the eruption of Krakatoa was in 1883, the bristlecones showed frost damage in their growth rings for 1884.

One notable frost-ring event occurred in 1626 BC and he suggested that this might well be the result of the explosion of Santorini – if so, the actual eruption would have occurred in 1626 BC “or one or two years earlier”.

To clarify one point at this stage, all the American prehistoric dates have to be moved back by one year.

tree ring dating ireland-21

These could be broadly dated because the layers in the ice sheets are basically annual in character (see Nature, 288 [1980] and 328 [1987]).

Then in 1984 an American dendrochronologist, Val Lamarche, who worked at the Tucson tree ring laboratory, drew attention to frost damaged rings which occurred in a lot of his high-altitude bristlecone pines.

In recent times such frost rings tended to occur in the years following major volcanic eruptions e.g.

should learn by heart; I believe that our work on tree-rings has revealed several major volcanic eruptions which may have caused climatic upset on a world wide basis.

When these major eruptions occurred, the climate of the northern hemisphere may have been altered for several years.

We have to envisage the possibility of failed harvests, famine – and no doubt plague and pestilence as well.

Empires could have been destroyed and vast tracts of land rendered uninhabitable.

In such circumstances the survivors would have been those who were more war-like than their neighbours – the consequences of such “aggression means survival” could have changed social behaviour for centuries.

While such claims may seem like rather fanciful extrapolation from a few dated “events” in the Irish oak record, they need to be suggested in the form of an hypothesis for archaeological testing.