The mountain before the laboratory

Before Chacaltaya was a physics laboratory it was a weather station. And before that it was a skiers' hut at the end of a dirt road. The sequence matters: when in 1947 César Lattes searched in Bristol for a high mountain on which to leave a set of photographic plates, he found Chacaltaya in a geographical yearbook because five years earlier a refugee of the Spanish Civil War had climbed up there to install thermometers. This mountain's scientific vocation was not born looking at the cosmos: it was born looking at the atmosphere.

The opportunity that passed by: Millikan, 1927

The history of cosmic-ray physics in Bolivia has a false start. In 1927 an expedition led by the American physicist Robert Millikan travelled through South America measuring how the intensity of cosmic radiation varies with latitude. It passed through Bolivia. It involved no Bolivian scientist and left behind neither equipment, nor a programme, nor any interest in continuing.

The contrast with what came afterwards is deliberate, and the site should say so: the difference between an expedition that uses a territory and a collaboration that builds an institution in it. Chacaltaya would end up being the second, and that is exactly the kind of argument that carries weight in a heritage dossier.

Who Ismael Escobar was

Ismael Escobar Vallejo (1918–2009) was born in Villafrades de Campos (Valladolid), the son of two schoolteachers, and trained as a teacher in Castellón de la Plana. The war made him a meteorologist: he served in the Flight Protection Group of the Spanish Republic's air force and fought at the Battle of the Ebro.

In January 1939 he crossed into France at Le Perthus and was interned in the refugee camp at Argelès-sur-Mer; his father managed to get him out. That December he sailed from Bordeaux on the ship Cuba, bound for the Dominican Republic, where he landed in January 1940. After a year in the Caribbean, he moved on to Bolivia in July 1941.

He was barely into his twenties when he arrived in the country where he would found his science.

1942: a meteorological service for a country

Escobar began working as a meteorologist in January 1942. His initial task was to set up and operate a network of stations to support the work of the Ministry of Agriculture. He was Sector Head at the Comité Fiscal de Fomento Agrícola y Regadío (State Committee for Agricultural Development and Irrigation), headed by the Mexican engineer Eligio Esquivel; the President of the Republic was General Enrique Peñaranda.

In his first report to the Director General of Agriculture, covering February and March 1942, Escobar included, behind the covering letter, the draft supreme decree that would create the Servicio Meteorológico de Bolivia (Bolivian Meteorological Service). On 21 December 1942, by memorandum 159/334/42 signed by the engineer Eduardo Palomo S., he was appointed Head of the Service; the post would later be raised to a Directorate General.

The first Central Station of the network was installed at the Escuela Militar de Aviación de El Alto (Military Aviation School of El Alto). From March 1942 Escobar taught meteorology there, which allowed him to make soundings of the upper atmosphere aboard a twin-engined Junker up to nearly 7,000 metres.

It is worth stressing, because it explains what was to come: the man who installed the Chacaltaya station was already, in 1942, measuring the upper atmosphere from an aeroplane.

September 1942: the station at 5,200 metres

In September 1942 one of the stations of the national meteorological network was installed on Mount Chacaltaya, at 5,200 metres. It included equipment for measuring the weather and the intensity of solar radiation.

The installation was possible because a road and a hut already existed, built two years earlier by the Club Andino Boliviano (Bolivian Andean Club), which had made the mountain a ski centre. Raúl Posnanski and Alfredo Hendel took part in the work — the latter would remain connected with the Laboratory from its earliest days and would become Professor Emeritus at the University of Michigan.

Escobar went on to become secretary of the Club Andino, and in 1943, together with the Minister of Education Rodas Eguino, the first skiing course for students and enthusiasts from La Paz was held there.

It is a detail usually told as an anecdote, and it is in fact structural: a city's sporting infrastructure made a country's scientific infrastructure possible. Without the Club Andino's road and hut there is no weather station in 1942; without a weather station there is no entry in the Bristol geographical yearbook; without that entry, Lattes does not find the mountain in 1947.

4 July 1942: the site is protected

On 4 July 1942, under the government of Enrique Peñaranda and pursuant to article 3 of the Supreme Decree of 2 August 1939, the Ministerio de Agricultura, Ganadería y Colonización (Ministry of Agriculture, Livestock and Colonisation) issued a supreme decree declaring a National Park the Andean group lying between the Condoriri and Yungas passes: Huayna Potosí, Chacaltaya and the Milluni lagoon.

✅ Checked against the index of the Gaceta Oficial (19 September 2026). The decree appears in the official index identified only by its date, Supreme Decree of 4 July 1942, with the summary line “Parque Nacional.- Declárase el grupo andino comprendido entre los pasos del Condoriri y de Yungas”. This confirms that it carries no number: it is cited by date. Source: index of the Gaceta Oficial de Bolivia, via D-Lex Bolivia (Derechoteca).

The document survives and its full text is transcribed in the site's archive (record CHC-DEC-1942-0001). It is not a second-hand mention: it is five articles that can be read.

Article 1 — The Andean group lying between the Condoriri and Yungas passes, named after its highest peaks Hayna Potosí [sic], Chacaltaya and the Milluni lagoon, is hereby declared a "National Park." (translated from the Spanish)

And what the other four articles say changes the weight of the find:

• Art. 2 prohibits within the park the hunting of condors, deer, foxes, vizcachas (an Andean rodent of the chinchilla family) and other Andean fauna.
• Art. 3 assigns to the Patrulla Andina (Andean Patrol), organised by the Club Andino Boliviano, the surveillance, protection and conservation of the National Park, accident prevention and first aid, and the upkeep of roads and control of traffic.
• Art. 4 gives that Patrol the status of Rural Police within the park.
• Art. 5 establishes that the building of roads and structures, the extraction of ice from the glaciers and similar activities may only be carried out with special permission from the Patrulla Andina, "so as not to damage the natural beauties of the region."

Three consequences, and all three matter:

First: this is not a declaration in name only. The decree creates a conservation regime with concrete prohibitions and a designated body of supervision. A national park with a guardian, not a name on a map.

Second: the guardian is the same body that built the road. The Club Andino Boliviano, which by around 1940 had put up the Chacaltaya hut and road, was placed by decree in charge of guarding the mountain. And Escobar, who installed the weather station in September of that same year, would become secretary of the Club. Sportsmen, meteorologists and park wardens were, in 1942, practically the same people.

Third, and this is what carries most weight in the dossier: article 5 explains the founding of the Laboratory. Aguirre Bastos records that, when Escobar submitted the draft proposal for the observatory in 1949, "since the site lay within a National Park, the University applied for a special permit." We now know exactly which rule required it and which body had to grant it. The documentary chain closes:

1942 decree, art. 5 → special permit applied for by UMSA in 1949 → creation of the Laboratory in 1951–52

The territorial protection of the site is therefore two months older than its first scientific instrument, ten years older than the Laboratory, and eighty-four years older than this nomination. And the Laboratory was not built in spite of that protection: it was built within it, by asking permission.

Priority archive task. The other end of the chain is missing: the special permit of 1949. If it turns up, the dossier will have documented, piece by piece, the compatibility between scientific use and conservation of the site over eight decades. It is probably the most valuable document still to be found in the whole project.

1943: the summit, the journal and the university

What was conceived in 1942 as a network for monitoring the weather became, thanks to Escobar's drive, an effective meteorological service. Three things happen in 1943:

• The summit hut. The President of the Republic, Colonel Gualberto Villarroel, inaugurated a new weather hut on the summit of Chacaltaya, at 5,600 metres. From that year onwards observations begin that made important contributions to the knowledge of local climatology; the reports improved the analysis of air-mass dynamics and, with it, the accuracy of forecasts for the airport and the city of La Paz.
• **The journal Nimbus. The Service's scientific journal begins to appear. The library of the Instituto de Investigaciones Físicas (Institute of Physics Research) at UMSA holds the complete run** — it is one of the project's most valuable and least exploited primary sources.
• The university enters the scene. On 19 June 1943, by Oficio (official letter) 54/953, the Universidad Mayor de San Andrés appointed Escobar Interim Professor of Cosmography and Meteorology at the Escuela de Ayudantes Técnicos (School of Technical Assistants). In September 1947, by memorandum 193/947 and after a competitive examination, he was appointed Professor of Supplementary Physics and of Cosmography and Meteorology at the Instituto de Ciencias Exactas (Institute of Exact Sciences).

"UMSA, through one of its professors, was involved in work on the Physics and Thermodynamics of the atmosphere, including solar and cosmic radiation, long before the creation of Chacaltaya as a Laboratory was made official…"

Ismael Escobar

That sentence is, legally speaking, a precedent. The University's connection with the science of the mountain predates the formal creation of the Laboratory, and it is documented with a letter number and a date.

Why this mountain and no other

Before Chacaltaya, cosmic-ray physicists had facilities at the Pic du Midi (Pyrenees), the Jungfraujoch (Alps) and the Aiguille du Midi (Chamonix), all between 3,000 and 3,500 metres. Chacaltaya was not simply one more alternative: it was a step up in category.

These four advantages have not expired. They are exactly the ones that in 2026 justify the installation of ALPACA. A site whose scientific value does not depend on the period is, precisely, what a heritage dossier needs to demonstrate.

Chronology of the milestone

Open points

⚠ The date of the summit hut. The source places the inauguration by President Villarroel "in 1943", but Gualberto Villarroel took office as president on 20 December 1943. Either the inauguration took place in the last eleven days of the year, or it belongs to 1944, or it was presided over by someone else. It is a minor discrepancy but easily verifiable and worth settling: the press of the period and the Meteorological Service archive should date it precisely. For a dossier before UNESCO, a date corrected against a source is worth more than a date repeated.

⚠ Escobar's name. Aguirre Bastos writes Ismael Escobar Vallejo; Vieira and Videira, Ismael Vallejos Escobar. Settle the correct form and use it consistently across the whole site and in all three languages.

⚠ The date of the Club Andino hut. "Two years earlier" than September 1942 places the construction around 1940, but it is worth confirming with the Club itself, which may also be able to supply photographs from the period.

✅ The 1942 decree — resolved. Located and transcribed from a typewritten copy held by the Ministerio de Agricultura, Ganadería y Colonización. Record CHC-DEC-1942-0001. Still pending: checking it against the Official Gazette to establish the decree number, which does not appear on the copy.

⚠ The special permit of 1949. Article 5 of the decree required permission from the Patrulla Andina in order to build within the park, and Aguirre records that UMSA applied for it. Locating it is now the project's most valuable archive task: it would documentarily close the chain between the protection of the site and the construction of the Laboratory.

People of this milestone

• Ismael Escobar Vallejo (1918–2009). Spanish republican schoolteacher and meteorologist in exile. Founded the Servicio Meteorológico de Bolivia and the Chacaltaya station. First director of the Cosmic Ray Laboratory (1952–1963).
• Alfredo Hendel. Took part in the installation of the station in 1942. Connected with the Laboratory from its earliest days; Professor Emeritus at the University of Michigan.
• Raúl Posnanski. Took part in the installation of the 1942 station.
• Club Andino Boliviano. Built around 1940 the road and the hut that made everything else possible. Under the 1942 decree, its Patrulla Andina was placed in charge of the surveillance, protection and conservation of the National Park, with the status of rural police. Escobar went on to become secretary of the Club.
• Enrique Peñaranda (president, 1940–1943). Under his government the Huayna Potosí – Chacaltaya – Milluni group is declared a National Park.
• Gualberto Villarroel (president, 1943–1946). Inaugurated the summit weather hut. ⚠ See open points.

Glossary for this milestone

• Radiosonde sounding. Measurement of atmospheric variables at altitude by means of instruments carried by balloon or aircraft.
• Direct solar radiation. Energy arriving from the Sun without being scattered in the atmosphere; its systematic measurement at altitude is among the first scientific data from Chacaltaya.
• National Park. A form of territorial protection which, in this case, precedes the scientific installation by two months and is still in force.
• Extensive air shower. A cascade of secondary particles generated when a primary cosmic ray collides with a nucleus in the atmosphere. Its development reaches a maximum at around the altitude of Chacaltaya.

The case for the UNESCO nomination

Short form (for the page):

Developed form (for the dossier):

1. A pre-existing protection regime, documented and with a body of supervision. The property has enjoyed state territorial protection since 4 July 1942, prior to its scientific use, and the decree survives. It is not protection in name only: it prohibits hunting, makes all construction subject to special permission and designates the Patrulla Andina of the Club Andino Boliviano as custodian with the status of rural police. The nomination is not asking that a site begin to be protected, but that recognition be given to the value of one that the Bolivian State has been protecting, with a conservation regime and a designated guardian, for more than eight decades.

1. Documented compatibility between science and conservation. Article 5 of the decree required special permission to build within the park, and it is the reason why UMSA applied for one in 1949 before erecting the observatory. The Laboratory was not installed despite the protection regime: it was installed within it, following its procedure. For a heritage dossier, being able to demonstrate eighty years of scientific use compatible with the conservation of the site is worth more than demonstrating either of the two separately.
2. The atmospheric origin of the scientific vocation. Chacaltaya's first measurement was not of particles but of solar radiation. That makes the site an observatory of double reading — cosmos and climate — from day one, and it gives coherence to the line running all the way to the World Meteorological Organization's GAW/CHC station, in operation since 2011 (see milestone 09).
3. Documentary authenticity. The facts of this milestone are supported by administrative instruments identifiable by date and number: the supreme decree of 4 July 1942 (located and transcribed), memorandum 159/334/42, UMSA's Oficio 54/953 and memorandum 193/947. Locating and digitising the remaining three is one of the project's most profitable archive tasks.
4. A university connection predating the formal foundation. UMSA engaged Escobar as a lecturer in 1943, nine years before the official creation of the Laboratory. The relationship between the University and the science of this mountain therefore predates the institution that formalises it.

Sources

1. Carlos Aguirre Bastos, Medio siglo de ciencia en Bolivia. El Laboratorio de Física Cósmica de Chacaltaya de la Universidad Mayor de San Andrés, Fundación Universitaria Simón I. Patiño, La Paz, May 1996, chs. I and II.
2. Ismael Escobar, address to the American Physical Society, March 1993. (Aguirre indicates that several passages of his essay derive from this text and from letters written by Escobar to the author in 1994 and 1995.)
3. Cássio Leite Vieira and Antonio Augusto Passos Videira, "Chacaltaya: um laboratório nas nuvens", in História da Física (2019), pp. 129–141.
4. Nimbus journal, Servicio Meteorológico de Bolivia, from 1943 onwards. Complete run in the IIF–UMSA library.
5. Supreme Decree of 4 July 1942, Ministerio de Agricultura, Ganadería y Colonización. Typewritten copy. Full transcription and archival record in documentos/doc_1942-07-04_ds-parque-nacional.md (identifier CHC-DEC-1942-0001); facsimile in documentos/1942-07-04_DS_Parque_Nacional_copia.pdf.
6. Supreme Decree of 2 August 1939, art. 3 (enabling rule, cited in the same copy). ⚠ Full text still to be located.