THE 2002 TUNGUSKA MEASUREMENTS

 
To complete the data collected by the Tunguska99 expedition two Bologna researchers, Romano Serra and Maurizio Serrazanetti, have gone to the Tunguska explosion site (July 19-30, 2002). The Italian researchers have been assisted in their work by Gennady Andreev, Larissa V.Pavlova, John Anfinogenov and Maria Shvedova, from Tomsk State University and from Tomsk Polytechnic University. The supplementary 2002 data refer to 1) magnetic field intensity measurements, 2) verification of reference points co-ordinates, 3) new data on surviving and flattened trees, 4) peat sampling, 5) iridium content in the Cheko lacustrine sediments and in the ground of the Cheko shore.

1) Magnetic field intensity measurements.

To perform the magnetic field intensity measurements a Geometrics G-858 portable Cesium Magnetometer, which uses a graphical interface to make survey design and data acquisition quick and efficient, has been used (see photo). The G-858 was interfaced with a standard portable computer. A solar battery charger USF-11 was necessary because the Tunguska explosion site is located at some hundreds kilometres from the nearest roads. The magnetic field intensity measurements were performed on the lake Cheko and its shore along 12 radial directions around the maximum depth point (see red lines on the photo).

2) Verification of reference points coordinates.

Complementary on-site measurements have been carried out to obtain the co-ordinates of different reference points in the explosion area. These data will allow to recognize ground elements on the aerial pictures and to connect them to the regional topographic net. The geographical co-ordinates of important points on the itinerary Cheko-Kulik's izba-Churgim-Khusma have been measured with a 3-5 meter resolution using a GPS system. An important result obtained in 2002 is the correction of Mount Farrington astro-radio point co-ordinates. These co-ordinates, measured in 1929 using astronomy and radio time signals, have been used in all the works up to now. The new measurements (60°55'00",8 N; 101°56'56",0 E) show that they contained an error of about 60 meters, both in latitude and in longitude.

3) New data on trees.

Surviving trees. On the shores of the lake Cheko there are some tenths of trees surviving the 1908 explosion. Many larches and some spruce are still growing at a distance of a few to some tenths of meters from the lake shore (see yellow marks on the photo). Some tree older than one hundred years show an anomalous directional growth of the rings following those of 1908 and 1909, thus witnessing the occurrence of phenomena that caused the tree inclination. Many trees surviving the catastrophe show a chaotic character and an irregular distribution of the tracheids of the 1908 ring. This ring has often an anomalously clear late wood characterized by narrower cells with thinner walls. Sections and cores of these trees have been collected to study the direction of the blast wave around the lake.

Flattened trees. The data on the azimuths of flattened trees have been obtained from on-site measurements performed by V. Fast and co-workers 60-70 years after the 1908 explosion. We have now checked and completed these data measuring the azimuths of fallen trees as seen 30 years after the explosion. These new data were taken from Kulik's 1938 aerophotosurvey, that has been compared with the new aerophotosurvey performed by the Tunguska99 expedition. To check some discrepancies between these data, complementary on-site measurements have been performed in 1999 and 2002.

4) Peat sampling.

Surface peat samples from nine different swamps (see map) have been collected to study their anomalous high Cs-137 content. To check our previous results a supplementary column of peat (red mark on the map) has been extracted from the same place as the KEM N21 peat column taken in 1999.

5) Iridium content.

The study of Cheko lacustrine sediments, extracted in 1999, was extended to the ground of the Cheko shore in 2002. For this purpose, a trench has been excavated nearby the lake (see blue square on the map). From the trench, 79 samples of the ground up to 167 cm depth have been packed. The group of Dr. Christian Koeberl (University of Vienna, Department of Geological Sciences) has searched these samples for Iridium and other related cosmic markers. The analyses were done by instrumental neutron activation. Samples were counted repeatedly after irradiation (for about three months) and counted for a duration of up to four days on a high-efficiency high-resolution HpGe detector.

Similar analyses on 110 samples of Cheko lacustrine sediments have been carried out by the team of Dr. Eric Robin in the CEA/CNRS Laboratoire des Sciences du Climat et de l'Environnement.

Other laboratories were involved in this work, but the results obtained are still contradictory.