THE ERUPTION OF PELEE. 229 



the British geologists saw no upright shaft of dust, but a cloud pro- 

 jected horizontally two miles broad and one mile high. They state 

 that mist and steam obscured their view of the mountain, and it does 

 not appear that they saw the great vertically projected column of dust 

 at any time. This was because they were too close to the volcano to 

 see it, and the up-jet was obscured by the down-jet. 



This leads to certain theoretical considerations. Flett and Ander- 

 son consider these eruptions unique with respect to the hot sand 

 avalanche and the black cloud, speaking of the 'Pelean type' of erup- 

 tion. I do not believe that these features are exceptional, nor that 

 they were wanting in the Yesuvian eruption of '79, nor in Tarawera, 

 Krakatoa or Bandai-san. 



Anderson and Flett believe the motive power which drives the lower 

 black cloud forward horizontally to be the falling weight of the mass. 

 Discussing the possibility of the out-blast being caused by the resistance 

 offered by falling materials to the ascent of subsequent discharges — 

 an explanation offered by the writer* in 1902 — they write : 



Tliis is quite incompetent to explain the behavior of the black clouds we 

 saw on the night of the ninth of July. Before the first black cloud arose no 

 very great amount of dust had been projected into the air, and the steam clouds 

 were drifting steadily westwards. . . . The black cloud took a different path, 

 and once it had rolled a short way down the mountain there was nothing above 

 it to prevent it rising in the air: but it hugged the sui'face of the ground so 

 closely that the conclusion was inevitable that it flowed down merely because 

 it was too hea^-y to ascend. 



That no great amount of dust was seen at Carhet projected verti- 

 cally, prior to the first black cloud, may be accounted for in the same 

 way as at the time of the incandescent avalanche — it was dusk, and 

 the mountain's summit was veiled in clouds. I have no question but 

 that there was a preliminary up-puff, not seen by observers close to 

 the crater. And because of the peculiar acoustic conditions men- 

 tioned, no sound would be heard, either, though at a distance this puff 

 might have been noticed as a distinct detonation. Without disputing 

 the possibility of dust giving weight to a vertically charged steam- 

 cloud, it is difficult to understand how mere gravitational move- 

 ment could produce destructive velocities on such gentle slopes — the 

 slopes of Pelee and Soufriere average only 15° to 17° (Fig. 3). The 

 horizontal discharges appeared to move with greater and greater 

 velocity until they struck the sea, then they slowed down and came to 

 rest almost suddenly. The motion was compared to that of a toboggan 

 on a snow-slide. 



The appearance of slow movement at the crater's lip I believe to 

 have been only apparent, probably because the mass was end on and 



The Popular Science Monthly, August, 1902, p. 366. 



