 Its size was first 1 km (south-north) and 300m 400m (east to west), but the production of a water exit river made it smaller and it is now 200 m by 70 m.

As a result of the destruction, Tsukumojima or 99 islets or rocks were distributed near Shimabara city.In the same Nagasaki Prefecture, there are 99 islands or Kujūkushima distributed from Sasebo city to Hirado city.These islands are different from Tsukumojima.