of the generating area is much greater than the width. When displace- 

 ment occurs along a substantial length of faultline, the divergence of 

 the wave rays of the generated wave (i.e., the spreading of wave energy 

 along the wave crest) will be much less than for a wave generated from 

 a small source. For a "locally" generated wave, i.e., a wave generated 

 near the coastline under consideration, the main component of the wave 

 energy will travel perpendicular to the faultline and the energy per 

 unit length of wave crest would remain approximately constant for an 

 unrefracted wave. 



2. Volcanic Activity . 



Although most major tsunamis have been caused by shallow-focus earth- 

 quakes, a small percentage have been caused by volcanic activity which 

 includes localized earthquakes, shoreline and submarine slumps, and 

 volcanic explosions. Examples of these are the volcanic activity of 

 April 1868 and November 1975 in Hawaii, with associated earthquakes off 

 the southeast coast of the island of Hawaii, and the August 1883 erup- 

 tion and explosion of the island of Krakatoa near the Sunda Strait in 

 Indonesia. The explosion of Krakatoa destroyed an estimated 8 cubic 

 kilometers (1.92 cubic miles) of the island. Large shoreline subsidences 

 were associated with the eruptions and earthquakes on Hawaii. 



Tsunamis with volcanic origins have the characteristics of waves 

 generated from a small source area. These waves spread geometrically 

 and do not cause large wave runup at locations distant from the source, 

 but may cause very large waves near the source. Also, there may be 

 refraction effects which trap waves along the coastline, or standing 

 edge waves may be generated along the coastline. 



Both the 1868 and the 1975 tsunamis in Hawaii caused high waves at 

 points on all sides of the island of Hawaii as well as waves on the other 

 islands (Pararas-Carayannis, 1969; Pararas-Carayannis, International 

 Tsunami Information Center, personal communication, 1975). The 1975 

 waves persisted for more than 4 hours at all points. Meyer (Department 

 of Mathematics, University of Wisconsin, personal communication, 1975) 

 indicated that trapped waves may exist with many nodes around the island. 

 These trapped waves would gradually decay, leaking energy to the sur- 

 rounding ocean. 



3. Landslides and Submarine Slumps . 



Landslides and submarine slumps can occur from various causes, but 

 are often associated with earthquakes. The waves generated by such events 

 will spread geometrically as they propagate from their source in an open 

 ocean, but can be very high near their origin. Waves can be particularly 

 high if they occur in a confined inlet, or if resonant or refraction 

 effects exist. 



Examples of landslide-generated waves have been reported by Miller 

 (1960) for Lituya Bay, Alaska, in 1853, 1874, 1936, and 1958. The 1958 



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