Geological magazine . nomenaof elevation which now fall to be described. (3) The elevation of the Xew Mountain is the main featureof interest iu the 1910 eruption of Usu-san. It first manifesteditself in the behaviour of Lake Toya. Thus, in spite of a lightrainfall, the waters of the lake rose more than a foot above theirusual level in the latter part of July, that is about the time of thecommencement of the eruption, and maintained themselves in thisposition throughout the following month of August. The accom-panying rise ill the Sobets River, the only outlet of the lake,meanwhile amounted to
Geological magazine . nomenaof elevation which now fall to be described. (3) The elevation of the Xew Mountain is the main featureof interest iu the 1910 eruption of Usu-san. It first manifesteditself in the behaviour of Lake Toya. Thus, in spite of a lightrainfall, the waters of the lake rose more than a foot above theirusual level in the latter part of July, that is about the time of thecommencement of the eruption, and maintained themselves in thisposition throughout the following month of August. The accom-panying rise ill the Sobets River, the only outlet of the lake,meanwhile amounted to 2 feet. This apparent increase of the watersof Lake Toya was of a general character and presumably due toa differential upward displacement of some portion of the lakebottom. That local movement of the type required did occur wasin fact demonstrated ou August 6, when Omori found that a reachof the coastline about a mile long at the foot of East Maru-yama hadbeen elevated nearly a metre out of the water. To study this. Usu-san, Japan. 251 phenomenon more precisely a graduated level-gauge was at onceerected in the lake near the east end of the elevated stretch of coast,and two others at convenient points on either side of the disturbedtract. The two control gauges gave concurrent results, so that itwas a simple matter to interpret very precisely the differentialmovement indicated by the instrument situated in between. It isextremely inteiesting to find that part of the elevation thusdetermined proved to be of a transient nature. Erora August 6to August 21 an elevation of 343 cm. was recorded (additional tothat which had occurred previous to the former date). A slight dropwas then experienced, but the same height was attained once more onAugust 27. Thereafter a gradual uneven downward movement setin, and by November 10 the lake bottom at the point investigatedstood merely 167 cm. higher than on August 6. Meanwhile a large inland tract, about 2,700 m. long and600 m. wide, was uphe
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectgeology, bookyear1864
