A storm surge is a rise in water level caused by a combination of wind and low atmospheric pressure. It is the most destructive force of a hurricane (an intense cyclone that forms over warm tropical oceans; called a typhoon when it occurs in the western Pacific Ocean and adjacent seas)
Formation of a storm surge
When a hurricane is forming over open, warm ocean waters, the wind pushing the water and the low atmospheric pressure in the eye of the hurricane cause the level of the sea to rise, whipping the water into gigantic waves. Because this is happening away from land, the water can escape and move freely away from the building storm. But as the hurricane moves towards land and the depth of the water becomes more shallow, the ever-increasing wall of water does not have a chance to flow away. Instead it is built up around the eye of the hurricane and forms huge waves. These mountainous waves pound against the land and anything in its path—buildings, homes, piers, and people. Storm surges can be more devastating depending upon the strength of the hurricane's winds and the shallowness of the off-shore waters.
A storm surge can also become much more destructive if it occurs during high tide (an increase in water level due to the Moon's gravitational pull on Earth). This is called a storm tide. For example, if a normal high tide for a particular area is three feet and a storm surge occurs at the same time with fifteen-foot waves, a storm tide with eighteen-foot waves is formed. This occurrence makes the storm surge even more devastating.
Words to Know
Atmospheric pressure: The pressure exerted by the atmosphere at Earth's surface due to the weight of the air.
Hurricane: A severe swirling tropical storm with heavy rains and winds exceeding 74 miles (119 kilometers) per hour.
Tide: The periodic variation in the surface level of the oceans, seas, and bays caused by the gravitation attraction of the Moon (and to a lesser extent the Sun).
Storm surge destruction
Storm surges have long been recognized as the most destructive part of a hurricane. Causing drownings and property destruction, this incredible wall of water stops for nothing in its path. As it moves across the land, it picks up and carries with it debris that it finds along the way, such as cars, utility poles, and boats. A hurricane hit Galveston, Texas, in 1900 and killed 6,000. The storm surge from the "Great Galveston Hurricane" formed waves that were twenty-five feet high. In 1970, the Bay of Bengal in Bangladesh suffered through a hurricane that produced a storm surge with thirty-foot-high waves that killed approximately 200,000 people.
Prevention of damage
After suffering through such incredible devastation, the city of Galveston completed the building of a seawall four years later. A little over three miles long and seventeen feet above average low tide mark, the Galveston seawall would act as a line of defense by interfering in the progress of the storm surge's attack on the land and by catching some of the destructive debris that it carries along its way. The city of Galveston
also actually raised the level of the city after devoting ten years to the project. The entire city—every church, home, and business—had 14 million cubic yards (10.7 million cubic meters) of sand poured in underneath it. The combination of building a seawall and raising the level of the city helped increase the odds of Galveston successfully surviving a storm surge. The investment in prevention paid off: On August 16, 1915, a hurricane of almost the same force as the 1900 storm hit the city. While the 1915 hurricane was still tragic—about a dozen people lost their lives—the number of deaths was far below the 6,000 in 1900.
[See also Cyclone and anticyclone ]
Storm surge, caused by very low atmospheric pressure, is a volume of ocean water driven by the wind toward the shore where, as the sea bed depth decreases, produces a localized increase in sea level.
Storm surges that accompany hurricanes and typhoons can be very destructive. In the wake of Hurricane Katrina, which in August, 2005 struck states along the Gulf of Mexico, caused a storm surge that produced waves almost 30 ft (9 m) high, that traveled hundreds of yards inland. The surge devastated the cities of Mobile, Alabama, Biloxi, Mississippi, and New Orleans, Louisiana.
In New Orleans, the storm surge caused water to breach barriers (levees) that normally prevented Lake Pontchartrain from spilling downhill into the city. The breach produced flooding of about 80% of the city.
During a hurricane or typhhon, a dome of water can form in the area of low pressure that moves across the ocean as the winds drive the storm. Upon reaching shallow coastal water, winds blowing toward the shore move over the domed water, and pile water along the coast, producing the elevated sea level that becomes the storm surge.
Tides—the rhythmic rise and fall of the ocean’s surface caused by the gravitational attraction of the sun and moon—can amplify the effect of storm surges. In most areas, two high tides and two low tides occur daily. Tides may rise and fall a few inches to more than 49 ft (15 m).
In addition to tidal influences, the shape of ocean basins, inlets and bays, and sea level rise may cause higher than normal storm surges. The geography around London, England, produced recurrent tidal flooding from storm surges until the Thames barrier was constructed in 1986. Ten steel gates reaching 546 yd (500 m) across the river now protect the city from storm surge impacts.
As of 2006, reconstruction of the Katrina-damaged levees around New Orleans continued. The technology being used to fortify the levees is not as advanced as that used in England, which has led to concern that another storm surge could again create havoc on the city.
Storm surge, caused by very low atmospheric pressure , is a volume of oceanic water driven by the wind toward the shore where it "builds up" along the coast producing a localized increase in sea level .
Such low atmospheric pressure occurs during cyclonic storms, called typhoons in the Pacific region and hurricanes along the Atlantic seaboard. During these storms, a dome of water forms in the area of low pressure that moves across the ocean as the winds drive the storm. Upon reaching shallow coastal water, winds blowing toward the shore move over the domed water, and pile water along the coast, producing an elevated sea level.
Storm surges are the deadliest element of cyclonic storms. These storms form in areas with warm surface water temperatures in the zone 8° north and 15° south of the equator. Winds may reach 328 MPH (100 km/h) and move in a counterclockwise spiral around a calm center. Winds of nearly 200 MPH (60 km/h) associated with cyclonic storms can extend the storm's diameter to more than 2,000 mi (640k). Hurricane Hugo, the most expensive cyclonic storm in U.S. history had a storm surge of 7.9 ft (2.4 m) above normal tide levels. However, smaller storms can produce storm surge when they coincide with high tides .
Tides, the rhythmic rise and fall of the ocean's surface caused by the gravitational attraction of the sun and moon , can amplify the effect of storm surges. In most areas, two high tides and two low tides occur daily. Tides may rise and fall a few inches to more than 49 ft (15 m).
Normal tides are driven by three astronomical occurrences. First, when the moon is nearest the earth , due to its oval shaped orbit , the moon's gravitational attractions is at its greatest; thus tides occurring during this period are greater than normal tides. Second, when the sun, moon and earth are aligned, "spring" tides occur. These are 20% greater than normal tides. When the sun, moon and earth are at 90°, to one another "neap" tides, which are 20% weaker than normal, occur. Finally, twice a month the moon crosses the earth's equatorial plane resulting in higher than normal tides.
In addition to tidal influences, the shape of ocean basins, inlets and bays, and sea level rise may cause higher than normal storm surges. In February 1976, Bucksport, Maine experienced a 5.8-ft (1.76-m) storm surge and Bangor, located 15 mi (24 km) inland from Bucksport, suffered a storm surge of nearly 11 ft (3.35 m). The difference in storm surges was due to the funnel shape of the bay. The great amount of water in the surge that was forced through a relatively narrow channel caused water levels to rise rapidly in Bangor. Damages of more than $2 million occurred.
London historically experienced recurrent tidal flooding from storm surges until the Thames barrier was constructed in 1986. Ten steel gates reaching 1,640 mi (500 m) across the river now protect the city from storm surge impacts.