Volcanic ash (tephra) layers can be preserved as thick visible deposits, or as microscopic markers (cryptotephra).

Volcanic ash and dating the past

Volcanic ash (tephra) deposits are routinely identified in sedimentary (palaeoclimate and archaeological) archives in and around Japan. These layers provide important markers able to precisely synchronise distal records and also provide insight into the tempo, behavior and dispersal of explosive volcanism.

Since my doctorate at the University of Oxford, I have been working on Lake Suigetsu sediments as part of the multi-national Suigetsu Varved Sediment Project. Lake Suigetsu is the most precisely dated palaeoenvironmental record for Japan, and the visible tephra sequence provides a key record of volcanism over the last 150 ka. We have identified that four times as many ash layers are preserved as non-visible markers (cryptotephras) through the sequence, which provides a very detailed catalogue of smaller and more distal eruption events (see McLean et al., 2018; 2020).

Suigetsu Tephrostratigraphy

I specialise in identifying non-visible ash layers that are preserved in these records. Volcanic glass shards can be extracted from the lake sediments (using density separation techniques) and counted to identify peaks in their concentration. These peaks represent non-visible ash layers preserved in the core. The compositions of the glass shards within these layers can be used to correlate them to their volcanic source and/or particular eruption.

The presence of many of these tephra layers in the Lake Suigetsu core also considerably extends the known ash dispersals of the eruptions, for example, the archive provides the most southerly tephra occurrence of the highly-explosive Changbaishan ‘Millennium’ eruption (McLean et al., 2016). This is the first direct tie-point between Lake Suigetsu for the Greenland ice cores, a major goal for the scientific palaeo-climate community.

A short video of the laboratory techniques can be viewed here.

The Fukui Varve Museum: Permanent and Temporary Exhibitions

This research continues in collaboration with other Suigetsu Project Members and further information on the project can be viewed on the external Suigetsu website. Furthermore, this research is presented in the newly opened Fukui Varve Museum. This is the world’s first museum of varves, opened in Wakasa-cho, Fukui Prefecture.

Permanent Exhibitions

The museum exhibits thin-sections of the annually laminated (varved) sediments collected at the bottom of Lake Suigetsu over the last 70,000 years. The display spans for over 45 m and contains numerous volcanic ash layers that we can now correlate to their source.

Doctoral work presented in the Suigetsu Varve Museum

Temporary Exhibition

In September 2023, a temporary exhibition opened at the Fukui Varve Museum that showcases the importance of the Suigetsu volcanic ash record. We have curated a range of specimens from the Oxford Tephra Research Laboratory for display. You can observe volcanic deposits collected as part of our fieldwork as well as microscope slides, and information about the different volcanic eruptions we can precisely date using the Lake Suigetsu sediments.