COMPOSITION OF THE FINE EJECTA, TAAL VOLCANO. 



95 



The physical composition of the distributed material is of interest 

 and importance. According to the geologists' records no pebbles were 

 can-ied beyond the limits of the island. Mechanical analyses of such 

 material as is available are given in Table II. 



Table II. — Mechanical analysis of ejecta from Taal Volcano. 



[The samples analyzed were air-dried. The numbers give percentages.] 



Sam- 

 ple 

 No. 



Mois- 

 ture. 



Soluble 

 matter. 



Size of grains in millimeters. 



Total. 



>0.5. 



0.5- 

 0.25. 



0.25- 

 0.1. 



0.1- 

 0.05. 



0.05- 

 0.01. 



0.01- 

 0.002. 



<0.002. 



■1 



"2 



5.03 

 6.35 



5.07 

 6.21 



27.10 

 7.15 



7.54 

 5.75 



27.42 

 48.51 



27.26 

 24.72 



0.15 

 0.38 



0.47 

 0.41 



0.00 

 0.00 



100.04 

 99.48 



" This is a sample of the finest "ash" collected on the upper southern slope of the 

 volcano. The detritus on a 2-millimeter sieve was 9.1 per cent and in a 20-gram sample 

 consisted of 70 particles the largest of which was 6 millimetei-s in diameter. 



•> This sample represents that from the area over which the mud was distributed to a 

 thickness of about 1 centimeter and beyond the devastated region. (See Map, fig. 1, in the 

 paper by VFallace E. Pratt.) There was no detritus on a 2-millimeter sieve. 



While a considerable amount of coarse material fell on the island, 

 the mud that was carried to a distance was comparatively finely divided, 

 in this respect not greatly unlike road dust. The mud was cool where- 

 ever its fall was observed, and it descended in the manner of rain, with- 

 out violence. Leaves retained only a thin coating on their upper sur- 

 faces, yet within a few hours many of them had fallen. Ordinary road 

 dust may fall on plants to any thickness without serious injury. Cer- 

 tain crops are reported as stunted by the volcano's action at the College 

 of Agriculture farm where the fall of mud was very slight. Garden 

 plants were injured in many places where only a very small quantity 

 of mud fell. 



There is nothing in the above analyses which indicates that the mud 

 is injurious to plants. However, it is probable that the chemical analyses 

 do not accurately represent its composition as it fell, for no heterogenous 

 substance is in a constant state of equilibrium, but rather in a changing 

 state of equilibrium according to known laws. 



There are at least two possible sources of the injury to the plants. 

 One of these is the presence of sulphuric acid. In the regions near the 

 volcano the odor of sulphur dioxide was pronounced during the erup- 

 tion. A mixture of this gas and water vapor under the oxidizing in- 

 fluence of the electric discharge may have produced sulphuric acid in an 

 amount sufficient to be injurious. There was unquestionably a large 

 amount of free acid in the vapors from another source during the erup- 

 tion, for analyses made by Dr. E. P. Bacon,^ formerly of the Bureau of 



^This Journal (1906), 1, 434; Sec. A (1907), 2, 118. ; 



102300 3 ; 



