Petrographic characteristics in the pumice clast deposited along the Gulf of Thailand, drifted from Fukutoku-Oka-no-Ba

Abstract

The 2021 eruption of Fukutoku-Oka-no-Ba (FOB) in the northwest Pacific on 13 August 2021 produced a large volume of pumice that drifted westward for ~1300 km to the Nansei Islands, Japan, and some extent. In February 2022, pumice with similar characteristics to the FOB pumice was deposited along the Gulf of Thailand. The pumice clasts deposited in Songkhla Province, Thailand, were fine-grained with <4 cm in size and rounded. Most of the clasts consisted of clinopyroxene, plagioclase (andesine), and olivine phenocrysts in a vesiculated grey groundmass, with black-coloured spots exhibiting signatures of a basaltic magma. The whole-rock compositions of the pumice are trachytic, with 61 mass% SiO 2 and 9 mass% total alkali (Na 2 O + K 2 O). The overall characteristics in the pumice from Thailand are similar to those in FOB pumice. These pumice in Thailand were from the 2021 FOB eruption, and drifted >2800 km south-westward across the South China Sea.