280 E. 0. Ilovey—New Cone of Mont PeU. 



mountain before the eruptions began, is the tilling of the gorge 

 of the Kiviere Blanche with calcined rocks and dust and ashes 

 (lapilli) which have been poured out of the crater by the numer- 

 ous eruptions (see PL XIY). This was the gorge extending sea- 

 ward from the great gash in the southwest side of the old crater 

 which determined the direction of the explosive volcanic blasts 

 which swept over St. Pierre on May 8 and succeeding days. 

 Isow the lower portion of the gorge has been entirely obliter- 

 ated and the adjoining plateau elevated, while the upper and 

 deeper portion near the crater has been ahiiost filled by the 

 ejecta. The line of this gorge is still the favorite direction 

 of discharge of the volcano, and the great bowlders scattered 

 thickly over the surface attest the violence of the explosions 

 (see fig. 9, PL XIV). 



The material has been carried into the gorge by the dry dust- 

 flows which have swept down from the crater and from the 

 new cone with great velocity and terrible force. These dust- 

 flows consist of steam saturated with dust to such an extent 

 that the mixture acts like a highly mobile fluid. Great masses 

 of rock are transported by it as easily as corks are carried along 

 by water. As the flows proceed on their way they drop their 

 load of stones and liberate vast volumes of steam which carry 

 into the atmosphere the finest dust from the flow. The clouds 

 of dust always are incandescent when they leave the cone, but 

 they lose their high temperature during the latter part of their 

 course to the sea.* The beds of ash may retain heat enough for 

 several months to furnish occasional dust-flows. This has been 

 observed in the re-excavated gorge of the Wallibou Piver, St. 

 Yincent. On March 6, 1903, a cauliflower column of dust was 

 seen to rise from one of the ash beds left in an angle of the 

 gorge, and the next day the author found that a dry dust-flow 

 had taken place, covering an acre or two of the bottom of the 

 gorge with a hot dust- and pebble-flow from one or two feet to 

 eight or ten feet in thickness. 



Unquestionably a portion of the filling of the gorge of the 

 Blanche has been done by fiows of mud. The mud-fiow which 

 overwhelmed the Usine Guerin seems to have been caused by 

 the waters of the Etang Sec breaking through a temporary 

 dam formed by new ash from the western vents within the cra- 

 ter, but succeeding mud-flows have been caused by the rain- 

 soaked dust and ash on the slopes of the great crater and the 

 remainder of tlie drainage-basin of the Blanche descending in 



* Lacroix (Comptes Eeiidus, 26 Jan.. 1903, author's separate p. 2) deter- 

 mined by means of metal wires put in the path of the dust clouds about 6 

 km. (3% mi.) from the center that the temperature at that locality was less 

 than 230° C. for the heavy cloud of December 16, 1902, while his thermometer 

 showed the dust to retain a temperature of 125° C. two days after the erup- 

 tion. 



