The Patomskiy Crater

Summary

On a larch-covered slope in the Patom Highlands stands a cone of shattered limestone blocks with a ring wall and a mound at its centre, about 150 to 160 metres across its base. A Russian geologist described it in 1949, the first outsider to reach it. Local people knew it already.

It is not an impact crater. Nickel in its carbonates is far too low for meteoritic material, and tree rings date its initial formation to around AD 1500, four centuries before the 1908 Tunguska event sometimes invoked to explain it. The published account is a phreatic steam explosion fed by deep carbon-dioxide-rich fluids, built in stages across centuries.

What is documented

The structure, measured. The cone base runs about 150 to 160 metres by 120 to 130 metres. The ring wall is about 80 metres in diameter. The crater is 12 to 15 metres deep. The central mound has a base diameter of about 34 metres. The cone stands between 10 and 12 metres above the surrounding hill slope at its lowest and 35 to 38 metres at its highest.

The dating, and how it was done. A dendrochronological study using thirty stem discs and forty core samples dates initial formation to the late fifteenth or early sixteenth century, inferred from trees aged 400 to 480 years and a mass windfall about five hundred years ago. An earlier estimate putting the structure at 250 to 300 years was revised after further sampling.

It was built in stages, and the trees show it. Trees get younger as the structures get later. The oldest trees on the cone and the early ring wall are about 300 years old. Trees on the late ring wall are 93 to 101 years old. The oldest tree on the central mound, which formed only after the crater was complete, is 71 years old. The authors describe the formation as long-lasting and multi-event.

Two later episodes are recorded in the wood. Tree rings register a catastrophic event in 1841 to 1842, with root disturbance, stem damage and compression wood. One sampled tree declined from 1843 and died in 1876. Separately, strontium in larch wood roughly doubled relative to the average during 1852 to 1859, a period the authors associate with significant activity at the crater.

The geochemistry that excludes an impact. Nickel in the carbonates measures only 1.9 to 3.5 grams per tonne, which the authors state rules out a meteoritic origin.

The geochemistry that points downward instead. Strontium in sandstone blocks reaches 810 grams per tonne against an average of 176, and in slates 680 against 406. Calcium oxide reaches 11.63 per cent in sandstones and 18.04 per cent in slates. Carbonate rocks are depleted in heavy oxygen by about 6.5 parts per thousand, which indicates water at 100 degrees Celsius or more. Rare earth element totals in some sandstone blocks reach 557 grams per tonne.

What the authors conclude. That the crater formed as the result of a phreatic, that is steam, explosion, either during magma intrusion into water-bearing rocks or through fault-related decompression of heated water-bearing rocks.

Where the evidence comes from, which matters here. The geochemistry, the isotope work and the dendrochronology all come from one Irkutsk-based team, published across 2008, 2011 and 2020, largely in Russian-language venues. The Registry read the detailed figures in the Russian original because the English translation is paywalled. There is no independent replication by an outside group in the literature the Registry could reach. One numeric discrepancy is worth flagging: the English abstract renders the oldest central-mound tree as seven years where the Russian original says seventy-one, and the Registry uses the Russian.

Leading explanations

A phreatic steam explosion driven by deep fluids (Voronin, Antipin and colleagues, 2011 and 2020; the published explanation, not independently replicated). That the cone was built by steam explosion as deep carbon-dioxide-rich fluids entered the upper crust, with the deposition cone building at varying intensity and at times erupting explosively. In the literature the Registry retrieved, it is the only explanation supported by published geochemical, isotopic and dendrochronological data, and it accounts for the staged build. It is not established in the strict sense, because the work comes substantially from one team.

A meteorite impact, including a Tunguska fragment (rejected). Nickel in the carbonates is far too low for meteoritic material, and the tree rings show a staged build across centuries rather than a single instantaneous excavation. The Tunguska variant fails on date as well: the cone predates 1908 by roughly four hundred years.

Hydrogen outgassing and pipe formation (Stazhevsky, 2012; hypothesis, untested). A paper on the origin of diatremes, karst and trap formations cites the Patomsky crater as a comparison case for structures formed by hydrogen outgassing and pipe formation in the Earth’s interior. The Registry read only the abstract and cannot report what evidence it marshals.

A secret Stalin-era uranium mine, or a non-terrestrial origin (rejected). ExplorersWeb reports both as held by "a small community of conspiracists", and calls the mine theory the least likely. No proposer in any citable venue and no supporting evidence. The five-hundred-year tree-ring age excludes any twentieth-century human origin outright.

Current status

Partially explained. The impact hypothesis is closed, by nickel geochemistry and by the date, and the structure is best described as a geologically recent feature built from below. The published explanation, a phreatic steam explosion fed by deep fluids and built in stages from roughly AD 1500 with documented later activity, is internally consistent and rests on real measurements. What keeps this record from being closed is provenance rather than evidence: the geochemistry, isotope work and dendrochronology come from a single Irkutsk-based group across three papers, and no outside team has reproduced them. Independent confirmation, in particular a published drill core or geophysical profile resolving the subsurface structure, and independent isotope and trace-element measurements reproducing the strontium enrichment and the oxygen depletion, would settle it. It would be undermined if an outside team found meteoritic markers in the structure, or if independent dating placed the structure outside the historical period.

Last reviewed: November 2026. Records are provisional. Where the evidence changes, the entry changes. Found an error? Tell us.