68 PRATT. 



volcanic eruptions. Special descriptive names have been applied to 

 this particular t}'pe of lightning.^ 



Its origin has been ascribed to the generation of electricity by the 

 intense friction occurring between the individual ash particles in the 

 moving cloud.* Probably friction between ash particles and the air 

 or friction of the vapor-laden gases of the rising cloud with the sur- 

 rounding drier atmosphere^ are contributing causes. 



Earthqtmkes.^ — The earthquakes accompanying the recent activity of 

 Taal are tabulated in chronological order in a report "The Eruption of 

 Taal Volcano, January 30, 1911" wi'itten by Father Miguel Saderra 

 Maso, Assistant Director of the Weather Bureau. Father Maso con- 

 cludes that the earth-movements were very local, that they emanated 

 from the immediate vicinity of the volcano and that they lost intensity 

 very rapidly as they traveled away from that center. The most violent 

 earthquakes recorded in Manila were of intensity IV of the earth- 

 quake scale of De Eossi Forel ^ and Father Maso thinks it probable that 

 even in the vicinity of the volcano no shock occurred more intense 

 than VII.'' Consequently, a shock of intensity III at the volcano 

 might not be felt in Manila at all. It is beyond question that a 

 great many more shocks really did occur near the volcano than were 

 recorded in Manila. The local extent of the earthquake shocks sug- 

 gests that the center of Taal's late activity was not at a great depth. 



A curve of earthquake occurrence (Plate V) has been prepared from 

 Father Maso's tabulation which suggests the nature of the change in 

 earth stresses throughout the ei"uption. It is conceived that the first 

 steep rise in the curve, showing many earthquakes, would correspond 

 to a period of developing stresses due to pent-up volcanic activity; the 

 intermediate flatter section would represent a period of relief occasioned 

 in a measure by the opening of earth fissures, but mainly by the explo- 

 sive outburst of the volcano ; the subsequent sharp rise in the curve marks 

 a period of readjustment to the relieved condition, during which vertical 

 displacement occurred along the fissures, and subsidence took place 

 over parts of the affected area. The final gradual flattening ^ denotes 

 the return of normal stability. 



Damage due directly to earthquakes was slight. The towns of Taal 



•Hovey. E. 0., Martinique and St. Vincent, Bull. Am. Mus. Nat. Hist. (1902), 

 16, 333. 



*Scrope, G. P., Volcanoes, London, 2. ed. (1862), 57. 



' The earthquakes in connection with the eruption of Taal will be the subject 

 of a special Bulletin of the Philippine Islands Weather Bureau. 



• Strong enough to shake movable objects, chairs, and windows, etc. 



' Strong enough to overturn movable objects, shake off plastering, etc. 



'Minor shocks continued to occur up to February 13. 



