16 



Oceanography 1951 



destructive impact on the shore and on man- 

 made structures, and they transport beach 

 sands, pebbles, and boulders. The piling up 

 of water along the shore by the waves 

 causes longshore currents which also trans- 

 port beach materials. Waves which affect 

 the shore line originate in part from local 

 storms and in part from storms many thou- 

 sands of miles away. For example, destruc- 

 tive erosion in Southern California is most 

 commonly caused during the fall months 

 by long swells generated by storm winds 

 in the southern hemisphere. This swell is 

 hardly perceptible in deep water off shore, 

 but as the waves come into shallow water 

 and approach the beach the distance be- 

 tween crests is greatly diminished, and 

 the waves peak up until at the point of 

 breaking they may be more than twenty 

 feet high. The height, period and direction 

 of waves coming into the beach zone is of 

 critical importance in determining long- 

 shore currents, and the character of erosion 

 and transportation processes. The height 

 and direction will be affected by the bot- 

 tom topography offshore, while the period 

 will depend primarily on the meteorological 

 conditions and the location of the generat- 

 ing area. The off-shore topography, par- 

 ticularly the presence of submarine can- 

 yons or other irregularities, will also deter- 

 mine the rate of loss of sedimentary ma- 

 terial from the shore. An understanding 

 of the many processes involved in the inter- 

 action of waves and bottom materials 

 should yield practical benefits in protecting 

 and improving shores and shore line struc- 

 tures. 



In addition to waves several other oceanic 

 processes play a major role in shore line 

 protection problems. Where the shore is 

 low and flat serious inundations may occur 

 because of piling up of water by storm 

 winds blowing on shore. Such inundations 

 may also be brought about by tsunamis 

 (seismic sea waves) from submarine earth- 

 quakes. The height and intensity of a 

 tsunami varies widely from one area to 

 another along shore depending on the bot- 

 tom topography and the configuration of 

 the ocean basin. Little is known of the 



probable height and intensity at any point 

 in the sea of a tsunami originating froin 

 an earthquake of given magnitude. The 

 solution of this problem will require an 

 increase in our understanding of the hydro- 

 dynamics of a compressible, viscous, strati- 

 fied fluid such as the ocean. 



PROBLEMS OF OVERSEAS TRANSPORT 



With the development of large, fast, engine- 

 powered ships and of modern communica- 

 tion, new problems concerning the ocean 

 have arisen and old ones have diminished 

 in importance. Yet the sailor still needs to 

 know as precisely as possible where he is 

 and how his course and speed are being 

 altered by currents, winds, and waves. He 

 must avoid collision on the high seas and 

 stranding on the shoals and rocks near 

 shore. His ship must be stout enough to 

 withstand the violent action of the waves 

 and yet as lightly constructed as possible 

 so as to eliminate useless dead weight and 

 volume. 



Until recently there has been inadequate 

 knowledge of the characteristics of ocean 

 waves and their effects on ships. As a result, 

 ships have been built to withstand very 

 high waves with a large factor of safety. 

 The greatly increased knowledge of the 

 shapes and motion of waves of the last 

 few years should result in radical improve- 

 ments in ship design. 



Sailors, ship-owners and government 

 have long recognized the need for knowl- 

 edge of tides, currents and bottom depths 

 in near-shore areas. More recently the de- 

 velopment of echo sounding and of accu- 

 rate means of surveying far from shore 

 have become possible. Accurate charts of 

 the deep ocean basins would be a consid- 

 erable aid to navigation. 



The sinking of the Titanic in 1912 em- 

 phasized the danger from icebergs in the 

 North Atlantic. Shortly thereafter the Inter- 

 national Ice Patrol was organized to give 

 warning of the presence and movement of 

 icebergs. The tracks followed by the bergs 

 from their origin in the fjords of West 

 Greenland are controlled by ocean currents 

 in Baffin Ray, Davis Strait, and the West- 



