Sedimentary Record of Island Formation

The exposed coastal rocks of Jogashima Island (Kanagawa Prefecture, Japan) reveal alternating layers of pyroclastic sandstone and mudstone that were deposited on the seafloor about 10 to 4 million years ago. Throughout the island’s shoreline visitors can see a low coastal terrace that was formed by uplift during the 1923 Great Kanto Earthquake.

The western end of the island has been a popular destination not only for tourists, but also for many high school and college students who use the island for geological field trips. Various deformations in the sedimentary record can be seen with the naked eye including imbricate thrusts, slumps, and flow folds.