70 PRATT. 



a wave or waves. Thus, the water would have literally been blown away 

 from the volcano to the lake shores.^ 



EJECTA. 



Character. — The known ejecta from Taal in this eniption were (1) 

 steam (probably water also), (2) sulphur dioxide, (3) angular pieces 

 of homogeneous extrusive rock, (4) fragmental blocks of volcanic tuffs 

 and agglomerates, and (5) volcanic mud or ash. 



Steam made up practically the whole volume of the gases. The odor 

 of sulphur dioxide was strong during the eruption and probably this gas 

 or its oxidation product was effective in killing vegetation.^" Other gases, 

 notably carbon dioxide, may have been present in the cloud. There was 

 apparently no odor of hydrogen sulphide and there is no evidence of 

 the presence of other infianm.iable gases.^^ 



The angular boulders thrown out ranged up to perhaps 300 kilograms 

 in weight. The large rocks fell on the upper slopes of the volcano near 

 the crater's rim. Andesitic specimens and others of basaltic character, 

 neither with any appearance of recent fusion, were noted. These rocks 

 may represent individual blocks from agglomerate phases of the tuff 

 which apparently supplied the rest of the solid ejecta. 



The blocks of tuff thrown out are identical in appearance with the 

 bedded material of the crater walls. Some of the fragments weigh 

 perhaps 200 kilograms. Other large pieces had broken from the impact 



"It is difficult to estiirfate the velocity of expansion of the eruption cloud at 

 the time it reached the lake level. Generally accessible data show that a wind 

 velocity of 100 miles (160 kilometers) per hour is sufficient to uproot large 

 trees. Large trees were uj)rooted 2 kilometers inland from the west lakeshore. 

 Since the velocity must have decreased very rapidly as the expansion progressed, 

 it may have been as high as 200 miles (320 kilometers) per hour at the foot 

 of the volcano. Wind moving with this velocity would exert a pressure of 200 

 pounds (Trautwine, John C, London, 17. ed. (1900), 321) per square foot (4 

 kilograms per square centimeter), sufficient actually to support a column of 

 water 1 meter high. This estimate does not take into account the considerable 

 inertia of the dense load of mud or ash -which traveled with the wind, and which 

 would increase its effect. 



^^ At Banadero, where cool mud fell without violence to the depth of 1 

 centimeter, the leaves of the trees retained only a thin coating on their upper 

 surfaces, yet within twelve hours many leaves and some fruit, such as oranges and 

 wild fruits, had fallen, suggesting an effect of poisoning from the mud. Ulti- 

 mately, all leaves and fruit in this section died. In several instances clothing, 

 such as brown flannel shirts, white towels, etc., on which mud fell at Banadero, 

 was stained yellow. In San Pablo the fall of mud was very light, "like sugar 

 sprinkled over a cake," yet garden plants were killed by it according to Mr. W. E. 

 Crowe, supervising teacher. 



" Brooks of the Bureau of Science found neither hydrogen nor carbon monoxide 

 in the gases from a very active vent which opened in the crater before the recent 

 eruption. 



