The famous Patomsky crater discovered in 1949 by the geologist Vladimir Kolpakov is still one of the most mysterious natural objects on the planet. It is located in the Bodaibo District of the Irkutsk Region: in its size and shape, the crater looks like a lunar formation. It is about 40 m high, the crest diameter is 86 m. Local dwellers, Yakuts, who know about the crater since ancient times, call it "the nest of the fiery eagle", and the river at its foot--"the fiery river". Scientists are intrigued by these names and even more by the origin of the crater.

There exist some dozens of hypotheses, but only two of them are the most probable. According to the first one, the crater is a result of meteoric fall. It was Kolpakov who first proposed this idea after geological surveying of the territory. Some of his disciples even tried to estimate the depth (180-200 m) of occurrence of a cosmic body in the crater and believed it was a fragment of the Tunguska meteorite that fell in the Siberian taiga in 1908*.

The second hypothesis was offered in 1951 by a famous volcanologist Sergei Obruchev, Corresponding Member of the USSR AS. His point of view is shared by many scientists, including Viktor Antipin, Dr. Sc. (Geol. & Min.), a staff member of the RAS Siberian Branch Institute of Geochemistry named after A. Vinogradov, who spoke up in the Science in Siberia newspaper in the end of 2010. He is sure that the Patomsky crater could form only as a result of breakthrough of a

* See: E. Galimov, M. Nazarov, "Centennial of the Tunguska Event", Science in Russia, No. 3, 2008.--Ed.

deep steam-and-gas stream in the area of tectonic faults. This is proved by geological and geochemical studies carried out by scientists, including Viktor Antipin, during the complex expeditions of 2006, 2008 and 2010. He writes that endogenous (or deep) reasons of occurrence of this event are likely preconditioned by development of the magmatic process.

Thus, as early as 2006, it was established: the Patomsky crater is a ring-type structure with clear zoning embodying the sequence of its formation. The main structural elements of the crater are an outer slope of the cone, a ring-type earthen wall, similar ditch and a central hillock. In other words, the crater is an artificial cone mainly composed of limestone and other rocks--sandstone, schist, and quartz veins.

When a map of the crater was being compiled, the scientists agreed that its peak--the ring-type earthen wall--is divided by a shallow lowering in the relief into two parts. At the early formation phase the inner wall was composed of grey limestone (there are schist and sandstone blocks where larches grow). The outer wall formed later of dark grey massive weathered crystal limestone (larch is already absent). According to Antipin, the overall formation of the Patomsky crater was completed with the central hillock composed of scarcely weathered massive crystal limestone blocks.

Chemical composition of separate sandstone and schist blocks of the artificial cone brought from the depths in the process of formation are the most interesting for scientists. It includes such chemical elements as strontium, calcium, barium and sulphur. Outside the

cone these elements occur in a lesser degree. So-called ferrum group elements, in particular nickel, are also very scarce, which means the crater could not form as a result of meteoric fall.

According to the experimental data, smaller blocks were brought to the surface by a gas stream formed after blast. They contain a lot of sulphur, strontium and carbon minerals (calcite, siderite, ankerite and fluorite). This means that geological characteristics of the rock make it possible to believe in the existence of a subvolcanic magmatic body in the depths of the crater.

How old is the crater? In 2008 Viktor Voronin, a scientist from the RAS Siberian Branch Institute of Physiology and Biology of Plants (Irkutsk), carried out a dendrochronological* analysis of cuts of the oldest larches located nearby and inside the crater and made the following conclusion: it formed in the 15th-early 16th centuries. Some trees, for example, those on the artificial cone are 400-480 years old, on the early ring-

* Dendrochronology--a discipline on the dating methods of archeological remains and acts of nature based on the tree-ring analysis.--Ed.

type wall--250-300 years old, on the central hillock-only 70 years old. Consequently, the geologists were right saying that this object was forming during a long period of time and was a result of a catastrophic event connected with different phases of endogenous activity. What can we say about the current state of the Patomsky crater, is its formation process over? Proceeding from the persistent hydrogen sulphide smell, some volcanic processes are still going on in it. Scientists are planning to continue studies of this unique natural phenomenon.

V. Antipin, The Patomsky Crater--a Unique Geological Complex in the Eastern Siberia, "Science in Siberia", No. 43, 2010