ERUPTION OF TAAL VOLCANO. 79 



Two streams of hot water, the combined flow of which was estimated at 

 100 to 150 cubic meters per minute, were pouring into the lake. These 

 streams came out of the crater walls about 50 meters above the lake level, 

 seeping from Just over a layer of fine-grained, impervious, bedded tuff. 

 On the west shore of the lake a conical rock 50 to TO meters in diameter 

 rose to a height of 115 meters above the lake level. The upper 50 

 meters of this natural obelisk appeared to be bedded tuflE, but the lower 

 portion is massive basalt. A week later, the streams pouring into the 

 crater lake had increased both in volume and in number, and the lake 

 itself had risen apparently about 5 meters. 



The center of the recent activity seems to have been at a point near 

 the south end of the former Green Lake, or between Green Lake and the 

 1904 crater, although the vicinity of the "Gas Vent," shown on the map 

 of the old crater, is stiU very active. Vents from which steam escapes 

 violently, and small craters gushing mud and hot water, are found at 

 various places over the new crater floor. The present lake is boiling at 

 a number of places and great volumes of steam arise from its surface. 

 There is no evidence of a general subsidence in the crater. Xo breaks 

 or fissures appear near the shelf outside of which the old floor is intact. 

 There are no faulted or tilted blocks which might indicate that the old 

 floor had dropped. On the other hand, the new floor, exposed by the 

 streams flowing across it, is composed of dense, basaltic material, hard 

 and flowlike in appearance, certainly in place. It is probable that the 

 change in the level of the crater floor was due to removal of material 

 from the crater, not to the collapse or subsidence of the old floor. 



An approximation of the volume of solid material ejected from Taal 

 Volcano during the late activity is readily obtained by calculation from 

 the data given in connection with the distribution of the ejecta. Dis- 

 regarding irregularities in the ground surface, the volume of the solid 

 represented by plotting sections, from the average depths shown, across 

 the area covered, is TO to 80 million cubic meters. 



Calculating in a similar manner the volume between the old and the 

 new floor lines in the crater according to areas and cross sections ob- 

 tained from Plates III and IV, the approximate figure of 45 million 

 cubic meters is obtained for the volume removed above the level of the 

 new lake. 



Examination of the crater walls below the old floor line reveals that 

 a large portion of the material removed was rather dense, bedded tuff. 

 If this material were ground up to a fine sand or ash and spread out in a 

 thin layer, as mud, it would probably occupy at least one and one-half 

 times its former volume, or about 68 million cubic meters. 



While these figures are approximate and represent at best only the 

 order of magnitude of the volumes sought, yet it is evident that enough 



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