HISTORICAL ARCHIVE OF CAVE AIR TEMPERATURES

Over time, in fact, speleologists and researchers have measured, often occasionally but precisely, the air temperature inside numerous Italian caves. These data, sometimes accompanied by information on the environmental conditions (presence of water, ice, humidity, ventilation), represent a precious archive for better understanding the underground microclimate of the past. In some cases these are simple observations made with a mercury thermometer; in others, measurements carried out during research campaigns or more structured explorations.

In most cases, the measurement is linked to a precise point in the cave and to a date (even just the year); sometimes, more detailed information is also present, such as the time, the type of instrument, or the external conditions. 

 Although there is no temporal limit to the data, the interest is in measurements carried out in the past century. 

The speleologist Martel, in 1894, described a 33 m-deep cavity in France (Creux-de-Soud), with a lake at the bottom: the air temperature was 1 °C, that of the lake between 1 and 2 °C, whilst outside 10.5 °C was measured. 

 In Italy, in the Sperlonga della Val del Palazzo, in 1909 a temperature at the bottom of just 1.06 °C was recorded. In the Buco della Piazza, on the Cansiglio plateau, covered with permanent ice, in 1904, 2 °C was measured at the bottom, versus 20.7 °C outside. 

However, the oldest and verified measurements begin in the 1920’s and 30’s: 

 In Friuli-Venezia Giulia, in the Bus de la Lum on the Cansiglio Plateau, there is a collection of temperatures taken in August 1924 using a sling psychrometer by Antonio Berani. 

 In Veneto, at Spluga della Preta, some measurements date back to 1927, with temperatures around 5 °C as reported in the memoirs of the Italian Institute of Speleology in the volume dedicated to the Corno d'Aquilio operation. 

 In Tuscany, in the Apuan Alps, some temperature measurements of 8.6 and 8.9 °C date back to 1846 at the Antro del Corchia, discovered a few years earlier as reported in Simi's 1847 account. Again at Corchia Mt., in the Buca dei Gracchi, at 1545 m altitude, temperature was recorded on 11 July 1929 (7.8 °C) and reported by Marchetti in 1932. The following year, in the Buca del Cacciatore, a temperature of 9.8 °C was measured. Other accurate measurements concern the Abisso Enrico Revel and the Tana che Urla. 

 In Latium, in the Grotta S. Luca, a 1928 survey published in 1996 by Gambari reports an inner temperature of 13 °C. 

 Later on, measurements become more frequent: in the 1940s and 1950s data are found for Piedmont, Emilia-Romagna and Campania; in the 1970s, also for Molise and Liguria.

The search for data from the literature already permitted the collection of over 600 temperature measurements in caves located in the following regions: Campania, Latium, Ligury, Molise, Tuscany and Veneto. The purpose of this collection, which will be expanded to other regions, is not so much to make comparisons between past and present situations, but rather to obtain a general picture of the thermometry of Italian caves at various latitudes and at different altitudes above sea level. 

 Over time, in fact, speleologists and researchers have measured, often occasionally but precisely, the air temperature inside numerous Italian caves. These data, sometimes accompanied by information on the environmental conditions (presence of water, ice, humidity, ventilation), represent a precious archive for better understanding the underground microclimate of the past. In some cases these are simple observations made with a mercury thermometer; in others, measurements carried out during research campaigns or more structured explorations. 

 In most cases, the measurement is linked to a precise point in the cave and to a date (even just the year); sometimes, more detailed information is also present, such as the time, the type of instrument, or the external conditions. 

 Although there is no temporal limit to the data, the interest is in measurements carried out in the past century. 

Since when have temperatures been measured in caves? 

 Historical measurements cover a very broad time span, ranging from the mid-19th century to the present day.

 Some documents from the past such as "Il bus de la lum nell'altopiano del Cansiglio" from 1929 report interesting measurements of temperature in Italian caves and chasms, even if often collected with simple methods and under non-standardised conditions. 

 In 1922, for example, it was recorded that in Rupa Cerconizza (Giulian Prealps), situated at 300 metres a.s.l., the air temperature at the bottom was 10 °C, whilst outside a value of  19 °C was measured. In a snow-covered chasm on Monte Tajur, at approximately 1400 metres of elevation, the temperature at the bottom was 5.4 °C, slightly lower than that at the surface (6.2 °C). 

 Similar phenomena were also observed abroad. The speleologist Martel, in 1894, described a 33 m-deep cavity in France (Creux-de-Soud), with a lake at the bottom: the air temperature was 1 °C, that of the lake between 1 and 2 °C, whilst outside 10.5 °C was measured. 

 In Italy, in the Sperlonga della Val del Palazzo, in 1909 a temperature at the bottom of just 1.06 °C was recorded. In the Buco della Piazza, on the Cansiglio plateau, covered with permanent ice, in 1904, 2 °C was measured at the bottom, versus 20.7 °C outside. 

However, the oldest and verified measurements begin in the 1920’s and 30’s: 

 In Friuli-Venezia Giulia, in the Bus de la Lum on the Cansiglio Plateau, there is a collection of temperatures taken in August 1924 using a sling psychrometer by Antonio Berani. 

 In Veneto, at Spluga della Preta, some measurements date back to 1927, with temperatures around 5 °C as reported in the memoirs of the Italian Institute of Speleology in the volume dedicated to the Corno d'Aquilio operation. 

 In Tuscany, in the Apuan Alps, some temperature measurements of 8.6 and 8.9 °C date back to 1846 at the Antro del Corchia, discovered a few years earlier as reported in Simi's 1847 account. Again at Corchia Mt., in the Buca dei Gracchi, at 1545 m altitude, temperature was recorded on 11 July 1929 (7.8 °C) and reported by Marchetti in 1932. The following year, in the Buca del Cacciatore, a temperature of 9.8 °C was measured. Other accurate measurements concern the Abisso Enrico Revel and the Tana che Urla. 

 In Latium, in the Grotta S. Luca, a 1928 survey published in 1996 by Gambari reports an inner temperature of 13 °C. 

 Later on, measurements become more frequent: in the 1940s and 1950s data are found for Piedmont, Emilia-Romagna and Campania; in the 1970s, also for Molise and Liguria. 

What these data tell us 

 The collected temperature values are highly variable, not only from region to region, but also within the same cave, depending on depth, presence of water, ventilation or exposure. 

"Normal" temperatures 

 In many caves the recorded temperature is between 10°C and 13°C, values that are coherent with the annual average temperature of the area, and with the limited depth of measurement points. These values are found, for example: 

 In Lazio, in the Grotta di Collepardo with a temperature of 12–13 °C in 1928 (Gambari, 1996); 

 In Campania, in the Grava del Fumo, with 5–7 °C between entrance and bottom (Vianello, 1962); 

 In Liguria, in cavities in the Triora area (11–12 °C); 

 In Emilia-Romagna, in the Risorgente di Monte Rosso of 10–10.3 °C, as reported by Catellani et al., 1988; 

 In Marche, in the Buco Cattivo of 11–13 °C, measurements from 2006-2007 (Felici et al., 2007). 

 In these caves temperature appears relatively stable and in line with the outer environment, especially in those parts close to the entrance. 

Presence of ice and thermal anomalies 

 In some cases, however, very low temperatures have been recorded, often accompanied by ice or particular microclimatic conditions: 

 In Veneto, in the Mercedeloch cave, in 1995 values between 0.8°C and 3°C were recorded, at varying depths between 7 and 32 metres. The presence of stable ice at several sites is documented (Baldo, 1997). 

 Still in Veneto, in the Hotroloch CA4, a 1995 measurement reports 0.9°C with ice (Baldo, 1997). 

 In Campania, in the Grava del Fumo, there are indications of very cold environments (5.2 °C at the entrance, 7.2 °C at the cave bottom) in morphologically deep and poorly ventilated contexts (Vianello, 1962). 

 These situations are rare but interesting, because they document cold hypogean environments that, in certain cases, could be likened to small "natural ice preservers". 

 The data being collected for the UCC project do not have systematic scientific validity, but constitute an historical archive. In an era in which many caves are subject to continuous monitoring with digital sensors, these notes help to reconstruct the past. 

 At the same time, these data help to recognise the variety of Italian karst heritage, where each cave represents a unique environment, with its specificities and its history. 

 This is a selection of the most curious data extracted from the historical dataset of cave thermal measurements. They represent the most extreme, ancient or particular situations recorded so far: 

Oldest measurements by region 

 Tuscany: in 1929, in the Buca dei Gracchi, a temperature of 7.8 °C is measured at the base of a shaft at 1545 m a.s.l. (Marchetti, 1932) 

 Latium: in 1928, the Grotta di S. Luca shows an internal temperature of 13 °C (Gambari, 1996). 

 Veneto: in 1927, in the Spluga della Preta, values around 11 °C are noted (Troncon et al., 2011). 

 Campania: measurements dating back to 1962 in the Grava del Fumo (Vianello et al., 1862). 

 Emilia-Romagna: in 1947, 10 °C is recorded in the Risorgente di Monte Rosso (Catellani et al., 1988). 

 Piedmont: data from 1955 onwards in caves of the Armetta massif (Gruppo Speleologico Piemontese, 1970). 

 Liguria: measurements between 1971 and 1975 in caves around Triora. 

 Molise: temperatures between 5 and 6 °C in the Pozzo della Neve in 1973 (Pasqualini, 1972). 

 Marche: instrumental measurements from 2003 onwards in the Buco Cattivo (Felici et al., 2007) 

The coldest caves 

 Mercedeloch (Veneto): down to 0.8 °C in 1995, with presence of stable ice (Baldo, 1997). 

 Hotroloch CA4 (Veneto): 0.9 °C in the same year, also with ice (Baldo, 1997). 

 Pozzo della Neve (Molise): 5.0 °C in 1973 at approximately 1200 m elevation (Pasquini, 1972). 

The highest temperatures 

 Grotta Punta Galera (Campania): 23.2 °C in 1989, probably linked to external summer conditions and shallow position (Muscio et al., 1989). 

 Grotta di Collepardo (Lazio): 13 °C already in 1938 (Gambari, 1996). 

 Grotta della Ciapella (Liguria): 11 °C at the bottom of a shaft. 

 Buco Cattivo (Marche): 13.8 °C in 2006 (instrumental measurement).