What is tephra?
Tephra, the Greek word for ash, is used to describe any material that is ejected by a volcano into the atmosphere (pyroclasts). Tephra includes dense blocks and bombs (>64mm), and lighter materials such as scoria, pumice and ash (<2mm). As one moves away from a volcano, the tephra deposits become finer grained (smaller particles) and thinner. This is because small airborne particles hover longer and stay within the atmosphere for a greater distance from the volcano. These particles of ash can be carried in the atmosphere for thousands of kilometers. The smallest particles are so-called crypto-tephra and are invisible to the naked eye.
In the laboratory for tephra analytics, samples taken from lake sediment cores are prepared for the identification and geochemical analysis of individual cryptotephras (glass shards). Identified cryptotephras are a prerequisite for the creation of a tephrochronology that allows the independent dating of our palaeoclimate and environmental archives.
Procedures, devices and applications:
- Dissolution of salts in heated shaking water bath
- Geochemical treatment with acids
- Wet-sieving to separate different size fractions (using mesh frames)
- Split into different density fractions using heavy liquid
- Microscopic analysis, identification of glass shards of tephra with a Binocular (Zeiss Jenapol)
- Separation with a Binocular (Zeiss Jenapol) or a Micromanipolator
- Embedding of glass shards in resin and manual preparation of a polished section
- Obtaining of major element composition of single glass shards on carbon-coated stubs at a JEOL JXA-8230 microprobe
