INTERESTING PHENOMENA ON THE ERUPTION OF USU 275 



2. Explosion craters. — The 45 craters are arranged in two 

 groups (Fig. 15). The first, consisting of 16 craters lying north- 

 northwest of Mount Usu, is aligned in a west-northwest to east- 

 southeast direction. The second group, lying 800 m. northeast 

 of the former, is composed of 29 cones lying in a line parallel to the 

 first group (Fig. 16). The altitude, date of formation, size, shape, 

 and the life-history etc., of each cone in the two groups are tabu- 

 lated in Table II. 



Fig. 19. — Ejection of smoke from crater No. XLII. Taken August 3, 1010 



The formation of the cones apparently has no order, though a 

 few in the first of the groups described above formed in sequence, 

 starting from the northwestern end and proceeding toward the east. 

 But in general the action was begun in the first group and finished 

 in the second group. 



3. Ejectamenta. — Ash, sand, and bombs, with S0 2 and H 2 S, 

 were ejected in the black smoke and carried to the lee by the wind, 

 some of the ashes quite a distance. From the first explosion ashes 

 were carried 44 km. toward the northwest of the Usu. Later, ashes 

 from a later eruption were carried 4 km. toward the east and 20 km. 



