A storm surge is a high flood of water caused by wind and low pressure, most commonly associated with hurricanes. It is the most deadly aspect of a hurricane, responsible for 90% of deaths during hurricanes. Storm surges are different from tidal surges, which are violent surges caused exclusively by the tidal shift in sea level.
A storm surge is primarily caused by the extremely high winds which accompany a hurricane. This wind pushes the water rapidly, building it up into a huge wave. At the same time, the low pressure caused by a hurricane also causes the water level to rise up in the lowest-pressure spots and to sink in areas of higher pressure, exacerbating the wave buildup caused by the winds. Additionally, the shape of the ocean floor may affect how high the waves of the surge are when they reach land.
It is not uncommon to see a storm surge in excess of 18 feet (6m), a wave that can potentially cause dramatic damage. The largest recorded one was in Australia in 1899, which reached heights of 43 feet (13m). In the United States in 2005, storm surges associated with Hurricane Katrina reached 30 feet (9m).
In the United States and many other countries, storm surges are not the primary cause of death associated with hurricanes. In fact, in the past twenty years, just over 1% of hurricane-related deaths in the United States have been caused by them. The majority of hurricane deaths in the United States come from inland flooding. In other parts of the world, however, virtually all hurricane-related deaths are a result of storm surges. Bangladesh is the area in the world most affected by storm surges, with over a hundred on record. These are responsible for hundreds of thousands of deaths in the Bangladesh area alone.
There is a growing concern in areas such as the United States' Gulf Coast region about the problem of public storm surge awareness. Since the United States has not been hit dramatically by surges since the 1920s, most of the public is unaware of the true dangers of this phenomena. With the growing frequency of hurricanes in this region of the world, there is a push to teach awareness and preparedness before events such as the 1900 Galveston hurricane storm surge, which killed over ten thousand people, are repeated.
