Observation of the rock slope thermal regime, coupled with crack meter stability monitoring

This article describes an innovative, complex and affordable monitoring system designed for joint observation of environmental parameters, rock block dilatations and temperature distribution inside the rock mass with a newly designed 310 meter borehole temperature sensor. Global radiation balance data are provided by pyranometers. The system introduces a novel approach for internal rock mass temperature measurement, which is crucial for the assessment of the changes in the stress field inside the rock slope influencing its stability. The innovative approach uses an almost identical monitoring system at different sites allowing easy setup, modularity and comparison of results. The components of the monitoring system are cheap, off-theshelf and easy to replace. Using this newly designed system, we are currently monitoring three different sites, where the 15 potential rock fall may endanger society assets below. The first results show differences between instrumented sites, although data time-series are relatively short. Temperature run inside the rock mass differs for each site significantly. This is very likely caused by different aspects of the rock slopes and different rock types. By further monitoring and data processing, using advanced modelling approaches, we expect to explain the differences among the sites, the influence of rock type, aspect and environmental variables on the long-term slope stability. 20


Introduction
The rock slope stability is crucially influenced by both endogenous rock properties and exogenous factors (D'Amato et al., 2016, Selby 1980. The rock physical properties are well known and numerous laboratory experiments and theoretical works exist in the field, however, there are very few in-situ experiments that would deal with real-world time and space scales (Fantini 25 et al., 2016;Bakun-Mazor et al., 2013Janeras et al., 2017;Marmoni et al., 2020) Thermal expansion and frost action are the main exogenous physical processes of the mechanical weathering of the rock surface, which together with chemical weathering ultimately results into a weakening of the rocks slopes and lowering their stability (Gunzburger et al., 2005, Vespremeanu-Stroe andVasile, 2010;do Amaral Vargas et al., 2013;Draebing, 2020). The loss of stability, caused by repeated changes in the stress field inside the rock eventually leads to a rockfall, one of the fastest et al., (2010) presented a review of monitoring techniques for open-pit mine walls monitoring. Carla et al., (2017) used GB 65 InSAR to monitor displacement of mine slopes failures. Large rock slides are monitored by Crosta et al., (2017) using GB InSAR, Satelite InSAR and borehole inclinometry. Loew et al., (2012) used borehole inclinometry and borehole extensometry combined with GB InSAR interferometry in the large Randa rockslide monitoring. Zangerl et al., (2010) used total station measurements, coupled with borehole inclinometers for a similar purpose. Long-term rock slope destabilization is monitored using total station measurements, multipoint surface extensometers, borehole inclinometers (Chen et al., 2017), or TLS 70 measurements eventually (Hellmy et al., 2019). Usually, these monitoring systems are designed as experimental, aiming to develop new early-warning sensors or approaches (Loew et al., 2017;Jaboyedoff et al., 2011) or to describe processes of rock slope destabilization (Fantini et al., 2016;Kromer et al., 2019;Du et al., 2017). However, these systems are site-specific and installation of a similar system on more sites is complicated and financially demanding.
These systems are sometimes complemented with environmental data observations. However, these are often limited to air 75 temperature and/or rock face temperature monitoring only (Jaboyedoff et al., 2011, Blikra andChristiansen, 2014;Marmoni et al., 2020;Collins and Stock, 2016;Collins et al., 2018;Eppes et al., 2016). Less commonly, the temperature is measured in rock mass depth (Magnin, et al., 2015a, Fiorucci et al., 2018. The absence of precise data about temperature changes in rock mass depth makes the assessment of the thermally-induced stress field response inside the rock mass complicated. Without indepth temperature data and incoming radiation, the determination of heating/cooling trends causing internal volume and stress 80 field changes is difficult. Also, the monitoring systems are usually designed specifically for the monitored sites, which brings difficulties for generalization of the results or installation of the system at more sites. Therefore, we have designed an easy to modify monitoring system, which measures the physical parameters in a 2D environment in the field conditions, both on the rock face and inside the rock mass. With just minor modifications we can instrument various rock slope sites. 85 a set of automatic induction crack meters, coupled with dataloggers ( Fig. 1) measuring relative block displacement a environmental station with a set of sensors measuring various meteorological data (Fig. 1), such as air temperature, humidity and pressure (Table 1), and global radiation balance of the rock face ( Fig. 4) using pair of 100 pyranometers a set of 12 thermometers placed along a 3 m deep borehole, carefully insulated between each neighbouring sensors, measuring rock slope thermal depth profile at ten minutes interval 105 Table 1: List of presented monitoring system components, with performance metrics and prices.
All the elements of the system are commercially available at affordable expenses (one site instrumentation costs approx. 5000 Eur (Table 1), and are easy to replace by even moderately experienced user. Additional costs are drilling works (1-2 000 EUR). Cost of drilling works depends on the site accessibility and rock mass hardness. The price of the specific monitoring system is also affected by the number of used crack meters and data loggers. On the other hand, system maintenance 110 costs are not higher than 300 Eur per year including data processing and storage. , which also contain accurate in-situ temperature sensors (Table 1). When a datalogger is placed within the discontinuity, the local temperature microclimate can be estimated. The joint dilatation and temperature data are stored in the datalogger and can be wirelessly transmitted at a distance of up to a hundred meters using wi-fi, which simplifies data collection 125 as it can be usually performed from below the rock face. Tertium TAG data can be sent to a server via IoT SigFox network.
The crack meters and dataloggers are powered with two AA batteries, which last typically 6-12 months. The displacement and https://doi.org/10.5194/gi-2021-5 Preprint. temperature are set to be measured every hour. This can be however remotely changed if necessary, for example during special experiments such as thermal camera monitoring campaigns (Racek et al., 2021).

Environmental monitoring 130
For the monitoring of the environmental and climatic parameters at the study sites, we use automatic environmental stations manufactured by Fiedler environmental systems. These are composed of registration, communication and control unit M4016-G, external tipping-bucket rain gauge, two temperature sensors, atmospheric pressure sensor, humidity sensor, and a pair of pyranometers, measuring the global radiation. All these sensors and the control unit are powered by a 12 V battery, which is charged by a small solar panel (Fig. 1). Except for precipitation, which is measured continuously using a pulse signal, all other 135 climatic variables are measured every 10 minutes. The control unit is equipped with a GSM modem, which sends the data automatically to the server of the provider every day. For information about accuracy, durability and price of environmental monitoring see table 1. To expand the spatial extent of temperature data, thermal camera time-lapse campaigns were performed and are also planned in future (Racek et al., 2021).
To compute the radiation balance of a rock face, it is necessary to measure both incoming and reflected radiation. For this 140 purpose, a set of pyranometers is used (Gunzburger and Merrien-Soukatchoff, 2011;Janeras et al., 2017;Vasile and Vespremeanu-Stroe, 2017). Our monitoring system uses two pyranometers placed perpendicular to the rock face, one facing the rock surface while the other the sky hemisphere. This setup enables to measure both incoming and reflected radiation. The sensors are not placed directly on the rock face, but on an L-shaped holder, which allows placing both sensors almost at the same point. The rock-facing pyranometer is placed at a distance of approx. 10 centimetres from the rock surface. The 145 pyranometers (type SG002) are supplied by Fiedler environmental systems company (FIEDLER, 2020), and have an output of 0-2 V, which corresponds to global radiation of 0-1200 W/m 3 , the monitored wavelength spans from 300 to 1200 nm.
Outputs from pyranometers are processed by a converter and then send to the control unit, to be sent with the other monitored meteorological variables to the data hosting server.

Borehole temperature monitoring 150
For the complex monitoring of the thermal behaviour of a rock slope, it is necessary to know temperatures at different depths of the rock mass. This is a crucial and innovative part of our monitoring system. Temperature from rock mass depth contributes to a better understanding of the rock slope thermal regime.
The sensors are placed in a 3 m deep borehole. The borehole is drilled close to the monitored unstable rock blocks.
However, to ensure safety during drilling and the long lifespan of borehole and sensors, the borehole itself is drilled to the 155 stable part of the rock slope, perpendicularly to the surface. The borehole is then equipped with a custom-designed device with a set of temperature sensors, placed along a tubular spine at different depths. Technical parameters of temperature sensors are the same as for air temperature sensors (Tab 1). Copper rings with 5 cm diameter, connected to thermal sensors, are placed at a given distance on the tubular spine (5 cm below the surface, 10 cm, 20 cm, 30 cm, 50 cm, 75 cm, 100 cm, 150 cm, 200 cm, https://doi.org/10.5194/gi-2021-5 Preprint. Discussion started: 19 March 2021 c Author(s) 2021. CC BY 4.0 License. 250 cm and 300 cm). Additionally, one temperature sensor is placed directly on the rock surface. The head of the borehole is 160 insulated, to prevent air and water inflow into the rock, and the sensors inside the borehole are separated by thorough thermal insulation, to ensure the temperatures are not affected by the air circulation in the borehole. The thermal data, collected every 10 minutes, are passed through a converter and send to the main control unit of the environmental station.

Instrumented sites
The monitoring system has been so far established at three different sites (Fig. 2), using the same instrumentation set-165 up. The sites were chosen deliberately in steep rock slopes built of various rock types, with various aspect, diverse geological history and, to integrate a practical applicability side, at locations where the potential rockfall endangers buildings, infrastructure or other social assets.

Pastýřská rock (PS)
The first instrumented rock slope (Fig. 2) called "Pastýřská rock" is located on the Elbe riverbank in Dečín town, NW Czechia.
Monitoring of meteorological variables was started in late 2018, followed by crack meters installation and in-depth borehole 175 temperature sensor. Pastýřská rock is formed by Cretaceous sandstone, with a general southeast orientation. The mechanical and physical properties of sandstone samples are listed in table 2. The rock slab with pyranometers and borehole is dipping 87° towards the east (85°). On this site, using traditional methods, three main discontinuity sets were identified (Table 3). This locality was known for extensive rock fall activity in past, which lead to rock slope stabilization works in the late 1980s.
However, the block monitored by the crack meters remained in its natural state, without any stabilization measures. At this 180 site, one block is monitored, using two pairs of crack meters. This partial block has dimensions of 6.7 x 10.7 x 2.5 m.
Monitoring at this rock slope has been in operation since autumn 2018. The monitored block is located in the overhang part of the rock slope and all four visible cracks are monitored. The colour of the rock slope surface varies from dark, to light grey ( Fig. 2). The rock slab, where the pyranometers are placed is coloured in light grey colour.

Branická rock (BS) 185
This rock slope ( Fig. 2) in Prague (Central Czechia) was instrumented in summer 2019 and is formed by several Silurian and Devonian limestone layers, with varying mechanical and physical properties ( Table 2). The rock slope was artificially created and used till the 1950s as a limestone quarry. The rock slope is located on a Vltava riverbank and it is generally facing westsouth-westwards. The pyranometers and the borehole temperature sensors are placed on a rock slab dipping 80° to the southwest (235°). Three main discontinuity sets were identified using a geological compass at Branická rock site (Table 3). 190 The site was known for extensive rock fall activity in the past, even after quarry closing, which resulted in partial stabilization of most unstable blocks in the 1980s. At this site, three unanchored blocks ( Fig. 2) are monitored with seven crack meters. In the upper part of the rock slope lies the largest monitored block at this site, with dimensions 0.9 x 4.5 x 3.7 m. This block is monitored with three crack meters. The second block is located at the bottom part of the rock slope, partly shaded by vegetation.
Dimensions of the second block are 2.5 x 1.6 x 3.6 m. The second block slowly slides on the bottom surface and is instrumented 195 with two crack meters. Finally, the third monitored block is smaller (0.8 x 1.4 x 0.4 m). It is located in a highly weathered part of rock slope and monitored with two crack meters. Monitoring at Branická rock site is running since autumn 2019. The colour of limestone varies from grey to yellow (Fig 2) and the colour of limestone facing pyranometer is light grey.

Tašovice (T)
The third instrumented site (Fig. 2) is a rock slope above a local road and Ohře river near Karlovy Vary town, W Czechia. 200 Rock slope is formed by partly weathered granite with varying mechanical and physical parameters (Table 2). Generally, it is facing south-south-east direction. The instrumented slab is dipping 88° to the south (170°). At this site, three relatively poorly https://doi.org/10.5194/gi-2021-5 Preprint. developed discontinuity systems were identified using a geological compass in the field (Table 3). At this site, small rock falls are frequent as it can be seen from the fresh rock and debris accumulation under the rock face. The locality was fully instrumented with borehole temperature sensors, environmental station and global radiation monitoring in spring 2020. Three 205 relatively small blocks are monitored at this site. Block 1 (1.7 x 1 x 2.1 m), Block 2 (0.9 x 0.8 x 0.4 m) and Block 3 (0.5 x 1.2 x 0.4 m). Each block movement is monitored with a pair of crack meters. The colour of the rock slope varies from black to dark grey. The granite surface at the pyranometers site has dark grey colour.

Fieldwork campaigns
Each instrumented rock slope was characterized using traditional geological, geomorphological and geotechnical methods, 210 such as measuring geometrical properties of joints and fault planes, relative surface strength measurement using a Schmidt hammer, discontinuity density measuring, and stability assessment estimated using geotechnical classifications (Racek, 2020).
Mechanical and physical properties of the rocks were determined by common laboratory tests, using collected representative rock samples (Table. 2). Traditional methods are supplemented with state-of-the-art methods of rock slope analysis, including analyses of 3D point clouds and derived mesh surfaces, based on SfM (structure-from-motion, a computerized photogrammetric technique based on the calculation of 3D point cloud from overlapping photos with varying focal axis orientation) (Westoby et al., 2012) 220 processing using the data collected with a UAV or TLS collected data. The obtained detailed rock surface models are then analysed using Cloudcompare and its plugins (Girardeau-Monaut, 2016; Thiele et al., 2018;Dewez et al., 2016) and DSE software (Riquelme et al., 2014) to derive the joint and fault planes and measure their spatio-structural properties. Moreover, three main discontinuity systems that were identified using a geological compass in the field at all three sites are summarized in Table 3. 225 Tašovice -granite weathered 2.399 -2.525 5 -11.9 1.  Point cloud data, that were produced by UAV SfM photogrammetry were analysed, edited in Cloud Compare and afterwards principal poles (Fig. 3) were automatically identified using DSE software (Riquelme et al., 2014).

First results
The monitoring systems are operational from 1 to 2 years. During most of the period, the gauges and sensors operated without 235 problems or interruptions. However, some accidents or breakdowns occurred, the most serious being the destruction of one pyranometer by boulders, washed down by a rainstorm. As the experimental sites are easy to reach and spare parts easy to obtain, any broken or damaged elements can be replaced within a few days. Workers within rock faces are using safety gear, such as full-body harness and helmet. Securing is done with static ropes and working grade brake. In the case of Pastýřská rock, workers can use Via Ferrata routes. 240

Environmental monitoring
Environmental monitoring on all instrumented sites works without problems. From measured time-series of meteorological variables (Table 4) rock slope microclimate can be defined. Also, the influence of these on monitored discontinuities position can be determined. Comparison of crack opening with measured rainfall events using simple graph does not indicate any visible influence of precipitation on the crack opening/closing. However, the measuring period is still short, with prevailing 245 dry, relatively warm weather. Conversely, there is a visible influence of air temperature to block dilatation, where both diurnal and annual cycles can be identified (Fig. 6). Basic statistical data descriptions of measured environmental variables are listed in Table 9.

Rock surface radiation balance
Monitoring of rock face radiation balance was installed at monitored rock slopes during 2020, therefore we still miss a fullyear global radiation cycle. Even from these incomplete data we can observe the differences between individual sites (Fig. 4).
Basic statistical description of so far measured data is listed in table 5. Local conditions influence incoming radiation pattern 255 by general aspect of the rock slope or by shading effect of pyranometer´s surroundings. Differences in the absolute reflected radiation are mainly caused by the different colour of rock faces, by different heating and cooling trends of the rock mass and by the different angle of incoming solar radiation caused by the aspect of the instrumented slab.

Figure 4: Example of the incoming and reflected radiation measured by pyranometers at BS, T and PS sites. 24-hour
time series of incoming and reflected radiation. Data were recorded 1.8.2020 with no clouds. Influence of slope aspect is obvious from peak incoming radiation shift.

Borehole temperature 265
By continuous temperature measuring in different depths inside a horizontal borehole, we can observe both diurnal and annual temperature amplitude in various depths (Fig. 5). In-depth measurements of temperature show differences in temporal thermal behaviour between monitored rock slopes (Fig. 5). From boxplots that represents data from all monitored sites (Fig X.), it is obvious that largest surface temperature variation has been measured at Tašovice site despite the shortest operating time.
However, in greater depths, this variation decreases. This is probably caused by the dark colour of Tašovice rock surface, with 270 lower albedo. Greater in-depth temperature variation is present at Pastýřská rock site. However, these data can be biased by different time-series lengths. Overall differences caused mainly by lithology and aspect are visible.

Blocks dilatation
At all monitored sites, we are observing the thermally-induced dilatation of individual blocks, however, due to relatively short time-series, the measured crack movements do not show significant opening or closing trends yet. From the measured dilatation 280 data, diurnal and annual amplitudes of crack opening for each instrumented block can be identified. temperature changes on the crack opening. Similar behaviour is observed on all monitored blocks ( Table 6). The amplitude of crack meters position differs between individual sites and blocks. These differences are caused by different blocks dimensions, crack meters placement and the regime of destabilization. 285 So far, relatively high crack meter amplitudes were measured on Block 1 (aprox. 170 m 3 ) at Pastýřská rock site and on Block 290 1 (aprox. 16 m 3 ) at Branická rock site. These blocks are the two largest ones instrumented. Measured crack meter amplitude is caused by block thermal expansion/contraction. On the other hand, relatively small block 3 (BS site) shows relatively large movements although is instrumented only since summer 2020. These movements points on possible gradual destabilization of this block. Blocks that are instrumented at Tašovice site seems to be more stable. Only Block 3 shows 0.85 mm of movement.
Again, this block was instrumented recently at the end of 2019. By further monitoring, trend analyses should reveal possible 295 blocks´ destabilization trends. Larger blocks (PS1, BS1; BS2) shows the largest overall amplitude of movements. Rest of smaller blocks shows smaller overall amplitudes, however these seams to be more influenced by the short-term diurnal temperature changes. Sensitivity to fast heating/cooling, makes these blocks more susceptible to temperature-induced irreversible movements.

Discussion
Commonly used rock stability monitoring systems are often designed to provide an early warning (Jaboyedoff et al., 2011;Crosta et al., 2017), aiming primarily at the identification of a hazard and not to investigate the causes or thresholds of 305 the movement acceleration. The presented complex monitoring system is designed to contribute to explaining the various influences on the destabilizing processes, which leads to the eventual loss of rock mass stability and rock fall event triggering. Fantini et al., (2017) have concluded that it is the temperature variations (rather than precipitation or wind) that cause changes in strain within the rock mass leading to its destabilization. However, to assess the strain changes within the mass, it is necessary to have information on the temperature distribution inside the rock. This is the crucial advantage of the presented 310 monitoring system, as the borehole temperature monitoring allows to identify short and long-term temperature changes up to 3 m depth.
To observe individual influences of the strain in the rock masses, we have placed the monitoring on rock slopes with various aspect (different insolation and its diurnal and annual changes) and built of different rocks (sandstone, granite and limestone) to include the influence of heat conductivity, capacity and colour of the rock. While there are numerous laboratory 315 studies on rock conductivity (cf. Blásquez et al., 2017), modelling of heat flow based on surface observation (Hall andAndré, 2001, Marmoni et al., 2020), or coarse, large-scale experiments usually aiming at heat management in the thermal energy industry (Zhang et al., 2018), only a few experiments have been carried concerning the shallow, first meters surface of the rocks (Greif et al., 2017), even though this is the most strained and weathered part of the rock mass (Marmoni et al., 2020).
Moreover, thermal conductivity can be spatially determined from heating/cooling rates of rock slope surface using thermal 320 camera (Pappalardo et al., 2016;Pappalardo and D'Olivo, 2019;Fiorucci et al., 2018;Guerin et al., 2019). The analyses of structural properties of rock were performed using traditional field compass measurements and using automatic discontinuity extraction from the point clouds. While generally, the results were similar, the point cloud analysis does not include discontinuity sets that are not forming the surface of the rock face. This effect is visible mainly in the case of the Tašovice 3D model, where the structural setting is not so straight forward as it is at Branická rock and Pastýřská rock sites 325 formed by sedimentary layers.
Concerning the proposed monitoring system, it is compact, built of cheap and easily accessible off-the-shelf components, and easy to modify according to specific conditions at rock the slope site. The performance of the monitoring system was so far without major problems. One crack meter datalogger was damaged and one pyranometer was destroyed by a rockfall triggered by a severe thunderstorm. Otherwise, monitoring works reliably at all instrumented sites. Maintenance is consisting of 330 changing datalogger batteries and cleaning rain gauge buckets. Online data transfer via Sigfox IoT network (dilatometers) and GSM (environmental stations) works without problems. Crack meters can record movements smaller than 0.1 mm (Tables 1,7). In comparison with other methods that 335 measure spatial change, their precision is high, with lower costs (Table 7). The temporal resolution of the measurement is nearly continuous when the crack meter position can be read every second (Table 7). Moreover, we have tested these in a controlled temperature environment using a climate chamber to find out any temperature-dependent errors. In this controlled test, we were able to measure the expansion of a concrete block. The resulting block expansion measurements matched theoretically calculated concrete block expansion. This way we made sure, that measurement of the crack meters is not biased 340

Method
Results by dilatation of the device itself. A disadvantage of crack meter use is that this method provides only one-dimensional spatial change data. To get full 3D data about an unstable feature´s spatio-temporal behaviour, more crack meters must be deployed.

Range Precision Sampling rate Online data Price
Also, the maximum range of this device is limited to 200 mm. That limits the use of this crack meters to changes with lower magnitude. In the case of environmental monitoring, we have found differences between sites (Table 4, 9), caused by aspect and local microclimate. Some differences between sites are caused by different length of meteorological variables time-series (Table 4). When temperature data from in-depth monitoring are compared, differences between monitored sites are apparent 350 ( Figures 5,6), both diurnal and annual temperature cycles, and as deep as 3 m. These differences are caused by the combination of the different orientation of rock slopes and by the thermal behaviour of the different rock types. As concerns the energy supply, the solar panel is capable of keeping the battery charged even during cloudy weather or snowy winters. In case of indepth temperatures, highest differences are observed in surface zone (Table 9). In 3 m depth, is at all sites temperature approx.  Solar radiation balance is not directly comparable, due to different aspect and slope of monitored rock slabs. However, the temporal shift in maximum radiance caused by rock slope aspect is visible from resulted radiation data (Fig. 4). When 360

same. 355
whole year data about solar radiance will be available in spring 2021, more differences should be found. Then the comparison of long-term solar radiation cycles will be possible.

365
It is necessary to remark that the destabilisation processes are rather slow and have a low magnitude in the central European mid-latitude climate. Therefore, long-term time series monitoring is necessary. Also, there are several cycles with different length, amplitude and depth-reach, ranging from diurnal cycles up to long-term cycles linked with solar activity or climatic oscillations (Gunzburger et al., 2005;Sass and Oberlechner., 2012;Pratt et al., 2019). Among these are the most prominent diurnal and annual cycles (Marmoni et al., 2020). Diurnal cycles have shallower reach (Fig. 5), but are fast and thus 370 cause high strain in the surficial rock layer, while annual cycles are slower, but with higher amplitudes and depth reach (Hall and André, 2001). This information helps to clarify the role of thermally-induced stress in rock disintegration. Also, in combination with the temperature and global radiation measurements, heat conduction velocity inside rock mass can be determined. Diurnal temperature cycles with higher magnitude can play a crucial role in rock fall triggering. This, together with mechanical properties of the rock mass (Table 2), will allow creating more accurate thermomechanical models of the 375 monitored rocks slope in the future. These models will be used to identify zones where the accumulation of thermally induced stress concentrates, as the places of potential destruction and following destabilization of the rock slope. On all sites, the highest diurnal measured crack meter movements are recorded in the spring and autumn months, when diurnal rock slope In other works that using similar instrumentation was published in past. (Matsuoka, 2008;Bakun-Mazor et al., 2013Dreabing, 2020;Draebing et al., 2017 Nishi andMatsuaoka, 2010), although in thermally induced rock mass deformations monitoring is still relatively marginally studied. Matsuoka (2008) presented long-term data of crack meter monitoring rock slope unstable parts in alpine environment. Same as in our results, measured joint dynamic is influenced by air and rock mass temperature. Similarly, to our first data, dynamic of monitored joints is highest in spring and autumn. Because 385 longer time span of monitoring Matsuoka (2008) measured gradual, temperature driven joint opening. Most significant joint opening is in his work linked with freeze-thaw conditions in alpine environment. Nevertheless, even in dynamic alpine environment, joint opening is slow, spanning approx. 0.4 mm in 2 years of monitoring. Is expected, that in temperate climate these processes are even slower. Nishi and Matsuaoka (2008) presented influence of temperature to large rock slide displacement. In this, to our sites different setup, they have measured large displacement over 1 m in 3 years of monitoring. 390 Largest movements velocities were documented during highest precipitations seasons. Due to different spatial extent of monitored rock mass movements are results almost incomparable. Bakun-Mazor et al., (2013 proposed monitoring system to distinguish thermally and seismically induced joint movements in limestone and dolomites a Masada cultural heritage site. In this work amplitude of thermally induced joint movements was approximately 0.3 mm in one year. Which is similar to our first results. In this work, they have estimated annually irreversible joint opening about 0.2 mm. However, in 395 this study, thermally induced movements are supplemented with seismically induced movements with higher magnitude. We hope, that in long-term, we will be able to observe similar wedging-ratcheting mechanism at our sites, where also effect of frost shattering should play not negligible role. Draebing et al., (2017) and Draebing (2020) observed crack opening in alpine environment. In this extreme environment, they were able to observe short-term ice wedging induced movements up to 1 mm in several days. These movements were active in snowmelt season, when ice wedging is most active. By comparing in situ 400 crack meter temperature and crack meter opening they have established linkage between in situ temperature and joint dynamic.
In this case joint dynamic was also influenced by snow cover, which has in alpine region longer time-span than in case of our monitoring sites. However, even in these conditions, gradual irreversible joint opening is relatively slow, about 0.1 mm/year. We hope, that data from winter 2020/21 bring similar results in case of our monitoring, however with lack of active permafrost and ice filled joints at our sites, these moments should have lower magnitude. Newly instrumented site in Krkonoše mountains 405 should provide data from dynamic mountainous region.
Measuring temperature inside rock mass is nowadays relatively uncommon technique. Only few works estimate in depth rock mass temperatures in surface zone (Magnin et al., 2015a;Fantini et al., 2018). In work of Magnin et al., (2015a) is measured rock mass temperature inside 10 m deep borehole. Boreholes were drilled in alpine, permafrost active areas and this research is oriented mainly to estimate active permafrost depth ant its temporal evolution. In shallow surface zone, they have 410 recorded annual temperature differences approx. 5°C in 3 m depth. Temperature amplitude is rising in shallower subsurface zones. Our data from horizontal boreholes shows amplitude in 3 m approx. 10° C. This is caused by warmer climate and https://doi.org/10.5194/gi-2021-5 Preprint.