The Tunguska event was a large explosion that occurred on the morning of 30 June [O.S. 17 June] 1908, at around 7:14 KRAT (0:14 UT) in Central Siberia, then part of the Russian Empire. This cataclysm occurred in a remote and sparsely populated region of the taiga, near the Podkamennaya Tunguska River after which it is named. The shock wave knocked several witnesses to the ground, killed at least three people as well as numerous animals, and shattered windows within a 200 km (120 mi) radius. The blast was recorded by various Russian and German seismological stations with a magnitude close to 5 on the Richter scale, while atmospheric waves generated by the shock wave were detected worldwide. From 30 June to 3 July, intense bright nights were observed across western Eurasia over an area of about 12,000,000 km2 (4,600,000 sq mi). Although the Russian press and various correspondents reported the blast in the following days, it was not until 1921 that a first scientific expedition was organized under the direction of Leonid Kulik, who discovered the site of the epicenter only in 1927.
Kulik and his successors research revealed that the explosion devastated nearly 2,150 km2 (830 sq mi) of forest in a radial pattern which implied an aerial origin. The scientific consensus thus attributes this event to a meteor air burst, the atmospheric explosion of a celestial body, although no fragment has been formally identified. By cross-referencing eyewitness accounts and physical modeling, researchers favor the hypothesis of a 50–60 m (160–200 ft) diameter meteoroid moving at high speed from south-east. The object would have exploded between 5–10 km (3.1–6.2 mi) in altitude, releasing an energy often estimated between 10 and 15 megatons of TNT, which is enough to destroy an entire major city. This interpretation is reinforced by data collected since the passage of the Chelyabinsk meteor in 2013, whose dynamics were similar. The Tunguska event thus constitutes both the most violent impact event on Earth recorded in modern times and one of the most powerful explosions ever documented. However, the exact nature of the object—that is, whether it was an asteroid or a comet—is still debated. Alternative, terrestrial hypotheses, such as the release of explosive underground gas, have also been suggested, though they remain marginal among the scientific community.
Lake Cheko, located approximately 8 km (5.0 mi) northeast of the epicenter and unrecorded before 1908, may be an impact crater formed by a secondary fragment of the celestial body that detached before its explosion. While its atypical shape and its orientation along the trajectory axis support this hypothesis, several sedimentary studies support a contrary conclusion. A 2019 study suggested that the explosion may have decimated the breeding population of the Sushkin's goose, contributing to its extinction in the following years. The incident remains the primary historical benchmark for assessing risks associated with near-Earth objects as well as for developing planetary defense strategies, and the explosion site is now protected in a nature reserve. The event is frequently depicted in works of fiction, particularly science fiction, through a wide variety of interpretations.
Background
The Tunguska event occurred in a remote and sparsely populated region of Central Siberia. It is named after the nearby Podkamennaya Tunguska, one of the main tributaries of the Yenisei River. Characterized by a taiga environment resting by permafrost, the area features gently undulating terrain with an elevation change of about 100 m (330 ft), where marshy lowlands alternate with wooded hills. The area is bounded by the Kimchu River to the north and the Khushma River to the south, the former feeding Lake Cheko. Within this boundary lie two large wetlands called the Northern and the Southern Swamp. The taiga's wetlands are divided between deep, impassable marshy tracts (sometimes reaching depths of up to 25 m (82 ft)) and firmer, raised peat mounds, which are colonized by lichens and sparse trees. Subject to a harsh climate, the site remains frozen for eight to nine months a year.
Geologically, the area lies at the heart of the Siberian Traps. The epicenter of the explosion is located near the Kulikovsky paleovolcanic complex, dating from the Early Triassic (around 250 million years ago). These same traps are associated with the Permian–Triassic extinction event, considered the most devastating biological crisis in the history of life on Earth. In particular, it led to the extinction of emblematic prehistoric animals of Russia, such as Inostrancevia and Scutosaurus. At the center of the paleovolcano lies Mount Stoikovich, which is the solidified plug of an ancient volcanic pipe. This feature is surrounded by the Great Central Swamp, itself bounded by the rim of the ancient crater where Mount Farrington rises. As the primary landmark of the region, the latter helps pinpoint the exact epicenter of the explosion, located about 3 km (1.9 mi) southwest of its summit.
At the time of the explosion, the affected area was located in the Yeniseysk Governorate, an administrative division of the Russian Empire corresponding to the present-day Evenkiysky District of Krasnoyarsk Krai, which is populated predominantly by the Evenks. They generally lived in small, scattered family groups, residing in conical tents called chums, and made a livelihood of reindeer herding, hunting, and fishing. Under the reign of Tsar Nicholas II, fur taxes (yasak) were levied on the Evenks through their traditional clan organizations. Alongside this nomadic population, Russian farmers and traders—present in Siberia since the 17th-century expansion—had established small villages along the rivers, notably Vanavara, located about 60 km (37 mi) south of the epicenter. Gold mines were being worked along the Yenisei River, while the Trans-Siberian Railway had reached Lake Baikal as early as 1898, bringing with it a large influx of peasant settlers from the western parts of the country. Academics exiled for their participation in the 1905 revolution were also present. Finally, the empire was still marked by the very recent Russo-Japanese War.
Disaster
On the morning of Tuesday, 30 June [O.S. 17 June] 1908, a bolide, described by several witnesses as having a brightness and apparent size greater than that of the Sun, traversed Earth's atmosphere over a distance of at least 1,000 kilometres (620 mi). Moving from south-east to north-west while leaving a thin white trail, the object was seen across Central Siberia from a distance of up to 600 to 1,500 kilometres (370 to 930 mi), observation being further facilitated by a perfectly clear sky that day. At around 7:14 KRAT (0:14 UT), a powerful and deafening explosion was heard over the taiga in the Podkamennaya Tunguska basin. The blast was accompanied by an intense reddish glow, compared by some observers to a "sparkling broom", while generating a column of fire and a cloud of smoke rising tens of kilometers into the air.
The explosion occurred directly above the Southern swamp and devastated the taiga, flattening several million trees over an area of more than 2,150 km2 (830 sq mi), while decimating numerous reindeer and dogs belonging to the Evenks. Under the effect of the shock wave, the trees were felled in a radial pattern forming the characteristic shape of two "butterfly wings" around the central area. At the epicenter itself, the blast stripped the trees of their branches but left them standing, forming a unique zone at the heart of the flattened forest. The initial thermal pulse simultaneously ignited several sporadic fires, with its heat felt up to about 80 kilometres (50 mi) from the epicenter. Perceived over 800 kilometres (500 mi) away, the shock wave spread over hundreds of kilometers and shattered windows within a radius of nearly 200 kilometres (120 mi). At similar distances, the tremors knocked people down or threw them to the ground.
The explosion was recorded by seismological stations in three cities in the Russian Empire—Irkutsk, Tashkent, and Tiflis—as well as by a station in Jena in the German Empire. However, the records from the Russian cities were first published in 1910 by geophysicist Grigori Levitski, while those from Jena were published three years later; it was not until 1925 that a paper formally linked these data to the Tunguska event. Since the Richter scale was not proposed until 1935, it was not until the late 20th century that the shock wave generated by the explosion was determined to be equivalent to a seismic magnitude near 5. Atmospheric waves generated by the blast were also detected by barographs across the world, but their connection to the 1908 event was only established in the 1930s. Among the stations involved were those in Berlin, Potsdam, and on the Schneekoppe in the German Empire, as well as in London, England, and Zagreb, Croatia. Changes in atmospheric pressure were also recorded thousands of kilometers from the explosion, notably as far as Batavia in the Dutch East Indies (now Indonesia) and Washington, D.C., in the United States.
In the days following the explosion, western Eurasia experienced unusual atmospheric phenomena. On the evening of 30 June, bright nights of rare intensity were reported across an area of about 12,000,000 km2 (4,600,000 sq mi), to the extent that it became possible to read a newspaper or photograph monuments around midnight without artificial lighting. The sky displayed various hues, described as white, pink, red, golden, yellow-orange, or green, although some of these colors likely corresponded to the usual shades of a sunset. Most of these observations were reported in various newspapers, such as the British daily The Times, from 2 to 4 July 1908. The phenomenon extended south as far as Bordeaux, France, and Tashkent, and north to Aberdeen, Scotland, and Stockholm, Sweden. In several communications published in Nature, astronomers—including William F. Denning regarding the night of 30 June in Bristol, England—reported having to abandon their astronomical observations due to the unusual brightness of the sky. While the bright nights faded in two or three days, luminous halos persisted for about ten days longer, and these twilight anomalies remained perceptible until the end of the summer of 1908.
Injuries, loss and eyewitnesses
Between 1908 and the 1970s, more than 700 eyewitness accounts describing the event were collected. However, the more recent accounts have lower scientific value, as time degrades memory and alters factual accuracy. Despite the low population density around the epicenter, the event caused an unknown number of injuries. In the tree fall zone, at least thirty people were exposed to the blast effects, and several lost consciousness for periods ranging from a few hours to several days. These losses of consciousness occurred notably due to the shock wave, fear, or stress. In some cases, they coincided with the arrival of the air burst, suggesting a form of concussion. Others may have lost consciousness due to smoke inhalation, the presence of burning materials nearby, or the emotional shock caused by the event. Nevertheless, the Evenks present in the blast area were generally inside their chums at the time of the explosion, which notably limited their exposure to burns. Furthermore, no injuries caused by shattered glass were reported, despite windows being broken hundreds of kilometers from the epicenter.
One of the most famous eyewitness accounts of the event comes from Semyon B. Semyonov, a farmer from Vanavara, who gave his account in a letter written in 1930:
I don't remember the year exactly, but more than twenty years ago when the fallow land was being ploughed up I was sitting in the porch of the house at the trading station of Vanovara at breakfast time and looking towards the north. I had just raised my axe to hoop a cask when suddenly in the north above Vasily Il'yich Onkoul's Tunguska Road, the sky was split in two, and high above the forest the whole northern part of the sky appeared to be covered with fire. At that moment I felt great heat as if my shirt had caught fire; this heat came from the north side. I wanted to pull off my shirt and throw it away, but at that moment there was a bang in the sky, and a mighty crash was heard. I was thrown on to the ground about three sajenes [around six meters] away from the porch and for a moment I lost consciousness. My wife ran out and carried me into the hut. The crash was followed by noise like stones falling from the sky, or guns firing. The earth trembled, and when I lay on the ground I covered my head because I was afraid that stones might hit it. At the moment when the sky opened, a hot wind, as from a cannon, blew past the huts from the north. It left its mark on the ground in the form of little paths, and damaged onion plants. Later, it turned out that many panes in the windows had been blown out, and the iron hasp in the door of the barn had been broken.
Another famous and frequently cited account is that of Chuchan (whose Russian name was Stepan Ivanovich, family name unknown), an Evenk from the Shanyagyr clan. Recorded in an account written in 1926, his testimony indicates that he was then located further north, at the very heart of the area where trees were felled by air bust: