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99-558: In 1908, an asteroid impacted near the river and later became known as the Tunguska event . The river's nutrition is mainly snow (60%); rain and groundwater nutrition account for 16 and 24%, respectively. The flood lasts from the beginning of May to the end of June, in the lower reaches until the beginning of July. From July to October, there is a summer low, interrupted by a rise in the level to 5.5 m during floods, which can be from one to four per year. The average annual water consumption at

198-465: A Prandtl–Meyer expansion fan . The accompanying expansion wave may approach and eventually collide and recombine with the shock wave, creating a process of destructive interference. The sonic boom associated with the passage of a supersonic aircraft is a type of sound wave produced by constructive interference . Unlike solitons (another kind of nonlinear wave), the energy and speed of a shock wave alone dissipates relatively quickly with distance. When

297-526: A carbonaceous chondrite . Typical carbonaceous chondrite substance tends to be dissolved with water rather quickly unless it is frozen. Christopher Chyba and others have proposed a process whereby a stony asteroid could have exhibited the Tunguska impactor's behaviour. Their models show that when the forces opposing a body's descent become greater than the cohesive force holding it together, it blows apart, releasing nearly all its energy at once. The result

396-408: A phase transition : the pressure–time diagram of a supersonic object propagating shows how the transition induced by a shock wave is analogous to a dynamic phase transition . When an object (or disturbance) moves faster than the information can propagate into the surrounding fluid, then the fluid near the disturbance cannot react or "get out of the way" before the disturbance arrives. In a shock wave

495-486: A supersonic jet's flyby (directly underneath the meteor's path) and as a detonation wave , with the circular shock wave centred at the meteor explosion, causing multiple instances of broken glass in the city of Chelyabinsk and neighbouring areas (pictured). In the examples below, the shock wave is controlled, produced by (ex. airfoil) or in the interior of a technological device, like a turbine . The wave disk engine (also named "Radial Internal Combustion Wave Rotor")

594-480: A 10-metre (33 ft) fragment survived the explosion and struck the ground. Lake Cheko is a small bowl-shaped lake about 8 km (5.0 mi) north-northwest of the hypocentre. The hypothesis has been disputed by other impact crater specialists. A 1961 investigation had dismissed a modern origin of Lake Cheko, saying that the presence of metres-thick silt deposits on the lake bed suggests an age of at least 5,000 years, but more recent research suggests that only

693-407: A body composed of cometary material, travelling through the atmosphere along such a shallow trajectory, ought to have disintegrated, whereas the Tunguska body apparently remained intact into the lower atmosphere. Sekanina also argued that the evidence pointed to a dense rocky object, probably of asteroidal origin. This hypothesis was further boosted in 2001, when Farinella , Foschini, et al. released

792-497: A boulder found at the event site, known as John's stone, is a remnant of the meteorite, but oxygen isotope analysis of the quartzite suggests that it is of hydrothermal origin, and probably related to Permian-Triassic Siberian Traps magmatism. In 2013, a team of researchers published the results of an analysis of micro-samples from a peat bog near the centre of the affected area, which show fragments that may be of extraterrestrial origin. The leading scientific explanation for

891-500: 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 AM 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

990-407: A component vector analysis of the flow; doing so allows for the treatment of the flow in an orthogonal direction to the oblique shock as a normal shock. When an oblique shock is likely to form at an angle which cannot remain on the surface, a nonlinear phenomenon arises where the shock wave will form a continuous pattern around the body. These are termed bow shocks . In these cases, the 1d flow model

1089-642: A configuration in which the rapidly moving material down the chute impinges on an obstruction wall erected perpendicular at the end of a long and steep channel. Impact leads to a sudden change in the flow regime from a fast moving supercritical thin layer to a stagnant thick heap. This flow configuration is particularly interesting because it is analogous to some hydraulic and aerodynamic situations associated with flow regime changes from supercritical to subcritical flows. Astrophysical environments feature many different types of shock waves. Some common examples are supernovae shock waves or blast waves travelling through

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1188-436: A crater left by the impact of a fragment of a cosmic body. Sediment cores from the lake's bottom were studied to support or reject this hypothesis. A 175-centimetre-long (69 in) core, collected near the center of the lake, consists of an upper c. 1-metre-thick (39 in) sequence of lacustrine deposits overlaying coarser chaotic material. Pb and Cs indicate that the transition from lower to upper sequence occurred close to

1287-402: 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

1386-702: A distance (not coincidentally, since explosions create shock waves). Analogous phenomena are known outside fluid mechanics. For example, charged particles accelerated beyond the speed of light in a refractive medium (such as water, where the speed of light is less than that in a vacuum ) create visible shock effects, a phenomenon known as Cherenkov radiation . Below are a number of examples of shock waves, broadly grouped with similar shock phenomena: Shock waves can also occur in rapid flows of dense granular materials down inclined channels or slopes. Strong shocks in rapid dense granular flows can be studied theoretically and analyzed to compare with experimental data. Consider

1485-449: 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

1584-510: A gigantic spread-eagled butterfly with a "wingspan" of 70 km (43 mi) and a "body length" of 55 km (34 mi). Upon closer examination, Kulik found holes that he erroneously concluded were meteorite holes; he did not have the means at that time to excavate the holes. During the next 10 years, there were three more expeditions to the area. Kulik found several dozen little "pothole" bogs, each 10 to 50 metres (33 to 164 feet) in diameter, that he thought might be meteoric craters. After

1683-402: A huge explosion. The destruction would have to have been so complete that no remnants of substantial size survived, and the material scattered into the upper atmosphere during the explosion would have caused the skyglows. Models published in 1993 suggested that the stony body would have been about 60 metres (200 ft) across, with physical properties somewhere between an ordinary chondrite and

1782-480: 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

1881-543: A joint US-European team was consistent with an iron meteorite. The February 2013 Chelyabinsk bolide event provided ample data for scientists to create new models for the Tunguska event. Researchers used data from both Tunguska and Chelyabinsk to perform a statistical study of over 50 million combinations of bolide and entry properties that could produce Tunguska-scale damage when breaking apart or exploding at similar altitudes. Some models focused on combinations of properties which created scenarios with similar effects to

1980-576: A laborious exercise in draining one of these bogs (the so-called "Suslov's crater", 32 m [105 ft] in diameter), he found an old tree stump on the bottom, ruling out the possibility that it was a meteoric crater. In 1938, Kulik arranged for an aerial photographic survey of the area covering the central part of the leveled forest (250 square kilometres [97 sq mi]). The original negatives of these aerial photographs (1,500 negatives, each 18 by 18 centimetres [7.1 by 7.1 inches]) were burned in 1975 by order of Yevgeny Krinov , then Chairman of

2079-477: A line or a plane if the flow field is two-dimensional or three-dimensional, respectively. Shock waves are formed when a pressure front moves at supersonic speeds and pushes on the surrounding air. At the region where this occurs, sound waves travelling against the flow reach a point where they cannot travel any further upstream and the pressure progressively builds in that region; a high-pressure shock wave rapidly forms. Shock waves are not conventional sound waves;

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2178-407: A loss of total pressure, meaning that it is a less efficient method of compressing gases for some purposes, for instance in the intake of a scramjet . The appearance of pressure-drag on supersonic aircraft is mostly due to the effect of shock compression on the flow. In elementary fluid mechanics utilizing ideal gases , a shock wave is treated as a discontinuity where entropy increases abruptly as

2277-550: A maximum activity around 28–29 June. The Tunguska event coincided with that shower's peak activity, the Tunguska object's approximate trajectory is consistent with what would be expected from a fragment of Comet Encke, and a hypothetical risk corridor has now been calculated demonstrating that if the impactor had arrived a few minutes earlier it would have exploded over the US or Canada. It is now known that bodies of this kind explode at frequent intervals tens to hundreds of kilometres above

2376-420: A metre or so of the sediment layer on the lake bed is "normal lacustrine sedimentation", a depth consistent with an age of about 100 years. Acoustic-echo soundings of the lake floor support the hypothesis that the Tunguska event formed the lake. The soundings revealed a conical shape for the lake bed, which is consistent with an impact crater. Magnetic readings indicate a possible metre-sized chunk of rock below

2475-516: A months-long decrease in atmospheric transparency consistent with an increase in suspended dust particles. Though the region of Siberia in which the explosion occurred was very sparsely populated in 1908, there are accounts of the event from eyewitnesses who were in the surrounding area at the time, and regional newspapers reported the event shortly after it occurred. According to the testimony of S. Semenov, as recorded by Russian mineralogist Leonid Kulik 's expedition in 1930: At breakfast time I

2574-414: A possible candidate for the Tunguska object's parent body as the asteroid made a close approach of 0.06945 AU (27  LD ) from Earth on 27 June 1908, three days before the Tunguska impact. The team suspected that 2005 NB 56 's orbit likely fits with the Tunguska object's modelled orbit, even with the effects of weak non-gravitational forces. In 2013, analysis of fragments from the Tunguska site by

2673-425: 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

2772-454: A range of assumptions about the object's composition as if it was made of iron, rock, or ice. The model that most closely matched the observed event was an iron asteroid up to 200 metres in diameter, travelling at 11.2 km per second, that glanced off the Earth's atmosphere and returned into solar orbit. The explosion's effect on the trees near the explosion's hypocentre was similar to

2871-795: A river in Siberia is a stub . You can help Misplaced Pages by expanding it . Tunguska event The Tunguska event was a large explosion of between 3 and 50 megatons 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 flattened an estimated 80 million trees over an area of 2,150 km (830 sq mi) of forest, and eyewitness accounts suggest up to three people may have died. The explosion

2970-442: A shock wave passes through matter, energy is preserved but entropy increases. This change in the matter's properties manifests itself as a decrease in the energy which can be extracted as work, and as a drag force on supersonic objects ; shock waves are strongly irreversible processes . Shock waves can be: Some other terms: The abruptness of change in the features of the medium, that characterize shock waves, can be viewed as

3069-405: A shock wave takes the form of a very sharp change in the gas properties. Shock waves in air are heard as a loud "crack" or "snap" noise. Over longer distances, a shock wave can change from a nonlinear wave into a linear wave, degenerating into a conventional sound wave as it heats the air and loses energy. The sound wave is heard as the familiar "thud" or "thump" of a sonic boom , commonly created by

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3168-424: A shock wave. It is assumed the system is adiabatic (no heat exits or enters the system) and no work is being done. The Rankine–Hugoniot conditions arise from these considerations. Taking into account the established assumptions, in a system where the downstream properties are becoming subsonic: the upstream and downstream flow properties of the fluid are considered isentropic. Since the total amount of energy within

3267-409: A stony mantle that allowed it to penetrate the atmosphere. The chief difficulty in the asteroid hypothesis is that a stony object should have produced a large crater where it struck the ground, but no such crater has been found. It has been hypothesised that the asteroid's passage through the atmosphere caused pressures and temperatures to build up to a point where the asteroid abruptly disintegrated in

3366-402: A study calculating the probabilities based on orbital modelling extracted from the atmospheric trajectories of the Tunguska object. They concluded with a probability of 83% that the object moved on an asteroidal path originating from the asteroid belt , rather than on a cometary one (probability of 17%). Proponents of the comet hypothesis have suggested that the object was an extinct comet with

3465-423: A zone, roughly 8 kilometres (5.0 mi) across, where the trees were scorched and devoid of branches, but still standing upright. Trees farther from the centre had been partly scorched and knocked down away from the centre, creating a large radial pattern of downed trees. In the 1960s, it was established that the zone of levelled forest occupied an area of 2,150 km (830 sq mi), its shape resembling

3564-572: Is a kind of pistonless rotary engine that utilizes shock waves to transfer energy between a high-energy fluid to a low-energy fluid, thereby increasing both temperature and pressure of the low-energy fluid. In memristors , under externally-applied electric field, shock waves can be launched across the transition-metal oxides, creating fast and non-volatile resistivity changes. Advanced techniques are needed to capture shock waves and to detect shock waves in both numerical computations and experimental observations. Computational fluid dynamics

3663-481: Is commonly used to obtain the flow field with shock waves. Though shock waves are sharp discontinuities, in numerical solutions of fluid flow with discontinuities (shock wave, contact discontinuity or slip line), the shock wave can be smoothed out by low-order numerical method (due to numerical dissipation) or there are spurious oscillations near shock surface by high-order numerical method (due to Gibbs phenomena ). There exist some other discontinuities in fluid flow than

3762-447: Is generally attributed to a meteor air burst , the atmospheric explosion of a stony asteroid about 50–60 metres (160–200 feet) wide. The asteroid approached from the east-south-east, probably with a relatively high speed of about 27 km/s (60,000 mph) (~ Ma 80). Though the incident is classified as an impact event , the object is thought to have exploded at an altitude of 5 to 10 kilometres (3 to 6 miles) rather than hitting

3861-588: Is no crater, with damage distributed over a fairly wide radius, and all the damage resulting from the thermal energy the blast releases. During the 1990s, Italian researchers, coordinated by the physicist Giuseppe Longo from the University of Bologna , extracted resin from the core of the trees in the area of impact to examine trapped particles that were present during the 1908 event. They found high levels of material commonly found in rocky asteroids and rarely found in comets. Kelly et al. (2009) contend that

3960-408: Is not valid and further analysis is needed to predict the pressure forces which are exerted on the surface. Shock waves can form due to steepening of ordinary waves. The best-known example of this phenomenon is ocean waves that form breakers on the shore. In shallow water, the speed of surface waves is dependent on the depth of the water. An incoming ocean wave has a slightly higher wave speed near

4059-436: Is similar to the blast energy equivalent of the 1980 volcanic eruption of Mount St. Helens . The researchers also concluded impactors of this size hit the Earth only at an average interval scale of millennia. In June 2007, scientists from the University of Bologna identified a lake in the Tunguska region as a possible impact crater from the event. They do not dispute that the Tunguska body exploded in midair, but believe that

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4158-453: Is weakened due to the location of the river basin in the permafrost zone and reaches the lowest values of 3-15 m3/s, the total winter runoff is 11% of the annual. The river was the set location in the Call of Duty: Black Ops Escalation DLC map, Call of The Dead. This Krasnoyarsk Krai location article is a stub . You can help Misplaced Pages by expanding it . This article related to

4257-547: The comet's tail across the upper atmosphere. The cometary hypothesis gained a general acceptance among Soviet Tunguska investigators by the 1960s. In 1978, Slovak astronomer Ľubor Kresák suggested that the body was a fragment of Comet Encke , a periodic comet with a period of just over three years that stays entirely within Jupiter's orbit. It is also responsible for the Beta Taurids , an annual meteor shower with

4356-404: The 1260 mm long core sample pulled from the bottom of the lake, representing an age older than the Tunguska event. Additionally, there are problems with impact physics: It is unlikely that a stony meteorite in the right size range would have the mechanical strength necessary to survive atmospheric passage intact while retaining a velocity high enough to excavate a crater that size on reaching

4455-441: 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

4554-656: The Committee on Meteorites of the USSR Academy of Sciences, as part of an initiative to dispose of flammable nitrate film . Positive prints were preserved for further study in Tomsk . Expeditions sent to the area in the 1950s and 1960s found microscopic silicate and magnetite spheres in siftings of the soil. Similar spheres were predicted to exist in the felled trees, although they could not be detected by contemporary means. Later expeditions did identify such spheres in

4653-502: The Earth shook, and when I was on the ground, I pressed my head down, fearing rocks would smash it. When the sky opened up, hot wind raced between the houses, like from cannons, which left traces in the ground like pathways, and it damaged some crops. Later we saw that many windows were shattered, and in the barn, a part of the iron lock snapped. Testimony of Chuchan of the Shanyagir tribe, as recorded by I. M. Suslov in 1926: We had

4752-413: The Earth's atmosphere. The Tunguska event and the 2013 Russian meteor event are the best documented evidence of the shock wave produced by a massive meteoroid . When the 2013 meteor entered into the Earth's atmosphere with an energy release equivalent to 100 or more kilotons of TNT, dozens of times more powerful than the atomic bomb dropped on Hiroshima , the meteor's shock wave produced damage as in

4851-400: The Earth's atmosphere. The largest asteroid air burst observed with modern instrumentation was the 500-kiloton Chelyabinsk meteor in 2013, which shattered windows and produced meteorites. In 2020, a group of Russian scientists used a range of computer models to calculate the passage of asteroids with diameters of 200, 100, and 50 metres at oblique angles across Earth's atmosphere. They used

4950-402: 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 occurred in prehistoric times. An explosion of this 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:

5049-464: The Tunguska body was a small comet . A comet is composed of dust and volatiles , such as water ice and frozen gases, and could have been completely vaporised by the impact with Earth's atmosphere, leaving no obvious traces. The comet hypothesis was further supported by the glowing skies (or "skyglows" or "bright nights") observed across Eurasia for several evenings after the impact, which are possibly explained by dust and ice that had been dispersed from

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5148-698: 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 by Space Shuttles . In the United States, a Smithsonian Astrophysical Observatory program at the Mount Wilson Observatory in California observed

5247-427: The approach of the object. In this description, the shock wave position is defined as the boundary between the zone having no information about the shock-driving event and the zone aware of the shock-driving event, analogous with the light cone described in the theory of special relativity . To produce a shock wave, an object in a given medium (such as air or water) must travel faster than the local speed of sound. In

5346-600: The area's isolation and significant political upheaval affecting Russia in the 1910s. In 1921, the Russian mineralogist Leonid Kulik led a team to the Podkamennaya Tunguska River basin to conduct a survey for the Soviet Academy of Sciences . Although they never visited the central blast area, the many local accounts of the event led Kulik to believe that a giant meteorite impact had caused

5445-426: The atmosphere; from there, it drifted downwind, in a sort of wick, which eventually found an ignition source such as lightning. Once the gas was ignited, the fire streaked along the wick, and then down to the source of the leak in the ground, whereupon there was an explosion. Shock wave In physics, a shock wave (also spelled shockwave ), or shock , is a type of propagating disturbance that moves faster than

5544-689: 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

5643-669: The bogs. The nitrogen is believed to have been deposited as acid rain , a suspected fallout from the explosion. Other scientists disagree: "Some papers report that hydrogen, carbon and nitrogen isotopic compositions with signatures similar to those of CI and CM carbonaceous chondrites were found in Tunguska peat layers dating from the TE (Kolesnikov et al. 1999, 2003) and that iridium anomalies were also observed (Hou et al. 1998, 2004). Measurements performed in other laboratories have not confirmed these results (Rocchia et al. 1990; Tositti et al. 2006)." Researcher John Anfinogenov has suggested that

5742-510: The bottom of Lake Cheko, they identified a layer of radionuclide contamination from mid-20th century nuclear testing at Novaya Zemlya . The depth of this layer gave an average annual sedimentation rate of between 3.6 and 4.6 mm a year. These sedimentation values are less than half of the 1 cm/year calculated by Gasperini et al. in their 2009 publication on their analysis of the core they took from Lake Cheko in 1999. The Russian scientists in 2017 counted at least 280 such annual varves in

5841-400: The bright timbre of the instruments. While shock formation by this process does not normally happen to unenclosed sound waves in Earth's atmosphere, it is thought to be one mechanism by which the solar chromosphere and corona are heated, via waves that propagate up from the solar interior. A shock wave may be described as the furthest point upstream of a moving object which "knows" about

5940-498: The case from a nuclear explosion and estimate that the air burst had an energy range from 3 to 5 megatons of TNT (13 to 21 PJ). The 15-megaton ( Mt ) estimate represents an energy about 1,000 times greater than that of Trinity , and roughly equal to that of the United States' Castle Bravo nuclear test in 1954 (which measured 15.2 Mt) and one third that of the Soviet Union 's Tsar Bomba test in 1961. A 2019 paper suggests

6039-449: The case of an aircraft travelling at high subsonic speed, regions of air around the aircraft may be travelling at exactly the speed of sound, so that the sound waves leaving the aircraft pile up on one another, similar to a traffic jam on a motorway. When a shock wave forms, the local air pressure increases and then spreads out sideways. Because of this amplification effect, a shock wave can be very intense, more like an explosion when heard at

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6138-409: The crest of each wave than near the troughs between waves, because the wave height is not infinitesimal compared to the depth of the water. The crests overtake the troughs until the leading edge of the wave forms a vertical face and spills over to form a turbulent shock (a breaker) that dissipates the wave's energy as sound and heat. Similar phenomena affect strong sound waves in gas or plasma, due to

6237-401: The dependence of the sound speed on temperature and pressure. Strong waves heat the medium near each pressure front, due to adiabatic compression of the air itself, so that high pressure fronts outrun the corresponding pressure troughs. There is a theory that the sound pressure levels in brass instruments such as the trombone become high enough for steepening to occur, forming an essential part of

6336-420: The effects of the conventional Operation Blowdown . These effects are caused by the blast wave produced by large air-burst explosions. The trees directly below the explosion are stripped as the blast wave moves vertically downward, but remain standing upright, while trees farther away are knocked over because the blast wave is travelling closer to horizontal when it reaches them. Soviet experiments performed in

6435-498: The event. Upon returning, he persuaded the Soviet government to fund an expedition to the suspected impact zone, based on the prospect of salvaging meteoric iron . Kulik led a scientific expedition to the Tunguska blast site in 1927. He hired local Evenki hunters to guide his team to the centre of the blast area, where they expected to find an impact crater . To their surprise, there was no crater at ground zero . Instead they found

6534-426: The explosion is a meteor air burst by an asteroid 6–10 km (4–6 mi) above the Earth's surface. Meteoroids enter Earth's atmosphere from outer space every day, travelling at a speed of at least 11 km/s (7 mi/s). The heat generated by compression of air in front of the body ( ram pressure ) as it travels through the atmosphere is immense and most meteoroids burn up or explode before they reach

6633-838: The explosive power of the Tunguska event may have been around 20–30 megatons. Since the second half of the 20th century, close monitoring of Earth's atmosphere through infrasound and satellite observation has shown that asteroid air bursts with energies comparable to those of nuclear weapons routinely occur, although Tunguska-sized events, on the order of 5–15 megatons , are much rarer. Eugene Shoemaker estimated that 20-kiloton events occur annually and that Tunguska-sized events occur about once every 300 years. More recent estimates place Tunguska-sized events at about once every thousand years, with 5-kiloton air bursts averaging about once per year. Most of these are thought to be caused by asteroid impactors, as opposed to mechanically weaker cometary materials, based on their typical penetration depths into

6732-445: The ground. Though scientific consensus is that the Tunguska explosion was caused by the impact of a small asteroid, there are some dissenters. Astrophysicist Wolfgang Kundt has proposed that the Tunguska event was caused by the release and subsequent explosion of 10 million tons of natural gas from within the Earth's crust. The basic idea is that natural gas leaked out of the crust and then rose to its equal-density height in

6831-429: The ground. Early estimates of the energy of the Tunguska air burst ranged from 10–15 megatons of TNT (42–63 petajoules ) to 30 megatons of TNT (130 PJ), depending on the exact height of the burst as estimated when the scaling laws from the effects of nuclear weapons are employed. More recent calculations that include the effect of the object's momentum find that more of the energy was focused downward than would be

6930-485: The ground. Military satellites have been observing these explosions for decades. In 2019 astronomers searched for hypothesized asteroids ~100 metres in diameter from the Taurid swarm between 5–11 July, and 21 July – 10 August. As of February 2020 , there have been no reports of discoveries of any such objects. In 1983, astronomer Zdeněk Sekanina published a paper criticising the comet hypothesis. He pointed out that

7029-422: The impact was caused by a comet because of the sightings of noctilucent clouds following the impact, a phenomenon caused by massive amounts of water vapour in the upper atmosphere. They compared the noctilucent cloud phenomenon to the exhaust plume from NASA's Endeavour Space Shuttle . A team of Russian researchers led by Edward Drobyshevski in 2009 suggested that the near-Earth asteroid 2005 NB 56 may be

7128-447: The insufficient aspects of numerical and experimental tools lead to two important problems in practices: (1) some shock waves can not be detected or their positions are detected wrong, (2) some flow structures which are not shock waves are wrongly detected to be shock waves. In fact, correct capturing and detection of shock waves are important since shock waves have the following influences: (1) causing loss of total pressure, which may be

7227-402: The interstellar medium, the bow shock caused by the Earth's magnetic field colliding with the solar wind and shock waves caused by galaxies colliding with each other. Another interesting type of shock in astrophysics is the quasi-steady reverse shock or termination shock that terminates the ultra relativistic wind from young pulsars . Shock waves are generated by meteoroids when they enter

7326-466: The isotopic ratios measured in the adjacent layers, and this abnormality was not found in bogs outside the area. The region of the bogs showing these anomalous signatures also contains an unusually high proportion of iridium , similar to the iridium layer found in the Cretaceous–Paleogene boundary . These unusual proportions are believed to result from debris from the falling body that deposited in

7425-401: The lake (between 100 and 90 cm), and again by subsequent fires (one local fire in the upper 40 cm). In 2017, new research by Russian scientists pointed to a rejection of the theory that the Tunguska event created Lake Cheko. They used soil research to determine that the lake is 280 years old or even much older; in any case clearly older than the Tunguska event. In analyzing soils from

7524-456: The lake's deepest point that may be a fragment of the colliding body. Finally, the lake's long axis points to the Tunguska explosion's hypocentre, about 7.0 km (4.3 mi) away. Work is still being done at Lake Cheko to determine its origins. The main points of the study are that: Cheko, a small lake located in Siberia close to the epicentre of the 1908 Tunguska explosion, might fill

7623-421: The limited instrumentation available at the time of the event, modern scientific interpretations of its cause and magnitude have relied chiefly on damage assessments and geological studies conducted many years after the event. Estimates of its energy have ranged from 3–30 megatons of TNT (13–126 petajoules). Only more than a decade after the event did any scientific analysis of the region take place, in part due to

7722-402: The local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a medium, but is characterized by an abrupt, nearly discontinuous, change in pressure , temperature , and density of the medium. For the purpose of comparison, in supersonic flows, additional increased expansion may be achieved through an expansion fan , also known as

7821-408: The lower unit (below ~100 cm) contains abundant forest tree pollen, but no hydrophytes, suggesting that no lake existed then, but a taiga forest growing on marshy ground (Fig. 5). Pollen and microcharcoal show a progressive reduction in the taiga forest, from the bottom of the core upward. This reduction may have been caused by fires (two local episodes below ~100 cm), then by the TE and the formation of

7920-517: The mid-1960s, with model forests (made of matches on wire stakes) and small explosive charges slid downward on wires, produced butterfly-shaped blast patterns similar to the pattern found at the Tunguska site. The experiments suggested that the object had approached at an angle of roughly 30 degrees from the ground and 115 degrees from north and had exploded in midair. In 1930, the British meteorologist and mathematician F. J. W. Whipple suggested that

8019-436: The mouth is 1587.18 m3/s, during summer floods it reaches 35,000 m3/s. Ice phenomena have been occurring since mid-October, the autumn ice drift of 7-16 days is accompanied by the formation of ice jams . The ice age is from the end of October to the middle of May. The ice drift lasts 5-7 days in the upper reaches and up to 10 days in the lower reaches, passes violently, with congestion the level rises by 29.7 m. Winter nutrition

8118-588: 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. 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-calibre artillery. Krasnoyaretz newspaper, 13 July 1908: Kezhemskoye village. On

8217-446: 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

8316-406: The properties of the fluid ( density , pressure , temperature , flow velocity , Mach number ) change almost instantaneously. Measurements of the thickness of shock waves in air have resulted in values around 200 nm (about 10 in), which is on the same order of magnitude as the mean free path of gas molecules. In reference to the continuum, this implies the shock wave can be treated as either

8415-407: The resin of the trees. Chemical analysis showed that the spheres contained high proportions of nickel relative to iron, which is also found in meteorites, leading to the conclusion they were of extraterrestrial origin. The concentration of the spheres in different regions of the soil was also found to be consistent with the expected distribution of debris from a meteor air burst . Later studies of

8514-545: The shock passes. Since no fluid flow is discontinuous, a control volume is established around the shock wave, with the control surfaces that bound this volume parallel to the shock wave (with one surface on the pre-shock side of the fluid medium and one on the post-shock side). The two surfaces are separated by a very small depth such that the shock itself is entirely contained between them. At such control surfaces, momentum, mass flux and energy are constant; within combustion, detonations can be modelled as heat introduction across

8613-458: The shock wave. The slip surface (3D) or slip line (2D) is a plane across which the tangent velocity is discontinuous, while pressure and normal velocity are continuous. Across the contact discontinuity, the pressure and velocity are continuous and the density is discontinuous. A strong expansion wave or shear layer may also contain high gradient regions which appear to be a discontinuity. Some common features of these flow structures and shock waves and

8712-437: The spheres found unusual ratios of numerous other metals relative to the surrounding environment, which was taken as further evidence of their extraterrestrial origin. Chemical analysis of peat bogs from the area also revealed numerous anomalies considered consistent with an impact event. The isotopic signatures of carbon, hydrogen, and nitrogen at the layer of the bogs corresponding to 1908 were found to be inconsistent with

8811-436: The supersonic flight of aircraft. The shock wave is one of several different ways in which a gas in a supersonic flow can be compressed. Some other methods are isentropic compressions, including Prandtl –Meyer compressions. The method of compression of a gas results in different temperatures and densities for a given pressure ratio which can be analytically calculated for a non-reacting gas. A shock wave compression results in

8910-412: The system is constant, the stagnation enthalpy remains constant over both regions. However, entropy is increasing; this must be accounted for by a drop in stagnation pressure of the downstream fluid. When analyzing shock waves in a flow field, which are still attached to the body, the shock wave which is deviating at some arbitrary angle from the flow direction is termed oblique shock. These shocks require

9009-928: The time of the Tunguska event. Pollen analysis reveals that remains of aquatic plants are abundant in the top post-1908 sequence but are absent in the lower pre-1908 portion of the core. These results, including organic C, N and δ C data, suggest that Lake Cheko formed at the time of the Tunguska event. Pollen assemblages confirm the presence of two different units, above and below the ~100‐cm level (Fig. 4). The upper 100‐cm long section, in addition to pollen of taiga forest trees such as Abies, Betula, Juniperus, Larix, Pinus, Picea, and Populus, contains abundant remains of hydrophytes, i.e. , aquatic plants probably deposited under lacustrine conditions similar to those prevailing today. These include both free-floating plants and rooted plants, growing usually in water up to 3–4 metres in depth (Callitriche, Hottonia, Lemna, Hydrocharis, Myriophyllum, Nuphar, Nymphaea, Potamogeton, Sagittaria). In contrast,

9108-498: The tree-fall pattern as well as the atmospheric and seismic pressure waves of Tunguska. Four different computer models produced similar results; they concluded that the likeliest candidate for the Tunguska impactor was a stony body between 50 and 80 m (164 and 262 ft) in diameter, entering the atmosphere at roughly 55,000 km/h (34,000 mph), exploding at 10 to 14 km (6 to 9 mi) altitude, and releasing explosive energy equivalent to between 10 and 30 megatons. This

9207-562: 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 kilometres away. The explosion registered at seismic stations across Eurasia, and air waves from

9306-473: 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

9405-463: Was covered with fire. At that moment I became so hot that I couldn't bear it as if my shirt was on fire; from the northern side, where the fire was, came strong heat. I wanted to tear off my shirt and throw it down, but then the sky shut closed, and a strong thump sounded, and I was thrown a few metres. I lost my senses for a moment, but then my wife ran out and led me to the house. After that such noise came, as if rocks were falling or cannons were firing,

9504-469: 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. 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]

9603-478: 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 p.m. completely disappeared. Since the 1908 event, an estimated 1,000 scholarly papers (most in Russian) have been published about the Tunguska explosion. Owing to the site's remoteness and

9702-449: 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

9801-408: Was sitting by the house at Vanavara Trading Post [approximately 65 kilometres (40 mi) south of the explosion], 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 [as Semenov showed, about 50 degrees up – expedition note]. The split in the sky grew larger, and the entire northern side

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