INTERESTING PHENOMENA ON THE ERUPTION OF USU 271 



water-level; very few showed a decrease. In most cases it was 

 noted that the water in the wells increased to about double the 

 normal volume, while at the same time it became turbid and dirty, 

 owing to the particles of dry mud which fell from the wells into the 

 water below. The rivers of the region also became brown and 

 turbid from slumping of the clay banks. On the southeast side of 

 the mountain several new springs were formed which are still flowing. 



III. EXPLOSIONS 



After July 22 fre- 

 quent earthquakes took 

 place, their in tensity and 

 numbers increasing hour 

 by hour till 10:00 p.m. 

 on July 25, when the 

 first explosion took place 

 on the northwest side of 

 Kompirayama, a para- 

 sitic cone, on the north- „ „, , _. . _. ' T . 



Fig. 15. — Two groups of craterlets. Group I is 



west slope of the main located at the southwest of Group II. 

 volcano (Fig. 9) . For a 



few hours red-hot bombs were ejected on the north side of the 

 cone and made numberless holes in the roofs of the houses in 

 the near vicinity. When the writer visited the region on the 

 following morning, the vent was entirely free from escaping 

 steam, making it possible for him to descend into the crater. 

 At 2:13 p.m. on July 26, a second explosion, preceded by roaring 

 and trembling, took place 200 m. southeast of the first crater 

 accompanying two small explosions. This explosion ejected 

 black and white smoke to a height of about 700 m. That night 

 the smoke stopped for a few hours, but again, beginning at three 

 o'clock in the morning, the roaring became louder and louder as of 

 strong thunder near by, till four o'clock, when it gradually sub- 

 sided. Meanwhile frequent earthquakes accompanied the forma- 

 tion of three or four explosion craters. In the afternoon of the 

 next day, July 27, the writer saw the ejection of smoke in two 

 craters east of the crater mentioned above (Fig. 10a). At 7 : 00 a.m. 



