OCEANOGRAPHY IN THE UNITED STATES 51 



Variations in the level of the sea attain increasing importance with 

 the development of coastal areas. Data obtained by the Coast and 

 Geodetic Survey at a number of key control tide stations distributed 

 along our coasts provide basic data covering more than half a century 

 for the determination of short period as well as progi-essive changes 

 in sea level. Our studies have disclosed that secular changes in sea 

 level differ on our two coasts. On our Atlantic coast there has been a 

 rise of the sea with respect to the land at a rate of about 1 foot per 

 century. On the Pacific coast, however, the rate has been only half 

 of that on the Atlantic. This summer we are making an investiga- 

 tion in southeast Alaska where the land as measured from sea level 

 appears to have risen as much as 5 feet in 60 years. 



As the need for accurate tidal predictions has increased over the 

 years we have increased the scope of our predictions from a handful 

 of stations in 1867 on the east and west coasts of the United States, 

 to 4 volumes containing daily predictions for 5,000 places dis- 

 tributed over the world. The accuracy of predictions has also been 

 increased by improved observations, greater density of station dis- 

 tribution, and improved instrumentation. The prediction process has 

 been changed from the slow, laborious curve and equation method 

 to fast automatic tabulation of tide predicting machine computations. 

 Predictions of the ebbing and flooding of the tidal currents are 

 also made by the same automatic equipment. Advance information 

 on currents is not only essential for safeguarding navigation along 

 our coasts, but is also invaluable in many oceanographic activities. 



Following the disastrous seismic sea wave at Hilo in 1940, the 

 necessity for protecting life and property in the Hawaiian Islands 

 against such natural catastrophes was forcefully impressed on all. 

 Under this impetus the seismic sea wave warning system was conceived 

 and organized. The system basically requires the quick detection 

 and location of submarine earthquakes which may or may not create 

 such waves. Approximately 10 seismograph stations and 21 tide sta- 

 tions in the Pacific area provide the primary information for detect- 

 ing and verifying the occurrence of an actual seismic sea wave. Data 

 from all stations are promptly fed by communication facilities of 

 the Department of Defense and the Federal Aviation Administration 

 into the central headquarters of the system at the Honolulu Magnetic 

 Observatory, which issues the necessary advisories and alerts. 



The warning system is the response to the need of the people of 

 Hawaii and of the Pacific military commands for such protection. 

 While the public may be concerned about the system only when a 

 destructive wave is imminent, it requires constant work and vigilance 

 to keep such a far-flung and seldom used organization ready for ui- 

 stant action in time of need. 



Subsequent to these successful alert actions, the Bureau computed 

 travel time charts to Neah Bay, Crescent City, San Francisco, San 

 Pedro breakwater, and La Jolla to facilitate estimates of seismic sea 

 wave arrival times on the west coast. 



Another phase of the overall oceanographic research program to 

 be considered is the study of sedimentation, particularly as it relates 

 to our coastal areas. Continual changes are occurring in the sub- 

 merged lands of coastal areas. Areas of sedimentation and shoaling 

 require resurveys for up-to-date charting. But in addition to proper 



