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‘Mini-tsunami’ strikes Wickford Harbor

June 29, 2013

The ‘mini-tsunami’ struck the docks along Wickford Harbor on June 13, damaging two boats. The event was supposedly caused by a weather phenomenon called a ‘derecho,’ or blast of high winds. (Standard Times File Photo)

NORTH KINGSTOWN—When one hears the word ‘tsunami,’ dramatic images of devastated coastlines and rushing surges of sea water come to mind. Although less damaging than the tsunamis that struck Indonesia in 2004 or Japan in 2011, Wickford Harbor was struck by a so-called ‘mini tsunami’ earlier this month, and local scientists have been trying to figure out the cause.

Chuck Ebersole, a member of the Wickford Yachting Club, witnessed the mini-tsunami first hand on June 13 when the tide began to sweep out of Wickford Harbor.

“I was located in the yacht club here speaking with a member when I noticed the current flowing very strongly out at low tide,” said Ebersole. “At that point, we heard a big bang and one of the boats had pulled out of the dock and was pulling out with the current.”

Ebersole estimated that the current was flowing out at five to seven knots. Moments later, Ebersole watched as the tide came rushing back in.

“Fifteen minutes after the whole thing started, the current switched and came back into the dock,” said Ebersole. “The boat went perpendicular to the dock, we cut the line with help of guys from the Pleasant Street Marina, and this variation in and out occurred four to six hours after that, gradually decreasing.”

Wickford Harbormaster Ed Hughes was astonished at the wave action that the mini-tsunami caused, stating that he had never seen such a phenomenon in Wickford Harbor before. 

“The water seemed to be coming in at a high rate of speed, and then 10 minutes later, started going out just as fast,” said Highes. “This happened a few times. The water normally doesn’t ever come in that fast or go out that fast, and had enough power to do some damage to a boat, so it was just fast.”

“It was a very strange, unique thing,” he added.

On one boat, only superficial scratches were made by upon striking the dock, while another had some of its stanchions and a turnbuckle ripped off, according to Ebersole. The event, which scientists at the University of Rhode Island’s Graduate of School of Oceanography are currently researching, is being identified as a ‘bow echo,’ a complex thunderstorm system that can produce significant straight line winds.

“A 'bow echo' is when there is a strong wind blowing out from underneath a thunder storm,” said GSO Professor John Merrill. “The surface air pressure goes up as the pulse  [of wind] passes by, and that pushes down on the water surface.”

“There are things that push on the water’s surface all the time, so what?” he continued. “If the downward push goes forward out over the sea surface at the same rate of speed that the shallow water wave is created, then the push is acting on that piece of sea surface for a longer period of time.”

Thus, a mini-tsunami is formed. Similar wave events, also known as ‘derechos’, have been recorded all along the Eastern Seaboard around the same time. According to the National Oceanic and Atmospheric Administration (NOAA), over 30 tidal gages recorded surges along the New Jersey and Massachusetts shorelines, and air pressure instruments recorded strong fluctuations in Delaware and Cape May, N.J.

At Barnegat Inlet, N.J., for example, divers were carried out and back onto a submerged reef after a strong outflow followed by a returning wave measured at six feet from peak to trough took hold of them. Other incidents of people being swept off rocks and boat damage have been recorded as well.

According to Paul Whitmore, a scientist with NOAA’s West Coast and Alaska Tsunami Warning Center, the mini-tsunami waves leaving the southern New Jersey shore impacted tidal gages along the coastlines of Bermuda and Puerto Rico.

“This may be the first meteo-tsunami recorded at trans-oceanic distances, at least that I have heard of, if it holds up that the Bermuda and Puerto Rico observations are directly related to the event and the source is shown to be wholly due to meteorological sources,” said Whitmore in an email.

Merrill further stated that winds of up to 60 miles per hour were recorded at inland locations on June 13, causing damage on land as well. He also stated that scientists throughout the East Coast will begin to look closer at the weather event to more specifically determine the full impact of the mini-tsunami.

“We’ll work collaboratively, but it is not a highly organized thing,” said Merrill. “Someone will look at things like tidal records and sea seismicity at the time. We each bring to the table what we can.”

“It turns out there are other groups working on this,” he added. “They are not sure and might think it is an underwater mudslide, but as scientists we are comfortable with multiple theories.” 

Source 
Southern Rhode Island Newspapers
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