William A bit more about springs and where to find them: The photo below taken from Yakuinbaru (役犬原) is legible if enlarged enough (an aside: the kanji 原, usually “hara,” is only pronounced “haru” in central/southern Kyushu). In a nutshell: ①There are many springs around Mt. Aso; ②This is due to Aso’s unique geology; and ③They are useful for various purposes. Of more interest (to me, at least) is the common use of the character “inu” (犬) in place names. I looked it up. According to this explanation https://tinyurl.com/2r6zxny9, its use as a place name may derive from the kanji for golden eagle, “inuwashi” 「犬鷲」or 「狗鷲」, apparently so named either as they are inferior in beauty to mountain hawk-eagles (kumataka, 熊鷹); that their rapid, graceful movement is reminiscent of the goblin tengu; or that their short, high-pitched cry sounds like that of a puppy. This all leads me to believe that places with (犬) in their names must once have been sites of golden eagle hunting. The updrafts common in the caldera (watch out for hang gliders!) would make hunting with birds there sensible. Thus, the place name 役犬原 would not have derived from “plain of useful dogs” but “plain of useful golden eagles.”