Temperature Logging (2024-2025)

Introduction

In 2022 we obtained several TinyTag™[1] temperature data loggers that could be left logging for over one year.  The ‘year’ of logging is important as several caves become inaccessible from September to about May (high water), less accessible in the winter months (snow) as well as the expedition being limited to one or two trips each year.

The results from 2022 to 2025 have been published in previous reports and are available on the expedition website[2].

There are many caves in the Tresviso – Andara area, some are resurgence caves at around 500m altitude and others high in the mountains between 1,700m and 2,000m in altitude. The loggers placed in entrances high up would be measuring the incoming, external, air temperature, whereas at the resurgence it would be water temperature. Water temperature would be subject to several factors: how long the water was underground equilibrating with cave temperature and the temperature that it was when it entered the cave system. The time underground will be related to flow (i.e., has it rained recently).

Some of the resurgence caves emit water from an unknown catchment area.  By monitoring the temperature, information about where the water came from may be identified. Where the detector is near a streamway or at a resurgence the catchment of the water (if known) is identified.  Where the detector is at the top of a cave, which at one time would have been a sink, the catchment is described as the ‘Top Entrance’.

Table: Logger locations 2024-2025.

Picture: Sensor locations 2024-2025.

Each detector was set to start logging at the end of September 2024 (after the expedition had completed) with 30 minutes interval logging.

Initial Results

If a day is picked when all the temperatures have been stable (most likely when there has been several weeks of dry weather),  the various cave temperatures can be compared.

On the 1^st August 2025 the following temperatures were measured:

Table: Temperature Comparison, 1^st August 2025

The temperature drops as altitude increases with a lapse rate of between 0.65°C and 0.9°C per 100m.  Thus, in the same conditions, a temperature of 12.5°C in Cueva de la Cabeza de Vaca (altitude 894m) would reasonably drop to 6°C at FT43 (altitude 1905m).  Where the temperature doesn’t agree, there is likely a draught leaving the cave that cools the location of the detector.

Cueva de la Cabeza de Vaca

Cueva de la Cabeza de Vaca is a resurgence cave near the bottom of the Sobra Valley.  The cave has been followed water upstream through a series of sumps to a fifth sump that continues into the hill.  The catchment is unknown but assumed to come from the ridge to the north (the Tajadura area).

This year the detector was moved away from the streamway and into the first chamber.

Graph: Cueva de Cabeza de Vaca – Annual temperature record (2022-2025).

The original location of the detector meant results were dominated by external air temperatures, with the detector moved away from the streamway there is now little influence from the temporary outside conditions, such as rain fall, but there is a greater seasonal variation. 

As the winter season starts, there is a gradual cooling that continues until April.  In June the temperature increases quite rapidly.  Possible reasons for the changes:

• A shift in the rocks leading to a change in draught.
• The detector was moved slightly
• The cold water from snow melt has finally exited the cave to be replaced by warmer water (at odds with saying there is no direct evidence of rainfall)

Cueva del Nacimiento Entrance

The detector is about 40m from the resurgence entrance and about 5m above the normal stream level.  It is in the main draught of the whole cave.  The cave takes water from the high eastern massive (Pico de Valdominguero and Pico de San Carlos), but also nearer sources such as the streamway in Cueva de la Marniosa.

Graph: Cueva del Nacimiento- Annual temperature record (2022-2025).

Comparing the three sets of data, the trend is similar qualitatively, with the ambient temperature being slightly lower during winter, and lots of dips which are identified as events of extra water flow (after rain fall).

Cueva del Nacimiento, locations compared

There are two detectors that can be compared, one at the entrance and the other at Consort Hall.  Consort Hall is a chamber about 1.1km from the resurgence entrance.

Graph: Cueva del Nacimiento, comparison between detectors.

The above graph shows the response of the detector at the entrance is much greater than the detector at Consort Hall.  Consort Hall is away from the stream.

Graph: Expanded Consort Hall data.

Together where the magnitude is less, the results seem reversed during the winter months.

Graph: The temperature response in Nacimiento from October 2024 to November 2024.

The two major responses during this period (28 Sept and 27 Oct) are both positive (upward) increases and the positive correlation continues into December (see below, 2 Dec).

Graph: The temperature response in Nacimiento from November 2024 to May 2025.

During the winter months (Dec – May) the drop in temperature at the entrance is opposite to Consort Hall until May, when the temperature change lines up again.

The winter months are when the cave is wetter and the main route for air may sump and becomes impassable.  The change could reflect a change in air flow, for instance, at the short duck/sump near Consort Hall or in the entrance series which is assumed to sump during winter.

Picture: Part survey of Cueva del Nacimiento.

Cueva de Entre Cuetos

The Cueva de Entre Cuetos is a dry entrance cave about 4km from the Cueva del Nacimiento resurgence and about 850m higher.  There is insufficient water to create a streamway within the known part of the cave.

Graph: Comparison of Cueva de Entre Cuetos and Cueva del Nacimiento (2024-2025).

In previous years the detectors in Cueva del Nacimiento and other resurgence caves have found some matching events, but some unique events.  The detector in Cueva de Entre Cuetos shows matching events suggesting that it is connected to Cueva del Nacimiento.

FT43 – Mazarrasa

FT43 is a high entrance pothole, at an elevation of 1905m, in the Mazarrasa mines area that leads into some mined levels with a strong draught.  The detector was placed at the top of a loose pitch, away from the open entrance shaft, in order to try and avoid outside temperature fluctuations.

Graph: Comparison of FT43 and Cueva del Nacimiento (2024-2025).

The data shows an almost 4°C difference between summer and winter, probably related to snow settling and being retained through winter. 

Not all events correlate between FT43 and Cueva del Nacimiento.  Those that do correlate, the FT43 data is typically lagging by a few hours (although in some cases it leads).

Graph:  FT43 vs Cueva del Nacimiento showing correlation and differing response

Torca del Picu Boru

The shaft of Torca del Picu Boru is on the slopes of Picu Boro, at an elevation of 1785m. The detector was placed in the traverse leading to the top of the 40m Teddy’s Pitch, this was away from the entrance series and about 45m lower.

Graph: Comparison of Torca del Picu Boru and Cueva del Nacimiento (2024-2025).

There is a 1°C drop in temperature through winter that recovers in May.  From May onwards the ‘noise’ represents a daily oscillation, although some weeks (late July) the oscillation is much reduced.

There is very little overlap between the data from Torca del Picu Boru and Cueva del Nacimiento.

Cueva del Nacimiento – Death Race 2000

This data was from the previous year (2023-2024) and does not represent a complete year.

Death Race 2000 is a dry chamber almost 2km into the cave and 100m above a small stream.

Graph: Cueva del Nacimiento, Death Race 2000 (from 2023-2024).

The most notable feature is the step change ending on 20 December that starts as a gentle increase on 24 Nov.

The assumption here is that the air currents are changed by either an entrance getting snowed in or the cave becoming sumped.  Although the year is different, there is no equivalent increase on the Consort Hall detector.

The spike at the end is an anomaly and assumed relates to the battery failing.

Conclusions

The Cueva de Entre Cuetos and Cueva del Nacimiento are very closely linked, probably with an air link.

[1] TinyTag Plus 2 TGP-4017 https://www.geminidataloggers.com/data-loggers/tinytag-plus-2/tgp-4017

[2] https://tresvisocaves.info/science/

[3]Covers the year 2023 to 2024 as sensor not collected on the 2024 expedition.