Alluvial plains (沖積平野, chūseki heiya) - flat areas created by dirt running off of mountains - constitute most of the habitable areas of Japan. While their flatness makes them great for building, they’re also subject to liquefaction during earthquakes. I’m currently commuting to a gig in Yatsushiro by train which skirts the mountains and the alluvial plain and am enjoying the view. Geology, I learned in college, is a key factor in understanding societies. - William