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*/Meteoritica,/* Vol. XXIII (1963)

**PRELIMINARY RESULTS FROM THE 1961 COMBINED TUNGUSKA METEORITE
EXPEDITION*** *

K P Florenskiy

/Report read at the Tenth Conference on Meteorites in May 1962/

/Translated by Spectrum Translation and Research, inc. /

/Published by Taurus Press, inc., copyright 1965./

*INTRODUCTION*

Interest in study of unique natural phenomena is, in general, not
confined to a single narrowly specialized viewpoint, and the 1908 fall
of the Tunguska meteorite is no exception to this. The interests of
various scientific disciplines converge on such investigations as at the
focus of a mirror, and science itself is spurred to further development
whose significance often ranges far beyond the framework of the original
specific problem.

In addition to questions pertaining to meteoritics, the fall of the
Tunguska meteorite in particular gave impetus to the development of a
number of concepts in such areas as the ballistics of supersonic
velocities, the theory of large explosions, the structure of comets and
features of their chemical composition, geochemical studies of cosmic
dust, etc.; furthermore, it encouraged investigation of a variety of
natural features in a remote and unexplored but promising area of
Siberia. We have the meteorite to thank for the initial investigations
of the swamps, soils and forests - studies that are important not only
from the scientific standpoint, but also in practical terms.

The conclusions derived from the study of this phenomenon bear on such
problems, seemingly unrelated to meteoritics, as the wind resistance of
trees in cold soils, improving timber harvests in northern areas, the
history of swamp formation, reserves of peat in Central Siberia, etc.
The results of this research represent not a random accumulation of
data, but merge organically into the integrated whole that is the
problem of the Tunguska meteorite.

The history of studies made at the Tunguska meteorite site is divided
into three basic stages which set the goals of the project and provided
for collection of the necessary factual material without which
theoretical consideration of the problem would have been unthinkable.
The first stage, begun by L. A. Kulik, called for the collection of
preliminary information, eyewitness accounts and data from observer
stations in order to pin point the area of impact and to describe the
physical phenomena that occurred outside the impact site. The second
stage, also linked with the name of Kulik, involved a thorough study of
a small area of ground in which a number of funnel-shaped depressions
had been discovered; these had erroneously been identified as meteorite
craters. The third stage was undertaken in 1938 with an
aerial-photographic survey of a considerable area of the terrain, but
essentially this stage did not develop fully until the author's 1958
expedition, which made an integrated study of the site and of all the
possible consequences of the fall.

The 1958 expedition [1] demonstrated the lack of justification for
classifying the Tunguska fall as a crater-forming type and established
that the center of the meteorite shock wave was located at some height
above the ground; in addition, the expedition provided the first general
map of the destruction that had been wrought, collected specimens of
extraterrestrial dust from the area of the fall, drew attention to
peculiarities of tree growth after the catastrophe and pointed to the
possibility of using biological indicators; finally, the expedition
pointed up the need for a careful study of the forest fire, etc.

As a result of the work accomplished in this stage, the earlier
theoretical concept of the fall was subjected to substantive review. A
program for further study of the Tunguska fall was proposed, accepted by
the Committee on Meteorites of the USSR Academy of Sciences, and
subsequently approved at the Ninth Conference on Meteorites. The
expedition set for1961 made provision for a further series of
investigations to determine details of the meteorite's effects and
called for an expanded search for fragments of meteoritic matter.

The great popular interest in the Tunguska meteorite that arose after
the 1958 expedition was to a considerable extent fostered by the
fantastic suggestion of a nuclear origin for the explosion, an idea
based on factual material of questionable competence. While I am aware
of the advantages of sensational publicity in drawing public attention
to a problem, it should be stressed that unhealthy interest aroused as a
result of distorted facts and misinformation should never be used as a
basis for the furtherance of scientific knowledge.

A number of independent groups left for the area of the Tunguska
meteorite fall in 1959 and 1960. Of these, the most serious was that of
G.F. Plekhanov, whose work in 1960 was partly financed by the Siberian
branch of the USSR Academy of Sciences, with support from the Committee
on Meteorites. Basically, the project followed a plan that had been
prepared in 1958; a substantial volume of factual material was
accumulated. At the same time, it would not be out of place to point out
that a number of projects carried out in 1959 and 1960 were based on
fantastic ideas, and this resulted in unproductive expenditures related
to the execution of the projects themselves, as well as in establishment
of the fact that they had no relation whatever to the problem of the
Tunguska meteorite.

In this connection, we should make particular mention of A.V. Zolotov's
group, which worked in this area in 1959 and 1960 and submitted hasty
and unfounded conclusions on the basis of extremely inadequate and
random data (see the resolution of the Ninth Conference on Meteorites.
/Meteoritika/, Volume XX, 1961).

Thus at the time when the 1961 expedition began its work, the situation
was basically as follows:

1. On the basis of visual observation the general contour of the
radially flattened forest area identified by Kulik was mapped out. Three
zones can be distinguished within the limits of this area: random
flattening (standing timber), mass flattening and partial flattening in
a specific direction; the general plotting of these zones was confirmed
in 1960. However, the boundaries of the zones (particularly to the
northeast) and the direction of flattening call for additional
refinement and quantitative characterization. There was no search for
isolated islands of fallen trees outside the area of general
destruction. Approximately 40 control plots, each 0.25 hectare in area,
were laid out to obtain quantitative characteristics of the destruction
[1, 2].

2. There are no traces of a powerful ground meteorite explosion in the
area; this is confirmed by a study of the south morass, where this fact
was established through a number of helological studies, profiling of
the bottom [3] and three magnetometric profiles [2]. The thermokarstic
funnels [4] are not directly related to the explosion of the meteorite
[l, 3, 5] and no magnetic anomalies were observed [2]. The possible
stimulation of thermokarst development as a result of the fall [4] calls
for additional helological research, as well as identification of the
1908 peat layer for purposes of a stratigraphic hunt for meteoritic matter.

3. The presence of live trees at the center of the catastrophe [1, 2, 4,
5] bears witness to the comparatively low level of any possible flash
burning, whose general nature, along with the causes of the forest fire
of 1908, requires additional study.

4. The large-scale map prepared from the results of the 1938 aerial
survey of the center of the catastrophe by the MIIGAIK [Moscow Institute
of Geodetic, Aerial Survey and Cartographic Engineers] on assignment
from the Committee on Meteorites requires considerable revision based on
field work. This map also confirms the existence of many stands of trees
that survived in the central section of the affected area.

5. The soil study made in 1958 [1, 6] shows that the magnetite and
silicate spheres first observed by L. A. Kulik and then by A. A. Yavnel'
occur in small concentrations in the impact area. At the moment they
represent the only possible fragments of the Tunguska meteorite and call
for further study.

Geochemical (metallometric) attempts to identify zones enriched with
meteoritic matter [l, 2] produced no clear results and are of doubtful
promise, unless the objects of the study are subjected to preliminary
concentration .

6. The features of accelerated tree growth established in 1958 [1] have
been confirmed by a great volume of data [7] and are peculiar to the
central region of the impact area. In view of the fact that the causes
of this phenomenon are not clear, work along this line should be
continued in order to seek out biological indicators characterizing
features of the 1908 fall.

7. On the basis of available data, it is at the present time held most
likely that the meteorite "exploded" in the air. By way of explanation
of this phenomenon a number of mechanisms have been proposed [8, 9, 10,
11, 12], but these cannot be regarded as reliable because of the
inadequacy of working data.

The most probable hypothesis is that which ascribes a cometary origin to
the meteorite [13, 14], whose structure was friable [1, 8, 15, 16].
Available data are inadequate to form a clear picture of the phenomenon.

/Organization of the project/. The expedition of 1961 was organized on
the initiative of the Committee on Meteorites on the basis of a decision
taken by the Ninth Conference on Meteorites and the 30 September 1960
Decree of the Presidium of the USSR Academy of Sciences [17]. In this
connection, we should give special mention to Doctor of Geological and
Mineralogical Sciences Ye.L. Krinov for his major organizational role as
Scientific Secretary of the Committee on Meteorites and his monumental
scientific contribution to the study of the Tunguska meteorite. The
entire problem received the untiring attention of Academician V.G.
Fesenkov, who directed the astronomical and physical investigations, and
Academician A.P. Vinogradov, who was in charge of the work associated
with the material composition of the meteorite.

The nucleus of the expedition was made up of members of the Committee on
Meteorites and the Vernadskiy Institute of Geochemistry and Analytic
Chemistry; however, individuals from other organizations also
participated (The Soil Institute, The Main Botanical Garden, Moscow
State University, etc.). The Helology Section of the Forestry and Lumber
Institute of the Siberian branch of the Academy of Sciences and the
Forestry Assessment Section of the All-Union Forest Aerial Photographic
Survey Association of the Main Administration of Forestry, USSR Ministry
of Agriculture ("Lesproyekt") demonstrated interest by participating
directly in the expedition. An outstanding feature of the expedition was
the enlistment of a large contingent organized with the support of the
Tomsk branch of the All-Union Geographic Society into the Combined
Autonomous Expedition, designated KSE, of whose work we spoke earlier.
This group joined the ranks of the 1961 expedition and worked under its
authority. G. F. Plekhanov, the elected leader of this group and both a
physician and an engineer, was put in charge of a section of the
expedition; the numerical strength of the entire group considerably
exceeded the original table for the expedition. In terms of
qualifications and conscientious attitude, the Combined Tunguska
Meteorite Expedition participants in the Combined Autonomous Expedition
were capable of carrying out independent assignments unrelated to the
responsibilities that they had assumed within the expedition.

We should stress that proper and well-organized scientific leadership of
such projects is of particularly great importance for the required
concentration of research on major problems.

The number of persons participating in the work of the meteorite
expedition reached a total of 80, of whom some did not stay out the
season. The program of the expedition called for extensive use of a
helicopter to deploy individual groups and to transport heavy specimens.
The actual unavailability of a helicopter, however, compelled the
members of the expedition to move on foot; this significantly reduced
both the total number and the size of the specimens collected. Some of
the equipment and supplies even had to be dropped by airplane to the
expedition base at Kulik's clearing.

Part of the expedition departed from Moscow on 10 June, arrived at
Vanavara on 16 June, and immediately began its work, gradually reaching
full strength with the arrival of other colleagues. The expedition's
works schedule was thrown off by the lack of the helicopter. There were
no communications with Vanavara. The greater part of the expedition
returned to Vanavara around the first of October, with the first
snowfall. During the next few days the Chamba and other slow-flowing
rivers began to freeze. The logistic-support group of the expedition
arrived in Moscow on 24 October, having successfully completed the
evacuation of all expedition equipment (I.N. Yeliseyev, Ye.I. Malinkin).

*I. STUDY OF THE EFFECTS OF THE METEORITE FALL *

*FOREST FLATTENING *

The flattening of the forest most accurately reflects the passage of the
destructive wave accompanying the fall of the 1908 meteorite and can
serve as a physical characteristic of the phenomenon.

*Fig. 1.* Dynamometric testing of tree resistance

A study of the devastated forest showed that the region of the forest
flattened in 1908 was not one of homogeneous primeval intact taiga, but
had had a complex history that must be taken into consideration in
interpreting the data. Thus fire expert N.P. Kurbatskiy (The Forestry
and Lumber Institute of the Siberian Branch of the Academy of Sciences)
draws the following conclusion: " ...the region of meteorite impact in
1908 was basically a fire-devastated area that had been subjected to a
treetop fire during the first half of the last century. A partly
flattened dead and rotting forest was standing in this area. New forest
growth had appeared among the dry and charred trees. By 1908, this
second growth was some 70 to 100 years old. The southern and
southeastern areas had apparently been subjected to fire somewhat
earlier in the past than the central basin. The dead-forest was first
flattened, and a fire then swept this territory. It is not out of the
question that the set two occurrences took place at the same time... The
fire did not destroy the trunks of living trees, but only scorched
conifer needles and small twigs. The forest destroyed by the fire of
1908 was not flattened at that time but has in large part remained
standing in the form of dead timber to the present time. The old stand
of dead and badly rotted timber left by the fire of the last century
could have been laid low during the fire itself and been scorched from
the bottom as a result of a ground fire... There is nothing out of the
ordinary in the suggestion that the larches were able to stand dead in
the area of the meteorite fall for a period of 70 years after the fire
of the previous century."

On the basis of the forestry-assessment records, V.G. Berezhnoy
(All-Union Lumbering Office of the USSR Ministry of Forestry -
"Lesoproyekt") draws the following preliminary conclusions: "...it has
been shown that at the time of the catastrophe the stand of trees in the
area had, to some extent, been weakened by the fire at the end of the
last century. For example, the great fire that produced the so-called
'western flattening' occurred in 1896. Larger diametral accretions are
found in the area over which this fire had passed. The northern and
eastern parts of this area (and quite possibly also the center) had been
subjected to a fire during the 1880's... There are stretches of
practically 'unburnable' forest within this area. These sections did not
burn during the fire." At the same time, it is obvious that an estimate
of the force of the shock wave that is based on the number of flattened
trees must necessarily take into consideration the condition of the
forest at that time. The wind resistance of a comparatively recent stand
of dead timber is greatly increased as a result of reduced area catching
the wind, particularly if the root system is still strong; later it
diminishes to zero as the trees and their roots decay. Dynamometry
studies of the flattening (wind resistance of the trees) in this area by
means of a winch and a dynamometer (Fig. 1) (K.A. Lyubarskiy, I.T.
Zotkin) yielded the following preliminary results (95 trees were
studied): "There is no relationship between the felling moment and the
species and age of the tree. There is a distinct relationship between
the moment and the tree diameter, analytically nicely described by a
parabola (Fig.2). These parabolas are completely identical for fine
(melkozem) and rocky soils. For moist riverside soil the parabola takes
a noticeably flatter course (the felling moments are significantly
smaller). The relative scatter diminishes in inverse proportion to the
diameter of the tree. It is not related to the azimuth of the felling or
to the direction of the slope (upward, downward, to the side). From the
standpoint of force there is no difference between snapping and
uprooting, i.e., both cases array themselves along the same parabola.
The parabolic relationship is retained for dead-timber logs, but the
parabola in this case is extremely flat, the felling moments are
minimal, and the scattering is therefore very wide" (the dead-timber
data pertain to timber killed in 1908, Table 1).

*TABLE 1*

*Average Felling Moments for Trees in the Area of the Tunguska
Catastrophe (Pines, Larches) (Preliminary Data)*

Area no. 	Nature of area 	

Tree diameter, cm

15 	20 	25 	30

Felling moment, ton-m

1 and 2

3

4

	Dry soil

Marshy soil

Brush dead 53 years

	1.1

0.7

0.4

	2.3

1.5

0.8

	3.7

2.8

1.3

	5.5

4.2

1.9

Unfortunately, we were unable to study the relationship between log
strength and age - a matter of unquestionable interest - because of the
difficulties which we encountered in determining the time at which this
stand of timber was killed off.

*Fig. 2.* Felling moment as a function of tree diameter.

1) Trees in fine and rocky soil; 2) dead-timber stand of 1908.

That there is no relationship between the strength of a tree and its
species would seem at first glance to be a rather bold conclusion: a
definite distinction is made in forestry between "wind-susceptible" and
"wind-resistant" species. Apparently this classification is not
applicable to regions of cold and frozen soils, where deep root systems
("tap roots") cannot develop and where the roots of virtually all
species develop in similar fashion, along the surface of the ground
("shield" or lateral root system), in virtual independence of the nature
of the soil, i.e., the slow thawing of the soils in the summer limits
the depth of root penetration.

The soil and soil-temperature variation studies conducted in the area by
soil scientist A.A. Yerokhina (Dokuchayev Soil Institute of the USSR
Academy of Sciences) demonstrated that there is virtually no permafrost
to a depth of 1.5 to 2 meters in the dry forest soils of this area, but
that the seasonal frost thaws out only toward the beginning of August.
The moist and marshy soils have permafrost base layers. The general
characteristics of the felling were studied in a number of ways.

*Fig. 3.* Distribution of flattened trees by direction in various sample
areas.

A histogram of this type, including about 100 trees, corresponds to each
of the arrows in Fig. 4.

To provide an over-all description of the flattening effect, we used a
graphic method (V.G. Fast and D.V. Demin) which involved taking the
azimuths of all of the fallen trunks in a sampling area containing
some100 flattened trees (generally 0.25 hectare) and plotting their
variation diagram (Fig. 3) with indication of the trunk thicknesses. The
numbers of dead-timber and old living trees were also noted. As a result
of the work carried out in 1960 (Plekhanov et al.) and 1961,
approximately 200 such areas were investigated to obtain a reliable
profile of the entire area of flattened forest. Both the mean direction
of the flattening, which reflects the direction of the wave front, as
well as the directional dispersion of the flattened trees, which is a
function of shock-wave force, can be used to describe the motion of the
wave. The evaluation yielded a somewhat exaggerated value, since areas
with the most clearly defined flattening were selected as controls and,
moreover, it was impossible to take into consideration the relationship
between the trees that had been felled live and those that were dead.

The total area of flattened forest covers approximately 2000 square
kilometers and generally coincides with the boundaries established by
the1958 expedition. However, it has now been established that the
flattening extended farther to the northeast, along the Sil'gami Range
to the summer trail leading to Strelka, a fact which had also been noted
in 1960. Thus the general contour of the felled forest takes the form of
a triangle, apex forward, symmetrical about the meteorite trajectory
determined by Krinov. It is characteristic that compilation of a large
volume of data shows no significant deviations from the radial in the
directions of the fallen trees. The arrows obtained by this method are
more or less uniformly distributed over the entire felled area (Fig. 4).

*Fig. 4.* Flattening of timber on the basis of 1961 data.

1) Sampling areas encompassing 100 trees; 2) directions based on
several trees; 3) 1960 routes; 4) stretches with limited or poorly
defined flattening; 5) stretches in which there was no flattening at
all; 6) positions of the forestry-assessment plots; 7) huts; 8)
boundaries of the 1908 fire where its natural propagation is seen
distinctly; 9) general boundary of flattening; 10) southeastward
variant of the meteorite trajectory, after Krinov.

*Figs. 5.* Present appearance of felled timber.

For purposes of evaluating the information from the control areas and in
order to establish a detailed picture of the forest destruction, special
forestry-assessment plots were surveyed and both the living and dead
tree son these areas described (Fig. 5). Over a number of years,
beginning with 1958, the methods employed for this part of the operation
were gradually improved and in 1961, in its final form, the work came
under the direction of V.I. Nekrasov (Main Botanical Garden of the USSR
Academy of Sciences), V.G. Berezhnoy and G.I. Drapkina (All-Union Forest
Aerial Photographic Survey Association of the Main Administration of
Forestry of the USSR Ministry of Agriculture). Some of the
forestry-assessment plots were staked out and partly described in 1960
(V.I. Nekrasov, Kolesnikov); they were distributed in the form of a
cross passing through the epicenter of the destruction to the boundaries
of the flattened forest (55 plots), with an additional 40 plots located
in the intervening quadrants. The relationship between the percentage of
fallen trees and their directional distribution can be established on
the basis of the control areas, which can also be used to describe the
general condition of the forest in 1908 and at the present time.

A special investigation was undertaken (Zotkinetal.) to detail the
felling in the center of the area covered by the chart prepared by the
Moscow Institute of Geodetic, Aerial Survey, and Cartographic Engineers.
This study involved the plotting of arrows indicating the direction of
the fallen trees at points not examined by aerial photography, and
surveys of special control areas to ascertain the effect of local relief
on the action of destructive wave. This results in rather convincing
evidence that there is a pronounced increase in directional flattening
on reverse slopes (with respect to the epicenter) near the epicenter-an
indication of an "explosion" at altitude.

As we have noted, the "zone of indifference," also known as the "chaotic
flattening" or "telegraph pole" zone, occupies an area somewhat smaller
than that indicated by the 1958 chart. This may indicate a somewhat
lower center of wave origin than had earlier been supposed (Fig. 6).

Thus the collected material on the flattening of the timber permits us
to draw the following conclusions:

1. The total area of flattened forest is in rather good agreement with
the map prepared in 1958. An exception is the extension of the flattened
area to the northeast, as can be seen from the map showing the
propagation of new forest.

2. The collected material is quite complete and there would be little
gained from further field refinements prior to complete evaluation of
the data obtained.

3. Nowhere in the directional studies of the fallen trees were any
significant deviations from radial flattening noted.

4. By 1908 the forest consisted to a considerable degree of standing
dead timber, and computation of both the over-all force of the shock
wave and its isobars must be accomplished with consideration of this
factor. Areas of forest that had not burned by 1908 survived to a
significant extent and were not flattened.

5. The influence of local relief on timber flattening in the vicinity of
the epicenter is of a nature such as to confirm that the explosion took
place at some height.

6. The slightly smaller central zone of random dead-stand flattening as
compared with the 1958 data speaks against an excessively high explosion
center.

7. The data collected must be subjected to careful evaluation.

*THE FOREST FIRE OF 1908 AND FLASH BURNING OF THE TREES *

As had been pointed out in 1958, a forest fire originated at the point
of meteorite impact and spread in the usual manner. Thus the boundaries
of the fire do not coincide with the boundaries of a possible flash
fire, as Zolotov sought to prove (1959). [* A report on the work of A.V.
Zolotov during his 1959 expedition.] While no one has dismissed the
possibility of a flash fire, it has not been definitely established
either. The 1961 investigations of the injuries inflicted on live trees
in the vicinity of the epicenter (Zenkin et al.) revealed a large number
of still surviving trees and the fact that the injuries to these trees
were oriented in nature.

*Fig. 6.* Schematic map show in a distribution of flattening, dead
timber and live trees at the epicenter.

1) Flattened trees; 2) dead timber; 3) surviving trees; 4) expedition
shelters.

N.P. Kurbatskiy, a member of the 1961 expedition, describes the features
of the fire in this area as follows: "...distinct signs of the spreading
of the 1908 treetop fire were found in the form of arcuate strips and
surviving older forest to the north of the Kimchu River, at a distance
of 1 to 2 km from the bank, in the stretch from Lake Cheko to the
extensive marshes on the left side of the river. In this area the fire
spread from south to north. Indications of the fire's spread were found
on heights to the north of Lake Cheko, as well as on the western slopes
of hills 373.6, 491.0 and 476.0. From here the boundary of the fire area
can be traced easily along an arc from the mouth of the Chavidokon River
to Mount Shakharma. The surviving traces of the fire-line advance
indicate that it spread toward the west and southwest, i.e., as if from
a central depression. The treetop fire here gradually changed into a
ground fire, with some damage to the old forest. On the northeastern
slopes of the heights where the headwaters of the Churgim River rise
there are arcuate strips of old forest, convex toward the south. We find
identical signs of the spreading fire on Mount Shakharma, but facing
east... The old forest remained intact only in narrow strips along the
banks of rivers with highly developed valleys and in the form of
solitary trees in the midst of swamps and rock streams."

"The rounded shape of the fire site and the complete destruction by fire
of the old forest over an extremely great area are outstanding features
of the area; it differs in these respects from ordinary forest burnouts
after the passage of treetop fires in the presence of a strong wind...
Of the surviving areas of primeval taiga, we inspected only two, 2 to 5
hectares in area, situated on the flat saddle slopes of the northwestern
heights surrounding the central depression... During the course of this
inspection on 28 June 1961, the sixth day after a heavy rainfall, the
ground vegetation in these areas was extremely wet and would not burn,
although flammable material on the ground ignited easily throughout the
rest of the impact area. It is obvious that these areas differ from the
remaining territory in having an elevated resistance to fire. In the
past (apparently, in 1908) a ground fire penetrated these sections from
the fringe growth of that time, but did not spread through them."

"The 1908 fire flared up at several points: in the central basin, on the
territory adjacent to the Khushmo River between the Churgim and
Ukagitrivers, as well as on the northeastern slopes of the Khladnyy
Range. The fire was preceded by a dry spell, which was responsible for
the widespread and uniform burning of the forest and the spreading of
the fire to the marshes. Such a set of circumstances is possible for
this area in the month of June, but not altogether usual. The 1908 fire
spread rapidly through the treetops of the meteorite area, before a wind
moving at a speed of 6 to 10 m/sec. At this velocity, the wind was a
local phenomenon and a result of powerful rising currents of combustion
products and heated air. The fire lasted for at least five days. During
this time the direction and velocity of the wind varied with the diurnal
variations in temperature and with changes in the intensity of the fire
front as it enveloped various elements of the terrain relief. The fire
died out during the first ten days of the month of July in 1908 as a
result of unfavorable weather conditions. The trunks of live trees did
not burn during the fire; only needles and small twigs were scorched."

As we are well aware, forest fires generally start on ignition of floor
litter, which is the most highly combustible material. To determine the
fire hazard in this area and the quantity of heat required to start a
fire, a series of experiments were carried out to ascertain the moisture
content of the various types of ground litter as a function of the
length of a dry spell (N.P. Kurbatskiy, T.M. Sleta). Evaluation of these
data by the Forest Fire Prevention Laboratory at the Forestry and Lumber
Institute of the Siberian Branch of the Academy of Sciences should make
it possible to establish a numerical scale for the minimum quantity of
radiant energy required to start the 1908 fire.

The maximum quantity of energy can be found on the basis of the fact
that various species of trees (larches, pines, and cedars) survived in
the area of the epicenter, in some cases even retaining live branches.

*Fig. 7.* Physiological scorching of larch twig near epicenter by
light. The oriented cambium injury of 1908 can be seen; the twig at
that time was no more than 8 mm thick. The injury was subsequently
completely invested.

Studies of live branches (older than 53 years) on trees growing in open
areas were undertaken to seek out evidence of a flash fire, to evaluate
its intensity and direction (G.M. Zenkin, A.G. Il'in, L.F. Shikalov et
al.); in part, this is a continuation of work started in 1960 (Plekhanov
et al.).

It was established in these investigations that branches (primarily of
larches) which in 1908 did not exceed 8 to 15 mm in thickness often show
traces of injuries that date from 1908, and have subsequently been
invested by bark (Fig. 7). The damage is noticeable on the upper
portions of the branches, thus making it impossible to associate these
injuries with ordinary fires. Moreover, they are oriented toward the
supposed center of the meteorite explosion. The severity of these
injuries diminishes significantly with increasing distance from the
epicenter. The damage indicates a fungus disease that affected the
injured parts of the cambium. We thus have a serious basis for assuming
that these injuries are a result of physiological scorching of cambium
cells during the fall of the meteorite.

Statistical reduction of the collected material will assist us in
establishing the factors responsible for the appearance of these
injuries, and, if they are associated with a flashfire, will be helpful
in determining its intensity and direction. The latter is of interest
from the standpoint of determining the spatial position of the meteorite
at the instant of maximum brightness. [* G.M. Zenkin places the emission
center at 1.5 km to the southeast of the epicenter of destruction, at a
height of about 5 km.]

*TABLE 2*

*Injury Distribution (Flash Fire?) at Various Distances from Epicenter**

Direction

Distance from epicenter, km

3

4

5

6

7

8

9

North ??????.

East ??????.

South ??????.

West ??????.

-

-

+ (1)

+ (1)

+ (2)

+ (2)

+ (1)

-

-

-

+ (2)

-

-

+ (2)

-

+ (1)

-

-

+ (1)

-

-

- (1)

-

-

- (3)

-

-

- (1)

The + sign indicates injury observed; the - sign indicates no injury
observed; (3) represents the number of trees inspected.

The distribution of the above injuries as a function of distance from
the epicenter, after the data of Zenkin and Il'in, is presented in Table 2.

Shikalov and Ivanova submit data indicating that analogous instances of
injury were observed in less pronounced form at distances up to 9 km to
the north and west of the epicenter, and as far as 10 km to the south.
Extremely rough and approximate calculations of the energy required to
produce physiological scorching and local mortification of the cambium
on a branch approximately 1 cm thick yield a value of 5 to 15 calories
per square centimeter. The illumination value cannot be significantly
higher (more than double this figure), since this would lead to marked
charring of the bark, and no such phenomenon was observed. Approximately
the same energy is required to ignite dry forest debris, and this could
lead to a forest fire.

According to a preliminary evaluation, this result for the energy of the
light pulse (at a distance of up to 9 km from the epicenter) is smaller
by approximately half an order than the result obtained by Zolotov.

For purposes of comparison we cite certain data (Table 3) on flash burns
suffered in atomic explosions (see "The Effects of Nuclear Weapons,"
[Deystviya yadernogo oruzhiya], translated from the English, Voyengiz,1960)

*TABLE 3*

*Luminous Irradiation Resulting in Injury, for Two Explosion Forces*

Effect

	Energy of irradiation by light, cal/cm2 for TNT equivalent of

20 kilotons

10 megatons

*Burns, human skin:*

First degree

Second degree

Third degree

*Charring of fir, pine and maple bark*

*Kindling:*

Dry rotten wood

Fine grasses

Fallen leaves

White-pine needles

-

2

5

7

10

-

4

5

6

6

-

3.5

7

11

15

-

9

10

12

14

*STUDY OF THE EFFECT OF THE METEORITE ON THE SWAMPS *

The observations of the 1958 expedition indicated that there was no
meteor crater in the south morass and that there was no relationship
between the formation of the thermokarstic funnels and the fall of the
meteorite; however, these observations were not sufficiently reliable.
Yu.A. L'vov, Kovalevskiy et al. undertook a rather detailed inspection
of the swamps in 1960. They established that "all of the structural
features of the basin's marshes are readily explained by terrestrial
factors. No interbedding of peat and soil in the south morass was
observed, Kulik's data not withstanding... The fall (B.I. Vronskiy) of
small meteoritic fragments cannot be used to explain the thermokarsts
<thermo.html>...a four-to-six-centimeter peat layer in which the 1908
stratum was deposited is easily identified... Even in the event of
negative results, the search for meteoritic matter in the peat must be
repeated" (taken from a letter by L'vov to Florenskiy, dated 28 December
1960).

The section of the helology team from the Forestry and Lumber Institute
of the Siberian Branch of the Academy of Sciences, headed by Doctor of
Biological Sciences N.I. P'yavchenko, worked from 22 June through 6 July
1961, while the main unit of the helological section headed by S.P.
Yefremov remained on the job to study the surrounding marshes throughout
the entire summer.

*Fig. 8.* A view of the south morass.

I cannot dwell here on a discussion of the extensive work program
undertaken by this unit, even though it is of considerable interest to
the helologist. N.I. P'yavchenko formulates his replies to questions
concerning study of the Tunguska fall in the following manner.

"Differentiation of the south and north morass surfaces into hillocks
and 'mochazhina' [land permanently wet from outflow of underground
water] is a result of thermokarstic processes and, possibly, a result of
phenomena related to ancient water erosion... The formation of funnels
in the swamps is not associated with the fall of the meteorite or
fragments of it. No embankments of ejected peat have been built up
around the funnels, the peat layer is not intermixed with the soil and
it is of rather along the line of contact with the peat hillocks are
steep and frozen... Numerous core samples of the peat deposit uniform
depth throughout the entire area of the funnel, the mineral base is
flat, and the walls in the south and north morasses fail to reveal any
mixing of the peat with the 'ooze' or subsoil. The peat deposit
exhibited rather clearly oriented stratification throughout... The
'embankments' on the surface of the south morass, which extend, with
slight separation from one another, in the direction perpendicular to
the runoff, are ordinary ridges 20 to 30 centimeters in height covered
with dwarf arctic birch, bog underbrush, hypnum and sphagnum, and quite
often with woody vegetation (Fig. 8). These ridges are formed in wet
marshes because of surface cracking due to frost and raising of the peat
around the edges of the cracks, which improves the drainage of the area
adjacent to the crack, thus favoring the growth of vegetation requiring
less moisture... Traces of fire stand out clearly in the peat deposits
of the hummock areas in the north and south morasses. In the majority of
cases two fire levels stand out clearly: an upper level approximately 20
and in spots 30 years old; a lower level, about 50 years old... The
lower level is quite thick, ranging from 3 to 5 cm, and occasionally
more. This level contains much charcoal, ashes and plant residue... All
of the old trees that survived on the peat hillocks show searing only on
the lower parts of their trunks, which indicates that the fire moved
along the ground; this is natural in view of the high degree of thinning
of woody growth in peat bogs... No regular intensification in the growth
of trees, dwarf arctic birches, bog underbrush, and mosses in the
marshes after 1908 was observed. Among the old larches, the increment
during the past 2 to 3 decades has been insignificant. Young larches and
pines appearing on the peat hummocks after 1908 are characterized by
growth satisfactory for frozen peat bogs and rather uniform height and
diameter increments. In addition, severely stunted trees are
encountered. These differences are associated with the ecological
conditions of vegetation growth... The increment in sphagnum in the
permanently wet ground and thermokarsts amounts to 2.4-2.5 cm annually,
which is quite normal for this zone. Under extremely dry conditions
/Sphagnum fuscum/ increases at a rate of about 1 cm per year on the peat
hummocks."

There were no clearly defined changes in the hydrological regime of the
marshes that were associated with the events of 1908. The gradual
aggrandizement of the morass at its boundaries and the partial
submergence of dead growth is typical of many of the marshy areas of
this region, bearing absolutely no relation to the fall of the
meteorite. The age of the south morass runs to many thousands of years,
and determination of the absolute age at which swamp formation began is
a matter of considerable interest, since it represents information
totally unknown with respect to the marshes of Central Siberia. This
determination can be accomplished by using the radiocarbon method on
specimens of wood raised from the very bottom of the south morass.

Thus as a result of detailed helological investigations in 1960 and 1961
we may regard as quite reliable the conclusion that there is no
relationship between the fall of the meteorite in 1908 and the manner in
which the south and north morasses were formed.

*THE BIOLOGICAL EFFECT OF THE FALL** *

The 1958 expedition drew attention to the pronounced change in the rate
of growth of a number of trees subsequent to 1908, and pointed up the
possibility of using "biological indicators to ascertain features dating
from 1908, as well as general changes in conditions brought about by the
fall of the meteorite." Yemel'yanov and Nekrasov showed in their
subsequent work that accelerated growth is characteristic of a wide
region around the center of the meteorite fall. A number of biological
indicators suggested the probability that this phenomenon was in some
manner associated with meteoritic matter and should be studied. In 1960,
together with a number of other colleagues, they began laying out the
forestry-assessment plots which made it possible to bring to light the
unusual nature of this phenomenon.

A group of biologists joined the 1961 expedition of the Committee on
Meteorites to establish the boundaries and causes of the accelerated
growth of forest in this area. Because the problem of accelerated forest
growth and increased timber harvests in the areas of the north is of
prime practical importance, the All-Union Forest Aerial Photographic
Survey Association of the Main Administration of Forestry of the USSR
Ministry of Agriculture participated in the project by dispatching a
forestry-assessment section to work together with the expedition. This
work was performed by Candidate of Biological Sciences Nekrasov, a
forestry specialist; by Berezhnoy, Drapkina, and a number of others. A
number of important details incidental to this work were brought to
light in connection with the nature of the meteorite-connected injuries
sustained by the forest. As a result of the work carried out in 1960 and
1961, a total of 95 forestry-assessment areas were laid out, and all of
the biological aspects of the phenomenon were studied here.

The change in the rate of forest growth can be associated either with a
change from the normal ecological conditions of growth due to the
tremendous forest fire and flattening of the forest which took place in
1908, or with the action of stimulants that appeared in the soil on
disintegration of an extraterrestrial body of unknown composition.

Although literature sources indicate that the aftereffects of ordinary
forest fires and forest uprooting with which we are familiar from
European silviculture should not last longer than 15 to 20 years, they
persist, occasionally without noticeable abatement, for a period of 40
to 50 years, in the area of the meteorite fall. Nekrasov has expressed
doubt as to the possibility of explaining this phenomenon in terms of
purely ecological factors (more sunlight as a result of thinning, the
effect of ash fertilizers, a change in the heat and moisture regime of
the soil, soil aeration, etc.).

The study of the soil heat regime which was conducted by Soil Scientist
A.A. Yerokhina to shed light on the influence exerted by frost phenomena
demonstrated that there was no evidence of permafrost in the dry forest
soils to a depth of at least 1.5 to 2.0 meters, and that it is difficult
to detect any change in the thermal regime of the soils with the methods
available to the soil scientist.

To supplement the silvicultural work, the growth rates of oats in the
soils of various sections of the region were determined (A.B. Osharov, a
plant physiologistat Tomsk State University); soil microflora were
identified (N. V. Vasil'yev, a microbiologist from the Tomsk Medical
Institute), and a study of the root systems of trees and their changes
subsequent to 1908 was carried out (Osharov). The possibility of
detecting a change in the thermal regime of the soil and the related
possible deeper penetration of the root systems after 1908 prompted this
last project. Particular attention was devoted to the growth pattern of
bog vegetation communities during the helological studies.

The office evaluation of the secured data, which should supply the
answers to these questions, has not been completed, and thus the
expedition has not as yet formed any final conclusion regarding the
results of the project. However, we can make the following preliminary
comments.

1. Where we have a similar combination of fire and forest flattening due
to ordinary causes outside the environs of the epicenter of meteorite
impact ("the western flattening" of 1896, the fire in the vicinity of
the Chamba in 1937), an equally persistent acceleration of forest growth
is encountered.

2. There is no indication whatever of any change in the growth rate of
bog communities beyond the moss layer which grew directly on the
mineral-rich 1908 layer over which the fire had passed.

3. Although acceleration of forest growth after 1908 was observed in
areas bearing no traces of the fire or flattening of the forest, these
areas are situated in the immediate vicinity of extensively destroyed
areas and are spatially limited, and thus subject to the over-all regime
of a much wider region.

4. No clear differences corresponding to boundaries of accelerated
forest growth were ascertained as a result of cultivation of oats in
various soil areas of the region in which the meteorite fell.

5. The boundaries of accelerated forest growth follow the boundaries of
the fire and flattening of the forest quite closely, but they do not
correspond to the distribution of meteoritic matter as obtained by other
methods.

All of the above compels us to express grave doubt as to the possible
participation of meteoritic matter (in one form or another) in the
stimulation of tree growth in this region, and suggests that the
prolonged aftereffects are associated with features of the ecological
conditions of forest growth in this zone of Central Siberia. Forestry
experts Berezhnoy and Drapkina (All-Union Forest Aerial Photographic
Survey Association of the Main Administration of Forestry of the USSR
Ministry of Agriculture) came to the same conclusion. This has no
bearing on the possible practical application of the features studied to
the promotion of silviculture in the northern regions of Siberia.

*II THE SEARCH FOR METEORITIC MATTER *

Various dispersion states must have been present during the flight and
disintegration of the Tunguska meteoric body in the atmosphere,
differing in the nature of their scattering over the surface of the
earth in accordance with time of formation and degree of dispersion. At
the very least, we may assume the presence of the following forms to
have been probable.

1. The dust-and-gas tail of a comet, torn away in the uppermost layers
of the atmosphere and dispersing over the entire surface of the earth to
produce bright nights.

2. The dissipation of ionized gas in the atmosphere along the flight
path of the meteorite, without any settling of meteoritic matter.

3. Liquid and vapor condensation products swept from the heated
substance of the meteorite to form its train. Coarse fractions of the
train may have reached the surface of the earth in the form of molten
droplets that froze into meteoritic spheres, settling along a more or
less clearly defined strip, the finer droplets scattering uniformly or
settling out over a great distance.

4. The "explosion" products of the meteorite. Their state depends
primarily on the composition of the meteoroid. Volatile cometary
components dissipate without leaving a trace; the remaining components
form local conglomerations depending on the nature of the explosion and
the degree of dispersion. Individual large meteoritic fragments may
reach the surface of the earth along the line of the meteorite's flight
path, beneath its train, or at a point beyond the epicenter of the
"explosion." There cannot be many such fragments, and in the absence of
precise data on the trajectory of the meteorite the discovery of such
fragments 50 years after the fall is a matter of pure chance. Fine
meteoritic dust in solid form is scattered and it is difficult to
distinguish it from ground formations unless it is composed of pure
unoxidized iron. The atomized fused meteoritic material should have
frozen into spheroidal particles that could be carried for great
distances by the wind to form local accumulations. The gaseous products
and their derivatives do not form distinct local accretions and any
search for these would be virtually hopeless. The deposits of these
various product types need not in principle coincide with one another.

Of all of the enumerated forms of meteoritic matter, the 1958 expedition
(Florenskiy et al.) identified only magnetite and silicate spheres, and
these in negligible concentrations. Additional specimens were collected
by B.I. Vronskiy in 1959 and 1960. All attempts (magnetometry,
metallometry, radiometry) to ascertain the presence of cosmic matter in
some other form (1958, 1959, 1960) remained entirely without result. At
the same time, however, the limited concentration of such particles
precluded definite classification as fragments of the Tunguska
meteorite, since they are indistinguishable from the ubiquitous meteoric
dust.

The question of meteoric (cosmic) dust is important and repeatedly
raised in the literature. However, it had not been the subject of an
adequately serious study until recently, and quantitative estimates of
meteoric dust varied over a very wide range: the estimates of various
authors sometimes differed by many orders of magnitude. The properties
of this dust are generally studied by astronomical methods, with only
the magnetic component being determined from ground deposits.

Thus the problem of studying the material composition of the Tunguska
meteorite is inseparably interwoven with the general study of meteoric
dust, and part and parcel thereof.

*Fig. 9.* A concentration installation at the Khushmo River.

Attempts to isolate material from the Tunguska meteorite were carried
out in the following manner.

1. Isolation of dust from the surfaces of tall stumps ("telegraph
poles") snapped by the 1908 explosion (Yu M. Yemel'yanov). The method
called for removal of the trunk surface, grinding it up, and boiling it
to a pulp in water. Large wood particles were removed from the resulting
mass by filtration, and the minute fractions were collected. This
concentrate was dried for subsequent separation in gravity solution. The
extremely laborious operation of collecting enough dust that had settled
in the cracks of the trunk surfaces failed to produce any large number
of specimens of adequate size. The upshot was a single specimen,
collected from a surface of approximately one square meter in the
vicinity of the Churgim falls, 3 km to the south of the "explosion"
epicenter. Preliminary study of some of the material showed a clear
preponderance of terrestrial quartz dust in the presence of minute
particles possibly associated with wood residues.

The specimen is of interest since it provides a characteristic of the
average dust fall in this region over a period of 53 years, including
possible residues of the Tunguska meteorite and other meteor particles.

2. Identification of strata in peat-bog and lake deposits. The
identification of the1908 peat layer was accomplished in two ways: a) in
the north morass and in the vicinity of Khoy Brook, about 20 square
meters of a scorched layer containing a large quantity of ash associated
with the 1908 fire was identified; the ash, together with the peat
residue, was concentrated by the customary method for soil samples; b)
successive layers of peat from the west morass in the bend of the
Khushmo River (which had not burned) were identified and set afire for
subsequent analysis of ash composition.

Silt specimens from Lake Chekoand the lake in the bend of the River in
the west morass were collected for subsequent stratigraphic study (P.N.
Paley et al.) with a grab dredge and a swamp drill designed by N.I.
P'yavchenko.

The various samplings from the bottom of Lake Cheko (P'yavchenko,
Kozlovskaya) revealed extensive development of silt up to 7 meters deep,
indicating an ancient origin for the lake (tentatively estimated at 5000
to 10,000 years), thus completely contradicting the hypothesis of the
formation of the lake as a result of the Tunguska meteorite fall (V.
Koshelev, 1960).

3. The search for meteoritic matter in the soils. The observations made
by Soil Scientist Yerokhina confirmed the validity of the soil sampling
method which we used in 1958; it was possible with this method to remove
a layer 2 to 3 cm thick, including the lower section of the litter and
the upper layer (1.5 cm) of the subsoil. With this sampling method, the
weight taken from an area of one square meter usually ranges up to 10 kg.

*Fig. 10.* Spheres of cosmic origin found in the area of the Tunguska
meteorite fall.

The average weight of a sampling collected by the two-man teams on foot
amounted approximately to 20 kg from a sampling area of two square
meters. Wherever possible, the samples were taken from unflooded dry
level areas without heavy vegetation cover. The collected specimens were
sent to the concentration section (Kozlov, Vronskiy, Malinkin,
Gorbunova), where the concentration was accomplished on a vibration
table (Fig. 9) and the heavy fraction consisting of particles smaller
than 0.25 mm was separated; the specimens were subsequently subjected to
magnetic separation and then they underwent preliminary inspection
through a binocular magnifier (N.I. Zaslavskaya, G.M. Ivanova, N.P
Rodionova). The silicate portion was not studied in the field, and the
concentrated specimens were brought back to Moscow for further
evaluation. We worked on the assumption that the earlier samples (1958),
which had been more crudely concentrated, contained both magnetic
(magnetite) and silicate spheres (Fig. 10).With the old concentration
method, in which a significant portion of the silicate spheres were
lost, these spheres were found to be present in proportions of 3:1. It
is not out of the question that the samples include polyhedral particles
of cosmic origin; however, a method has yet to be developed for their
identification. Under field conditions it is precisely the magnetic
spheres that most readily lend themselves to concentration and
identification. If we assume that the number of these spheres bears some
relation to the total number of cosmic particles, they represent the
most convenient indices to the presence of meteoritic matter. Based on
these spherical particles, preliminary field analysis of their
composition becomes possible, as does a purposive search for the
scattering ellipse of the meteorite on the basis of even a slight
increase in the concentration of meteoritic matter.

All of the previous samples that were collected in the vicinity of the
epicenter (as well as the 1961 samples) exhibited an altogether
negligible concentration of spheres. Since the average number of such
particles had not been established for the soils, they can easily be
attributed to the back ground concentration of meteoritic dust of this
type. At the same time, the general pattern of the physical process
involved in the scattering of these particles appears completely clear
to us. We have already mentioned the dissipation of the meteorite train.
In addition, the scattering of the meteoritic matter is governed by the
explosive disintegration of the meteorite, accompanied by the liberation
of a large quantity of thermal energy. This inevitably led to the
formation of a powerful ascending current of hot air the analog of the
radioactive cloud that rises from a nuclear explosion. Unlike the
nuclear explosion of the pure air-burst type, which is virtually free of
any dust particles ,the cloud resulting from the Tunguska explosion may
have contained a significant quantity of dust and liquid particles,
although it was on a considerably lower energy level. From this
standpoint, it would more nearly resemble the cloud which results from
an atomic explosion at or very near the ground, which draws up a
substantial quantity of dust particles.

Without insisting on absolute consistency between the explosions, which
involve markedly different levels of energy, we are nevertheless obliged
to seek an analogy to the Tunguska fall in nuclear explosions, since
they most nearly approximate the fall in terms of force. The base of the
mushroom cap of an atomic cloud rises to a height of 8 to 16 km, while
the height to which the top of the cloud rises is a function of the
force of the explosion and ranges between 20 and 40 km. The cloud
produced by the eruption of Mount Bezymyannyy on Kamchatka in 1956
reached a height of 36 km. The dust particles picked up by the thermal
currents settle out at a comparatively slow rate and may be scattered
far and wide by the wind. Following Stokes' law, the fall velocity of
particles ranging in size from 5 to 300 microns is given as /v/ =
0.11/d/^2 /p/ m/hr in air, where /p/ is the particle density in grams
per cubic centimeter and /d/ is the particle diameter in microns.

*Fig. 11.* Map showing the distribution of phenomena accompanying the
Tunguska meteorite fall. The circles are drawn at 20-km intervals.

1) Approximate boundary of area with trees subject to physiological
light scorching- 2) boundaries of felled-timber area and directions
of fall- 3) sites of samplings rich (x > 8) in magnetite spheres.
The areas of the small circles are proportional to the
concentrations of particles; 4) samplings with few magnetite
spheres; 5) hypothetical scattering ellipse of the meteorite.

Quartz particles descend from a height of 24,000 meters at the following
fall velocities:

Particle diameter, microns . .250 150 75 33

Fall time, hours . . . . . . .1.4 3.9 16 80

Thus, on the basis of particles 150 microns in diameter, which
correspond to the largest sizes found earlier, and assuming that these
particles had risen to a height of 12km, the time for their descent
would be 2 hours.

*TABLE 4*

Mean Concentration of Magnetite Spheres as a Function of Distance
from the Center of the Explosion of the Tunguska Meteorite
(Preliminary Data, with the Concentration Given for an Arbitrary
Unit of Area)

Distance from epicenter, km 	

Average content

Number of particles

Average of samples

0-10

1.5

6

20-30

4

16

40

8

11

60-80

21

6

*TABLE 5*

Mean Concentration of Magnetite Spheres for the Southern and
Northern Halves of the Investigated Area as a Function of Distance
from the Epicenter

Distance from epicenter, km 	

Southern part

Northern part

Number of particles

Average of samples

Number of particles

Average of samples

20-30

40

60-80

5

3

10

8

6

2

2.5

15

26

8

5

4

Following accepted practice, assuming the average wind velocity to be 24
km/hr, we find that particles will be carried 50 km from the center of
the explosion before settling to earth.

*TABLE 6*

Mean Concentration of Magnetite Spheres of Cosmic Origin as a
Function of Distance from the Epicenter for Averaging over Quadrants
(Preliminary Data Concentrations given for an Arbitrary Unit of Area)

Distance from epicenter, km

Northwest

Southeast

Northeast

Southwest

Number of particles

Average of samples

Number of particles

Average of samples

Number of particles

Average of samples

Number of particles

Average of samples

20-30

40

60-80

1

14

33

4

3

3

7

3

10

5

4

2

4

17

5

4

2

1

2

3

_

3

2

_

*Fig. 12.* Concentration of magnetite spheres in the soil as a
function of distance from the epicenter: a) Averaging over quadrants
from the southeast to the northwest; b) averaging over quadrants
from the southwest to the northeast; c) averaging over all
samplings, without consideration of direction.

In response to an inquiry from the Committee on Meteorites, the Central
Weather Forecasting Institute provided the following description of the
day on which the Tunguska meteorite fell (from a letter dated 11 May
1961, Ref. No. K-573): "On the basis of data available to the Institute,
on 30 June 1908 the site of the meteorite fall was under the influence
of a zero-gradient pressure field, with weak southeasterly winds at 2 to
5 meters per second."

*Fig. 13.* Recurrence of samples with a specific number of magnetite
spheres.

The synoptic situation provides a basis for the contention that there
were no strong air currents at heights of 3 to 4 km. The air currents
were moving from the southeast and south to the northwest and north. The
velocity of the wind ranged approximately between 30 and 40 km/hr. The
direction of the air currents remained constant from the site of the
meteorite fall to 65-70^ø North Latitude. The air currents then
deflected eastward, becoming almost westerly, assuming a northwesterly
direction over the basin of the Lena River and the Far East."

In view of the rather indeterminate nature of the hypothetical initial
data (and in view of completely contradictory data based on a synoptic
analysis of the same situation, as obtained through G.F. Plekhanov from
Tomsk) it was decided to break the sampling network up into circles with
a distance of 20 km separating them and with the sampling areas in
checkerboard array (Fig. 11).

Had there been a helicopter at our disposal, we would have been able to
complete the entire program of work and to obtain background
concentrations as well as the increase in these concentrations at the
hypothetical scattering ellipse, of which various versions have been
computed. For reasons beyond our control, the entire sampling operation
had to be carried out on foot, with the consequence that the results
lacked the necessary statistical buttressing and we were able only to
discern the probable direction of the scattering ellipse, without any
opportunity of describing the contours of the area.

Figure 11 shows the actual sites at which the soil samples were taken.
The areas of the stippled circles are proportional to the concentrations
of magnetite spheres per arbitrary area unit (Table 4). If we average
all of the data over the various distances from the epicenter, we obtain
in complete agreement with theory the distribution shown in Table 5,
which clearly characterizes the comparative sparsity of particles in the
central section and their concentration at the periphery (see also Fig.
12c).

This qualitative relationship fully explains the unsuccessful attempts
on the part of previous expeditions to detect a noticeable concentration
of meteoritic matter at the epicenter.

A comparison of the northern and southern halves of the investigated
area clearly shows the difference in the nature of particle distribution.

The clearest results are given by averaging over quadrants (Fig. 12a, b).

As many as 90 magnetite spheres were found per unit area in the richest
specimen - indeed, the only one - taken on the unflooded bank of the
Chunya River (10 km above the mouth of the Kimchu River, 80 km north
northwest of the epicenter).

It is our opinion that the above relationship is not accidental,
although it may be of inadequate statistical certainty. The meteorite's
flight path from the southeast in the presence of a south-southeast wind
might serve as an explanation, and it would also clarify the slight
drift of matter from the meteorite train to the northeastern quadrant
(Table 6), with the main mass of the explosion products falling farther
to the north and northwest. The scarcity of meteoritic matter in the
southwestern quadrant is characteristic.

The indicated distribution pattern for meteoritic matter corresponds to
the meteorite trajectory projected by Krinov and to the synoptic
conditions of 30 June 1908 as per the data provided by the Central
Weather Forecasting Institute.

Zotkin accomplished the preliminary statistical evaluation of these
materials. The histogram (Fig. 13) shows the distribution of 36 samples
(/n/) as a function of the number (/x/) of spheres contained in the
sample. If the fractional values of /x/ are combined with the next-lower
whole numbers for greater clarity, we obtain the following distribution
of /n/ with respect to /x/ from the 28 poor samples (7 spheres or fewer):

Number of spheres, /x/ 	0 	1 	2 	3 	4 	5 	6 	7
Number of samples, /n/ 	4 	13 	5 	3 	0 	2 	0 	1
Frequency, /w/ 	0.14 	0.46 	0.18 	0.11 	0.00 	0.07 	0.00 	0.04
Probability, /p/ 	0.17 	0.31 	0.27 	0.15 	0.07 	0.02 	0.01 	0.00
Number of samples expected from formula. /n/_/s/ 	4.9 	8.5 	7.4 	4.3
1.9 	0.7 	0.2 	0.05

It may be concluded that the poor samples pertain to the background. In
this case, the fluctuations in the number of spheres in the sample must
be subject to the Poisson distribution:

/p(x)/ = /_a(x)_/ /e/^/-a/
^^^^^/......../ ^^^^^/x!/

where /a/ is the average number (mathematical expectation) of spheres in
the sample and /p(x)/ is the probability of /x/ spheres being present in
the sample. The Poisson distribution gives the probability that a given
number of events will occur in a given interval, provided that they are
randomly distributed in the area being studied. The number of meteors
noted during the course of a specific interval of time, for example,
satisfies the distribution almost exactly. In our case we can assume
that the cosmic spheres falling to the earth over an extended period of
time will, in general, be uniformly and randomly distributed over its
entire territory.

From the preceding conclusion we find that the average /a/ = 1.7 and
that the dispersion /d/^2 = 2.6. For this volume of statistical data /a
= d/^2 is a satisfactory test. This derivation uses probabilities /p/
calculated from the Poisson distribution, and the theoretical number
/n/_/s/ of samples. Agreement with the empirical frequency /w/ and the
actual number of samples is also quite good.

The probability of eight or more spheres appearing in the background
samples is extremely small, i.e., p (x_>_8)_<_10^-3 . Thus the existing
rich samples cannot be explained by fluctuations in the background and
point to a certain additional in flow of material to the points at which
these samples were taken.

Doctor of Chemical Sciences Paley undertook a field microchemical
analysis for nickel in two samples of spheres in order more reliably to
classify the subject magnetite spheres as meteoritic matter and
differentiate them from industrial dust; the results of this analysis a
represented below:

Sampling conditions Ni:Fe, %

Averaged sphere sample from various samplings ...........11.0

Spheres from Vanavara sample, 300 m from airfield .............4.0

These data completely confirm the correctness of classifying the
overwhelming majority of the spheres under investigation as meteoritic
matter. The significant difference between the averaged sample and the
Vanavara sample, clearly exceeding the error of the experiment, can be
explained either by accumulation of several generations of cosmic matter
(meteoritic dust) in the vicinity of Vanavara, or by some contamination
of the sample taken in the immediate vicinity of Vanavara by dust of
industrial origin, e.g., from welding apparatus.

The next stage in our work calls for careful inspection of the collected
samples, separation and study of the silicate particles, and detailed
description of all the various types of extracted meteoritic particles
to determine the possible composition of the infusible components of the
Tunguska meteorite.

If we assume that the spheres that O.A. Kirova had extracted from the
samples taken from this region pertain exclusively to the Tunguska
meteorite, and not in any considerable measure to the scattered
background of meteoritic dust, we can assign an iron-and-silicate
composition to the infusible portion of the meteorite, although for the
time being this remains to some extent hypothetical. The total quantity
of matter distributed over the investigated area can, in approximate
terms, be estimated at several tons.

We believe that the work of the 1961 expedition represents a great
forward stride in the search for the meteoritic matter. A distinct
concentration of particles of cosmic origin was discovered to the north
northwest of the epicenter, fitting well into the theoretical pattern
for the scattering of the Tunguska meteorite. However, in view of the
fact that the distribution of the over-all meteoritic-dust background
has not been thoroughly studied, and because of the inadequate number of
samples taken, the composition of the meteorite and the conditions of
its fragmentation cannot be regarded as having been determined with
complete certainty.

We are now faced with the quite specific problem of looking for
particles of a definite type by a specific method and in a specific
region. Materials collected in this manner must be investigated as part
of a general study of the cosmic dust, which represents an extremely
important task for the geochemist.

In conclusion, we feel we must make a number of critical remarks with
respect to Zolotov's observations, which provided the basis for a whole
series of unfounded statements with regard to the nature of the Tunguska
meteorite in the popular literature. Despite the serious criticism of
A.V. Zolotov's reports, his works have appeared in the Doklady Akademii
Nauk SSSR (see the first issues of Volumes 136 and 140, for the year 1961).

The observations which serve as the basis of these papers are erroneous.

1. From among a mass of trees that had died at various times, Zolotov
selected one with a certain arrangement of knags supposedly
characterizing the relationship to the ballistic and shockwave near the
trajectory of the meteorite. The expedition has at its disposal material
indicating surviving lateral stumps oriented in all possible directions,
so that a solitary observation without any indication of the time at
which the branches were lost is of no significance.

2. In determining the pressure at the front of the shock wave, Zolotov
proceeds from the idea that in comparison with tree trunks, an excess
air pressure of proportionally reduced intensity would be required to
snap off thin branches. However, it is a well-established fact that
considerable force is required to snap off the flexible branches of
evergreens and that in the case of a windfall the conifer itself
generally breaks, retaining virtually all of its branches.

3. The inadmissibility of equating the color temperature and brightness
of a bolide with the temperature of the shock wave has been demonstrated
in a study by Stanyukovich and Bronshten [10].

4. In his estimate of the luminous energy produced by the explosion,
Zolotov identifies the boundary of the forest fire with the boundary of
flash burning and bases his calculation on the most distant point of the
fire (16 km to the southeast). The spread of the fire to the west,
however, was not nearly as great and has absolutely nothing in common
with the boundary of flash burning. By no means were the living trees
ignited by the initial flash, but rather only such easily fired
materials as the forest litter and dead wood. The luminous energy of the
explosion was estimated at 60 to 100 calories per square centimeter at a
distance of 17 to 18 kilometers from the point of the explosion, which
works out to a luminous energy of the order of 600 to 900 calories per
square centimeter at the epicenter of destruction, in complete
contradiction to observational data, since a rather large number of live
trees survived in the vicinity of the epicenter, bearing only traces of
physiological cambium scorching, which corresponds to an energy of 6 to
12 calories per square centimeter.

5. Zolotov based his calculations on an unrealistic absorption
coefficient of 0.033 km^-1 for the atmosphere, which corresponds to a
visibility of 120 km; the use of a realistic coefficient of 0.1 km^-1 ,
which corresponds to a visibility of 45 km and excellent atmospheric
transparency, nullifies all of the calculations, altering the result by
several orders of magnitude.

6. Evaluation of the eyewitness accounts suggests no thermal effect nor
any of the electrical background phenomena of a great meteor.

In a second paper (Doklady Akademii Nauk SSSR, 1961, Volume 140, No. 1)
Zolotov draws the correct conclusion that "...the difference in the
conditions of radioactive fallout (contemporary - K.F.) fully explains
the variations in the total specific radioactivity of the Tunguska tree
and topsoil specimens," as had been pointed out in the report of the
1958 expedition sponsored by the Committee on Meteorites. This Committee
has at its disposal data from radiochemical isotope analyses of tree
sections by the annual rings, conducted under Prof. V.I. Baranov, and
these definitely point to a contemporary nature for the radioactive
contamination of the trees, since it does not stop with the tree ring
which corresponds to the time of contamination, but rather penetrates
the wood to a considerable depth.

The investigation methods used by Zolotov are not up to current
standards and thus cannot be used for any evaluation of the phenomena
accompanying the fall of the Tunguska meteorite.

*III. GENERAL RESULTS *

The work of the expedition can be summarized as having virtually
completed the collection of materials which will provide descriptions of
all the various forms of the physical effects produced by the Tunguska
meteorite on the area of the fall. It is, of course, not out of the
question that individual craters formed by small pieces of the meteorite
will yet be found - or, for that matter, the pieces themselves. However,
in view of the projects that have already been carried out, it becomes
quite clear that such finds would be only fortuitous.

The maps of the felled-timber area are no longer based on estimates, but
are well documented and prepared on the basis of a considerable volume
of statistical material. The data collected on the mean direction of the
fallen trees, on the characteristics of the forest, on the degree to
which the possible flash burning was directional, and on the influence
of the terrain relief on the nature of the shock-wave effect at the
epicenter must provide the basis for physical characterization of the
air "explosion" of the Tunguska meteorite. We have no hesitancy in
expressing our conviction that the study of this material will shed
light on the over-all physical circumstances of the fall in a quite
thorough and definite manner.

The investigation into the distribution of meteoritic dust in the area
of the fall permits us, with a high degree of probability, to speak of
physically observed fragments from the Tunguska meteorite and the nature
of their scattering. However, to transform the probability into full
certainty, the distribution of this material must be the subject of
study, in conjunction with the general study of cosmic dust and its
propagation. At the same time, methods must be worked out to isolate
identify cosmic dust - something that will be possible only behind the
walls of a major institution such as the Vernadskiy Institute of
Geochemistry and Analytical Chemistry, which should coordinate the study
of this problem.

I should now like to take advantage of the opportunity to express my
heartfelt gratitude to the many individuals who participated in the
discussion and implementation of the Tunguska meteorite study program.

*List of Participants in the 1961 Combined Tunguska Meteorite Expedition:*

1. Florenskiy K.P. Chief of expedition

2. Yeliseyev I.N. Deputy chief of expedition

3. Antonov I.V.

4. Avdeyev V.I.

5. Andreyev Yu.

6. Balkovskiy V.S.

7. Bekhterev V.M.

8. Biychaninova A.

9. Bobukhova V.

10. Babakov A.

11. Boyarkina A.P.

12. Berezhnoy V.G.

13 Vronskiy B.I.

14 Ven'yaminov S.Yu.

15. Vasil'yev N.V.

16. Verba D.K

17. Vycherov Ye.

18. Gorbunova T.M.

19. Demin D.V.

20. Drozdov S.N.

21. Drapkina G.I.

22. Yemel'yanov Yu.~.

23. Yerokhina A.A.

24. Yegorshin A.O.

25. Yefremov S.P.

26. Zhuravlev V.K.

27. Zotkin I.T.

28. Zaslavskaya N.I.

29. Z enkin G. M.

30. Zenkina Ye.

31 Ivanova G.M.

32. Il'in A.G.

33. Kozlov A.N.

34. Krasnov V.P.

35. Karpunin G.F.

36. Kurenkova Ye.M.

37. Kolobkova G.P.

38. Kuvshinnikov V.M.

39. Kurbatskiy N.P.

	40. Kulakov Yu.

41. Kuz'minykh S.

42. Kambalova G.

43. Kandyba Yu.L.

44. Kozlovskaya L.S.

45. Lyubarskiy K.A.

46. Malinkin Ye.I.

47. Makarova-Zemlyanskaya Ye.A.

48. Mil chevskiy V.I.

49. Matushevskiy V.V.

50. Nekrasov V.I.

51. Nekrasova L.N.

52. Nikolayenko I.P.

53. Osharov A.B.

54. Ogrin Yu.

55. Plekhanov G.F.

56. Paley P.N.

57. Pustovalov V.

58. P'yavchenko N.I.

59. Prozorov Yu.S.

60. Pisarenko V.I.

61. Permikov V.M.

62. Pape V.E.

63. Prokashev V.A.

64. Popov L.I.1961.

65. Rodin V.F.

66. Rodionova N.P.

67. Stolpovskiy A.A.

68. Smirnyagin Ye.P.

69. Sleta T.M.

70. Tibikova T.M.

71. Trukhachev G.

72. Florenskiy V.K.

73. Fast V.G.

74. Chernikov V.M.

75. Shikalov L.F.

76. Shugayev Ye. P.

77. Shapovalova R.D.

78. Shuykin N.N.

*REFERENCES*

1. K.P. Florenskiy, B.I. Vronskiy, Yu.M. Yemel'yanov, I.T. Zotkin, O.A.
Kirova. Preliminary Results from the 1958 Tunguska Meteorite Expedition.
Meteoritika, Volume XIX, 1960.

2. G.F. Plekhanov et al. A Report on the Work of the Combined Autonomous
Expedition. Tomsk, 1961 (manuscript).

3. Yu.A. L'vov, N.V. Vasil'yev et al. Verification of a Hypothesis. Is
the Felled Forest in the Keta River Basin Associated with the Fall of
the Tunguska Meteorite. Priroda, No. 7, 1961.

4. B.I. Vronskiy. Priroda, No. 3, 1960.

5. Ye.L. Krinov. The Tunguska Meteorite. USSR Acad. Sci. Press, 1949.

6. O.A. Kirova. A Mineralogical Study of Soil Samples from the Site of
the Tunguska Meteorite Fall, Collected by the 1958 Expedition.
Meteoritika, Volume XX, 1961.

7. V.I. Nekrasov, Yu.M. Yemel'yanov. Priroda, No. 2, 1962.

8. M.A. Tsikulin. An Approximate Evaluation of the Parameters of the
1908 Tunguska Meteorite Based on the Destruction of the Forest Area.
Meteoritika, Vo1ume XX, 1961.

9. K.P. Stanyukovich, V.P. Shalimov. The Motion of Meteoroids through
the Atmosphere of the Earth. Meteoritika, Volume XX, 1961.

10. K.P. Stanyukovich and V.A. Bronshten. The Velocity and Energy of the
Tunguska Meteorite. Doklady Akademii Nauk SSSR, Volume 140, No. 3, 1961.

11. V.A. Bronshten. On the Motion of the Tunguska Meteorite through the
Atmosphere. Meteoritika, Volume XX, 1961.

12 G.I. Pokrovskiy. Possible Mechanical Phenomena in the Motion of
Meteoroids. Meteoritika, Volume XX, 1961.

13. I.S. Astapovich. The Great Tunguska Meteorite. Priroda, No. 2, No.
3, 1951.

14. V.G. Fesenkov. The Cometary Nature of the Tunguska Meteorite
Astrorlomicheskiy zhurnal, Volume 38, No. 4, 1961.

15. V.I. Vernadskiy. Mirovedeniye, No. 5, 1932.

16. V.I. Vernadskiy. Problemy Arktiki, No. 5, 1941.

17. Resolution of the Ninth Conference on Meteorites with Regard to
Studying the Fall of the Tunguska Meteorite. Meteoritika, Volume XX, 1961.

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