or danger is likely, and what steps should be taken 
so that they do not become disasters. In addition, 
heavy investment in scientific equipment and other 
support systems is usually involved; therefore, the 
public turns to the government for programs to deal 
with these problems. 
Natural Hazards 
Many of the dangers to people and property that 
are created by natural hazards are similar even 
though caused by different natural forces or condi- 
tions, and many of the applied methods of manage- 
ment and mitigation are similar. The ten major 
coastal hazards and the particular types of danger 
and damage involved follow: ‘2 
Hurricanes are storms that develop in the tropics 
and attain windspeeds of 74 mph or greater, accom- 
panied by dangerously high seas. The most destructive 
part of these storms is found within 50 to 75 miles 
of the center, yet lesser winds and seas can cover 
areas as large as 600 miles in diameter. Hurricanes 
can affect almost all of the U.S. coastline (including 
USS. territories), except in the eastern Pacific where 
they have little impact north of Southern California. 
The hurricane’s storm surge and high seas are the 
greatest threats to life and property. They account 
for 90 percent of the fatalities and about 60 percent 
of the property that is destroyed or receives major 
damage. Storm surges are caused by air pressure 
differences between the hurricane and the rest of the 
atmosphere. However, the actual impact of the storm 
surge on a specific area depends upon many other 
factors (e.g., shape of the coastline, depth of the 
coastal water, speed of movement of the hurricane). 
The other dangers from a hurricane include high 
winds, heavy rains, and tornadoes. While hurricanes 
have average speeds of 10 to 15 mph in the tropics, 
they tend to move faster as they go further north. 
Some have reached forward speeds of 40 mph or 
more, leaving little time for the coastal population or 
mariners to prepare for them. 
Coastal floods, or inundations of flood plains, 
usually affect larger areas in the South Atlantic and 
Gulf States than in the Great Lakes, New England, 
and Pacific States. Within the coastal area, the most 
vulnerable urban areas are along the Gulf coast, 
especially when they are near the mouths of rivers. 
The problem of flooding is aggravated along the 
Gulf coast by the fact that many of the urban areas 
have subsided. There are two major types of floods 
in coastal areas: localized flash floods may result 
when large amounts of rain fall in short periods of 
time, and coastal flooding may result from hurri- 
180 U.S. Department of Commerce, National Oceanic and 
Atmospheric Administration. Some Devastating North Allantic 
Hurricanes of the 20th Century. Revised 1977. 
131 Much of the material in this section on definitions is taken 
from: U.S. Department of Commerce, NOAA, Office of Coastal 
Zone Management. Natural Hazard Management in Coastal 
Areas. November 1976, pp. II-4 through I1-74. 
canes. The flooding from hurricanes is of two kinds: 
flooding caused by the storm surge as seawater 
moves inland, and riverine flooding that occurs as 
rain runoff heads for the ocean. The major threats 
are loss of life, personal injury, property damage or 
loss, and ecological disturbance from freshwater or 
saltwater incursion. 
Tornadoes are violently rotating columns of air 
that descend from thunderstorm cloud systems. With 
a path averaging an eighth of a mile wide and mov- 
ing several miles at an average speed of 30 mph, 
tornadoes spread their destruction quickly, primarily 
through their high wind velocities, and then dis- 
appear back into the thunderstorms as quickly as 
they appeared. Although the highest incidence of 
tornadoes is in the Plains States, tornadoes are not 
inconsequential along coastal areas in Gulf and 
Atlantic coast States. To a lesser extent, the Great 
Lakes area also experiences tornadoes. Along the 
Gulf coast an added problem is large waterspouts 
that occasionally move inland as much as one-half 
mile. Tornadoes have been reported with hurricanes 
as they move ashore. In this case the tornadoes 
develop well away from the center of the hurricane 
and generally extend far inland in advance of the 
storm. 
Earthquakes occur when the massive plates of the 
Earth’s crust, which are slowly moving in opposition, 
release a portion of the accumulated pressure. The 
level of destruction accompanying an earthquake 
varies according to the magnitude and intensity of 
the movement of the Earth, with most earthquakes 
causing little damage but major earthquakes having 
the possibility of massive property destruction with 
thousands of fatalities. The amount of danger 
is also based on proximity to the epicenter of the 
earthquake, the type of soil involved, and the types 
of structures that exist in any particular spot. 
Tsunamis, or seismic sea waves, are series of 
traveling waves of extremely long wavelength gen- 
erated by underwater disturbances in the Earth’s 
crust, usually earthquakes, but sometimes explosive 
volcanic eruptions. Localized tsunamis can also be 
generated by subaerial or submersive landslides. 
These waves are much longer from crest to crest 
than ordinary waves, and as coastal waters become 
more shallow, the waves may build to heights of 
more than 50 feet above the normal tide level and 
strike coastal areas thousands of miles from their 
epicenter. Damage is caused by flooding, rapid 
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