MECHANISM AND WORK OF PELE 



249 



marked by the destruction of the Usine Guerin on May 5 and the great 

 eruption of May 8, when the ascending column of magma reached the 

 outer atmosphere and discharged from the vents the old material which 

 previously had clogged them. 



Since then the work has been relatively that of a free conduit, through 

 which incalculable quantities of the earth's interior were transferred to its 

 outer crust. This fourth or free stage was fully attained as early as the 

 eruption of May 26, when sheets or flows of incandescent lapilli began to 

 well over the summit rim. This continued freely for over a year, and 

 was still continuing when Pele was last heard from. 



The material erupted was projected upward by expansive force and 

 distributed by air currents and gravity, the lighter and larger portions 

 ascending into the atmosphere as clouds of steam and ash and floating 

 away to fall over the wide expanse of the adjacent oceans. A fraction of 

 this material, not rising to heights, fell around the vent to add elevation 

 to the rims of its caldera. Some of the largest and more tenaceous ma- 

 terial flowed or rolled down the deep canyons of La Fente and into the 

 Rivieres Seche and Blanche. 



Although Professor La Croix,* conductor of the French scientific ex- 

 pedition sent to Martinique, has reported an account of how blocks of 

 the incandescent magma rolled in the direction of the Riviere Blanche 

 and filled it, all evidence tends to show that the liquid magma mostly 

 changed into a fragmental condition on reaching the atmosphere and did 

 not flow on the surface as a molten rock — that is, as lava. 



During this free working stage the eruptions were marked also by the 

 welling over from the summit crater rim of vast quantities of incandes- 

 cent particles of ash, which, at the moment of their ejection, resembled 

 fountains of fire, and, as they rolled down the upper slopes of the moun- 

 tain, were taken for molten lava. This was observed in the eruption of 

 May 26 by the writer and by Messrs Henry, Morse, Smith, and others. 



The eruption of July 9, observed by the Royal Society Commission 

 (Flett and Anderson), was typical of the free working stage. It was 

 described as follows : 



" First, spasmodic burst of steam and dust and stones accompanied by discharges 

 of torrents of water and mud ; secondly, the welling up in the crater of an overflow 

 like that of a liquid fountain of red-hot dust, which descended the mountain slope 

 at first relatively slowly, but with ever increasing velocity, like an avalanche of 

 snow. . . . As soon as the throat of the crater is reached a mass of incandes- 

 cent lava rises and rolls over the top of the crater in the forms of red-hot dust. It 

 is a lava blown to pieces by the expansion of the gases it contains. . . . This 

 avalanche of incandescent sand was accompanied by a dense cloud, black as night, 

 which soon concealed it from view and swelled in convolutions with terrible energy 



*See Nature, December, 1902. 



