Red Lake · Harghita · summer 1837 # The night a lake was born Most sources tell it this way: in the summer of 1837, after heavy rains, a waterlogged slope of Mount Ghilcoș slid across the Bicaz valley and dammed it. The dam — the 1914 guide says — rose in a single stormy night; the lake gathered over years. What remained is a drowned forest of firs, whose trunks still show. Below you can replay that night on the real terrain of the valley, in 3D — and weigh the evidence yourself: the rains of 1837 or the great earthquake of January 1838? Scroll to descend into the valley as it was before the lake. By Marius Comper · 29 September 2026 ## Where Red Lake is The lake sits at the mouth of the Bicaz Gorge, in Harghita county, about 17 kilometres north-east of Gheorgheni as the crow flies, and about 49 kilometres from Miercurea Ciuc. The Lacu Roșu resort grew up on its banks. Bucharest Iași Brașov Constanța Cluj-Napoca Red Lake 16.8 km Gheorgheni Red Lake Miercurea Ciuc 10 km Outlines: Natural Earth (public domain) and geoBoundaries (CC BY 4.0). ## The valley before the lake Where the lake lies today was once a mountain valley of meadows and conifer forest, its floor at about 950 metres altitude. Down it ran the streams of the Bicaz: the Oii, the Vereșcheu, the Licaș, the Suhard. The area was uninhabited, far from roads and rarely used. That is why the night that followed had, by all appearances, no witnesses: no witness account has ever surfaced. ## The summer of the rains The Iași limnology school places the formation in the summer of 1837, “when, after abundant rains, a mass of landslide debris broke away from Mount Ghilcoș (Ucigașu) and blocked the Bicaz stream” (our translation). Below the Ghilcoș cliff, scree had accumulated for thousands of years and weathered into a mixture of rock fragments and clay. The rains and the snowmelt soaked it to the limit. ## The night the slope started moving The 1914 guide says that “after heavy rains, on a stormy night, part of the Ghilcoș started moving”. As it slid, the material piled up and subsided, forming the lake (our translation). It was not the mountain collapse once imagined. After fieldwork in 1940, geographer Vintilă Mihăilescu identified a secondary landslide “at the front of the scree complex decayed by infiltrated waters” (our translation). ## The valley closes The landslide tongue reached the Bicaz and blocked it. Where it met the left bank, the Bicaz later cut a narrow channel through the dam — today's outflow. Behind it, the water began to gather. Filling took years: Orbán Balázs, the first to describe the lake at length (on the evidence so far), says in 1869 that the closed valley “kept filling over several years” until Lake Ghilcoș was born (our translation). ## The water climbs the trunks As the water rose, it submerged the roots of the valley's firs. In 1869 Orbán wrote that their tops “still jut out above the lake”, serving also as a measure of its depth (our translation). The trees died standing. Their trunks, barkless and bleached by weather, still pierce the water mirror today — living proof that here was forest, not lake. ## The lake today 12.01 hectares, 10.5 metres maximum depth, about 721,400 cubic metres of water — the 2009 survey, with over 80,000 sonar points. The lake has also shrunk markedly: on the 2005 reconstruction, its formation volume halved in less than two centuries. The story of the numbers, below. ## Look at the valley yourself Pick the moment, then rotate the valley with a mouse or your finger. Use the scroll wheel, pinch with two fingers, or press + and − to zoom. ## The rains of 1837 or the earthquake of 1838? What pulled the trigger? Researchers have proposed two explanations, and the English Wikipedia has already picked one: the earthquake of 23 January 1838. But the evidence, read in full, points more strongly to the rains of 1837. First the two camps — then you decide. ### The rains of 1837 - Vintilă Mihăilescu, in the field, 1940: a slide in the scree “decayed by infiltrated waters” (our translation), after rains and snowmelt. - The Iași school, 2010: the lake “was formed in the summer of 1837, when after abundant rains a mass of landslide debris broke away” (our translation). - Cluj, 2005: the siltation study takes 1837 as the formation year. - Orbán Balázs, 1869: the first writer to describe the lake at length writes 1837 — no earthquake, no legend. - The 1914 guide: “after heavy rains, on a stormy night” (our translation). - Herbich — cited by Wikipedia as favouring the quake — is reported by both papers discussing him as favouring rain as the cause; Ilinca even attributes 1838 rains to him. ### The earthquake of 1838 - The quake was real and large: 23 January 1838, magnitude Mw 7.5, epicentral intensity IX, felt from Lviv to Constantinople. - Two seismological catalogues — Réthly (1952) and Florinesco (1958) — tie the lake to this quake. They are not digitised; we have not read them. - A 2014 table gives intensity 8.5 at Red Lake, citing the catalogues — and a 1924 folklore compendium. - The contemporary report by Schüller, from 1838, covers only the Carpathian-bend counties — it contains no observations from the Bicaz area. - No contemporary record from the Ghimeș–Bicaz area, 1837–38, has surfaced: none in church records, newspapers or official documents. Your pick — the rains or the quake? ### The verdict of the sources read in full The evidence leans toward the rains of 1837: two limnology papers, the siltation study and the first writer to describe the lake at length date the formation to the same year; the water-soaked-slope mechanism is explicit in the 1940 field study and the limnology, and the 1914 guide speaks of a stormy night after heavy rains. The quake theory rests on two catalogues we could not read and on a table partly citing folklore. The quake's role stays open — it may have been the final spark, or nothing at all. Until a contemporary record from the valley appears, the question stands. The key correction is this: the English Wikipedia pins the lake on the quake, attributes to Herbich a thesis two specialist papers deny him, and mixes one catalogue's time with another's magnitude. On the sources read in full, the lake formed in 1837 — the quake came in January 1838. ## The forest that stayed standing The drowned trees are firs. In 1940 Mihăilescu wrote of the “firs drowned in the wake of the catastrophe” (our translation), and the French summary of his paper speaks of “the fir forest you see drowned in its waters” (our translation). The Iași limnologists agree: “tops of old fir trees” guard the lake mirror. The drowned trunks in 1943 — over a century after the formation, still standing. Photo: Fortepan / Kurutz Márton, CC BY-SA 3.0. The “multitude of tree trunks” complicated the 2009 survey: they produced spurious sonar echoes, which the team had to remove from its measurements. ### But the “petrified forest”? That is what the national park brochure calls it — and many guides. Yet no scientific source read uses the word “petrified”, and we found no study of the trunks' wood that explains why they remain standing, how long they may last or what is degrading them. Until the wood is analysed, “petrified” stays a label, not a fact. There is not even a stump census. Rowing among the stumps, in 1961. Photo: Fortepan / Pálfi Balázs, CC BY-SA 3.0. ## The lake today: 12 hectares, shrinking The most comprehensive survey, from 2009, puts the water level at 965.10 metres: 12.01 hectares of water, 2,905.79 metres of shoreline, 1,361.72 metres long, 10.5 metres maximum depth and about 721,400 cubic metres of water. The sonar gathered over 80,000 points; the greatest depths lie in the central sector, near where the two streams enter the lake. On the lake, among the stumps. Photo: Christo, 2005, CC BY-SA 4.0, via Wikimedia Commons. ### How much has the lake shrunk? Two reconstructions disagree about the starting point: the simulation cited by the Iași limnologists estimates that the lake initially covered about 40 hectares and reached roughly 25 metres deep; the 2005 one starts from 20 hectares and 1,250,000 cubic metres, down to 606,500 on the measurements of around 2004 — over half gone. A 2009 sonar survey estimated 721,400 cubic metres instead; the figures come from different surveys and methods, and against the 2005 starting point the 2009 figure would mean a loss of about 42%. At the last full survey, in 2009, the lake covered 12.01 hectares. The measurements, by year: in 1859 Herbich attempted the first survey — 750 stânjeni long, 120 wide, 56 iugăre in area — warning the lake was inaccessible and the data imprecise. In 1864 the records give 36 iugăre. In 1940 the lake ran about 1,000 metres, plus a 400-metre arm up the Suhard valley. In 2002: 11.65 hectares. In 2009: 12.01. ### How long might it last? The streams carry silt: 2009 dating puts the average bottom rise at 1.23±0.6 centimetres a year, and at the southern tail, where the streams enter, at up to 3.77. An older calculation has the shores retreating by 2–5 metres a year. A 2005 linear model projected 184–257 more years before the lake filled with silt; its non-linear model projected filling before the end of this century, assuming the conditions of the time stayed unchanged. People have tried to slow the siltation: since 1960 silt-retention dams stand on the Oii and on Pârâul Roșu. The Oii dam is clogged almost completely, the Roșu one 80–90%. ### Why it is red Sources offer three explanations for the name: at sunrise the sun lights the reddish clays of Piciorul Licaș, which are reflected in the water; the reddish sediment comes mostly from the Vereșcheu (Red) stream; and the iron-oxide-rich clay slid from the Ucigașul can tint the water red. It is nobody's blood — whatever the legends say. ### Who guards it The lake lies in the Bicaz Gorge–Hășmaș National Park (IUCN category II, founded 1990, delimited 2003, 6,575 hectares under Law 5/2000), and “Bicaz Gorge and Red Lake” is a 2,128-hectare nature reserve inside it. The area also has Natura 2000 designations under both the Habitats and Birds Directives. ## The “Killer” name came from the mountain Three names in less than two decades: Verestó in 1853, Vörös-tó (Red Lake) in 1866, Gyilkos-tó (Killer Lake) — popularised by Orbán's 1864 lecture and printed by him in 1869. But the “Killer” does not come from the lake: the mountain above appears in charters as Gyilkos-havas as early as 1773, long before any lake existed. Orbán states plainly that the lake took its name “from the mountain above it” (our translation). In English it was likewise called the Killer Lake for a time. ### The legend remains a legend The earliest known printed variant of the legend dates to 1895: a robber abducts the beautiful Anikó and drags her to his cave; at the girl's prayer the walls open, and the robber strikes the rock with his club so hard that the mountain collapses onto him. The Eszter variant, the buried-shepherds story and the story of a village buried beneath the slide are late or undated. One detail matters: Orbán, who in 1869 diligently gathered Székely legends, prints no legend for this lake. ## Eight statements: true or false? Use what you've read above. Choose an answer, then check it against the text. - Red Lake formed in the earthquake of January 1838. - The drowned forest is a fir forest. - Researchers have shown that the trunks in the lake have turned to stone. - The “Killer” name comes from the lake. - On the simulation cited by the limnologists, the lake initially covered about 40 hectares — over three times today's area. - The lake is shrinking mainly because the streams fill it with silt. - The first to describe the lake at length, on the evidence so far, was Orbán Balázs, in 1869. - The oldest known printed legend of the lake is the Eszter one. Share ## How we worked, and what we don't know ### The 3D scene The scene uses a digital terrain model of the Bicaz valley. The displayed water level is raised to cover the model's coarse relief, which misses the real basin: the lake's level cannot be read from the image. Today's lake outline is the OpenStreetMap one (11.11 hectares on the community drawing, against 12.01 measured in 2009 — close). The slide, the dam and the filling are a schematic reconstruction after Mihăilescu's mechanism, not a physical simulation. The stump positions in the scene are illustrative, and the trunks are drawn thicker so they remain visible from a distance: no source gives positions or a count. ### What we could not verify We could not verify Herbich's 1878 text, for which we found only conflicting secondhand reports. We located Puskás's History of Borsec but could not inspect its passage about the storms. The Réthly and Florinesco catalogues are not digitised; no contemporary 1837–38 record from the Ghimeș–Bicaz side has surfaced; no study of the trunks' wood turned up; the interwar history of the resort stays unwritten here. For the water level we take 965.10 m from the 2009 survey; the 978.17 m of an older study is explicitly rejected by the survey's authors (“by no means at 978 m”, our translation). ### Images and data Photos: Jan Pešula (public domain), Fortepan / Kurutz Márton and Fortepan / Pálfi Balázs (CC BY-SA 3.0), Christo (CC BY-SA 4.0), via Wikimedia Commons. Maps: the Josephine survey, section 133 (1769–1773, public domain) and the 1:75,000 Spezialkarte, zone 18, column XXXIII “Oláh-Toplicza” (NYPL, CC0). Relief: Terrarium tiles (SRTM sources). Outlines: Natural Earth (public domain) and geoBoundaries (CC BY 4.0). ## Sources - Vintilă Mihăilescu, “How Red Lake formed at the mouth of the Bicaz Gorge” (in Romanian), Bulletin of the Royal Romanian Geographical Society LIX, 1940 (offprint 1941), facsimile at the [Neamț County Library](https://bibgtkneamt.ebibliophil.ro/d.php?l=bjn_cum-sa-format-lacul-rosu-dela-intrarea-cheilor-bicazului-pdf-xhpnrk76). - Viorel Ilinca & Ion Gheuca, “The Red Lake landslide (Ucigașu Mountain)”, Carpathian Journal of Earth and Environmental Sciences, 2011, [CJEES](https://www.cjees.ro/viewTopic.php?topicId=142). - Andrei Enea, Gheorghe Romanescu & Cristian Stoleriu, “Morphometric characteristics of the Red Lake basin” (in Romanian), 2010, [limnology.ro (PDF)](https://www.limnology.ro/water2010/Proceedings/15.pdf). - Gheorghe Romanescu, Cristian Stoleriu & Andrei Lupașcu, “Morphometric characteristics of the Red Lake basin”, Annals of the University of Oradea – Geography XX(1), 2010, [PDF](http://istgeorelint.uoradea.ro/Reviste/Anale/Art/2010-1/05_OK_AUOG-480-Romanescu.pdf). - Gheorghe Romanescu & Cristian Stoleriu, “Morphobathymetric parameters of the Red Lake basin” (in Romanian), 2010, [limnology.ro (PDF)](http://www.limnology.ro/water2010/Proceedings/44.pdf). - Gheorghe Romanescu & Cristian Stoleriu, “The Red Lake basin: morphometry and evolution”, Forum Geografic XII(1), 2013, [PDF](https://forumgeografic.ro/wp-content/uploads/2013/1/Romanescu.pdf). - Andrei Enea & Gheorghe Romanescu, “Silting rate of the Red Lake”, D. Cantemir Geographic Seminar Proceedings 33, 2012, [PDF](https://www.seminarcantemir.uaic.ro/index.php/lsgdc/article/download/205/201/793). - Gavril Pandi & Gyula Horváth, “Risks of the Red Lake siltation” (in Romanian), Risks and catastrophes IV(2), 2005, [PDF](https://riscurisicatastrofe.reviste.ubbcluj.ro/Volume/IV_Nr_2_2005/PDF/Pandi_Horvath.pdf). - Răzvan Begy, Constantin Cosma & Gyula Horváth, radioisotope dating of the siltation, Romanian Journal of Physics 54(9-10), 2009, [PDF](https://rjp.nipne.ro/2009_54_9-10/0943_0950.pdf). - Mircea Rogozea et al., “The 23 January 1838 Vrancea earthquake”, Romanian Reports in Physics 66, 2014, [PDF (archive)](https://web.archive.org/web/20220118193853/http://www.rrp.infim.ro/2014_66_2/A21.pdf). - Anca-Luminița Constantin, Angela Pantea & Raluca Stoica, “Parameters of the 1838 Vrancea earthquake”, Romanian Journal of Physics 56, 2011, [PDF](http://www.nipne.ro/rjp/2011_56_5-6/0813_0826.pdf); modern parameters: [AHEAD/EPICA](https://www.emidius.eu/AHEAD/event/18380123_1836_000). - Orbán Balázs, The Description of Székely Land II, ch. XXIII “Outing to Lake Gyilkos” (in Hungarian), Pest, 1869, [MEK](https://mek.oszk.hu/04800/04804/html/98.html). - Vákár P. Arthur, Gyilkos Lake Guide (in Hungarian), Gyergyószentmiklós, 1914, [MEK (PDF)](http://mek.oszk.hu/07800/07861/07861.pdf). - Dombay István & Magyari-Sáska Zsolt, on the lake's formation and names (in Hungarian), MFK2004, [PDF](http://geography.hu/mfk2004/mfk2004/cikkek/dombay_magyarisaska.pdf). - Bicaz Gorge–Hășmaș National Park regulations (Romsilva, 2017), [PDF](http://cheilebicazului.itxs.ro/files/Regulamentul%20PNCB-H.pdf); CEDDU “Treasures of nature” brochure, [PDF](https://ceddu.ro/documente/Comorile_naturii_din_Parcul_National_Cheile_Bicazului_-_Hasmas.pdf). - Today's map and the lake outline: © [OpenStreetMap](https://www.openstreetmap.org/copyright) contributors, ODbL licence. [mariuscomper.uk](https://mariuscomper.uk/) · [Română](/lacul-rosu/)