58 U. S. COAST AND GEODETIC SURVEY 
maximum in July. The range of the variation varies somewhat at the different stations 
but approximates three-quarters of a foot, the lowest value being at Adak with 0.67 
foot and the highest at Skagway with 1.03 feet. 
Yearly Sea Level 
In the previous section monthly sea level was found to be subject to an annual 
variation with a range up to a foot. This means that, due to this cause alone, mean 
sea level determined directly from one month of observations may be in error by half a 
foot. This error may be further augmented very considerably by the nonperiodic 
variation from month to month arising from variations in wind and weather. Within 
a year, however, the annual variation balances out, and it now remains to consider 
whether there are any variations in sea level from year to year. 
Atlantic Coast.—In Figure 30 the yearly heights of sea level at eight stations along 
the Atlantic coast of the United States are shown for the period of observations available 
at each station. It appears at once that sea level does vary from year to year, though 
generally by relatively small amounts. In general the change in sea level from one 
year to the next is less than one-tenth of a foot, but at times it may be as much as 0.2 _ 
foot. 
Two features stand out strikingly in Figure 30. The first is that the change in 
sea level from year to year is much the same for long stretches of the coast. When sea 
leve] at any station in Figure 30 during any year is high (or low), it is also high (or low) 
at stations several hundred miles distant. Thus, in the 500-mile stretch of the coast 
from Portland to Baltimore the year 1919 was one of high sea level at all five stations, 
while the years 1926 and 1930 were years of low sea level at these stations. In the 
same way the sea-level changes from year to year in the nearly 500-mile stretch from 
Charleston to Miami Beach parallel each other fairly closely. 
The second striking feature is the steady progressive rise in sea legal at all eight 
stations since about 1930. Prior to that year, both New York and Baltimore indicate 
a rise of sea level at the rate of less than 0.01 foot per year, but since 1930 the rise has 
been at the rate of about 0.02 foot per year. 
Formerly it was thought that there were cycles in sea level of something like 4 
years and 9 years, reflecting perhaps similar cycles in wind and weather. Apparently 
such cycles are accidental, ssl in any event are completely submerged in the progressive 
rise of sea level since 1930. 
The up and down changes in sea level from year to year of a tenth of a foot or 
more must obviously be ascribed to the disturbing effects of wind and weather, which 
do not repeat themselves exactly from year to year. But the steady rise from 1930 
must be due to more deep-seated causes, such as subsidence of the coast or actual rise 
in the level of the ocean waters. 
Gulf Coast.—For the Gulf coast, Figure 31 gives the yearly sea levels at four 
stations from Key West to Galveston. At Cedar Keys there was a break in the ob- 
servations between the years 1926 and 1939. 
At Key West the change in sea level is much the same as on the Atlantic coast— 
little change from 1912 to about 1930 after which sea level has risen steadily, at the 
rate of approximately 0.02 foot per year. For Cedar Keys the break from 1926 to 
1939 obscures the time of change but it is clear that from 1915 to 1925 there was 
