Long Waves in Canals and Standing Waves in Closed Basins 237 



According to this relation, the following values of r] L :rj h0 respectively r] L :2rj h0 

 correspond to the values Ii 'Vq- The latter values apply, if r\ at the right in 

 (VI. 144) is ignored: 



Consequently, when approaching the shore it is necessary to consider 

 the increasing values with decreasing depth to obtain more accurate values. 



An extensive theory of the formation of tsunami has been given by 

 Nomitsu; however, its fundamentals do not deviate considerably from 

 Proudman's method in his paper on the action of atmospheric disturbances 

 on the sea level (p. 227). 



A phenomenon similar to that of tsunami occurs on the Baltic coast and 

 is called "Seebar". The Seebar always sets in quite unexpectedly when the water 

 is calm, often even smooth; out from the sea a high-towering wave rolls 

 on to the brech, and floods it to a height of 1 or 2 m. These waves appear 

 at rhythmic intervals with decreasing height a few times in succession. These 

 Seebars have been described by Doss (1907, p. 368), Credner (1888), 

 Renquist (1926, p. 230) and Meissner (1924, p. 14, 63, 76). The phe- 

 nomenon of the Resaca in the harbours of northern Spain might be related 

 to the Seebar. 



The cause of such catastrophic seiches appears to be certainly meteoro- 

 logical, whereas a more precise synoptical explanation of the whole phe- 

 nomenon is still lacking. 



7. Dislocation and Explosion Waves 



Besides the waves forced by atmospheric influences, there are in the ocean 

 other wave-like oscillations due to natural catastrophes. First of all a sub- 

 marine earthquake may cause longitudinal elastic oscillations which travel 

 with the velocity of sound waves. On ships they are felt as shocks which, 

 depending on the force and the distance from the epicenter, may violently 

 rock the ships. 



Rudolph (1898, p. 273) has made an extensive compilation on the subject 

 of seaquakes, which comprises also observations on dislocation waves. These 

 dislocation waves are of two types, according to their origin. Dislocation 

 waves are waves caused by earthquakes, submarine landslides, etc. Explosion 

 waves are caused by submarine earthquakes which are sometimes accompanied 

 by the release of large amounts of gas that rise toward the surface and may 

 lift the surface up like a dome, thus producing a transverse wave that behaves 

 like any other gravitational wave. At a certain distance from their origin, 

 the variations of the sea surface are similar for both kinds of waves. In 

 Kruemmel's (1911, vol. II, p. 137) text-book there is a whole series of 



