THE VOLCANO ASO AND ITS LARGE CALDERA 503 



island and much of the southern part is volcanic. The Japanese 

 geologists count twenty volcanoes in Kiushiu, including two that 

 form small islands near the coast on the south. The period of 

 volcanic construction extends into the present — eight of the twenty 

 volcanoes being still living — but the general activity seems to be on 

 the decline. The volcanic forces must have reached their climax 

 sometime during the middle Quaternary, to judge from the amount 

 of erosion that has taken place since the greatest outpourings occurred; 

 and it is probably from this period that the long since extinct crater of 

 Aso dates. In its prime Aso doubtless held a position of pre-eminence 

 among the volcanoes and mountains of Kiushiu, as is indicated by the 

 extent of territory that is covered by material derived from its erup- 

 tions, and by the grandeur of the scale upon which the crater was 

 built and the probability that a cone formerly rose to a great height 

 above it. Its present peaks are surpassed by a few others in the 

 island, the highest of which is the non-volcanic mountain Sobo-san, 

 6,600 feet in altitude. 



APPROACH TO THE CALDERA 



Aso-san may be most easily reached from Kumamoto, a city 

 situated on the coastal plain near the western coast of Kiushiu. From 

 there a road runs up into the mountains and down into the caldera, 

 which is about twenty miles away. The volcano does not form a 

 prominent cone as seen from this side and appears merely as a high 

 portion of the mountain mass that occupies the island's interior. The 

 caldera becomes apparent only on an approach to its very edge, or 

 from the summit of one of the high mountains within a score of miles 

 of Aso. From such a summit one looks down upon it and obtains an 

 impressive view of the huge bowl and the high volcanic peaks that 

 spring from within it. 



THE FLOOR 



Viewed broadly, the floors of the' two basins into which the caldera 

 is divided are level plains lying at the same elevation. They slope 

 gently upward from west to east. On the east they break into low 

 sweeping ridges and knolls that rise gradually and merge with the 

 wall and central range, which are there convergent, (See Fig. 3). 

 Throughout the centra portion of each of the two basins the floor 



