At the Chijiwa Youth Outdoor Learning Center, you can have a good view of the criffs of Chijiwa Fault.
The Japanese archipelago is constantly pushed toward the Eurasian Continent by the plates subducting underneath the archipelago. Due to the combination of the pressure from subducting plates and the push back from the continent, the Shimabara Peninsula is moving southwards slowly. The rate of movement is about 2cm per year at the north end of the peninsula, Kojiro, and about 3cm per year at the south end of the peninsula, Kazusa. Kazusa is moving away from Kojiro by only 1cm, but it goes farther every year, and this means the Shimabara Peninsula is being pulled southwards. The earth's surface is made up of solid rock strata, so when a force is applied across the entire rock strata in this way, it inevitably causes a crack somewhere on the earth's surface. One of such cracks is the Chijiwa Fault.
The Chijiwa Fault is a normal fault located around Chijiwa Town, Unzen City, and it shows the most distinct fault topography in the Shimabara Peninsula. The total length of the fault is 14km, and its largest drop is over 450m around the Tashirobaru area. The south side of the fault has been subsiding at the rate of 1.5m per 1,000 years (1.5mm per year). Due to the subsidence of the southern side of the fault, the coastline has moved inland at the border of this fault, and it has formed the beautiful arc-shaped coastline of Tachibana Bay.