the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Feb 2024
Spring-water temperature suggests widespread occurrence of Alpine permafrost in pseudo-relict rock glaciers
Abstract. Runoff originating from ground ice contained in landforms like rock glaciers and talus slopes represents an important water supply for the lowlands. Pseudo-relict rock glaciers host patchy permafrost, but appear to be visually relict, and therefore can be misinterpreted by using standard classification approaches. Permafrost content, spatial distribution and frequency of this type of rock glaciers are poorly known. Therefore, identifying pseudo-relict rock glaciers that might still host permafrost, and potentially ice, is crucial for understanding their hydrological role in a climate change context.
This work analyses rock-glacier spring-water temperature in a 795 km2 catchment in the Eastern Italian Alps to understand how many rock glaciers classified as relict could have spring-water temperature comparable to intact rock glaciers, as possible evidence of their pseudo-relict nature. Spring-water temperature, often used as auxiliary to other approaches for specific sites, was used for a preliminary estimate of the permafrost presence in 50 rock glaciers classified as relict. In addition, we present electrical resistivity tomography (ERT) results on two relict rock glaciers with opposing spring-water temperature and surface characteristics to constrain spring-water temperature results at local scale.
The results show that about 50 % of rock glaciers classified as relict might be pseudo-relict, thus potentially containing permafrost. Both supposedly relict rock glaciers investigated by geophysics contain frozen sediments. The majority of cold springs are mainly associated with rock glaciers with blocky and sparsely vegetated surface, but geophysics suggest that permafrost may also exist in rock glaciers below 2000 m a.s.l., entirely covered by vegetation and with spring-water temperature up to 3.7 °C. We estimate that pseudo-relict rock glaciers might contain a significant portion (20 %) of all the ice stored in the rock glaciers in the study area. These results highlight the relevance of pseudo-relict rock glaciers in periglacial environments. Even if not a conclusive method, spring-water-temperature analyses can be used to preliminarily distinguish between relict and pseudo-relict rock glaciers in wide regions.
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Status: closed
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RC1: 'Comment on egusphere-2023-2689', Anonymous Referee #1, 08 Mar 2024
- AC1: 'Reply on RC1', Luca Carturan, 26 Jul 2024
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RC2: 'Comment on egusphere-2023-2689', Cristian Daniel Villarroel, 28 Jun 2024
Dear Authors,
I have read in detail the work entitled ¨Spring-water temperature suggests widespread occurrence of Alpine permafrost in pseudo-relict rock glaciers ¨. Personally, I consider that it is a work of very good quality and according to the readers of this journal. The research topic is of particular interest in the Alps, and also in other mountainous regions. The use of spring-water temperature is a method that can provide valuable information on the presence and distribution of mountain permafrost, which is an issue where there are current uncertainties, mainly in the relict/pseudo-relict category. One of the advantages of this method is that it is relatively easy (the measurement device is light) to perform on the ground, regardless of the climatic and topographic difficulties of all mountainous regions. In addition, registered values, which are not conclusive by themselves, can help in the decision of other methods to apply and in the selection of the sites to be measured. This method can be applied in other mountainous regions, but I consider that in arid/semi-arid regions the presence of springs is scarce to cover spatial variability.
On the other hand, I consider that the spring-water temperature analysis is a complementary method in studying the presence and distribution of mountain permafrost. The application only of this method would generate ambiguous results. Warm temperatures (such as some registered in this work) are not enough to rule out the presence of permafrost. For their part, cold temperatures, they would not be enough to confirm the presence of permafrost. In this last point it is important to highlight that the ground ice stored seasonally in active layer can have influence on the temperature of the springs. Therefore, it is highly recommended to carry out other methods. EC and TDS measurement and hydrochemical and isotopic analysis could provide valuable information.
ERT profiles made in this work contribute to determining the presence or not of ground ice in the two rock glaciers studied. However, in one of them (Preghena) the resistive anomaly that would indicate the presence of ground ice is located at the 2D profile edges. In these sectors the reliability of the results decreases considerably. In addition, in this same rock glacier, a 20% error is considerably high.
In general, the work is well structured, the reading is pleasant, the data is relevant, and the figures are of good quality and enriching.
Specific comments are made below.
Line 13: This work is not focused on the water contribution of the talus slopes. Nor are there many background to mention the importance or not of the talus slopes in the water supply to the rivers. Where does this statement arise?
Line 68-71: InSAR or DInSAR would not be useful techniques for this case since the relict or pseudo relict rock glaciers have no movement or the movement can be very slow and be in the same range as the uncertainty of the method.
For this reason, since it is not a method applicable to this study, this sentence should be removed.
Line 73-75: The measurement could be at the end of summer or principles of autumn. The temperature trend in every summer should be considered, because with colder summers the thermal wave takes longer to enter the subsoil and completely defrost the active layer.
This research methodology assumes that the water in which the temperature is being measured is influenced by ground ice. But, so that the temperature value registered in the springs is a real evidence of permafrost existence, it should not exist seasonal ice in the active layer.
Line 94-96: It should be specified that lithology is composed of each rock glacier. Considering that ERT has been applied, which are of the relict or pseudo-relict type, and that the amount of ice present can be small, the changes or gradients in the values of the electrical resistivity could be influenced by lithology. This information could also be added in section 3.4.
Line 156 (Data collection): Has a monitoring of temperature variation in springs during the day been performed? If there is a variation of temperature during the day this will influence the results depending on the measurement time.
Line 161-162: It is not completely clear to me. In the previous paragraph it is mentioned that 133 springs located downslope of rock glaciers were measured. This paragraph says that 67 (17 + 50) springs in rock glaciers were measured. What is the amount of spings in rock glaciers that have been measured?
Line 175: How were those streamflows measured? With what criteria was that threshold (0.11 l/s) established?
Line 251-252: In these cases of high contact resistance it is advisable to add under the sponge an aluminum foil of approximately 20 cm side and cover it if possible with fine material.
If contact resistances remain high, after incorporating abundant salt water and aluminum foil, it is advisable to move the profile position to a more favorable sector. Personally, I do not recommend measuring with such high contact resistances.
Figure 8: The scale of values should be expressed in Ωm or kΩm, as in the text. In addition, it is convenient to add the RMS in each profile.
Line 464 (section 5.3): One of the main uncertainties is that it is not known if there is ground ice from the previous winter that has been stored in an active layer and that is influencing the temperature of the springs. In a way, the monitoring of the springs over the years would allow to eliminate this situation to a certain degree.
Another uncertainty factor is that water inside a rock glacier can follow different paths (Villarroel et al., 2022). In pseudo-relict rock glaciers, with the presence of ground ice in the form of islands, the water could follow paths without contact with the ice.
I consider that this situations must be discussed.
Citation: https://doi.org/10.5194/egusphere-2023-2689-RC2 - AC2: 'Reply on RC2', Luca Carturan, 26 Jul 2024
Status: closed
-
RC1: 'Comment on egusphere-2023-2689', Anonymous Referee #1, 08 Mar 2024
- AC1: 'Reply on RC1', Luca Carturan, 26 Jul 2024
-
RC2: 'Comment on egusphere-2023-2689', Cristian Daniel Villarroel, 28 Jun 2024
Dear Authors,
I have read in detail the work entitled ¨Spring-water temperature suggests widespread occurrence of Alpine permafrost in pseudo-relict rock glaciers ¨. Personally, I consider that it is a work of very good quality and according to the readers of this journal. The research topic is of particular interest in the Alps, and also in other mountainous regions. The use of spring-water temperature is a method that can provide valuable information on the presence and distribution of mountain permafrost, which is an issue where there are current uncertainties, mainly in the relict/pseudo-relict category. One of the advantages of this method is that it is relatively easy (the measurement device is light) to perform on the ground, regardless of the climatic and topographic difficulties of all mountainous regions. In addition, registered values, which are not conclusive by themselves, can help in the decision of other methods to apply and in the selection of the sites to be measured. This method can be applied in other mountainous regions, but I consider that in arid/semi-arid regions the presence of springs is scarce to cover spatial variability.
On the other hand, I consider that the spring-water temperature analysis is a complementary method in studying the presence and distribution of mountain permafrost. The application only of this method would generate ambiguous results. Warm temperatures (such as some registered in this work) are not enough to rule out the presence of permafrost. For their part, cold temperatures, they would not be enough to confirm the presence of permafrost. In this last point it is important to highlight that the ground ice stored seasonally in active layer can have influence on the temperature of the springs. Therefore, it is highly recommended to carry out other methods. EC and TDS measurement and hydrochemical and isotopic analysis could provide valuable information.
ERT profiles made in this work contribute to determining the presence or not of ground ice in the two rock glaciers studied. However, in one of them (Preghena) the resistive anomaly that would indicate the presence of ground ice is located at the 2D profile edges. In these sectors the reliability of the results decreases considerably. In addition, in this same rock glacier, a 20% error is considerably high.
In general, the work is well structured, the reading is pleasant, the data is relevant, and the figures are of good quality and enriching.
Specific comments are made below.
Line 13: This work is not focused on the water contribution of the talus slopes. Nor are there many background to mention the importance or not of the talus slopes in the water supply to the rivers. Where does this statement arise?
Line 68-71: InSAR or DInSAR would not be useful techniques for this case since the relict or pseudo relict rock glaciers have no movement or the movement can be very slow and be in the same range as the uncertainty of the method.
For this reason, since it is not a method applicable to this study, this sentence should be removed.
Line 73-75: The measurement could be at the end of summer or principles of autumn. The temperature trend in every summer should be considered, because with colder summers the thermal wave takes longer to enter the subsoil and completely defrost the active layer.
This research methodology assumes that the water in which the temperature is being measured is influenced by ground ice. But, so that the temperature value registered in the springs is a real evidence of permafrost existence, it should not exist seasonal ice in the active layer.
Line 94-96: It should be specified that lithology is composed of each rock glacier. Considering that ERT has been applied, which are of the relict or pseudo-relict type, and that the amount of ice present can be small, the changes or gradients in the values of the electrical resistivity could be influenced by lithology. This information could also be added in section 3.4.
Line 156 (Data collection): Has a monitoring of temperature variation in springs during the day been performed? If there is a variation of temperature during the day this will influence the results depending on the measurement time.
Line 161-162: It is not completely clear to me. In the previous paragraph it is mentioned that 133 springs located downslope of rock glaciers were measured. This paragraph says that 67 (17 + 50) springs in rock glaciers were measured. What is the amount of spings in rock glaciers that have been measured?
Line 175: How were those streamflows measured? With what criteria was that threshold (0.11 l/s) established?
Line 251-252: In these cases of high contact resistance it is advisable to add under the sponge an aluminum foil of approximately 20 cm side and cover it if possible with fine material.
If contact resistances remain high, after incorporating abundant salt water and aluminum foil, it is advisable to move the profile position to a more favorable sector. Personally, I do not recommend measuring with such high contact resistances.
Figure 8: The scale of values should be expressed in Ωm or kΩm, as in the text. In addition, it is convenient to add the RMS in each profile.
Line 464 (section 5.3): One of the main uncertainties is that it is not known if there is ground ice from the previous winter that has been stored in an active layer and that is influencing the temperature of the springs. In a way, the monitoring of the springs over the years would allow to eliminate this situation to a certain degree.
Another uncertainty factor is that water inside a rock glacier can follow different paths (Villarroel et al., 2022). In pseudo-relict rock glaciers, with the presence of ground ice in the form of islands, the water could follow paths without contact with the ice.
I consider that this situations must be discussed.
Citation: https://doi.org/10.5194/egusphere-2023-2689-RC2 - AC2: 'Reply on RC2', Luca Carturan, 26 Jul 2024
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