43° The National Geographic Magazine 



Richmond Estate, St Vincent, May 25, 1902 



Dunes of wind-drifted volcanic lapilli and dust from La Soufriere on a previously cultivated 

 area. The tree trunks are the remains of palms. The rill channels show the beginning of the 

 erosion of the freshly added layer, which is from three to ten or more feet thick (see page 432) 



cant. From the various accounts of 

 the eruptions of Mont Pelee available, 

 it now seems evident that the blasts 

 which destroyed so much of the vegeta- 

 tion of Martinique and wrought havoc 

 in St Pierre came from the crater with 

 a deeply notched rim, and that the 

 direction taken by the blasts, at least on 

 May 8 and May 20, was determined by 

 that rift in the crater's rim. 



As stated by T. A. Jaggar, the down- 

 ward blasts from volcanoes do not re- 

 quire a horizontal nozzle to project 

 them. " They are simply the result of 

 the down-blast after the heavy gravel 

 has begun to fall, acting against the 

 upblast from the throat of the volcano, 

 and both together deflected and thrown 



into terrific whirls or tornadoes. ' ' This 

 explanation, although briefly stated, 

 may seemingly be taken as the leading 

 cause of the downward sweep of the 

 steam charged with rock fragments on 

 both Mont Pelee and La Soufriere. It 

 does not seem clear, however, that the 

 down-blasts occur only after a towering 

 column of debris-charged steam has 

 reached a great height and the fall of 

 the heavier material within it has be- 

 gun. Then, again, it may be asked 

 why it is that every strong eruption is 

 not followed by a down-blast ? 



Variations in the character of vol- 

 canic eruptions of the type under con- 

 sideration occur on account of variations 

 in the energy of the explosions and the 



