158 OUR HERITAGE THE SEA 



several fathoms depths of water. Then suddenly the 

 waters return in an immense wave, looking as if it 

 would shut out the sky. I shall not give any of the 

 estimated heights of these waves, confining myself to 

 saying that in the nature of things they must be much 

 higher than those raised by the wind in the most 

 terrific gale, and their speed must also be much 

 greater. For the conditions are quite different. It 

 has been before noted that the drive or drag of the 

 wind along a water surface produces, accelerates, or 

 retards currents, but it never excites the surface to 

 any great rate of speed, while the furious waves 

 have a very short range, doing hardly more, indeed, 

 than rise and fall. 



In the shoreward rush of the earthquake wave or 

 volcano wave we have a sudden movement of the whole 

 body of water of incalculable force and tremendous 

 velocity, because, in the first case, there has been an 

 upheaval of the sea-bed at its margin, and the waters 

 have had perforce to roll backward, seaward, and pile 

 themselves up in a heap, as it were. But when the sea- 

 bed subsides again, of course that mighty mass of water 

 seeks its former level with all the vehemence that might 

 be expected of it, rushing over the land to a height far 

 beyond high water-mark, and completing the destruc- 

 tion begun by the earthquake. Practically the same 

 effect is caused by the volcanic rending open of the 

 earth's crust beneath the sea ; indeed, the effects are 

 even more dire. For now, in addition to the displace- 

 ment of a vast body of water, owing to its having 

 rushed down into the chasm just opened, that water 

 has fallen into an incandescent abyss of enormous 

 area, and most of it has been simultaneously converted 



