172 



KNo\vi,i:i)r,i-. 



May. 101; 



and Kdinpira-yania. ciglit hinuiifd and littv-llinc 

 and seven Imndri'd and ci^^lity-si'vcii Icit in licii^lit 

 respectively. A little niore tlian lialf a inih' nortli- 

 east of the latter, is a small roundcil liill called West 

 Maru-\ania, five liundred and ninety feet liif^li. 



The last known criii)tions of Usu-san took |)lace 

 in the vears 166J. 1769, 1822 and 

 185-5. those of 166J and 1822 were 

 great eruptions, and. for two or three 

 days before the first outbursts, were 

 preceded by numerous earthf]uakes 

 and earth-sounds. 



The same symptoms luialdcd the 

 eruption of l''l(1. In the town of 

 Nishi-Monbets. which lies about five 

 miles to the south of the crater, 

 twenty-five shocks were recorded on 

 July 22nd, one hundred and ten on .lo 

 the following day, three hundred and 

 fifty-one on the 24th, and one hundred 

 and fifty-two up ti> Id p.m. on Jul\- '" 

 25th. wlieii the first explosion 

 occurred. The shocks, as illustrated 

 by the lower curve in Figure 201, 

 reached their greatest frefjuenc\' 

 twenty-four hours before this 

 erujition. During the immediateh' 

 preceding twelve hours, only thirty- 

 four were recorded. None of the 

 shocks was of great intensit}-. Only 

 two of them were strong enough to 

 poorly-built houses, and both disturbed small areas. 



The upper curve in Figure 201 represents the 



be noticed that the first prcmonitor\' shocks occurred 

 on July 21st when the barometric pressure was a 

 minimum, and that the first volcanic e.xplosion took 

 place on July25th,when the fjressure wasa maximum. 

 Roughly, also, the variation in time of earthquake- 

 frequency follows that of the barometric pressure. 



25th 36 



"lOL'KK 201. 



lid the 



damage some 



Ko-Tipira-yaflia ~ 



fMGUKi-: 202, 

 Plan of tlie Cvaterlcts. 



variation in barometic pressure at Hakodate, fifty 

 miles south of L'su-san,'from July 21st to 29th. It w ill 



ustr.•lli^,^' tlip number of EartfiiiuaUc Slit; 

 barometric pressure. 



The first volcanic outburst was a small explosion 

 at 10 p.m. on July 25th, from the north-west side of 

 Kompira-\-ama, followed by a second from the west 

 side of the same mountain. 

 These were succeeded by explos- 

 ions from a number of new 

 craterlets. On August 10th, there 

 were at least twenty-eight crater- 

 lets, but explosions from new 

 openings continued to occur until 

 the end of the vear. On 

 November 12th. forty-five 

 different craterlets (indicated by 

 the small circles in Figure 202) 

 were counted, the diameters of 

 which \aried from one hundred 

 to eight hundred feet. They are 

 situated along three well-defined 

 bands. The most important of 

 these is a curve (.\ .\. Figure 202), 

 rather more than a mile in 

 length, about half a mile from 

 the southern shore of the Toya 

 lake and from six to se\en 



I hundred feet above it. It reaches 

 from the western flank of East 

 Maru-\ama to the eastern flank 

 of Kompira\\ama. Two other 

 bands diverge, one (C) at right 

 angles to the principal band 

 along the axis of West Maru-yama. and the (^her 

 (H) at a small angle along the axis of Kompira-yama. 



