Cunning radiocarbon and dating volcanic eruptions

By Anna Sandiford 19/05/2010

It is excellent to see a new AMS radiocarbon dating set-up in New Zealand (NZ scientists fire up $3.4 million mass spectrometer).  When I was working on climate reconstruction I was hugely reliant on the previous 14C volcanic ash (light) peat (dark)(radiocarbon) device to help put Before Present (BP) ages on volcanic ash layers (tephra) that occurred in sections and cores for my PhD and post-doc – we did this by collecting peat samples that were in direct contact with the tephra layers and submitting the peat samples for analysis.
The numerous volcanic eruptions in New Zealand over the past one million years, and particularly over the last 50,000 years within the Auckland Volcanic Field, mean that by using AMS dates (in conjunction with other radioactive dating methods) we have been able to date accurately each volcanic eruption. Because there are so many eruptions and each is chemically different (generally speaking), we can age-correlate sites over wide geographical areas.

By also reconstructing climate using methods such as pollen analysis and particle analysis (to reconstruct vegetation and environmental conditions), we have been able to reconstruct climate change over, for example, the last 1.1 million years for many areas in New Zealand, particularly the North Island. We have also been able to say how volcanic activity affected the local vegetation in the time immediately after the eruption.  That clearly has implications for future planning and mitigation procedures for future eruptions.

The palaeoclimate records that have been established in New Zealand are world-class, partly because of our volcanic history but also in large part to the presence of a radiocarbon dating facility actually being in New Zealand – long may it last.

[Example literature: Sandiford et al, 2003. A 28,000-7,600 cal yr BP pollen record of vegetation and climate change from Pukaki Crater, northern New Zealand. Palaegeography, Palaeoclimatology, Palaeoecology, 201, pp. 235-247]