04-06/07/2019 Field trip report Vajont valley & Latemar ()

Participants: Baville Paul Bonneau François Caumon Guillaume Clausolles Nicolas Frantz Yves Gouache Corentin Raguenel Margaux Schuh-Senlis Melchior

IAMG Student Chapter Nancy RING TEAM - GEORESSOURCES

Summary Introduction ...... 1 Chronostratigraphy of the field trip ...... 2 1. Vajont Formations (1 Figure 2, 65 – 160 Ma) ...... 2 2. Calcare del Vajont Formation (2 Figure 2, 160 – 170 Ma)...... 3 3. Ignee Formation (3 Figure 2, 170 – 183 Ma) ...... 4 4. Soverzene Formation (4 Figure 2, 183 – 200 Ma) ...... 4 5. Dolomia Principale Formation (5 Figure 2, 200 – 230 Ma) ...... 4 6. Rodella Formation (6 Figure 2, 230 – 247 Ma) ...... 5 7. Latemar Formation (7 Figure 2, 247 – 250 Ma) ...... 6 8. Bellerophon Formation (8 Figure 2, 250 – 258 Ma) ...... 8 9. Gardena sandstone Formation (9 Figure 2, 258 – 265 Ma) ...... 8 10. Variscan plutonic rocks (10 Figure 2, > 265 Ma) ...... 8 Contextualisation of the Vajont disaster ...... 9 1. Dam network in the Piave valley ...... 9 2. The Vajont dam disaster ...... 10 Conclusion ...... 11 Bibliography ...... 12 Annex: Expanses ...... 12 Figures Figure 1: Localization of the field trip...... 1 Figure 2: Chronostratigraphic scale of the formations we saw during the field trip...... 2 Figure 3: Top: 3D model of the 1963 Vajont landslide (Bistacchi et al., 2013). Middle and bottom: Picture of the Vajont lanslide and its interpretation...... 3 Figure 4: Left: Picture of the Calcare del Vajont Formation partially dolomitized. Middle: Interpretation of faults and one of the dolomitzed bodies (in green). Right: 3D modelisation (GOCAD) of faults and dolomitized bodies in the Vajont valley (Bistacchi et al., 2015)...... 4 Figure 5: Picture of the Stella platform from the Rodella pass. The limit between the Rodella Formation and the Dolomia Principale Formation is known as the Carbonate Platform Erosion (CPE). Notice the two Géolien specimens at the forefront! ...... 5 Figure 6: Transition between volcanic and limestone deposits within the Rodella Formation (Rodella pass)...... 6 Figure 7: Top: Panorama from the Latemar. All the area is a network of preserved platforms. Bottom: Interpretation of the panorama. Blue parts are the flat preserved platforms. Violet parts are platform talus. Yellow part is basin...... 7 Figure 8: Localized dolomitization of Latemar limestones...... 7 Figure 9: Limit between the undeformed Latemar Formation (mainly limestone) and the strongly deformed Bellerophon Formation (mainly gypsum). Valles pass...... 8 Figure 10: Scheme of the dam network summing up the location and the capacity of each Piave valley dam...... 9 Figure 11: Measurments of the Vajont dam...... 10 Figure 12: Group picture at with our Italian colleagues at Rodella pass...... 11

Introduction

This field trip in Vajont valley and Latemar (Italy, Figure 1) took place between the 4th and the 6th of July, 2019. Eight members of the RING Team (1 professor, 1 research engineer and 6 PhD student members of the IAMG student chapter) discovered the geology of this area. The main objectives of this trip were to observe geological outcrops (the team’s main focus is on their numerical representation), to create an emulation environment with our Italian colleagues for scientific discussions, and to discover our co-workers in a different context. We especially focused on the complex dolomitization of limestones in the Vajont valley and on the calcareous platforms uplifted and undeformed of Latemar.

Figure 1: Localization of the field trip.

Several geologists from the Universities of Milan and Padova (Figure 1) were involved in the organization of this field trip and were our guides during the visits: - Andrea Bistacchi, Milan, - Silvia Mittempergher, Milan, - Luigi Berio, Parma, - Mattia Martinelli, Milan, - Marco Franceschi, Padova. We would like to thank them for their involvement and availability.

During this 3 full days field trip we saw various rocks with a large range of ages: from the Permian base to the Cretaceous top (Figure 2). This covers a time period about 250 Ma. We propose to present this field trip report formation by formation, starting with the youngest one we saw. Furthermore, a special part dedicated to the Vajont dam disaster is presented at the end of this report.

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Figure 2: Chronostratigraphic scale of the formations we saw during the field trip.

Chronostratigraphy of the field trip 1. Vajont Formations (1 Figure 2, 65 – 160 Ma) The youngest units we observed in the region are the one which were affected by the Vajont landslide (Figure 3). The top of the sequence is the Calcare di Soccher Formation (1a Figure 2, 150 m), mainly made of massive limestones, grading to marly limestones. This formation is deposited over the thin Rosso Ammonitico Formation (1b Figure 2, 5-15 m), a fossiliferous nodular limestone unit. Under this last formation the Fonzaso Formation (1c Figure 2, 10-70 m) is observed. This is a thinly stratified cherty limestone unit containing centimetric smectite beds of volcanic origin that served as sliding surface for the Vajont landslide. For more information on the Vajont lanslide, please see the last part of the report.

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Figure 3: Top: 3D model of the 1963 Vajont landslide (Bistacchi et al., 2013). Middle and bottom: Picture of the Vajont lanslide and its interpretation.

2. Calcare del Vajont Formation (2 Figure 2, 160 – 170 Ma) This formation is composed of 370-450 m thick reworked carbonate slope deposits made of whitish oolitic limestones. They have been locally dolomitized later (Figure 4), due to fluid circulations (70°C) through the pre-Alpine extensional fault network. The dolomitization makes origin limestones change colour from grey to brown. Moreover, it makes origin limestones loss its stratification, originally well visible. This dolomitization of carbonate rocks is observable all along the region (see another example within the Latemar Figure 8), giving its name: the Dolomites.

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Figure 4: Left: Picture of the Calcare del Vajont Formation partially dolomitized. Middle: Interpretation of faults and one of the dolomitzed bodies (in green). Right: 3D modelisation (GOCAD) of faults and dolomitized bodies in the Vajont valley (Bistacchi et al., 2015).

3. Ignee Formation (3 Figure 2, 170 – 183 Ma) This formation is an impermeable layer with various thickness in space (0-150 m). Localized under the large Calcare del Vajont Formation, the Ignee Formation is only visible locally in the Vajont valley. The impermeable behaviour doesn’t allow fluid circulations from bottom formations to the Calcare del Vajont Formation. However, the fact that the region has been fractured due to the pre-Alpine extension allows fluid circulations and, inter alia, dolomitization of the Calcare del Vajont Formation.

4. Soverzene Formation (4 Figure 2, 183 – 200 Ma) The Soverzene Formation is a 600 m thick layer mixed of diagenetic dolomites and hydrothermal ones. These last have also been dolomitized due to hydrothermal fluid circulations (70°C). We didn’t see this formation on the field.

5. Dolomia Principale Formation (5 Figure 2, 200 – 230 Ma) We observed this large formation (1 km) at Rodella pass. The diagenetic dolomites that constitute this Dolomia Principale Formation are the origin of the dolomitization of the Soverzene and Caclare del Vajont Formations observed in the Vajont valley. Some progradation figures are visible in this formation. These figures underlight the fact that during the deposit stage the sedimentation rate was greater than the subsidence.

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6. Rodella Formation (6 Figure 2, 230 – 247 Ma) This large formation, mainly observed at Rodella pass, regroups various smaller sub formations distinguished by different lithologies. - The top of the Rodella Formation is called the Pordoi Sub Formation. It is a mix of carbonate/soliciclastic deposits with volcanic-origin sandstones, peritidal dolomites and marlstones above. It has been deposited after the standstill of the platform growth (230 – 235 Ma). This formation has often been eroded and is so called the Carbonate Platform Erosion (CPE). This limit is visible Figure 5. - The middle of the Rodella Formation is the Cassian Dolomite Sub Formation (235 – 240 Ma). This sub formation corresponds to an M-type carbonate platform having an atoll- like geometry. M-type means carbonate precipitation through microbial or abiotic processes (bio-induced, Schlager, 2003). - At the bottom of the Rodella Formation, volcanic deposits progressively replace the limestones and dolostones (Figure 6). These volcanic deposits are assumed to be the Mg source for the dolomitization of the upper formations (from Calcare del Vajont Formation to Dolomia Principale Formation).

Figure 5: Picture of the Stella platform from the Rodella pass. The limit between the Rodella Formation and the Dolomia Principale Formation is known as the Carbonate Platform Erosion (CPE). Notice the two Géolien specimens at the forefront!

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The Rodella and Dolomia Principale formations form the Stella platform, also observable at Rodella pass (Figure 5). On this Stella platform the Dolomia Principale and Rodella Formations are separated by the CPE limit (Pordoi Sub Formation). This limit doesn’t only represent the separation between two formations but also corresponds to a differentiation in the deposit condition. In fact, before CPE (Rodella Formation), the carbonate deposit is bio- controlled whereas after it (Dolomia Principale Formation), the carbonate deposit is bio- induced. Organisms that precipitate carbonate are the difference between these two processes: microbial and abiotic for bio-induced, auto/heterotrophic for bio-controlled (Schlager, 2003). This observation means a change in the ocean mechanism around 230 Ma.

Figure 6: Transition between volcanic and limestone deposits within the Rodella Formation (Rodella pass).

7. Latemar Formation (7 Figure 2, 247 – 250 Ma) The Latemar Formation is a large limestone platform localized North-East from Trento. The fact that the entire platform has been uplifted up to 2,800 m without been deformed makes its exceptional. In fact, the flat summit of the platform as well as the talus have been preserved. As visible Figure 7, all the summits of this region are preserved platforms made of limestone (in blue Figure 7) surrounded by slopes that represent platform talus (in violet Figure 7) while the valleys are former underwater basins (in yellow Figure 7). This way, Latemar platform isn’t the only preserved structure: a whole platform network is preserved!

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Figure 7: Top: Panorama from the Latemar. All the area is a network of preserved platforms. Bottom: Interpretation of the panorama. Blue parts are the flat preserved platforms. Violet parts are platform talus. Yellow part is basin.

Moreover, volcanic events at the origin of volcanic deposits in the above formation (Rodella Formation) caused some dykes within the Latemar platform. These dykes bring Mg that provokes localized dolomitization around it (Figure 8), as observed in the Vajont valley.

Figure 8: Localized dolomitization of Latemar limestones.

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8. Bellerophon Formation (8 Figure 2, 250 – 258 Ma) After marine transgression, the Bellerophon Formation has been deposited on shallow marine environment. This formation is a mix of gypsum and carbonate. Due to the gypsum rheology this formation accommodates a large part of the deformation and lets the above Latemar Formation undeformed (Figure 9). We observed this formation only in the Valles pass where the gypsum is strongly deformed (inset Figure 9).

Figure 9: Limit between the undeformed Latemar Formation (mainly limestone) and the strongly deformed Bellerophon Formation (mainly gypsum). Valles pass.

9. Gardena sandstone Formation (9 Figure 2, 258 – 265 Ma) Deposit environments are more and more proximal to reach continental deposits with the Gardena Formation, observed in the Valles pass. These red sandstones from alluvial deposits are the “cousin” of our red sandstones in the Vosges.

10. Variscan plutonic rocks (10 Figure 2, > 265 Ma) We only saw one kind of these rocks: a pink granite at Mezzolombardo.

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Contextualisation of the Vajont dam disaster 1. Dam network in the Piave valley represents the major source of electricity in the alpine regions of Italy. The Piave River is associated to a very large watershed. In order to benefit from this huge amount of hydro energy, Italian early installed , especially the Pieve one with a capacity larger than 45 Mm3 (Figure 10). This dam network aims at redirecting this water energy toward the Soverzene power plant. However, Italian early saw that these installations weren’t sufficient to resist the continuous water input from the enormous watershed. Thus, they decided to create another huge dam localised in the Vajont valley (Figure 10 & Figure 11) in order to avoid Pieve one to collapse. The Vajont dam was constructed by the SADE Society (Società Adriatica Di Elettricità). It was planned to gather up to 150 Mm3 of water from the Piave River. Its construction lasted from 1956 to 1959 and the dam was put in operation in 1960. It is for almost 200 m long and was, at the time of its inauguration, the highest operational dam in the world at a height of 722.5 m (Figure 11).

Figure 10: Scheme of the dam network summing up the location and the capacity of each Piave valley dam.

The water flow that came from the six dams of the network and passed through each of the four turbines localized in the Soverzene power plant was 22 m3/s. This water flow was able to produce in total 180 MW making Soverzene the most powerful Italian power plant. We would like to thank Gian Luigi, from (Figure 10 & Figure 11), for the visit and the historical presentation of the Vajont dam.

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Figure 11: Measurments of the Vajont dam.

2. The Vajont dam disaster No proper detailed geological studies were done by the SADE before the dam construction. The first studies of the side of the Monte Toc were only done after a landslide observed in another dam site. During the first filling of the artificial lake in February 1960, a huge crevice opened, caused by the reactivation of the initial subterranean landslide. On November the 4th of the same year, after reaching and height of 650 m of water, a first landslide of 700,000 estimated m3 happened near to the dam. The first studies concluded that the risks were minimal, likely because of financial and political reasons, but the actual problems were at least known since February the 3rd 1961, as a report estimated a potential landslide of 200 Mm3. It was also stated that no practical means could be used to stop it. The water level was then lowered to 600 m and another filling-draining was done between October 1961 and November 1962 and the landslide was still observed. In April 1963, the third filling of the dam started and the speed of the landslide increased even more, with observable surface deformations associated to small earthquakes. In the days before the catastrophe, measurements proved the imminent danger but it was still minimised. After a new draining decision, an evacuation of the population was decided on October the 8th 1963.

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The side of the mountain finally collapsed on October the 9th 1963 at 10:39 pm, with an estimated volume of 260 Mm3. The very high speed of the landslide wasn’t predicted because the thin centimetric smectite beds of volcanic origin that served as sliding surface mentioned above weren’t observed. It led to the formation of three waves. Two of them caused great destruction on the sides of the lake and upstream in the valley while the last one flowed over the dam, almost without damaging it. This last wave, along with the associated shockwave, devastated the downstream villages. This incident led to the death of more than 2000 people.

Conclusion Thanks to the IAMG funding, we had the opportunity to make a field trip far from our computer laboratory. We discovered the morphology and the geological history of the North- East Italian Alps. We also discovered the Vajont valley through the dolomitization of its limestones and the catastrophic dam disaster. During these days, we enjoy the quality of the scientific discussions we had with our Italian colleagues as well as the local gastronomy. This field trip was also a wonderful opportunity to strengthen our team spirit.

Figure 12: Group picture with our Italian colleagues at Rodella pass.

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Bibliography Bistacchi, A., Massironi, M., Superchi, L., Zorzi, L., Francese, R., Giorgi, M., Chistolini, F., and Genevois, R. (2013). A 3D GEOLOGICAL MODEL OF THE 1963 VAJONT LANDSLIDE. Italian Journal of Engineering Geology and Environment 531–539.

Bistacchi, A., Balsamo, F., Storti, F., Mozafari, M., Swennen, R., Solum, J., Tueckmantel, C., and Taberner, C. (2015). Photogrammetric digital outcrop reconstruction, visualization with textured surfaces, and three-dimensional structural analysis and modeling: Innovative methodologies applied to fault-related dolomitization (Vajont Limestone, Southern Alps, Italy). 11, 18.

Schlager, W. (2003). Benthic carbonate factories of the Phanerozoic. International Journal of Earth Sciences 92, 445–464.

Annex: Expanses Student Chapter account before the field trip 2721.84€ Accommodation (including some meals) -1,144.60€ Food -322€ Oil -305.89€ Visits -284€ Gifts to Italian colleagues -34.99€ Marco Franceschi defrayal -200€ IAMG Student Chapter funding 2,049.50€ Field trip balance (paid by the 8 participants) -241.99€ Remaining money on the Student Chapter account 672.34€

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