Hydrogeology of the Torrener Joch Fault Zone, Salzburg, Austria Giorgio Höfer-Öllinger 1,2,3, Michael Schneider2, Erik Buske2, Friedrich Volkmer2, Tim Schöne2, Timo Kessler3, Franz Neubauer4, Kathrin Müggenburg1, Klaus Heimlich1, Ines Ripper-Würtz1 1
GEOCONSULT ZT GmbH; Hölzlstraße 5, 5071 Wals, Salzburg, Austria,
[email protected] 2 FREIE UNIVERSITÄT BERLIN, Fachbereich Geowissenscha>en, Malteser Straße 74-100, Haus A, 12249 Berlin, Germany 3 GEORESEARCH Forschungsgesellscha> mbH, Hölzlstraße 5, 5071 Wals, Salzburg, Austria 4 Paris Lodron Universität Salzburg, Fachbereich Geographie und Geologie, Hellbrunnerstraße 34, 5020 Salzburg, Austria
Introduc%on The Torrener Joch Fault Zone belongs to a strike-slip system with regional relevance, separaCng the Hoher Göll massive in the north from the Hagengebirge plateau in the south. The hydrogeological processes of this fault zone are governed both, by karst and fault bound groundwater flow in the southern part of the fault zone. As the groundwater seems to percolate through Riedel structures in the Hagengebirge, a special emphasis was given to the tectonic seEng of this zone. The southern branches of the Torrener Joch Fault Zone are commonly intercalated by upper Triassic and Jurassic rock mass on the one and by lower Triassic evaporates on the other hand. Due to high fluctuaCons o> the karst groundwater level, water is in contact with the evaporates and dissolves them. This study provides a profound background for a new understanding of tectonic and landscape development in combinaCon with hydrogeological processes.
Objec%ves ♦ ♦
Understanding of the karst flow dynamics by detailed observaCons and monitoring campaigns. InvenCon of new methods and combinaCon of exisCng methods to merge different parts of the scienCfic community.
Study Area Hagengebirge and Torrener Joch Fault Zone The principal study area is located around 25 km south of Salzburg City at the northern border of the Hagengebirge plateau parallel to the Torrener Joch Fault Zone (Fig.1). Here, the Bluntau Valley and Torren Spring area are located (Fig.2) containing the complete discharge regime of Hagengebirge. What are the highlights of this area? The tectonic situaCon provides a unique structural seEng with faults, shear zones, flower structures and riedels, hindering or— respecCvely—permiEng the groundwater to percolate. EvaporiCc rock mass intercalated in the faults is subject to parCal soluCon by groundwater in wet season.
Fig.1: Torrener Joch in the middle; Hoher Göll on the right hand side; Torrener Joch Fault Zone highlighted in red.
Why is this test area of interest? At this area, groundwater fluctuaCon is around 300 m, 225 m of which are proved physically by data loggers. The Bärenhöhle Cave (Fig.3) provides a natural access to a part of this karst aquifer and underground structural geological outcrops.
Fig.2: Bluntau and Lammer valleys from Schneibstein, Hagengebirge; Torrener Joch Fault Zone highlighted in red.
Fig.3: Hubert Trimmel‘s longitudinal secCon and layout map of Bärenhöhle Cave and locaCon of the monitoring devices (Klappacher & Knapczyk, 1979).
Structural Geology
Methodology Method
Torren Spring Area and Bärenhöhle Cave The Torren Spring Area was selected for detailed studies. It is located at the end of the Bluntau Valley. The Bärenhöhle Cave is a natural spill-over of the springs, only acCve in 100 year’s events of runoff (or higher) and unCl yet only observed two Cmes by human beings.
Fig.4: KönigseeLammertalTraunsee strikeslip system a>er Decker et al. (1994)
Purpose
Structural geological mapping and modelling Aquifer geometry Hydrogeological mapping
Hydrogeological layout
Con%nuous groundwater monitoring
Aquifer parameters
Time wrap cameras
Spring behaviour
Long term monitoring of stable isotopes
Catchment determina%on
Mul% tracer tests
Flow paths
Hydrochemical modelling
Aquifer characteriza%on
Groundwater modelling
Hydrogeological processes
Fig.5: Strikeslip faults within the Torrener Joch Fault Zone
The Torrener Joch Fault Zone is part of the sinistral Königsee-Lammertal-Traunsee strike-slip fault system (KLT, Decker et al., 1994), that cuts the Torrener Joch in East-West direcCon (Fig.5). In recent field campaigns orientaCon data were collected to resolve the complex fault system including conjugated faults and to idenCfy tectonic structures. Stereographic data from different locaCons suggest that the strike orientaCon is E-W to ESEWNW and high numbers of Riedl- and P-shears have been found, deviaCng around 15 degrees from the principal strike-slip direcCon (Fig.6). The tectonic acCve seEng in the Torrener Joch Fault Zone is further proven by numerous tectonic indicators such as fault cores, fragmented damage zones and Harnisch surfaces (Fig.7).
Table 1: Used methods at the Torrener Joch Hydrogeology research study.
Fig.6: Stereographic projecCon of fault orientaCons within the Torrener Joch Fault Zone indicaCng Riedland P-shears
Fig.7: Images of Fault Cores and Harnisch surfaces in the Torrener Joch Fault Zone
Preliminary Results
Fig.8: 6 years of conCnuous groundwater monitoring at Bärenhöhle Endsyphon. Monitoring frequency is 5 min.(2012-2016) and 15 min. Shown parameters are pressure and temperature.
Fig.9: Images of one of the six stop moCon cameras installed in the Torren Spring area. The frequency is 15 minutes. Here, only the Cme at 14.15 p.m. is shown, depicCng one week shown in detail in Fig. 10.
Fig.11: Discharge (l/s, le> y-axis) and head (m above gauge, right y-axis) of springs and caves in Torren Spring area.
Fig.10: Detail of Fig.8, showing one week of monitoring in May 2016.
Fluctua%on and mineraliza%on
Tracer Test
Stable Isotopes
Grundwater fluctuates with more than 220 m (measured) and is supposed to fluctuate up to 300 m. The fluctuaCons correlate well with the discharge of the „Schwarzen Torren Spring“ (Fig.11).
In February 2018 a tracer test has been conducted. Uranin and NaphConat were induced into the upper and the lower cave creeks of the Bärenhöhle Cave.
The „Schwarze Torren Spring“ shows relaCve high annual fluctuaCons of the stable isotopes Oxygen 18 (Fig.15), Oxygen 17 and Deuterium. This can be explained by the snowmelCng period around April and May, when the lowest values are measured. In the lakes of the Bluntau Valley, the peaks arrive significantly delayed.
The mineralizaCon of the spring is low with high or low discharge, and with increasing discharge. Only with decreasing discharge, the mineralizaCon increases significantly up to almost ten Cmes with respect to the iniCal condiCons (Fig.12). The high mineralizaCon is cut by any new precipitaCon event.
The water samples indicate a direct hydrological connecCon between cave and “Schwarze Torren Spring“. Uranin, placed into the lower stream, reappears a>er 7.5 hours and develops two beauCful peak concentraCons- a minor peak a>er roughly 12 h and a major peak a>er 18.5 h (Fig.13). Around 36 % of the Uranin has been recovered at the spring, the rest is supposed to infiltrate directly into the porous aquifer of the Bluntau Valley.
Fig.13: Result of uranine tracer test.
Fig.14: Result of naphConat tracer test.
Fig.16: Meteoric water line MWL for the „Schwarze Torren Spring“ in relaCo to ISOLAB Salzburg / Wals trend.
Fig.12: As above, with electrical conducCvity (µS/cm).
Outlook By performing conCnuous monitoring, the hydrogeology of the Torrener Joch Fault Zone showed unexpected surprises. The “lessons learnt” message is: If you want to understand an aquifer, monitor conCnuously.
Fig.15: Oxygen 18 (‰ SMOW) for selected creeks and lakes and the „Schwarze Torren Spring“. Note the high amplitude of this spring with respect to the surface waters.
References ♦
Decker, K.; Peresson, H.; Faupl, P. (1994): Die miozäne Tektonik der östlichen Kalkalpen: Kinematik, Paläospannungen und Deformationsaufteilung während der „lateralen Extrusion“ der Zentralalpen. Jahrbuch der Geologischen Bundesanstalt, 137 (1), pp. 5-18.
♦
Klappacher, W.; Knapczyk, H. (1979): Salzburger Höhlenbuch Band 3. - Landesverein für Höhlenkunde in Salzburg.
