Date: 7. julij 1997 11:48
Subject: Tree Rings, Volcanoes & the Bishop of Armagh
More on the ~2300 BC Abrupt Climate Change: Tree Rings, Hekla 4 & the Irish Annals
from: Prof Mike Baillie <firstname.lastname@example.org>
Detail from Baillie, M.G.L. (1995) "Dendrochronology and the Chronology of the Irish Bronze Age"
paper in "Ireland in the Bronze Age". Ed
Waddell, J. and Shee-Twohig, E, Stationery Office, Dublin, 30-37.
The earliest of the four (extreme tree-ring events) takes place at a time which must be very close to the beginning of the Bronze Age in Ireland. This is the so-called Hekla 4 volcanic eruption. It shows up as an extremely narrow band of rings, beginning in 2354 BC and reaching lowest growth - the narrowest rings - at 2345 BC. It is apparent that trees in Lancashire also show reduced growth at the same time, reinforcing the view that this is a widespread event. While the event was very apparent in the ring width patterns, it was a surprise to discover a highly unusual growth defect in one of the sample from the Motorway complex (trees which grew in the fenlands just to the south of Lough Neagh). The sample shows a change in the character of growth, from normal ring porous to diffuse porous - an anomaly which lasts for about a decade and which could be consistent with the tree being inundated. So, there is clear evidence for an environmental event affecting oak growth generally and trees near Lough Neagh specifically. However, the evidence in this case is not limited to the oaks themselves.
Tephrochronology involves the identification and dating of microscopic volcanic glass shards and their use as marker horizons in ancient deposits. Recent work has indicated that Hekla 4 tephra, which can be specifically identified to that Icelandic volcano on chemical grounds, is found in numerous Irish peat bogs at 2310 +/- 20 Cal BC. The dating exercise used a series of high-precision radiocarbon measurements on stratified peats across the Hekla 4 layer and it is likely that the date given above is correct in absolute terms to within a half century. So the implication may well be that the narrow growth rings and associated tree-ring effects after 2354 BC are directly due to the environmental effects of Hekla 4. Now that raises interesting questions. Because the radiocarbon dates associated with this event would be almost indistinguishable from radiocarbon dates for the earliest section of the Beaker period, it becomes possible to ask if the Hekla 4 event was in any way related to the arrival of the first metal users in Ireland? It is also known that pine pollen disappears from pollen spectra in the north of Ireland just a few centimetres above this event in most pollen diagrams. Is it possible that the demise of pine is linked to the arrival of those same metal-using people? We may be beginning to see the start of the Bronze Age in some sort of wider context, involving a package of
(a) environmental events,
(b) the arrival of at least a new technology and
(c) the disappearance of a species (pine) which had been present in Ireland for millennia
This sort of package is suggestive that humans were almost certainly involved in the demise of pine trees in Ireland. However, irrespective of the pine issue, it is clear that some interesting things took place in the 24th century BC. The evidence is indelible and is not going to go away. I would suggest that this is a classic "marker date" i.e. a date which will show up on a regular basis in studies of various kinds.
It has to be noted that Warner sees the 2354 BC to 2345 BC event as very close to one of only four major disasters recorded in the Anno Mundi section of the Irish Annals. One of these references bears the date AM 2820 (which Warner interprets as "2380 BC") and says 'Nine thousand ... died in one week. Ireland was thirty years waste' (i.e. to 2350 "BC"). A coincidence perhaps? In fact, although Warner draws attention to the human aspect of catastrophe in the Annals, it transpires that things are even more curious. The Annals go on to say that in "about AM 2859 and after" (i.e. "2341 BC" and after) "lakes erupted". Of course we know that these ancient annals have no basis in fact - or do they? Incredibly, there is an even more bizarre coincidence.
While we are talking about innundation of oaks at the south of Lough Neagh (in Co Armagh) in the period 2354 BC to 2345 BC (dated by totally independent dendrochronology), an earlier scholar with Armagh connections, namely Bishop Ussher, worked out the date of the biblical Flood to be 2349 BC (see King James Bible)! There are several things which could be said about these coincidences, two of which seem appropriate. The first is a question; did the scholars who worked up the Anno Mundi section of the Irish Annals in fact use the same Biblical sources as Ussher to derive their chronology? Indeed, is it possible that the various scholars came into direct contact somewhere in Donegal? If they did, then the prehistoric section of the Annals are probably as compromised as critics suggest. The second point is merely amusing; maybe all those aged farmers who said the bog oaks were "all washed down in The Flood" weren't so completely wrong after all.
School of Geosciences, Queen's University, Belfast