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Lyne J.E., Tauber M. Origin of the Tunguska event
Giuseppe Longo and Romano Serra, SOME ANSWERS FROM TUNGUSKA
MUTE WITNESSES, Meteorite!, 4, p.12-13; 1995
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by Giuseppe Longo and Romano Serra


(Published on: Meteorite!, 4, p.12-13; 1995)


Many witnesses of the Tunguska catastrophe are still alive.
Some of them are two or three hundred years old. They felt the tremendous strength of the blast, their flesh was severely injured, but they remained silent and for more than 80 years kept their secret about the Tunguska event. These mute witnesses are the trees that survived the dreadful explosion of 30 June, 1908.
That day, over the desolate region of the Podkamennaya Tunguska river a cosmic body vaporized in the atmosphere at a height of about 8 km with an energy release which would have been equivalent to more than a thousand Hiroshima bombs. 60 million trees were uprooted, one thousand square kilometers of forest were charred by radiation, innumerable plants and animals were killed over a vast region, but miraculously several trees survived this terrible devastation. After many years of intensive research no impact craters or meteorite fragments have ever been found over an area of 15,000 km 2 , so that the nature and composition of the cosmic body remain controversial.

To obtain information about what happened more than 80 years ago, the authors, together with their colleagues Menotti Galli and Stefano Cecchini, decided to interrogate the only witnesses still alive, the surviving trees. Our group followed Galli's idea that the fluid resin, emitted around dead branches during the 1908 vegetation period, could have acted as a trap, as happens in amber, for aerial particles present at the moment of the event.
The resin became enclosed within the growing wood so that the annual rings of the tree would give information on the age of the resin and therefore on the time when the particles were trapped in it.

Figura 1


Figure 1

A transversal stem slice from a Tunguska spruce. The accelerated growth of the tree after 1908 is clearly visible from the dimensions of the growth rings before and after the catastrophe

Figura 2


Figure 2

The Italian group extracts a core from the "Twins", a larch about 170 years old surviving at a few hundred meters from the epicentre.

One of the wood samples taken in Tunguska, in the form of a transversal stem slice, is photographed in Fig. 1. A branch merged in the stem and surrounded by resin is visible on the tree section in correspondence with the 1909-1924 growth rings. The resin emitted in the preceding years is also present under the surface wood of this sample as shown by the shadow on the older growth rings. Most of our samples were extracted from living trees with a corer. The wounds caused by perforation were immediately treated with an appropriate cream and the trees not only survived the catastrophe but also our intrusion of their privacy (see Fig. 2).

With an electron microscope we examined the resin deposited in the years from 1885 up to 1930 and we observed more than 7,000 trapped particles whose dimensions were equal to a few thousandths of a millimeter. The time distribution of these particles shows clear abundance peaks centred on 1908 for some elements.
This made it possible to identify iron, calcium, aluminium, silicon, copper, sulphur, zinc, titanium, nickel and other elements as probable constituents of the Tunguska body, thus hinting at its asteroidal origin [1-2].
The trees told us not only about the composition and nature of the exploded body, but also narrated their suffering on the day of the event and in subsequent years, providing information about the shock wave and about the extreme heat caused by the explosion [3].

Many 1908 growth rings of trunks and branches showed traumas, while in the rings grown before 1908 there were visible traces of a kind of internal haemorrhage, i. e. of the resin emitted by the wounded tree to protect it against infection. The 1908 ring itself generally has a normal width, showing that its growth was practically complete on 30 June, 1908. This ring, however, has an anomalously clear autumnal wood, characterized by narrower cells with thinner walls (see Fig. 3), indicating a reduced lignification in the months following the catastrophe. Defoliation, as a consequence of the explosion damage and heat, is responsible for the minimal width (often less than one or two tenths of a millimeter) of the 1909 growth ring. In 1910-1913, some rings had a very irregular shape, due to a possible compression by the bark damaged in 1908. Finally, an observation of the tree section as a whole indicates that trees not overthrown by the explosion were left leaning in the leeward side of the shock wave, thus causing an eccentricity in the tree section corresponding to the direction of the shock wave.

Figura 3

Figure 3

The anomalously clear late wood in 1908 is followed by the thinnest 1909 growth ring. From 1910 the rings become wider.

The most spectacular phenomenon observed in all the Tunguska trees examined is their accelerated growth, usually starting from 1909 but sometimes from some years later. In the example, Fig. 1, we can see the ring widths after the blast increased on average by more than four times. This growth has only weakened in recent years, when the tree reached the respectable age of more than 150 years.
Up to today the cause of the anomalous growth is controversial. The fact that the markedly accelerated growth was observed not only in surviving trees, but also in younger trees germinated after the catastrophe has been interpreted as a proof of genetic mutations ascribed to a nuclear explosion. However, we have found no trace of a nuclear process by examining the radiocarbon abundance in the 1903-1916 tree rings of one of our wood samples[1].
Some researchers have found correlations between the anomalous tree growth and the position of the trees. They have explained their findings by hypothesizing a scattered fertilization by a "meteoric dust" that encouraged growth in some places and not in others. Indeed, we found a ring width increase of 300-500 % for some trees and of only 20-30 % for others. These differences, however, did not correspond to the position of the trees but to the dimensions of the growth rings before the catastrophe. The trees that grew more slowly before 1908 have been more advantaged by the explosion, with respect to the others, so that the event had an averaging influence on the final tree dimensions.

The testimonies collected from surviving trees lead us to the conclusion [3] that the reason for accelerated tree growth seems to derive from the improved environmental conditions after the explosion: ash fertilization by charred trees, decreased competition for light, greater availability of minerals due to the increased distance between trees, etc. The more favourable conditions were relatively more fruitful for trees that had been more oppressed before the catastrophe and also favoured younger trees born after the explosion.
Thus, some answers have been obtained from usually mute witnesses that are probably willing to narrate other recollections if patiently questioned.



[1] Longo G., Serra R., Cecchini S. and Galli M., Planetary and Space Science, 42, n. 2, 163-177, 1994.
[2] Serra R., Cecchini S., Galli M. and Longo G., Planetary and Space Science, 42, n. 9, 777-783, 1994.
[3] Galli M., Longo G., Serra R., and Cecchini S., Contribution to the Moscow-Tomsk-Vanavara Conference on Tunguska, 18-24 July 1995.



Giuseppe Longo is Professor of Physics at the University of Bologna (Italy); he has published more than 60 scientific papers on nuclear physics and, in recent years, has been involved in research on the Tunguska event.
Doctor Romano Serra is the Director of the Giorgio Abetti Observatory at San Giovanni in Persiceto, near Bologna.


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