the East Coast
there is clear vidence of numerous underwater landslides ("terrigenous debris-flow deposits") on the Outer Continental Shelf along the East Coast
Source: US Geological Survey (USGS), U.S. EEZ Atlantic Continental Margin GLORIA

As sediments flow down the Continental Slope, they push water forward. About 20,000 years ago, landslides flowed towards the East Coast from salt diapirs off the North Carolina coast at Cape Fear. Even if an underwater landslide flowed away from the East Coast, such an event could cause a surge on the Virginia shoreline.10

landslides from Cape Fear diapirs have flowed towards the East Coast, increasing the potential impact from a surge of water
landslides from Cape Fear diapirs have flowed towards the East Coast, increasing the potential impact from a surge of water
Source: National Oceanic and Atmospheric Administration (NOAA), Exploration of the Cape Fear Diapir

Research indicates that even a large 7.5 magnitude quake "must be located offshore and within 100 km of the continental slope to induce a catastrophic slope failure" to trigger a tsunami large enough to flood Virginia Beach, Norfolk, or the Eastern Shore. That assessment has reduced fears that earthquakes in the seismically-active Caribbean might pose a serious risk to Virginia.11

The Virginia shoreline is far from the closest zone in the Caribbean Sea where tectonic plates, sliding in a quick jerk, could generate a giant wave. Tectonic plates in the Caribbean caused the 2010 Haiti earthquake, and will move again. However, wave energy from that region would be deflected by Florida or directed into the open Atlantic Ocean, and would have minimal impact in Virginia.12

Another unlikely risk is that the Cumbre Vieja volcano in the Canary Islands could collapse. Lanslides and earthquakes do cause tsunamis that affect shorelines far away. The 1964 Alaskan earthquake created a killer tsunami far away at Crescent City, California. An underwater quake near Indonesia in December, 2004 created a tsunami that killed people all the way across the Indian Ocean in Kenya.

After 10,000 more years, Cumbre Vieja could become unstable enough to threaten the East Coast of the United States.13

In a worst-case scenario such a landslide could generate a 10-25 foot high tsunami on the Virginia coast on the other side of the Atlantic Ocean. If the flank of the volcano moved as a coherent block in a rapid mega-landslide, it might generate the sort of mega-tsunami that Hollywood shows in disaster movies that portray the destruction of New York City.

The hypothesis, while possible, is highly unlikely. Major landslides have occurred at the Cumbre Vieja volcano, but they occured in phases rather than all at once. Each phase may have generated a local tsunami, but there is no evidence of a collapse that generated a mega-tsunami large enough to affect the East Coast of the United States.14

A 2016 Discovery Channel program highlighted the rare possibility that a tsunami created by a landslide on the other side of the Atlantic Ocean could threaten the United States. The Tsunami Society recognized that many viewers might consider the risk to be significant rather than understand the very low probability, and responded with:15

While the active volcano of Cumbre Vieja on Las Palma is expected to erupt again, it will not send a large part of the island into the ocean, though small landslides may occur. The Discovery program does not bring out in the interviews that such volcanic collapses are extremely rare events, separated in geologic time by thousands or even millions of years.

No such event - a mega tsunami - has occurred in either the Atlantic or Pacific oceans in recorded history. NONE.

Canary Islands, far across the Atlantic Ocean from Virginia...
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

Potentially, warming of methane hydrates (natural gas) now buried in ice crystals in coastal shelf sediments could "bubble up" if warm ocean currents shift location. The gas is frozen, for now.

If there was a change in water pressure, perhaps triggered by ocean warming, a strong hurricane, or small landslide, a burst of methane could be released. A series of giant gas bubbles could create a massive underwater landslide on the Continental Slope. That coul displace enough Atlantic Ocean water to generate a tsunami that could reach the Eastern Shore, Norfolk, and other coastal areas.10

The potential of a tsunami generated by a volcano collapse in the Canary Islands, an underwater earthquake or landslide, or the release of a gas bubble catches the attention of those interstedin rapid, catastrophic change. The greatest flooding threat to Hampton Roads is from a storm surge associated with a hurricane, and the risks of such flooding increase as sea level rises.

Storm surges are a clear and present danger. Tsunamis caused by landslides or collapsing volcanoes are a much smaller risk. Disaster management specialists still plan for a tsunami because one could have a devastating impact on Tidewater Virginia, while they take advantage of Tsunami Ready funding to prepare for the greater risk of storm surges.

The Chesapeake Bay "Bolide" That Shaped the Groundwater in Southeastern Virginia

Floods and Floodplains

Will Norfolk (and the Rest of Hampton Roads) Drown?

flee to high ground
Source: National Oceanic and Atmospheric Administration (NOAA)

Links

References

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. R. D. Norris J. V. Firth, "Mass wasting of Atlantic continental margins following the Chicxulub impact event," in Catastrophic events and mass extinctions: impacts and beyond, Christian Koeberl, Kenneth G. MacLeod (editors), Geological Society of America Special Papers, Volume 356, January 2002, p.80, p.93, https://dx.doi.org/10.1130/0-8137-2356-6.79 (last checked October 24, 2017)
4. "A Virginia tsunami? It already happened," Richmond Times-Dispatch, January 2, 2005, Page B1; D.S. Powars, T.S. Bruce, "The Effects of the Chesapeake Bay Impact Crater on the Geologic Framework and the Correlation of Hydrogeologic Units of Southeastern Virginia, South of the James River," US geological Survey Professional Paper 1622, 1999, http://pubs.usgs.gov/pp/p1612/powars.html (last checked August 27, 2012)
5. "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)
6. J. Roger, M. A. Baptista, A. Sahal, F. Accary, S. Allgeyer, H. He´bert, "The Transoceanic 1755 Lisbon Tsunami in Martinique," Pure & Applied Geophysics, Volume 168 (2011), p.1019, https://doi.org/10.1007/s00024-010-0216-8 (last checked September 28, 2017)
7. "1929 Grand Banks Tsunami," Tsunami, http://www.ess.washington.edu/tsunami/general/historic/grandbanks29.html (last checked August 20, 2011)
8. "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)
9. Matthew J. Hornbach, Luc L. Lavier, Carolyn D. Ruppe, "Triggering mechanism and tsunamogenic potential of the Cape Fear Slide complex, U.S. Atlantic margin," Geochemistry, Geophysics, Geosystems, Volume 8 Issue 12 (December 2007), p.12, http://dx.doi.org/10.1029/2007GC001722 (last checked June 11, 2013)
10. "Exploration of the Cape Fear Diapir," Ocean Explorer, July 29, 2003, National Oceanic and Atmospheric Administration (NOAA), http://oceanexplorer.noaa.gov/explorations/03windows/logs/jul29/jul29.html (last checked November 28, 2017)
11. 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)
12. "Can It Happen Here?," US Geological Survey Earthquake Hazards Program, http://earthquake.usgs.gov/learn/topics/canit.php; "US East Coast Faces Variety of Tsunami Threats," Our Amazing Planet, http://www.ouramazingplanet.com/3774-east-coast-tsunamis.html (last checked January 31, 2013)
13. "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)
14. 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://dx.doi.org/10.1029/2001GL013110; Dave Petley, "Killing off the Canary Islands landslide megatsunami scare," The Landslide Blog, December 13, 2013, https://blogs.agu.org/landslideblog/2013/12/13/canary-islands-tsunami/ (last checked Vovember 26, 2017)
15. "The Next Mega Tsunami," Discovery Channel, 2016, http://channel.nationalgeographic.com/galleries/the-next-mega-tsunami/at/127-2089089/; "What is a mega-tsunami and can it happen today?," International Tsunami Information Center, http://itic.ioc-unesco.org/index.php?option=com_content&view=article&id=1203 (last checked October 21, 2014)
16. "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)

bathymetric-topographic digital elevation model (DEM) of Virginia Beach area, used to calculate tsunami inundation risk
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


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