ERUPTION OF TAAL VOLCANO. 75 



the outline features of both island and lake. Xo recent fissure could 

 be traced across the island itself, a fact scarcely explained by the 

 greater fall of ash. If the fissures noted owe their trend entirely to 

 movement radial from the crater their location is still significant, since 

 careful search discovered no other radial fissures around the lake. 



The fissures are vertical, remarkably regular, and show only a vertical 

 (no lateral) displacement. Where the displacement exceeds about 20 

 centimeters there is a sharp break and resulting scarp, otherwise only 

 a gentle roll along the line of trend is evident. Generally speaking, 

 the maximum displacement is along the central portion of the fissure, 

 decreasing gradually to each end. It shotild be noted that displacement 

 did not take place completely at the time the fisstires appeared. It 

 increased perceptibly for several days, during which earthquakes were 

 frequent, after the opening of the fissures. 



The two most prominent fissures occur along the bases of the walls of 

 bedded tuff which form the main terrac-es of the Pancipit Eiver Valley. 

 Their vertical displacements vary up to about 3 meters, and their scarps 

 face each other across the valley. The intermediate fissures have displace- 

 ments not exceeding 1.5 meters (averaging about 0.8 meter). The 

 whole system bears an evident relation to the existing structure. The 

 intermediate fissures occur on relatively high ground (see text figure 

 Xo. 3), around which the Pancipit Eiver makes a wide detour to the 

 west. The ground surface slopes to the east, the strata (tuff) dip 

 slightly to the east and the fissure scarps generally face the east. In 

 the town of Lemery, a minor fissure leaves the general trend of the systerh 

 to follow the contact between the tuff and recent alluvial for a short 

 distance. 



1 



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Text Fi6. No. 3, 



There is a noticeable tendency to maintain the displacement along the 

 trend of the system by alternate parallel fissures. One fissure begins 

 where another ends ; thus the system presents a staggered arrangement.^^ 



Along the main fissure in the town of Lemery the displacement was 

 accomplished by dropping of the lower side, while the upper remained 

 stationary. This is evidenced by the fact that the sea now comes inland 

 farther than formerly on one side of the fissure, and remains at its old 



"See Hobbs, William Herbert, Earthquakes, Xew York (1907), 72. 



