F'ROCEEDINGS 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VII, pp. 277-2S2. Plate XIII. July 24, 1905. 



A FEATURE OF MAYON VOLCANO. 



By George F. Becker. 



The U. S. Coast and Geodetic Survey in March, 1905, pub- 

 lished Chart No. 4,237 showing Mayon Volcano and neighbor- 

 ing portions of Sorsogon on a scale of i to 40,000. It gives the 

 elevation of the summit as 7,943 feet, which is a little lower than 

 the determinations of Jagor and Abella. About the time that 

 these surveys were being made in 1901, Mr. Henry Gannett 

 was in the neighborhood and took a small photograph of the 

 volcano from the bridge at Legaspi. This point is 8^ miles, 

 measured horizontally from the summit of the mountain, which 

 bears north 30° west from the bridge. There being water in 

 the foreground of the photograph, it is possible to determine 

 with a close degree of accuracy the direction of a level line, and 

 therefore to compute or construct elevations at the distance of 

 the cross-section of the volcano. It may thus be determined 

 that, on the scale of the photograph, 26 millimeters in the per- 

 pendicular through the summit of the volcano are equal to 

 7,943 feet, or 305.5 feet per millimeter. 



The most thorough investigation of the lava of Mayon was 

 published in 188 1 by Mr. K. Oebbeke, who had at his disposal 

 the lithological collections made by Carl Semper. Mr. Oebbeke 

 pronounces the rock an olivinitic augite andesite. Eruptions at 

 Mayon are of very great frequency. They occur every couple 

 of years and oftentimes last several months. Many of these out- 

 bursts have been described and they all appear to belong to a 

 single type. Large quantities of ash are ejected, but the ejecta 

 are by no means all ash. Lava streams descend the side of the 



Proc. W^ash. Acad. Sci., July, 1905. 



277 



