ERUPTION OF TAAL VOLCANO. 67 



west shore of the lake, large trees were either uprooted or broken off 

 close to the ground. These too, almost invariably fell away from 

 the crater, and the bark was abraded from their exposed surfaces. 

 On the island, broken ends of tree stumps and branches were literally 

 shredded, as though exposed to the action of a powerful sand blast. 

 This abrasive eifect was imdoubtedly accomplished by the sand grains in 

 the ash or mud which the expanding cloud carried with it. Outside the 

 central area over which this explosive expansion of the gases was felt, 

 the eruption caused only a rain of mud, which fell gently. 



This downward and outward movement is difficult of conception to 

 those who saw the steadily rising cloud above the volcano during the 

 recent activity. However, when it is recalled that explosions tend to 

 act equally in all directions, downward as well as upward, and when it 

 is remembered that the air above the crater was already heav}- ^vith 

 condensing steam and falling mud when the main explosion occurred, 

 it is apparent that expansion would naturally take place in the manner 

 described. A photograph taken during the less violent activity shows 

 the cloud spread downward over the base of the volcano. (Plate X, 

 fig. 1.) 



It is probable that at a greater distance from the crater than was 

 attained by this outward expansion, the atmosphere moved toward the 

 volcano, as a center of low pressure resulting from the upward rush of 

 the cloud. Such a movement is evidenced by the sudden falling of 

 barometers around the volcano. In ^lanila, an otherwise regular baro- 

 graph at the Weather Bureau Observatory shows a sharp drop of 1 

 millimeter at the moment of the eraption. At Batangas a similar drop 

 amounted to 2 millimeters. At both these places there was a slight 

 wind toward the volcano after the eruption. At Talisay, the natives 

 said that the wind first came strongly from the volcano bringing mud, 

 then changed and blew toward the mountain. It is shown by the dis- 

 tribution of ejecta that the prevailing wind during the eruption came 

 from the southwest (off the sea) . 



Electrical phenomena. — For an hour or more during the greatest 

 activity the cloud above the volcano was vivid with lightning which 

 played in streaks, often branched or forked, and ran either up or down 

 or obliquely over the cloud. A subdued thunder, less distinct than 

 would be expected from seeing the lightning, accompanied it. Flashes 

 or sheets of light were also quite generally noted, and were explained 

 by many who saw them as resulting from the combustion of inflammable 

 gases within the cloud. It is more probable that they were merely 

 reflections of the streak lightning from the surfaces of other parts of 

 the cloud. 



Spectacular electric displays have been prominent' features of many 



