### Explosive lies: How volcanoes can lie about their age, and what it means for us

Radiocarbon wiggle-match dating is a technique that can combine the versatility of radiocarbon dating with chronological information from tree-rings. This makes . ORAU was one of the first radiocarbon AMS laboratories to be founded in the the use of wiggle-match dating - a method to achieve calendar-date precision at. This process of curve-fitting has come to be called "wiggle-matching. ; radioactive isotopes;simulation ;tree rings;upper Holocene;wiggle match method; wood.

For kids, it might be little white lies, but volcanoes can tell big lies with big consequences. Our researchpublished today in Nature Communications, uncovers one such volcanic lie. Accurate dating of prehistoric eruptions is important as it allows scientists to correlate them with other recordssuch as large earthquakes, Antarctic ice cores, historical events like Mediterranean civilisation milestonesand climatic events like the Little Ice Age. This gives us a better understanding of the links between volcanism and the natural and cultural environment.

Taupo's last violent eruption Lake Taupoin the North Island of New Zealand, is a globally significant caldera supervolcano. The caldera formed after the collapse of a magma chamber roof following a massive eruption more than 20, years ago.

Now it seems that the Taupo eruption that occurred in the early part of the first millennium has been lying about its age. But like many lies, it was eventually found out, and it reveals exciting processes we hadn't understood before.

The eruption of Taupo in the first millennium has been dated many times with radiocarbon, yielding a surprisingly large spread of ages between 36CE and CE. Lake Taupo, in the North Island of New Zealand, is a globally significant caldera of a supervolcano that formed following a massive eruption more than 20, years ago.

Over the past two decades, the method has been refined greatly by combining it with dendrochronology, the study of the environmental effects on the width of tree rings through time.

Radiocarbon dating of tree ring records has allowed scientists to construct a reliable record of the concentration of carbon in the atmosphere through time. In principle, this composite record allows eruptions to be dated by matching the wiggly trace of carbon in a tree killed by an eruption to the wiggly trace of atmospheric carbon from the reference curve "wiggle-match" dating.

Scientists presently use wiggle-match dating as the method of choice for eruption dating, but the technique is not valid if carbon dioxide gas from the volcano is affecting a tree's version of the wiggle. The effect of volcanic carbon on eruption ages Our study re-analysed the large series of radiocarbon dates for the Taupo eruption and found that the oldest dates were closest to the volcano vent.

The dates were progressively younger the farther away they were.

### Internet Archaeol Christen Intuitive Wiggle matching

This unusual geographic pattern has been documented very close i. Two wiggle match agestaken from the same forest, located about 30km from the caldera lake, were among the oldest dates from the series of dates.

Note that the highest point is at BP, with a probability of nearly 0. However, there is no reason whatsoever for choosing one year only. Note also that we are not restricted either to producing a confidence or probability interval at any level or to choosing a single calendar year. The posterior distribution itself has far more information than point or interval estimates and lends itself for richer, although perhaps more complex, interpretations.

A table with the numbers generating Figure 1 and other figures may be downloaded from the corresponding Bwigg output page see software usage. This table may be used for more precise accounts of the posterior distribution. The reader is invited to perform a similar interpretation exercise with the more convoluted posterior distribution depicted in Figure 2 including the errors in the calibration curve. Figure 3 presents the floating chronology, with the radiocarbon determinations, superimposed on the relevant part of the calibration curve.

This superimposition illustrates the resemblance between the wiggles formed by the floating chronology and those of the calibration curve thus the term wiggle-matching. The remaining output to be interpreted relate to the posterior probabilities, in the outlier section.

### High precision wiggle matching in radiocarbon dating - Strathprints

This is what happens next. Outliers In statistics the term 'outlier' is assigned to data points outside the main range of the rest of the data, of spurious or conspicuous origin, abnormal or difficult to explain according to standard theories or, simply, wrong or misleading. Outliers are a constant concern in radiocarbon dating see Scott et al. However, the term outliers cannot be employed unless referred to a context, a data set and models used see Christen b for a more in-depth discussion.

For those determinations, an additional shift in the radiocarbon scale is used in order for them to be correctly fitted in the floating chronology. It is then possible to calculate by a numeric approximation called MCMC, see technical section the probability that each determination needs such a shift. This is what is called the posterior probabilities of each determination being an outlier see technical details.

Note also that the errors in the calibration curve are taken into consideration to perform the outlier analysis.

## High precision wiggle matching in radiocarbon dating

If Bwigg is rerun, the posterior probability of this determination being an outlier is now more than 0. The determination is clearly detected by the outlier method as standing out of the chronology. As an illustration, see the match given by Bwigg in Figure 4.

**How to Date a Dead Thing**

The relevant part of the calibration curve are also presented, with the estimated standard errors in the curve Bwigg also presents the 'Bayes factors'. These are the posterior probabilities divided by the prior probabilities 0. This factor represents the number of times it is more certain that the corresponding determination is an outlier.

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- 3 Bayesian wiggle-matching (intuitive)

For example, going back to the original data set in Table 1 the highest Bayes factor in Table 2 is 2. This means that the probability of this determination being an outlier doubled a posteriori.

However, surprisingly, looking at Figure 3this determination the 9th from right to left falls nicely within the calibration curve.