You can observe the strata of the beginning of Unzen Volcano.
The bottom black stratum is a stratum that was deposited when Shimabara Peninsula was still sea.
The white layer above it is a stratum formed by the eruption of ancient Unzen volcano 500,000 years ago.
Furthermore, the layer containing pebbles above is the stratum where debris flow has flowed out from Unzen volcano.
The Tatsuishi Coast is an important place to talk about how the Shimabara Peninsula was made.