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Dep. of Geophysics
Niels Bohr Institute

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Volcano World



A cold fingerprint on history

A microscopic ash particle from the Greenland Ice cap can make the chronology of the Aegean and Egyptian history fall apart. Since long the ice core specialist Claus Hammer has maintained that the volcanic eruption on the Greek island Santorini took place as early as 1645 B.C. Now much indicates that he is very close to the final proof and this will move the historical chronology up to 150 years and make the archaeologists and historians work on overtime.

By Poul-Erik Philbert

The glaciologist Claus Hammer spent an uneasy journey by train back from Vienna in May 1998. He had participated in a conference about the volcanic eruption on Santorini and had stated that according to ice-cores from the Danish GRIP-drilling on the Greenland Ice cap, the eruption should be dated back to 1645 B.C. But an American scientist had compared ash particles in the ice-core from the American GISP2-drilling with the ash on Santorini and did not consider Hammer's to be the right eruption. The ash came from a local volcano in Alaska, the American concluded.

This had silenced the leader of the Danish ice-core drillings of many years. Together with Professor Gero Kurat from the Natural History Museum in Vienna, he had just started to analyse micro-particles from the GRIP-core to find volcanic ash in the ice with a composition that could fully and finally prove the theory that the eruption on Santorini took place in 1645 B.C.

- I did not have the original curves from the American drilling, and therefore I could not respond to the assertion, Claus Hammer tells. The more I thought about the problem, the more the feeling grew that something must be wrong with the American core in exactly that part where the eruption on Santorini should be.

A disputed dating
You shouldn't be surprised that a glaciologist with the Inland Ice as working field is invited to participate in a seminar about Minoan archaeology. Actually, the ice-core scientists are about the only ones able to answer precisely when the volcano on Santorini, in a giant eruption, ejected c. 30 km3 ashes and lava and sent a couple of hundred millions of tons sulphuric acid 20-30 km up into the stratosphere.

For many years, the dating of the Santorini-eruption has been the cause of many hot-tempered discussions among archaeologists and historians. Even more so after Claus Hammer and his colleagues in an article in the magazine Nature in 1987 dated the eruption to 1645 B.C., and principally moved it 150 years back in time.

It is not the year itself that is at the centre of the dispute. But the eruption is an important point of reference, when scientists are to do the chronological puzzle for the history of the Aegean area and Egypt about 1500 B.C. If you move the Santorini-event 150 years, it will have widespread consequences because a laboriously constructed network of datings will fall apart.

You can find the answer in the ice-cores from the Greenland Inland Ice drilled throughout the 1980'ies and 1990'ies by Danish scientists. The largest eruptions in history have sent several million tons of sulphuric acid into the stratosphere leaving in the ice chemical traces that are very easy to date.

But the trace of sulphuric acid is not enough to upset the archaeologists' chronology. Principally, the acid trace can relate to another volcanic eruption. And this was exactly what the American glaciologists concluded when they had carried out the ultimate test: a comparison of the ash particles from the ice-core with ash-remains from Santorini.

Close to the final proof
When Claus Hammer was back in Copenhagen after the conference in Vienna, he immediately made a rush at the series of data from the American GISP-2 and the Danish GRIP-drillings. His suspicion was confirmed that the American ice-core did not have a proper indication of the eruption on Santorini.

- The Americans were right that their ash particles did not originate from the Santorini eruption. But luckily it turned out that it was not Santorini they had investigated but some other local volcanic eruption. Their ice-core was quite damaged at the depth where the traces from the Santorini eruption were supposed to have been. So we decided to go on with the analyses of the micro-particles in the ice to find volcanic ash from Santorini.

It is a major job finding ash particles in the ice because only very little ash reaches the Inland Ice even from a major eruption in the Aegean Sea. Furthermore, it is only minute particles that are capable of floating so far. The scientists are looking for pieces of ash at 0.001-0.005 mm in their electron microscopes.

- If we shall convince the historians and the archaeologists, the laborious work by investigating thousands of tiny particles is the only feasible way, Claus Hammer says. The traces of ash act as a kind of finger-print comparable with the ash from the volcanic eruption. Only when we can state that the ash from the ice-core fits with the ash from Santorini, our 1645 B.C. dating of the eruption can be acknowledged.

After more than a year's fiddling work, the analyses are now so far that Claus Hammer and Gero Kurat are close to the final proof.

- It does look all right, because we have found ashes with the same chemical composition as on Santorini, but still some investigations of the glass particles in the ice are lacking before we can be absolutely sure.

On overtime
The ice-core dating has truly been taken seriously among archaeologists, but they have postponed the revising of the chronology waiting for the final proof. If Claus Hammer and Kurat succeed to prove their dating, waiting time will be over:

- If they do present the final proof, it will have repercussions among archaeologists occupied with the Aegean pre-history, says archaeologist Birgitta Hallager, the University of Aarhus. Then we must start the extensive work going through the whole chronology puzzle in the history of Egypt and the Aegean area with the ceramics from Santorini as a reference point and the year 1645 B.C. as the chronology fix-point.

Also European history will be hit by the waves from a redating of the Santorini eruption, because the chronology of the European bronze age is extensively connected to the disputed volcanic eruption.

Claus Hammer has already a new volcanic eruption in sight. He has found a signal in the ice-core at year 79 A.D. If it is the Vesuvian eruption, which buried Pompeii and Herculanum, the sulphuric acid rain should in fact not reach the Greenland Inland Ice until year 80. But an error margin of 1 year does not seem to knock out the professor. An ash particle might disclose to us in the future, if it really is Vesuvius.

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Updated March 19, 2002