When one thinks of hurricanes, normally the first image that comes to mind is the high winds that come with them. However, it isn't the wind that brings the most death or destruction, but the storm surge that accompanies the hurricane when it approaches land. So what exactly is a storm surge and how is it created?
As a hurricane or tropical cyclone spins and the winds gain speed, water is pushed ahead of the storm, on the surface of the ocean. In deep seas, this water normally dissipates into the ocean's murky depths. In shallower areas, this water builds up, creating waves up to 40 feet high. It's this giant wave that smashes into coastal areas, creating havoc and destruction.
It isn't high winds alone that cause those waves to form, however. Low pressure is also a factor in the creation of a surge. The storm creates low pressure areas, which in turn causes the level of water in those areas to rise up. This effect, coupled with the lowering of water in high pressure areas, helps the storm to create even higher surge waves.
A third factor in the creation of a storm surge is the contour of the ocean floor beneath the storm and wave. Areas of the continental shelf with shallow slopes permit larger surges to make it to shore. Steeper shelves tend to allow more of the surge's energy to dissolve. This doesn't mean that storm surges are harmless in areas with steep continental shelves. In fact, the opposite can be true since the surge is now confined to areas such as harbors and marinas, where ships and boats are often located.
Other issues contributing to the storm surge include the size, strength and speed of the storm in question. Weaker storms will produce smaller surges while stronger storms usually produce larger surges. Another consideration is the tide. During high tide, storm surges are higher and therefore more destructive. This is especially true if the difference between low and high tide great. Wind stresses also play a part in the size of a surge. During cyclones or hurricanes, water levels tend to rise toward the downwind area of shoreline and drop at the upward end. This causes some areas of a surge to be even more deadly than others.
Land masses located higher above sea level usually take less damage than those at or below sea level. In either case, most structures near the shoreline are built to withstand incredible winds. Unfortunately, their foundations are not usually built to stand up to the constant pounding of a storm surge. As the surge continues to assault the shore, it erodes the very ground around buildings, weakening their foundations and causing them to collapse or break apart. Other damage occurs when relocated salt water from the surge mixes with fresh water estuaries and the like. This often causes serious damage to both flora and fauna.
Storm surges are not confined to ocean shorelines. Large, inland bodies of water can also be affected by a surge. Lakes located on peninsulas or close to the ocean can also be damaged by these giant waves. There have been at least two documented incidents of hurricanes cutting a swathe across Florida, smashing through dikes and levees and causing lakes to swell out of their confines.