Roundness of gravel particles is widely used as an indicator of sediment transport, yet its potential for discriminating provenance between mainstem and tributary rivers has not been fully tested. In this study, we applied an image‐analysis‐based roundness measurement (Rgrains) to gravel samples from mainstem and tributary deposits in the Tama and Doushi river basins in central Japan. We used both modern riverbed sediments and...

Pumice is a pyroclastic material of low density and is occasionally buoyant in water. When it erupts from submarine volcanoes, it can drift long distances and wash ashore at remote beaches. Pumice from the eruption of Fukutoku‐Oka‐no‐Ba volcano in the Izu–Bonin arc in October 2021 drifted for about 2 months over a distance of > 1300 km onto the Nansei Islands of Japan, disrupting shipping, fishing, and coastal ecosystems. In M...

A tephra layer offers an isochronous surface in sediments, thus serving as a key bed and/or an age marker. Recent high‐resolution sediment research (e.g. varved sediments) has revealed optically invisible tephra fingerprints and provided high‐precision tephra ages. However, a tephra‐based correlation cannot succeed without detailed knowledge of the tephra characteristics in a proximal area to correlate with tephra in high‐reso...