Matching volcanic ash to its source

Scientists often use chemistry to identify which volcano erupted deposits they find in the field. In Auckland, we have more than 53 potential sources for the volcanic ash fragments (tephra) we find.

DEVORA researchers have developed a method to correlate tephra samples to their source volcanic centres. It is based on the collation of whole-rock major and trace element data.

The method produces reasonable results based on major element signatures alone, but the use of trace element signatures strengthens correlations.

Tephra-derived glass compositions have been compared with past and new data for the entire field.

The results show that incompatible trace element ratios vary widely across the field. However, there is a more restricted range within samples from a single volcanic centre.

By linking tephra to their source centres in volcanic fields, the eruptive history, and fragment dispersal patterns can be revealed, along with potential hazards.

The findings suggest that each volcanic centre does not have a unique geochemical signature in the field as a whole. Additional criteria have been utilised to further constrain the source centres, including age, eruption scale, and location.

The combination of tephra correlation, dating and stratigraphic constraints allow – for the first time – the relative and absolute ordering of 48 of 53 volcanic centres. A relationship between short quiet periods and close eruption sites has also been found for several centres.

Tags:Auckland Volcanic Fieldbasaltcorrelationmonogeneticpublicationstephratephrochronology