The Small Siberian Lake That Some Italian Geologists Think Is the Tunguska Crater

Lake Cheko is a small, elliptical, anomalously deep lake in the central Siberian taiga, about 8 km northwest-by-north of the 1908 Tunguska blast epicentre. It is approximately 500 metres long on its principal axis, approximately 300 metres on its minor axis, and approximately 50 metres deep at its centre — substantially deeper and substantially more regular in outline than the small Siberian taiga lakes elsewhere on the regional map.

In 2007 a research team from the University of Bologna led by Luca Gasperini published in the journal Terra Nova a proposal that Lake Cheko is the impact crater of a small unfragmented portion of the 1908 Tunguska body — the only known surviving solid trace of the event.

The Italian case

The Gasperini team had run an instrumented field expedition to Cheko in 1999. They identified a single magnetic-anomaly target at the geometric centre of the lake bottom about 10 metres beneath the sediment surface. They cored the lake floor and identified a transition between approximately 1908 and pre-1908 sediment layers (consistent with the lake having been created by the event rather than having existed before it). They modelled the lake’s elliptical shape as consistent with an oblique low-angle impact and computed an arrival vector that broadly matched the main Tunguska blast trajectory.

The team’s 2007 Terra Nova paper proposed that a 5-10 metre fragment of the original Tunguska object had separated from the main body before the atmospheric airburst and had survived to ground impact in a low-velocity, low-angle trajectory — producing the small Cheko crater while the main body produced the 2,150 sq km airburst destruction further to the southeast.

The Russian objections

The Russian Tunguska research community — the inheritor of the Leonid Kulik expedition tradition that had been working on the event since 1927 — rejected the Gasperini interpretation in a series of counter-papers through 2007–2012. The Russian objections were three.

First, the historical record. The Tungus indigenous-population witnesses to the 1908 event knew Lake Cheko as a place name; the lake appears in pre-1908 cartography (most notably on the 1883 surveys of the Russian Geographical Society); the lake is therefore demonstrably older than the event.

Second, the sediment chronology. Russian sediment-core work on the Cheko floor showed continuous lacustrine deposition extending back several centuries before 1908, with no discontinuity at the proposed event horizon.

Third, the dynamical implausibility. The Tunguska object’s mass and atmospheric ablation history preclude the survival of any solid fragment large enough to produce a 500-metre impact crater — the standard atmospheric-entry models produce complete vaporisation of the body well before ground impact.

The dispute

The dispute continues. Subsequent Italian and Russian field work through 2010–2020 has not produced a definitive resolution. The mainstream international consensus tilts toward the Russian objections — Lake Cheko is now treated as a pre-existing geomorphic feature, not as a Tunguska impact crater — but the Bologna group has continued to defend its interpretation in subsequent publications.

If Cheko is indeed the impact crater, it is the only known physical remnant of the 1908 event. If it is not, the Tunguska object left no surviving physical trace beyond the pattern of flattened forest.

The 2013 Chelyabinsk meteor — a smaller object than Tunguska — produced a recovered solid fragment from Lake Chebarkul. The physical evidence from Chelyabinsk is the principal modern parallel to the Cheko question.