12.Cluster of Springs in Aso Valley District Geosite
Miyaji and Yakuinbaru District Springs
On the northeast foot of the central volcanic cones in Aso Caldera at Miyaji and Yakuinbaru, flowing wells are commonly found everywhere. The well water has its origin in rain warter fallen on the volcanic cones, which then infiltrates deep into the ground, reappearing at the surface under pressure. The height of the water heads sometimes reaches 2m above the ground, and is utilized for domestic and agricultural purposes. In Monzen Shopping Street, the water is called ‘Mizuki (Springs)’ and is utilized for local promotional activities.
Fig. 1 Major flowing artesian wells in northernfloor of Aso Caldera (Kumamoto Prefecture, 1993)
Fig. 2
Artesian spring in Yakuinbaru
Fig. 3
Mizuki (Springs) in Miyaji
Fig. 4
Mizuki (Springs) in Miyaji
Alluvial fan and artesian aquifer
This area is an alluvial fan formed by repeated floods and deburi avalanches from the central cones. Rain water fallen on the volcanic cones infiltrates deep into the ground, and appears again on the ground surface after flowing under the alluvial fan. The water spurts out due to the positive pressure; artesian springs, and we call this underground water, artesian aquifer.
Fig. 5 Geological cross-section of northeast floor of Aso Caldera (Tanaka, 2000)
