Coastal Maine tide change a mystery
October 30, 2008
BOOTHBAY HARBOR, Maine"Meteorologists are baffled by rapid tidal changes along the Maine coast, which damaged some boats and piers.
Witnesses say low tide turned and became high within a matter of minutes on Tuesday afternoon. The changes occurred six or seven times. The National Weather Service says reports from several locations indicated that water levels fell and rose from 4 feet to as much as 12 feet during the event.
In a public information statement, the weather service says the cause "remains a mystery and may never be known."
It said significant rapid rises and falls in tide levels were observed around 3 p.m. in Boothbay Harbor, Southport and Bristol. The statement said rapid surges can be caused by the underwater movement of land, most often due to an earthquake, or due to slumping of sediments along a steep canyon or shelf, but no earthquakes were reported in the area Tuesday.
A similar event occurred on Jan. 9, 1926, in Bass Harbor, the statement said.http://www.boston.com/news/local/maine/articles/2008/10/30/coastal_maine_tide_change_a_mystery/?p1=Well_MostPop_Emailed7
PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE GRAY ME
630 PM EST WED OCT 29 2008
...TUESDAY'S UNUSUAL TIDE FLUCTUATIONS ALONG THE MID-MAINE
THE CAUSE OF YESTERDAY'S UNUSUAL TIDE FLUCTUATIONS ALONG THE
MID COAST OF MAINE REMAINS A MYSTERY...AND MAY NEVER BE KNOWN.
SIGNIFICANT RAPID RISES AND FALLS IN TIDE LEVELS WERE OBSERVED
AROUND 3 PM IN BOOTHBAY HARBOR, SOUTHPORT, AND BRISTOL. ONLY
VERY MINOR FLUCTUATIONS WERE NOTED AT TIDE GAUGES ALONG THE
THERE ARE SEVERAL POSSIBLE EXPLANATIONS FOR YESTERDAY'S EVENT.
RAPID SURGES CAN BE CAUSED BY THE UNDERWATER MOVEMENT OF LAND,
MOST OFTEN DUE TO AN EARTHQUAKE, OR DUE TO THE SLUMPING OF
SEDIMENTS ALONG A STEEP CANYON OR SHELF. NO EARTHQUAKES WERE
REPORTED IN THE AREA YESTERDAY. IN RARE INSTANCES, LARGE AND
RAPID SURGES CAN BE GENERATED BY STORMS. IN EITHER CASE, THE
BATHYMETRY OF THE OCEAN FLOOR REFLECTS AND REFRACTS THE WAVE
ENERGY AND CAN CAUSES SIGNIFICANT VARIATIONS IN TIDE LEVELS
ALONG THE COAST...AND RAPID CHANGES IN TIDE LEVELS AT A
PARTICULAR LOCATION. THESE SURGES ARE QUITE UNLIKE THE MUCH
SLOWER SURGES NORMALLY ASSOCIATED WITH COASTAL STORMS.
EYE-WITNESS REPORTS FROM SEVERAL LOCATIONS INDICATED THAT WATER
LEVELS FELL AND ROSE FROM 4 FEET TO AS MUCH AS 12 FEET ALONG
THE COAST DURING THE EVENT. THESE RAPID CHANGES IN TIDAL
LEVELS GENERATED THE STRONG CURRENTS THAT DAMAGED PIERS AND
BOATS IN THE AREA.
ALTHOUGH THESE EVENTS ARE RARE ALONG THE MAINE COAST, THEY HAVE
OCCURRED IN THE PAST. ON JANUARY 9, 1926, AN EVENT SIMILAR TO
YESTERDAY'S EVENT WAS OBSERVED IN BASS HARBOR. DURING THAT
EVENT, THE HARBOR DRAINED RAPIDLY AND THEN WAS FOLLOWED BY A 10
FT SURGE OF WATER, FOLLOWED BY TWO OTHER SMALLER WAVES. THERE
WERE NO EARTHQUAKES REPORTED ON THAT DAY. NO ONE WAS INJURED
IN THAT EVENT BUT ABOUT 50 FISHING BOATS WERE HURLED ASHORE.
NATIONAL WEATHER SERVICE
That's my wild guess for the evening.
It doesn't sound so wild to me. You're making good sense.
And the waves bounce back and forth on the various landmasses?
A similar occurrence in Florida more than 15 years ago continues to baffle researchers. A series of 12- to 15-foot waves hit Daytona Beach on July 3, 1992, injuring more than 20 people and lifting and tossing dozens of cars.
Jeff List, an oceanographer at the US Geological Survey at Woods Hole said he and other researchers studied the occurrence, but no one has been able to pinpoint the cause. And he said similarly enormous waves appeared once on the Great Lakes.
Could such a wave or waves enter Boston Harbor, or even engulf the Massachusetts coast?
"It seems a little unlikely one could hit Boston," List said. "But then again, these things are always surprises when they occur."
A squall line surge, which occurs when fast-moving storm winds sweep over water that is traveling the same speed, can create such a wave. (The speed of waves is directly related to wind speed and the depth of the ocean at any given point.)