Tunguska
The Siberian Explosion With No Crater
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- Astronomy
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The book examines eyewitness accounts from local reindeer herders and Russian observers, along with scientific investigations that ruled out conventional meteorite impacts. Chapters cover the airburst model, glancing impact theories, and the unusual blast pattern. Researchers also consider whether the object was an asteroid or comet, comparing it to the more recent Chelyabinsk meteor event.
While some fringe theories suggest alternative explanations for the explosion, this audiobook focuses on the scientific consensus that a large airburst caused the devastation. Anyone interested in astronomical events and their earthly consequences will find this detailed investigation compelling.
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On 30 June [O.S. 17 June] 1908, around 7:17 in the morning, people in the hills northwest of Lake Baikal saw a bluish light moving across the sky, as bright as the Sun, leaving a thin trail behind. Closer to the horizon, a flash created a thick cloud, followed by a pillar of fire lighting up the land. That pillar split into two and disappeared, turning black. About ten minutes later, sounds like artillery echoed through the air. Witnesses said the source moved from east to north. The noise was followed by a shock wave that knocked people down and shattered windows hundreds of kilometers away.
The explosion was felt across Eurasia, detected by seismic stations from Germany and Denmark to Croatia and the United Kingdom. Even as far away as Batavia in the Dutch East Indies—now Indonesia—and Washington, D.C., in the United States, air waves from the blast were recorded. In some locations, the resulting shock wave equaled a 5.0-magnitude earthquake on the Richter scale.
Over the next few days, the night skies over Asia and Europe glowed brightly. There are reports of photographs being taken at midnight—without flashbulbs—in places like Sweden and Scotland, showing a vividly lit scene. Some have theorized that this glow came from light passing through ice particles high in the atmosphere, formed by extremely low temperatures after the explosion. This same phenomenon was later seen on a smaller scale when Space Shuttles created similar conditions. In the United States, the Smithsonian Astrophysical Observatory at Mount Wilson Observatory in California recorded a months-long drop in atmospheric transparency, which matched what you'd expect from increased dust particles in the air.
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At breakfast time I was sitting by the house at Vanavara Trading Post, facing north. I suddenly saw that directly to the north, over Onkoul's Tunguska Road, the sky split in two and fire appeared high and wide over the forest. The heat was intense, so much that my shirt felt like it was on fire, coming from the direction of the flames. Then the sky shut closed with a loud thump, throwing me several meters. I lost consciousness for a moment before my wife helped me inside. Soon after, the Earth began to shake and sounds like falling rocks or firing cannons filled the air. When the sky opened again, a hot wind rushed through the houses, leaving paths in the ground and damaging crops. Windows shattered, and part of an iron lock on the barn snapped.
We were sleeping in a hut by the river with my brother Chekaren when we both woke up at once. Someone shoved us, and we heard whistling and felt strong wind. Chekaren asked, "Can you hear all those birds flying overhead?" We couldn't see outside, but then I was shoved again—so hard I fell into the fire. We cried out for our parents, but no one answered. Trees were falling beyond the hut. We tried to run out, but the thunder struck first. That was the first thunder. The ground began to shake, and the wind knocked over our hut. My body was pushed down by sticks, but my head stayed clear. Then I saw trees falling, branches on fire, as bright as a second sun—my eyes hurt, I even closed them. It looked like lightning. Right after, there was a loud thunderclap. That was the second thunder. The morning was sunny, no clouds, the Sun shining brightly, and suddenly there came a second one. We struggled free from under the hut, then saw another flash above, followed by more thunder. That was the third thunder strike. Wind knocked us off our feet, struck the fallen trees.
They stared at the broken trees, at the tops torn away, at the flames consuming the forest. Then Chekaren shouted, “Look up,” and gestured. The speaker turned his gaze upward and saw a second flash, followed by a clap of thunder. The sound was softer than the first. This felt like the fourth strike—normal thunder, perhaps. There was one more, faint and distant, as if the sun were sinking into sleep.
On the morning of June 17th, around 9:00 UTC+7, peasants in Karelinski village, about 200 versts north of Kirensk, saw a strange, bluish-white object high in the clear sky to the northwest. It looked like a "pipe," a cylinder, and moved downward for ten minutes. As it approached the forest, it began to smudge, then turned into a huge black cloud of smoke. A loud knocking sound followed—like falling stones or artillery firing—and all buildings shook. Flames appeared from the cloud, and panic spread through the village. At the same time, someone in the forest about six versts north of Kirensk heard what sounded like an artillery barrage repeating every 15 minutes at least ten times. In Kirensk, window glass in some buildings facing northeast also rattled.
At 7:43 on the 17th, residents of Kezhemskoye village were startled by a sound like strong wind, followed almost immediately by a terrifying thump, then another, then a third. Between the first and third thumps came an unusual rumble from underground, as if many trains were moving at once. For five or six minutes afterward, the noise resembled artillery fire—about fifty to sixty blasts, evenly spaced and growing weaker. Then, 1.5 to 2 minutes after one of the barrages, six more thumps shook the ground, each loud and accompanied by tremors, like individual cannon shots. Near Lovat village in the Kansk uezd, two powerful explosions were heard, as though from large-caliber artillery.
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Since the 1908 explosion, around a thousand scholarly papers have been written about the Tunguska event, most in Russian. Because of the site’s remote location and limited instruments available at the time, scientists have had to rely on damage reports and later geological studies to understand what happened. Estimates of the blast’s energy range from three to thirty megatons of TNT. It wasn’t until more than a decade later that any serious scientific study began. In 1921, the Russian mineralogist Leonid Kulik led an expedition to the Podkamennaya Tunguska River basin for the Soviet Academy of Sciences. Though he never reached the center of the blast, local accounts convinced him a large meteorite had struck the area. He persuaded the Soviet government to fund another mission, hoping to find meteoric iron.
In 1927, Kulik led a scientific team to the Tunguska site, hiring Evenki hunters to guide them to where they expected an impact crater would be. Instead, there was no crater at ground zero. The area, roughly 8 kilometers across, showed trees that were scorched and branchless but still standing. Further out, trees had been knocked down in a large radial pattern, away from the center. By the 1960s, it was confirmed the damaged zone covered 2,150 square kilometers, shaped like a giant butterfly with a wingspan of 70 kilometers and a body length of 55 kilometers. Kulik found holes he mistakenly believed were meteorite craters, though he lacked the tools to dig them deeply.
During the next ten years, three more expeditions went to the area. Kulik found dozens of small bogs, each ten to fifty meters across, wondering if they might be meteoric craters. One, called "Suslov's crater," was drained, but an old tree stump at the bottom ruled it out. In 1938, Kulik arranged for an aerial survey covering 250 square kilometers. The original 1,500 negatives were destroyed in 1975 by order of Yevgeny Krinov. Positive prints were saved in Tomsk. Expeditions in the 1950s and 1960s found microscopic spheres in soil samples—silicate and magnetite. Later studies detected similar spheres in tree resin, and chemical analysis showed high nickel content relative to iron, typical of meteorites. Their distribution matched what would be expected from a meteor air burst. Further studies revealed unusual metal ratios not found in the surrounding environment, supporting their extraterrestrial origin.
Chemical analysis of peat bogs near the Tunguska site showed unusual isotopic signatures in carbon, hydrogen, and nitrogen from the year 1908, matching patterns not found in surrounding layers or areas outside the region. These anomalies also included an unusually high amount of iridium, similar to what's seen at the Cretaceous–Paleogene boundary. Scientists believe this debris came from the exploding object and may have fallen as acid rain. Some researchers disagree, noting that while certain papers reported isotope compositions matching CI and CM carbonaceous chondrites and found iridium traces, other labs have not confirmed those results.
Researcher John Anfinogenov believes a boulder known as “John’s stone” found at the site might be leftover from the meteorite, but tests on the quartzite show it likely formed through hydrothermal processes, possibly connected to ancient volcanic activity from the Permian-Triassic Siberian Traps. In 2013, another group of scientists shared findings from tiny samples taken from a peat bog near the explosion’s center, which may contain material of extraterrestrial origin.
It's often said that the explosion flattened over 80 million trees, but that figure came from an early estimate that used tree density and impacted area in a way that ended up exaggerating the damage by four times. So that number is probably wrong. What’s more certain is the size of the biggest trees that actually fell—those measures come from careful records and show they were around 44 centimeters, or about 17 inches, across at the trunk. Some accounts have claimed they were a meter wide, but that’s not supported by what was actually observed.
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The most widely accepted scientific explanation for the Tunguska explosion is that it was caused by a meteor air burst—an asteroid exploding in the sky—about 6 to 10 kilometers above Earth’s surface. Every day, meteoroids from outer space enter our atmosphere, moving at speeds of at least 11 kilometers per second. As they travel through the air, the friction and compression create intense heat, and most burn up or explode before hitting the ground. Early estimates of the energy released by the Tunguska air burst ranged from 10 to 30 megatons of TNT, depending on how high the explosion occurred, with calculations based on nuclear weapon scaling laws.
More recent calculations that factor in the object’s momentum show that the energy was focused more downward than it would have been in a nuclear explosion, estimating the air burst at 3 to 5 megatons of energy. That 15-megaton estimate is about 1,000 times stronger than the Trinity test, and roughly equal to the Castle Bravo test in 1954, which measured 15.2 megatons. It was also about one-third the power of the Tsar Bomba test in 1961. A 2019 paper suggests the actual explosive force might have been as high as 20 to 30 megatons.
Since the second half of the 20th century, scientists have been watching Earth’s atmosphere closely, using infrasound and satellite technology, and they’ve found that asteroid air bursts with energies similar to nuclear weapons happen regularly. Most of these are small, but events like the one at Tunguska, which released energy equivalent to 5 to 15 megatons, occur much less often. Eugene Shoemaker estimated that 20 kilotons worth of explosions happen every year, and Tunguska-sized events occur about once every 300 years. More recent estimates suggest they happen about once every thousand years, with five-kiloton bursts occurring roughly once per year. Most of these are thought to come from asteroids rather than comets, based on how deeply they penetrate the atmosphere. The largest asteroid air burst recorded with modern tools was the 500 kilotons Chelyabinsk meteor in 2013, which broke windows and left behind meteorites.
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In 2020, Russian scientists ran computer simulations to figure out what happened during the Tunguska event, using models that tested how asteroids of 200, 100, and 50 meters would behave if they hit Earth’s atmosphere at a shallow angle. They tried different compositions—iron, rock, and ice—and found that an iron asteroid up to 200 meters across, moving at 11.2 kilometers per second, best matched what was seen. The model showed the object didn’t actually crash into the ground but instead skimmed off the atmosphere and went back into space.
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The explosion left a distinctive pattern in the trees near where it happened, similar to what was seen during a famous test called Operation Blowdown in Australia. That test was a large air-burst explosion, and the damage it caused to trees helps explain what happened here. The trees directly under the blast were stripped of their branches and bark but stayed upright, because the force moved straight down. As the blast wave spread outward, it became more horizontal, so trees farther away got knocked over entirely.
In the mid-1960s, Soviet scientists ran experiments that mirrored the strange blast pattern seen at Tunguska. Using model forests made of matches on wire stakes and small charges dropped down wires, they recreated a butterfly-shaped damage pattern similar to what was found in Siberia. The tests suggested the object had approached the ground at about 30 degrees and came from a direction 115 degrees from north, exploding high in the air before hitting the surface.
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In 1930, F. J. W. Whipple, a British meteorologist and mathematician, proposed that the object responsible for the Tunguska explosion was a small comet. He suggested that comets, made of dust and volatile materials like water ice and frozen gases, could have burned up completely upon entering Earth’s atmosphere, leaving no crater or obvious remains. This idea gained support from reports of glowing skies, or “skyglows,” seen across Eurasia for several nights after the event. These bright nights may have been caused by dust and ice from the comet's tail spreading into the upper atmosphere. By the 1960s, this cometary explanation had become widely accepted among Soviet Tunguska researchers.
In 1978, Slovak astronomer Ľubor Kresák proposed the Tunguska object was a fragment of Comet Encke, a periodic comet with a three-year orbit inside Jupiter’s path. That comet is also linked to the Beta Taurids meteor shower, which peaks around June 28–29. The Tunguska explosion happened during that peak, and the object’s trajectory matches what you'd expect from such a fragment. A risk corridor has since been calculated showing the impactor could have hit North America if it had arrived just minutes earlier. These kinds of objects are known to explode tens to hundreds of kilometers above ground, something military satellites have observed for decades. In 2019, astronomers searched for asteroids about 100 meters wide from the Taurid swarm between July 5–11 and July 21–August 10, but as of February 2020, no such objects were found.
In 2001, a study by Farinella, Foschini, and others recalculated the odds using orbital models from the object’s atmospheric flight path, concluding an 83% chance it came from the asteroid belt rather than a comet, which had only a 17% probability. That same year, Zdeněk Sekanina had already argued in a paper that a body made of cometary material, moving through the atmosphere on such a shallow course, should have broken apart long before reaching the lower atmosphere. Instead, the Tunguska object remained intact. Sekanina believed this pointed to a dense, rocky object — likely of asteroidal origin. Some comet supporters have since proposed it might have been an extinct comet with a stony outer layer that allowed it to survive the journey.
The main problem with the idea that Tunguska was caused by an asteroid is that a stony object should have left behind a large crater, and none has ever been found. One explanation is that the asteroid exploded in the air after passing through the atmosphere, breaking apart from the extreme heat and pressure. The explosion would have been so powerful that nothing substantial survived, and the debris spread into the upper atmosphere, causing the skyglows. In 1993, scientists proposed that the object was about sixty meters across, with a composition between a regular chondrite and a carbonaceous chondrite. Carbonaceous chondrites usually dissolve quickly when exposed to water, unless they’re frozen.
A stony asteroid could have caused the Tunguska event, according to Christopher Chyba and other researchers. Their models explain that as the object descended, the forces working against it grew stronger than the cohesive strength holding it together. This caused the asteroid to break apart midair, releasing almost all of its energy at once. Because of this, there was no crater formed. Instead, the damage spread across a wide area, and the destruction was largely due to the thermal energy from the blast.
In the 1990s, Italian scientists working under the direction of physicist Giuseppe Longo from the University of Bologna studied tree rings in the Tunguska area. They took samples from the cores of trees and analyzed trapped particles from 1908. The results showed high levels of material typical of rocky asteroids, which is uncommon in comets.
Kelly and others in 2009 suggested the Tunguska event was caused by a comet, pointing to sightings of noctilucent clouds afterward— a sign of water vapor in the upper atmosphere. They drew a comparison to the exhaust plume from NASA’s Endeavour Space Shuttle. At around the same time, Russian researchers led by Edward Drobyshevski proposed that the near-Earth asteroid 2005 NB56 might be the object’s parent body. That asteroid passed within 0.06945 astronomical units of Earth on June 27, 1908—just three days before the explosion. The team noted its orbit could match the Tunguska object’s modeled path, even factoring in weak non-gravitational forces. In 2013, a US-European team analyzing fragments from the site found evidence consistent with an iron meteorite.
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In February 2013, a bolide exploded over Chelyabinsk, giving scientists new data to study the Tunguska event. Using information from both occurrences, researchers ran a statistical analysis on more than 50 million possible combinations of bolide and entry properties that could have caused Tunguska-scale damage. Some models focused on matching the tree-fall pattern and pressure waves from Tunguska. Four different computer models produced similar results, suggesting that the most likely Tunguska impactor was a stony object between 50 and 80 meters in diameter, entering the atmosphere at about 55,000 kilometers per hour, exploding at an altitude of 10 to 14 kilometers, and releasing energy equivalent to 10 to 30 megatons. That’s similar to the explosive power of the 1980 Mount St. Helens eruption. The researchers also determined that impactors of this size hit Earth only once every few thousand years on average.
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In June 2007, scientists from the University of Bologna said they had found a lake in the Tunguska region that might be an impact crater from the event. They don’t question that the Tunguska object exploded in the air, but they think a piece about ten meters across made it through and hit the ground. That lake is called Lake Cheko. It's a small, bowl-shaped body of water roughly eight kilometers north-northwest of where the explosion was centered.
The idea that Lake Cheko was formed by the Tunguska explosion has been challenged by other experts. A team in 1961 said the lake must be at least 5,000 years old, pointing to thick silt on the bottom. But newer studies suggest only about a metre of that sediment is normal lake buildup, matching an age of roughly 100 years. Sonar scans show the lake floor has a cone-shaped structure, which fits with an impact crater. Magnetic tests also found something possibly about a metre across beneath the deepest part of the lake — maybe a piece of the object that caused the blast. And the lake’s long axis points toward the explosion’s centre, about 7.0 kilometres away. Scientists are still working to figure out exactly how the lake formed.
Lake Cheko in Siberia, near the 1908 Tunguska explosion site, may have formed from a crater left by a cosmic impact. Scientists studied sediment cores from the lake’s bottom to test this idea. One core, 175 centimeters long and taken from the center, showed a clear layering: an upper section of fine lacustrine deposits sitting on coarser chaotic material. The transition between these layers happened close to 1908, based on measurements of lead-210 and cesium-137. Pollen found in the top part of the core, from after 1908, indicated aquatic plants were thriving—something missing in the older layers before the explosion. Data on carbon, nitrogen, and isotopes also support the idea that Lake Cheko formed at the time of the Tunguska event.
Pollen found in Lake Cheko shows two distinct layers, one above and one below about 100 centimeters down. The upper layer, within the last 100 centimeters, includes pollen from taiga trees like Abies, Betula, Juniperus, Larix, Pinus, Picea, and Populus, along with remains of aquatic plants such as Callitriche, Hottonia, Lemna, Hydrocharis, Myriophyllum, Nuphar, Nymphaea, Potamogeton, and Sagittaria—plants that grow in water up to four meters deep. This suggests the area was once a lake, similar to today’s conditions. In contrast, the lower layer has tree pollen but no signs of aquatic plants, indicating there was no lake then, just a forest growing on wet land. Pollen and microcharcoal show this forest gradually disappeared, likely due to fires, then possibly by the explosion that formed the lake between 100 and 90 centimeters down, followed by more fires in the upper section.
In 2017, Russian scientists released new research challenging the idea that the Tunguska explosion created Lake Cheko. Using soil samples from the lake’s floor, they found evidence that the lake is at least 280 years old—much older than the 1908 event. The team discovered a layer of radionuclides from nuclear tests at Novaya Zemlya in the mid-20th century. By measuring how deep this layer was, they calculated the lake’s sedimentation rate at between 3.6 and 4.6 millimeters per year. That’s less than half the rate previously estimated by Gasperini et al. in their 2009 study. The 2017 researchers counted at least 280 annual layers in a 1260-millimeter core sample from the lake bottom, confirming the lake formed long before Tunguska.
There are issues with how impact physics would work in this case. It's unlikely that a stony meteorite, if it was the right size, would have had the strength to survive passing through the atmosphere intact. Even if it did, it wouldn't have kept enough speed to dig out a crater as large as the one supposedly formed. That’s the problem with the idea of an impact at Lake Cheko. The physics just don’t add up for a stone object of that size to behave the way it would need to in order to create such an explosion.
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While most scientists agree that the Tunguska explosion resulted from a small asteroid impact, one alternative theory has gained attention from astrophysicist Wolfgang Kundt. He suggests the event was caused by the release and sudden explosion of about 10 million tons of natural gas escaping from deep within the Earth’s crust. According to his idea, the gas rose in the atmosphere until it reached a point where its density matched that of the surrounding air. It then moved downwind like a wick, drifting until it encountered an ignition source—perhaps lightning. Once ignited, the fire traveled along this gaseous pathway, eventually reaching the original leak site underground, triggering a massive explosion.
Another explanation for the Tunguska event is what’s called the verneshot hypothesis, which suggests a specific geophysical mechanism might have caused the explosion. Researchers have explored this idea as a possible cause, offering a different perspective on how such a massive airburst could have occurred without leaving a crater. This line of thinking looks into natural forces that could produce effects similar to what was observed in Siberia. While the exact process remains debated, these theories attempt to account for the lack of a visible impact site and the immense damage reported. The idea continues to be studied as part of ongoing efforts to understand this mysterious event.
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On 15 February 2013, a meteoroid exploded in the air above Chelyabinsk in Russia’s Ural district. The object, an asteroid about 17 to 20 meters across, had an initial mass of roughly 11,000 tons and released energy equivalent to 500 kilotons. The resulting air burst caused over 1,200 injuries, mostly from shattered glass as the shock wave hit windows.
A powerful meteor air burst shook the skies again in December 2018, this time near the Kamchatka Peninsula in Russia. The event marked the third-largest meteor recorded since 1900. It followed closely behind the Chelyabinsk meteor in February 2013 and the Tunguska explosion.
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