The Tunguska event was a large explosion of between 3 and 50 megatons TNT equivalent that occurred near the Podkamennaya Tunguska River in Yeniseysk Governorate (now Krasnoyarsk Krai), Russia, on the morning of 30 June 1908.

The explosion over the sparsely populated East Siberian taiga felled a large number of trees, over an area of 2,150 km2 (830 sq mi) of forest, and eyewitness accounts suggest up to three people may have died. The explosion is attributed to a meteor air burst, the atmospheric explosion of a stony asteroid about 50–60 m (160–200 feet) wide.

The asteroid approached from the east-south-east, probably with a relatively high speed of about 27 km/s; 98,004 km/h (Mach 80).[2] Though the incident is classified as an impact event, the object is thought to have exploded at an altitude of 5 to 10 km (3 to 6 miles) rather than hitting the Earth's surface, leaving no impact crater.

The Tunguska event is the largest impact event on Earth in recorded history, though much larger impacts are believed to have occurred in prehistoric times, including the Chicxulub impact that ended the Cretaceous period. An explosion of the Tunguska magnitude would be capable of destroying a large metropolitan area. The event has been depicted in numerous works of fiction. The equivalent Torino scale rating for the impactor is 8: a certain collision with local destruction.

On 30 June 1908 N.S. (cited as 17 June 1908 O.S. before the implementation of the Soviet calendar in 1918), at around 7:17 a.m. local time, Evenki natives and Russian settlers in the hills northwest of Lake Baikal observed a bluish light, nearly as bright as the Sun, moving across the sky and leaving a thin trail. Closer to the horizon, there was a flash producing a billowing cloud, followed by a pillar of fire that cast a red light on the landscape. The pillar split in two and faded, turning to black. About ten minutes later, there was a sound similar to artillery fire. Eyewitnesses closer to the explosion reported that the source of the sound moved from the east to the north of them. The sounds were accompanied by a shock wave that knocked people off their feet and broke windows hundreds of kilometers away.

The explosion registered at seismic stations across Eurasia, and air waves from the blast were detected in Germany, Denmark, Croatia, and the United Kingdom – and as far away as Batavia, Dutch East Indies, and Washington, D.C. It is estimated that, in some places, the resulting shock wave was equivalent to an earthquake measuring 5.0 on the Richter scale.

Over the next few days, night skies in Asia and Europe were aglow. There are contemporaneous reports of brightly lit photographs being successfully taken at midnight (without the aid of flashbulbs) in Sweden and Scotland. It has been theorized that this sustained glowing effect was due to light passing through high-altitude ice particles that had formed at extremely low temperatures as a result of the explosion – a phenomenon that decades later was reproduced on a much smaller scale by Space Shuttles. In the United States, a Smithsonian Astrophysical Observatory program at the Mount Wilson Observatory in California observed a months-long decrease in atmospheric transparency consistent with an increase in suspended dust particles. (From Wikipedia)

Sibir newspaper, 2 July 1908
On the morning of 17th of June, around 9:00, we observed an unusual natural occurrence. In the north Karelinski village [200 verst (213 km (132 mi)) north of Kirensk] the peasants saw to the northwest, rather high above the horizon, some strangely bright (impossible to look at) bluish-white heavenly body, which for 10 minutes moved downwards. The body appeared as a "pipe", i.e., a cylinder. The sky was cloudless, only a small dark cloud was observed in the general direction of the bright body. It was hot and dry. As the body neared the ground (forest), the bright body seemed to smudge, and then turned into a giant billow of black smoke, and a loud knocking (not thunder) was heard as if large stones were falling, or artillery was fired. All buildings shook. At the same time the cloud began emitting flames of uncertain shapes. All villagers were stricken with panic and took to the streets, women cried, thinking it was the end of the world. The author of these lines was meantime in the forest about 6 versts [6.4 km] north of Kirensk and heard to the north-east some kind of artillery barrage, that repeated at intervals of 15 minutes at least 10 times. In Kirensk in a few buildings in the walls facing north-east window glass shook.

Krasnoyaretz newspaper, 13 July 1908
Kezhemskoye village. On the 17th an unusual atmospheric event was observed. At 7:43 the noise akin to a strong wind was heard. Immediately afterward a horrific thump sounded, followed by an earthquake that literally shook the buildings as if they were hit by a large log or a heavy rock. The first thump was followed by a second, and then a third. Then the interval between the first and the third thumps was accompanied by an unusual underground rattle, similar to a railway upon which dozens of trains are travelling at the same time. Afterward, for 5 to 6 minutes an exact likeness of artillery fire was heard: 50 to 60 salvoes in short, equal intervals, which got progressively weaker. After 1.5–2 minutes after one of the "barrages" six more thumps were heard, like cannon firing, but individual, loud and accompanied by tremors. The sky, at the first sight, appeared to be clear. There was no wind and no clouds. Upon closer inspection to the north, i.e. where most of the thumps were heard, a kind of an ashen cloud was seen near the horizon, which kept getting smaller and more transparent and possibly by around 2–3 pm completely disappeared.

Siberian Life newspaper, 27 July 1908
When the meteorite fell, strong tremors in the ground were observed, and near the Lovat village of the Kansk uezd two strong explosions were heard, as if from large-caliber artillery.

Testimony of Chuchan of the Shanyagir tribe, as recorded by I. M. Suslov in 1926
We had a hut by the river with my brother Chekaren. We were sleeping. Suddenly we both woke up at the same time. Somebody shoved us. We heard whistling and felt strong wind. Chekaren said "Can you hear all those birds flying overhead?" We were both in the hut, couldn't see what was going on outside. Suddenly, I got shoved again, this time so hard I fell into the fire. I got scared. Chekaren got scared too. We started crying out for father, mother, brother, but no one answered. There was noise beyond the hut, we could hear trees falling down. Chekaren and I got out of our sleeping bags and wanted to run out, but then the thunder struck. This was the first thunder. The Earth began to move and rock, the wind hit our hut and knocked it over. My body was pushed down by sticks, but my head was in the clear. Then I saw a wonder: trees were falling, the branches were on fire, it became mighty bright, how can I say this, as if there was a second sun, my eyes were hurting, I even closed them. It was like what the Russians call lightning. And immediately there was a loud thunderclap. This was the second thunder. The morning was sunny, there were no clouds, our Sun was shining brightly as usual, and suddenly there came a second one!

Chekaren and I had some difficulty getting out from under the remains of our hut. Then we saw that above, but in a different place, there was another flash, and loud thunder came. This was the third thunder strike. Wind came again, knocked us off our feet, struck the fallen trees.

We looked at the fallen trees, watched the tree tops get snapped off, watched the fires. Suddenly Chekaren yelled "Look up" and pointed with his hand. I looked there and saw another flash, and it made another thunder. But the noise was less than before. This was the fourth strike, like normal thunder.

Now I remember well there was also one more thunder strike, but it was small, and somewhere far away, where the Sun goes to sleep.

The Mineralogical Museum is collecting more and more materials about the fall of a large meteorite in Central Siberia in June 1908. All reports confirm the scale of this phenomenon, which affected a vast territory in Central Siberia. Eyewitnesses tell of the flight of a blindingly bright fireball that obscured the sunlight. Flames and a cloud of smoke were observed above the crash site, followed by deafening explosions, roars, crackles and vague, merging noises. The ground shook over a large area. According to the stories of the Evenks, a huge part of the forest at the crash site was uprooted.

Over the years, Kulik periodically and unsuccessfully raised the issue of a special expedition to the site. In 1924, geophysicist Professor Arkadiy Voznesenskiy handed him his rich materials about the fall of the meteorite, as well as data on seismic and barographic records processed by him. Two years later, Academician Vernadskiy returned from Paris and also supported the idea of ​​organizing a special expedition to the Podkamennaya Tunguska River region. Since the Academy of Sciences did not have sufficient funds, Kulik turned to the Moscow and Krasnoyarsk State Committees for financial assistance, and finally the expedition was allowed to proceed.

The expedition set off for Siberia in early February 1927. It consisted of only two people – leader Kulik and assistant Alexander Gulykh. They arrived by train in Taishet and from there set off by sled to the village of Kezhma, 380 km from the city.[35] There they stocked up on food and traveled another 200 km by sled through the taiga to the Vanovar factory. From there they set off on horseback to the crash site, led by local Evenks, but they failed to reach it. The snow was very deep, the horses were stuck in it up to their chests, and packs of wolves followed them. Exhausted, they returned to the trading post to look for other means of transport. In early April, they set off again, this time on skis, covering 5 to 7 km a day. They were accompanied by a Tungus family, whose reindeer were loaded with luggage. After a long journey and complaints from the Tungus, they reached a huge forest, felled to the ground in dense rows, and the trunks of the centuries-old trees were broken like reeds. Further on, there was bare ground, the trees on which had been completely burned. Only in the center of the bare area did trees stand without branches or leaves.

The Tungus and the reindeer refused to accompany them any further and had to return to the factory. There they reorganized and managed to cover 40 km in 6 days. They continued on rafts, which broke and were repaired along the way, but they managed to reach the Khushmu River. They pulled the rafts upstream on horses for 16 days. They reached bare trees without any branches, where the ground was covered with dead wood, on which it was possible to walk hundreds of meters without touching the ground. They organized their camp on completely bare terrain and began to circle around the center of the fall, covering tens of kilometers. Near its northeastern section, they discovered numerous flat craters, similar to lunar ones. The funnel-shaped depressions have a very diverse diameter, but more often - from 10 to 50 meters. Their depth does not exceed 4 meters, and their bottoms are already covered with swamp moss.

Since their food is running out, the whole group returns to Vanovar, where Kulik releases the workers accompanying him. With only two workers, he descended the Podkamennaya Tunguska to the mouth of the Yenisei in a flat-bottomed boat, passing 7 large and turbulent summer rapids and dozens of faults. They rowed alternately day and night, covering 1,300 kilometers in 3 weeks and 3 days and returned to Krasnoyarsk. Kulik gave a number of reports on his work in Krasnoyarsk and Novosibirsk, and with his enthusiasm and faith in the cause, he raised the spirits of Siberian public and government organizations.

After his return to Leningrad, in a report to the Presidium of the USSR Academy of Sciences, Kulik wrote that the positive results of this expedition were undeniable and had exceptional scientific significance. He insisted on a new expedition, which was necessary to study all traces of this phenomenon that had still survived.

Kulik's second Tunguska expedition, which began on April 7, 1928, became the most famous of all. From Petersburg to the Taishet station, its members traveled by train and from there continued by sledge. In Kezhma, they hired four hunters, bought food and two more horses, and on April 21, they set off again for Vanovar. At the factory, the expedition already numbered 7 people - Kulik, the future writer and naturalist Viktor Sytin, the cinematographer Nikolai Strukov, and three hunters, led by the experienced taiga worker Konstantin Syzikh. With sledges and horses, the expedition reached Podkamennaya Tunguska, the sacred river of the Evenks. There, they made two birch bark boats and three shtik boats - "Bolid", "Comet" and "Meteor". On May 22, they set off down the river without the Evenks, who had refused to continue with them. Then horses and men dragged the boats up the Chamba River, a tributary of the Podkamennaya Tunguska. With great effort, they pulled them over the rapids, reached the rapids and shallows of the Khushmu River, and finally reached the "Land of the Dead Forest", known from the first expedition. There, almost in the very center of the meteorite fall, they organized Base Camp №13, according to the expedition’s diary. They built a small bathhouse and a so-called “storage” for food to protect it from bears.

The expedition’s real work began on June 23 with a tour of the surrounding area. Their path was blocked by fallen tree trunks and newly sprouted bushes, and they moved slowly—they covered only 2–3 km per day, clearing the terrain. To protect themselves from the huge number of mosquitoes from the surrounding swamps, they wore 3 cotton shirts, gloves and mosquito nets made of horsehair. For 4 days they made their way to the Churdim gorge, where the Tunguska meteorite fell in the Great Swamp.

The forest around the epicenter lies in continuous rows, the fallen trees are arranged like a fan in all directions from the place where the meteorite fell. The area emits a slight glow. There are no animals or birds, and only sparse, thin vegetation rises from the place of the fire. They make a geodetic survey with a theodolite and give names to the highest mountain peaks in the area. Thus, the Farrington, Khladnaya, Vernadsky and other peaks appear on the map. After about a month, the excavation of the craters begins in search of fragments of the meteorite. However, the holes quickly flood and they have to make a pump from a hollowed-out cedar trunk. Despite the persistent, hard and strenuous work, nothing was found.

Gradually, food began to run out, the people were exhausted and became apathetic. In July, Strukov finished the photographs and Kulik sent him home with three of the weaker hunters. Only four remained. Soon, some of them began to fall ill with acute furunculosis and large abscesses appeared on their skin. In addition, the first signs of scurvy appeared in all of them. Since they were unable to carry out the very important magnetometric measurements, Kulik decided to continue his work alone, in early August the others were released, and Viktor Sytin left for Petersburg to take care of his health and collect new equipment and food for the expedition.

After a series of disturbances, in mid-October Sytin arrived back with a whole group of assistants, food, tools, 10 pack horses and 4 dogs, a breed of husky. The craters were examined with magnetometers, but none of them showed any indication of metal at depth. Not a single trace or fragment of a fallen meteorite was found anywhere. At the end of October, the instruments, geological collections, and equipment were packed up and the expedition headed back to Vanovar. They moved through deep snow and frozen ice blocks, at temperatures of minus 35–40 °C.

After returning to Leningrad, the participants were surprised by the great popularity that the expedition had received. The film shot by Nikolai Strukov was shown, and his article on the subject was published in the magazine "Ogonyok". Eduard Bagritsky wrote the poem "Explorer", dedicated to Kulik. One of the factories even released a board game for children called "In the Taiga for a Meteorite. In the Footsteps of L.A. Kulik".

In Leningrad, without even resting, Kulik planned a new, third expedition to Podkamennaya Tunguska. On January 5, 1929, at a meeting of the Expeditionary Research Commission of the USSR Academy of Sciences, Academician Fersman reported on a new expedition planned for the current year, under the leadership of Kulik. The third expedition to Podkamennaya Tunguska turned out to be the longest and most numerous, but not much reliable material has been preserved about it. Since experienced boreholes, zoologists, botanists, and chemists were not willing to join it, Kulik gathered amateurs with the necessary specialties.

The new expedition set off on February 24, 1929. Kulik's assistant was the future geodesist and meteorite specialist Yevgeny Krinov. On April 6, the team arrived at the site of the meteorite fall, accompanied by 50 carts with equipment and food supplies. According to an agreement with the organizations in Kezhma, they found two houses and a storage shed already built, and on the Khushmu River, next to the bathhouse, a house with a shed. They began by clearing the Suslovsky funnel, which had become a swamp. To drain the water, they dug a trench 38 m long and 4 m deep, then cleared the vegetation along the bottom. But the soil quickly thawed and the pit filled with water again, despite continuous pumping. On July 14, a group of surveyors arrived to help determine astronomical points before the upcoming aerial survey.

Some of the people began to drill well №1 in the Suslovsky funnel. By this time, the expedition had already completely exhausted all funds and found itself in significant debt to local commercial organizations. In January 1930, the Academy of Sciences sent money to pay off debts, complete the work, and return the expedition from the taiga. By March 1, drilling in well №1 on the northern side of the funnel was completed. And although they penetrated the permafrost to a depth of 25 m and passed through a 6 m aquifer, nothing was found. Drilling in the central and southern parts of the funnel was also fruitless.

In early June, Kulik traveled 320 km on horseback to Kezhma, where he prepared a landing strip for a contracted seaplane, needed for aerial photography of the area. He set up observation posts on the bell tower, on an island, and by the burning fires at the runway. The seaplane did not arrive until July 18, and was greeted by crowds of curious people. They flew to the expedition, but soon returned to Kezhma, having encountered a storm. A rumor spread in the village that the plane had returned because Kulik had died of fright during the flight. In fact, the seaplane crew had another upcoming engagement, so they abandoned a new flight to Podkamennaya Tunguska and flew to Irkutsk, while Kulik set off on the return journey to the expedition, where the research continued.

All the work done by the expedition, and especially the drilling, did not lead to the discovery of fragments of the meteorite. The researchers also did not come to a comprehensive answer to the question of the origin of the rounded depressions, which are sometimes referred to in the literature on the Tunguska meteorite as craters. At the end of October, the expedition returned to Leningrad.