|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.
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.
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
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 .
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.
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
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  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
Thus, some answers have been obtained from usually mute witnesses that are probably
willing to narrate other recollections if patiently questioned.
 Longo G., Serra R., Cecchini S. and Galli M., Planetary and Space Science, 42, n.
2, 163-177, 1994.
 Serra R., Cecchini S., Galli M. and Longo G., Planetary and Space Science, 42, n. 9,
 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.