The Urban Geoheritage of Clermont-Ferrand: From Inventory to Management

Urbanization is a global phenomenon, seen in the constant increase of urban population – reaching 56% globally (UN DESA 2018) – and in urban sprawl that is the dynamic growth of areas covered by infrastructure, housing projects, industrial facilities and so on. This sprawl constantly diminishes natural or semi-natural areas, destroying their biotic and abiotic values, or placing them into a new, urban context. Densification of existing urban areas at the expense of remnant natural spaces adds to the loss of natural environment.

To address these problems, multiple and often interdisciplinary studies have examined the complex interactions of the urban environment with natural elements, for example, urban geology combining engineering and risk management (de Mulder 1993, Huggenberger et al. 2011), and urban geomorphology considering the relationship between landforms and the urban fabric (e.g., Cooke 1976, Thornbush 2015).

Research on urban geoheritage, which aims to understand the complex interactions between geodiversity elements and the urban environment and its potential for geotourism, is an emerging domain of geoheritage studies. Several studies have discussed the geotouristic potential of cities by designing special itineraries (e.g., Robinson 1982, del Lama et al. 2015, Pica et al. 2018) and others have addressed the assessment and conservation of geoheritage in urban areas (Pica et al. 2016, Zwoliński et al. 2017, Erikstad et al. 2018). A separate, but linked theme is the description of heritage stones, which reveal the importance of locally-extracted, natural building materials in the cityscape and in cultural heritage (Přikryl, Török 2010, Pereira et al. 2015, Brocx, Semeniuk 2019).

Reynard et al. (2017) synthesized the principal considerations of urban geomorphological heritage. An urban geomorphological site could be either any geomorphosite situated within the limits of the urban space (sensu lato definition) or solely a site that helps understand the interactions between geomorphology and urban development (sensu stricto).

Geoheritage in the urban context could: –

contribute to the landscape, the cityscape,

Urban geoconservation requires a different approach due to the high vulnerability of sites and the specific management challenges of an urban context compared to rural areas. Human impact and disturbance is severe, with frequent construction works, a tendency to reduce natural areas, and often significant throughflow of people. Indirect forms of protection for geoheritage through biodiversity or natural diversity reserves are less common in cities than in rural or natural areas. Direct protection of geoheritage values is also limited, as geoheritage inventories dedicated to cities are still scarce and are rarely integrated into urban planning (e.g., the example of London, GLA 2009).

Landforms are often covered up, therefore, the reliance on indirect information sources (e.g., historical maps, satellite images, drilling data) is more common than in geosite inventories and assessments of natural or semi-natural areas, and field evaluation is often limited or challenging. Potential sites are often already disturbed or partially destroyed, therefore, scientific values such as representativeness or integrity are often much lower than in rural places and the effectiveness of standard assessment methods could be limited.

Situated in central France, the city of Clermont-Ferrand is the historic capital of the Auvergne region, and the capital of the Puy-de-Dôme department (Fig. 1). The administrative area of the city, home to ca. 140,000 people, is concentrated on the central-western section of the Grand Limagne plain, while its agglomeration, the Clermont Auvergne Métropole, extends eastward to the Allier river valley (a tributary of the Loire). Westwards, the Métropole communities of Orcines and St. Genès Champanelle are located in the domain of the Chaîne des Puys – Limagne Fault World Heritage area. This designation does not directly affect the territory of the city itself (sensu stricto), but the chain of monogenetic volcanoes (locally called puys) rising from the elevated Plateau des Dômes provides an iconic background to the cityscape, uplifted by the Limagne Fault. The fault, part of the World Heritage site, has a direct boundary with the city and the geology whose outstanding nature justified the UNESCO site continues into the city.

Earliest traces of human occupation date back to the Neolithic, with a remnant of a dolmen at the national geosite of Puy de la Poix. The important Gallo-Roman settlement of Augustonemetum was situated on the Butte de Clermont, as was the medieval city of Clairmont, the latter being of international historic importance as the location of the Council of Clermont that called the First Crusade in 1095. The present day administrative unit of Clermont-Ferrand was created in 1630 with the unification of Clairmont and Montferrand, both of them preserving their historical centres, with important cultural monuments and the widespread use of local rocks for building, such as the Volvic Stone.

Massive urbanization occurred in the 19^th and 20^th centuries due to the growing economic importance of companies such as Michelin (the headquarters of this global company are still in Clermont-Ferrand), and the regional cultural and economic influence of the city. Large-scale neighbourhoods were constructed, covering up the eastern alluvial plains of the small Tiretaine and Artière rivers, and sprawling onto the flanks of plateaus capped by lava flows at the city’s limits (Fig. 2). These developments form the present day, highly urbanized area, which continues to expand.

The cityscape is formed by major elements of the geology of the Massif Central including the Limagne Plain, Limagne Fault and the adjacent features of the volcanic Chaîne des Puys. They are expressed in the relief and can be directly seen in outcrops.

The city centre Clermont has been located since Roman times at the edge of the Maar de Jaude (also called the Maar de Clermont-Chamalières), a late Pleistocene phreatomagmatic crater, completely filled by sediments and lava flows (Fig. 2). The main square (Place de Jaude) is situated on the boundary of the 1.5 km – diameter maar crater, dated at 160,000 years (Boivin et al. 2017). The maar’s ejecta, a tuff ring, forms the Butte de Clermont, where the medieval core of the city is located, including its emblematic black cathedral. The phreatomagmatic sequence of the tuff ring is well exposed in the so-called Caves de la Butte de Clermont. These are hundreds of cavities dug below the houses from Roman times, and used for a multitude of purposes, including cellars to store wine or cheese.

Northwards, the hill and park of Montjuzet conserves the remnants of Oligocene rift sedimentation, with reported stromatolites, and is covered by Quaternary tephra layers from the Chaîne des Puys volcanoes that may crop out in building sites and as rare outcrops on the hillsides. Neighbourhoods of the northeast perimeter of the city are built on Oligocene sediments that form the flanks of inverted relief lava flows. Montferrand, with its historical architectural centre, is also located on Oligocene sediments and a probable alluvial terrace. A cluster of high-standing Miocene lava flows (Plateau of the Côtes de Clermont, Puy de Chanturgue, Puy de la Mouchette and Puy de Var) border the Nohanent and Blanzat municipalities. They also form the highest relief of the city, reaching 600 meters on the Plateau of the Côtes de Clermont.

The eastern and southern parts, which represent 60% of the total city area, are dominated by alluvial and colluvial deposits that are part of the Limagne Plain and are associated with the Tiretaine and Artière rivers (Fig. 2). Residential areas and industrial districts have nearly completely covered this territory but the destruction of the fluvial geomorphological microforms probably occurred during the medieval agricultural activity, of which a few scattered fields remain.

However, the predominantly flat, alluvial plain is intersected with some important geological features. The Oligocene sedimentary quarry of Gandaillat and the only source of bitumen in France at Puy de la Poix, are located close to the eastern perimeter of the city near the airport. Further south, Puy de Crouël is an exhumed peperite volcanic neck from the Miocene, while the Maar de la Gantière – infilled by sediments and almost invisible in the present topography – is another representative of the late Pleistocene maar volcanism of the Limagne plain (Fig. 2).

The border with the Aubière and Beaumont municipalities and the areas south of the Butte de Clermont are dominated by the lava flows of the Puy de Grave Noire scoria cone that were emplaced ca. 60,000 years ago (Boivin et al. 2017). Constituting a small plateau of recently formed inverted relief, the lava flow front is exposed in numerous outcrops that display fundamental aspects of the internal structure of the flows and their complex interaction with the subsurface. The lava flows follow paleostreams that still feed springs, some of which can be observed along the flow front.

Finally, the district of Les Ormeaux, south of the city centre, is constructed on a slope of eroded Oligocene sediments topped by the volcanic neck of Montaudoux, itself just outside the city borders, in the municipality of Ceyrat (Fig. 2).

Field data was recorded with the open-source framework of ODk (Open Data kit) Collect and Aggregate application (Vereb et al. 2018A) and then converted to a Microsoft Access database. The inventory database closely followed the structure of the French National Inventory and its central database, the iGéotope (de Wever et al. 2015), the background and structure of which is described below.

The Inventaire National de Patrimoine Géologique (INPG), which we followed, is the comprehensive framework that controls and guides the assessment of geoheritage, as well as the collection, processing and publication of geoheritage data in France. The conceptual background and the description of the methodology was first published by de Wever et al. (2006), and updated later as Géopatrimoine en France (de Wever et al. 2014). A publication in English summarizes this work and addresses its global relevance (de Wever et al. 2015).

The INPG is a predominantly qualitative assessment form, with numerous fields for text description, but includes some quantitatively assessed criteria. Information is grouped into fields, namely Identification, Localization, Physical Description, Geological Description, Interests, Status, Vulnerability/Need for protection, Documentation and Sources. Textual fields appear as a list of options (e.g., Accessibility, Actual State), while in other cases, a detailed, free text description is permitted or required (e.g., contact information, itinerary for access, justifications for the scoring of Pedagogical Interest, Natural hazards, etc.).

Quantitatively assessed criteria are organized into two groups (Table 1). The first, Geoheritage Interest (intérêt patrimonial) consists of Primary and Secondary geological interest, Rarity, Preservation status, Educational interest, and Importance for the history of geology. Each of these criteria is scored on a scale of 0 to 3, and then the values are multiplied by a coefficient (weighting) and summed up, 48 points being the maximum total score. According to their total score, geosites receive an importance grade marked with a number of socalled geoheritage interest stars (from 1 to 3) that can be used to compare between similar sites in order to assess their regional, national or international importance. The total score of the second group, the Vulnerability and need for protection is calculated separately (Table 1). Natural vulnerability, Anthropic threats and Effective protection are measured here as individual criterion, also on a scale of 0–3. The number of geoheritage interest stars is also used as a fourth criterion. Values for each criterion are summed without a weighting, with 12 points being the maximum score.

By closely following the framework of the INPG, it means that the selected geosites at a local level can easily be incorporated into the national inventory in the future, if the representativity justifies it. A slight modification we made was the addition of some descriptive fields (e.g., identification of canton and cadastral number inside the city), which could be of administrative help in the city municipality where the database is to be integrated. The identification number of geosites has also been adapted to the local context using the following naming standard: CFxxyy, where xx is the official number of the city canton, while yy is the individual number of the site.

The majority of the city area is a widespread alluvial and colluvial plain as noted in the geological description (Fig. 3). Fluvial microforms commonly associated with changes in the location of river channels or areas of sediment deposition were not observed, probably because they have been eradicated or highly modified by urbanization. This area on the map only displays anthropogenic features such as buildings and road networks, and some residual (e.g., Montferrand) or exhumed (e.g., Puy de Crouël) landforms.

In contrast, a high diversity of geomorphological and geological features is observable in the western part of the city area (Fig. 3). The Quaternary lava flow of Grave Noire in the southwestern part of the city forms an inverted relief capped by relatively erosion-resistant trachybasalts and bordered by steep slopes that suggest the existence of outcrops. The northern part of the city, with the plateaus of the Côtes de Clermont, the Puy de Var, smaller sedimentary residual features, such as Montjuzet, and slopes articulated by several small ravines and ridges is also a favourable area for good exposures.

A total of 53 sites were recorded and assessed with the INPG methodology as of 2019 (Fig. 4, Table 2).

Fig. 4

The geosites in the inventory are organized geographically in two main clusters: the sedimentary features and inverted relief in the north (22 sites), and the lava flow of Puy de Grave Noire in the south (26 sites). The local geosites of the Grave Noire lava flow can be considered as distinctive representations of the national geosite AUV0088 as they represent individual outcrops of this collective feature (Fig. 4).

Individual, isolated sites include the Petrified Source of Saint-Alyre (CF-1401), the outcrop of the sedimentary infill of Maar de la Gantière (CF1221), and the national level geosites of Puy de Crouël (CF1101 in the Clermont-Ferrand inventory, AUV0093 in the national inventory), Puy de la Poix (CF1001 – AUV0094) and the quarry of Gandaillat (CF1102 – AUV0097). These latter sites have not been divided into smaller units according to their microforms, because they have limited spatial extent. Most of the other geosites are small outcrops compared to the city scale, therefore they have been recorded as point type features as well. Some sites that should also be considered as geomorphosites (Reynard et al. 2009) have been marked as points according to the database structure of INPG, although they cover larger areas that could be specified in additional maps and included as annexes to the inventory, like the plateau of Puy de Var (CF1003) or the park of Montjuzet (CF1404).

The results of the quantitative evaluation are summarized in Figures 5 and 6 according to the two main criteria of INPG: 1) the geoheritage interest, and 2) protection and vulnerability, respectively. Indicators are visualized by the scores of each individual criterion, permitting a detailed analysis of each indicator, as well as their total score.

Fig. 5

Fig. 6

Figure 5A shows that geoheritage interest values cover a wide range, and that every site has reached a minimum total score of 10 points or 1 geoheritage interest star (cf. de Wever et al. 2015). This confirms that all of the selected sites have a certain level of geoheritage value, therefore, their inclusion in a geoheritage inventory is justifiable.

Several studies on the inventorying and assessment of geosites (e.g., Reynard et al. 2016, Brilha 2016) recommend that only sites of exceptional or high value (especially from a scientific perspective) selected from an initial list of potential geosites should be considered as geosites and included in a final inventory. Sites in the present inventory with a low total score and low scientific value might be viewed as sites not fulfilling this geosite requirement (e.g., CF1105, CF1208). However, the urban context significantly raises the vulnerability of sites, and those sites that are not listed in an official inventory would be more likely to undergo destruction or irreversible modification. Even sites of limited scientific importance, such as minor outcrops or small landforms can have important additional values (e.g., recreation spots for locals or habitat for flora and fauna). Taken together, they have a greater cumulative importance, combining to create a geodiversity background worthy of protection.

In order to ensure the inclusion of every surviving geological outcrop, geomorphological landform and other important geoscience elements in the inventory, but also acknowledging the necessity to rank the sites especially for their scientific value, we combined the INPG method with the terminology of Brilha (2016). The latter distinguishes between geosites, which are sites with high scientific relevance, and geodiversity sites, which are sites with low to moderate scientific significance but high additional value (e.g., for supporting biodiversity). The Geoheritage Interest Rating scale of 0–3 (stars) has then been used to classify sites into geosites and geodiversity sites in the following way (Fig. 5A): –

0–1 star or 0–20 points: geodiversity sites, 28 sites out of a total of 53.

Since the Primary Geological Interest (PGI) has the highest weighting coefficient (4), all sites with the maximum value (3) have been effectively classified as geosites (Fig. 5B). All sites that scored the highest value (3) for Secondary Geological Interest (SGI) and Rarity also fell into the category of geosites, while sites with PGI, SGI or Rarity values of 1 fell into the category of sites to be validated by experts as geosites or geodiversity sites (those with PGI values >2 ended up as geosites). Therefore, the sites of highest scientific importance are all confirmed as geosites.

Preservation status strongly correlates with the heritage star ranking (Fig. 5B). The group of 3-star sites or confirmed geosites only includes one site with slight preservation problems (CF1511 – 185 rue Nohanent: stromatolites) and only 4 out of the 13 sites in the 2-star category received 1 or 0 point for preservation. In contrast, for the geodiversity sites or 1-star sites, only 3 out of 28 received good preservation status scores (2). Not only has preservation affected the geoheritage ranking of these sites, but also the scores of specific individual indicators. The lack of preservation induced limited educational interest (27 of 28 sites receiving 1 point or less) and even their Primary Geological Interest and Rarity was generally lower; only 10 sites out of 28 received a value of 2.

However, it must be noted that increased preservation efforts would probably not cause a rise in Primary Geological Interest or Rarity values. Apart from where cleaning up vegetated sections or excavation would bring to light new parts with a higher geoheritage interest, rarity and geological interest rates will remain unchanged even with increased preservation status.

The score for educational (or pedagogical) interest has been calculated by combining several considerations into one value in the quantitative evaluation, but it can be explained in detail in the textual fields of the INPG sheets (Fig. 5B). Each site could present a coherent story for geology and geography students in higher education, but geosites that are the best examples of a given phenomenon have been given higher scores than, for example, a standard outcrop of Grave Noire lava flow or Oligocene sediments. The criteria of accessibility and preservation status of the site are considered separately during the evaluation process, but they affect the educational interest values as well: sites located in private areas, or that are highly eroded and/or vegetated receive lower scores for educational interest.

In the Geoheritage Interest ranking of the city inventory, sites included in the national geosite inventory (INPG), namely Puy de la Poix (CF1001 in the local, AUV0094 in the national inventory), Puy de Crouël (CF1101 – AUV0093) and the quarry of Gandaillat (CF1102 – AUV0097), all gained high scores and have been categorized as 3-star geosites. This clearly demonstrates that the most important elements of the geodiversity of Clermont-Ferrand have already been recognised on a national level.

As noted before, the national geosite of Puy Grave Noire and its lava flows (AUV0088) has been divided into 24 local sites located in the southwest part of the city. Three of these sites were categorized into the highest, 3-star group: the outcrops of Saint-Astrimoine (CF1219), Rue Desdevies du Dèzert 20 (CF1210) and the geomorphosite of Creux de l’Enfer (CF1217). Together with some quality outcrops of lesser-ranked sites, such as the tramway stop of Margeride (CF1220) or Rue Henry Arnaud 21 (CF1207), they offer the best representations of the overall, holistic site; therefore, their references should be included in the national inventory as well.

The highest-ranking category of the inventory also includes other key sites and elements of the geodiversity of Clermont-Ferrand (and the broader context of the Limagne Plain and Limagne Fault) that are under-represented in the national inventory. Inverted relief of the Mio-Pliocene volcanism of the Auvergne is only represented so far in the INPG by the Plateau of Gérgovie (AUV0026). We suggest that the plateaus of Côtes de Clermont (CF1501) and Puy de Var (CF1003) are equally valuable representations of relief inversion, and their inclusion in a national level inventory should be considered. This is supported by their outstanding geoheritage interest in our local inventory. The Petrified Source of Saint-Alyre (CF1401) also represents an important element: the Quaternary travertine deposits of the Limagne, a feature that is currently not represented on the national list.

The need for protection and vulnerability values are moderate to high, underlining the fragility of geological outcrops and geomorphological landforms in an urban context (Fig. 6). However, geoheritage interest directly affects the need for protection and vulnerability total score, because the number of heritage stars is used as an input value (de Wever et al. 2015). Hence, the higher the geoheritage interest is, the higher the need for protection and vulnerability total score will be. This emphasizes the need for independently assessing the level of effective protection for 2 or 3-star geoheritage sites, although even sites with low geoheritage interest (1-star) have moderate need for protection and vulnerability scores, which indicates that action should be taken to guarantee their preservation.

Note that 42 of the 53 sites lack effective protection so far, either physically in the form of slope stabilization or regulatory in the form of a legislative framework. An example of such protection for biodiversity and archaeology is the protection of CF1505 (Plateau of Côtes de Clermont).

One of the principal reasons for compiling the present local-level geoheritage inventory in addition to the existing national one has been to give a powerful tool to the city municipality for the customized, site-specific management of urban geosites (Prosser et al. 2018).

With the above evaluation of geoheritage aspects, geosites should also be examined for:

biodiversity importance (e.g., habitat for flora and fauna elements),

As the majority of geosites on the current list are outcrops with steep slopes or cliffs, stabilization is highly important for safety, especially in the vicinity of infrastructure such as roads or buildings.

The lithological context of the sites controls much of the conservation scenario. For example, the outcrops of the Oligocene marls, limestones and clays have gentle slopes that are often covered with colluvium or scree (Fig. 7). Depending on the local slope conditions, they can be relatively stable, however, potential landslides might occur following heavy rain when the mixture of permeable and impermeable layers tends to be mobilised (e.g., at CF1104 and CF1105, CF1502 to CF1505). They are often stabilized by natural and planted vegetation. Such growth may be effective from an engineering viewpoint and desirable for preserving habitats, but it could greatly diminish the geoheritage values of the site by reducing the level of exposure. Therefore, each site should be considered individually to create a solution that allows a compromise to be found between the preservation of geoheritage and biodiversity.

Fig. 7

The trachybasaltic lava outcrops of the Grave Noire lava flow are the most resistant to erosion, and can sustain steep slopes, even vertical or overhanging walls. In that case, natural fractures of the rock further opened up by the action of ice and roots, or undercutting created by quarrying or roadcuts can lead to rockfalls. Unstabilized rock surfaces can be hazardous, but stabilization attempts that do not consider the geological values could significantly modify or even eliminate the geoheritage value of a site (Fig. 8).

Fig. 8

Geological outcrops and landforms as well as hydrological sites, besides their geoheritage interest, usually function as habitats for wildlife. The partial covering of sites by vegetation inevitably hides some geological elements, but it can also have a protective function (see above), and enhance the aesthetic value, while additionally aiding biodiversity. Natural cracks in lavas and loose material of some sedimentary rocks can house a significant insect population, while larger cavities such as natural caves in lavas or cellars in the tuff ring of Clermont-Ferrand are used by small mammals (e.g., bats) and birds. Biodiversity appears as an additional value in several inventories, but its detailed assessment in the present inventory should be carried out separately by appropriate experts.

This study has primarily focused on the surface elements of geodiversity, specifically outcrops, landforms and hydrological elements. However, the subsurface elements of Clermont-Ferrand’s geoheritage also have significant value. The main example of these are the so-called caves or cellars of the Butte de Clermont that are already acknowledged on a national level as site AUV0092 of the INPG. A detailed, exhaustive, publicly available record or even a restricted-access inventory for local authorities of the exact location of the cavities is not yet available. A municipal non-exhaustive inventory connected to cadastral and architectural documentation exists, and the Association of the Old Cellars of Clermont (ACAVIC) has an extensive list of cellars with references to geoheritage values, in addition to the documentation of their dimensions and cultural references (archaeological evidence, history of construction, type of use). However, the latter inventory is not publicly available, due to privacy concerns. The centuries-old structure of the cellars and natural caves could be a potential hazard for the surface buildings without effective stabilization. They were often used as garbage dumps during the 20^th century and especially after World War II (ACAVIC 2001), and quite a few remain unexplored. The inclusion of the privately-owned cellars and caves in an official inventory might press the authorities to carry out necessary stabilization work and take action to remove the garbage of the previous decades. Although these actions are desirable from a conservation viewpoint, the accompanying costs and the potential of regular future checks or taxation make many landowners prefer to conceal the existence of cavities under their properties (ACAVIC: personal comm.).

Taking into consideration the present situation and the significant geoheritage potential of the cavities, several measures should be taken in the short to mid-term: –

In order to visualize the distribution of the currently known cellars, while still respecting privacy, the data inventoried by ACAVIC and the municipality could be compiled in the form of a heatmap, following the example of Nisio et al. (2017) for Rome, Italy, where only the density of caves and cellars in certain areas is observable, and their exact coordinates are not shown.

The issue of private property is also an issue for surface elements of geoheritage. Only those sites that are located in public areas or private ones that are directly visible from the streets have been inventoried in this first phase. There are several outcrops in private gardens (e.g., CF1202, see below) or in buildings (e.g., CF1210) that might have scientific significance, or at least have additional value, such as forming habitats for flora and fauna. Their management, such as adequate slope stabilization, could only be carried out effectively if they are inventoried and assessed from geoheritage, biodiversity and engineering viewpoints as well. We note that while they may be in private property, often the rock itself is the responsibility of the municipality, who could then interact with the inhabitants to develop a community-based action plan of such sites.

The inclusion of these sites in an inventory would only be possible with the broadest cooperation of citizens and the municipality, and can be done with a campaign to record privately owned outcrops, sharing good management practices especially in terms of slope stabilization and the allocation of financial funds for the latter. A possible way of inventorying could be participatory mapping or crowdmapping (Brown et al. 2017), where the owners themselves report the existence of an outcrop or interesting geomorphological landform in their properties and ask for help about their effective management, respecting the heritage values.

An example of the importance of raising the issue of geoheritage values of an outcrop in a private area is the CF1202 (Impasse Dr. Cohendy) geosite, previously owned by one of the authors of the present study, then sold to a neighbour (Vereb et al. 2018B). The steep walls of this Grave Noire lava flow outcrop have had sporadic block falls during the past 20 years. After a small, but significant rock fall in 2017, reported by the owner to the municipality, the latter confirmed that the safety of the cliff was their responsibility. Their agents first proposed massive concrete coverage to stabilise the cliff (as seen in Fig. 8C). With the inclusion of this site in the inventory, we have been able to draw the attention of local authorities and neighbours to the geoheritage and associated biodiversity values of the outcrop, leading to the original plan being abandoned. The council proposed a less-damaging stabilization technique of bolting and wire mesh, partially preserving the integrity of the site. One property owner made a special request for his part of the outcrop to be kept as it was (after removing loose blocks), therefore bare, unadulterated rock is still observable in some places. The part of the outcrop that is well stabilized and protected by vegetation was left untouched (Fig. 9).

Fig. 9

This case study clearly demonstrates that the municipality agents still have little knowledge of the concept of geoheritage, and tend to apply off the shelf methods for site security instead of considering the value of the site and looking for measures that can be adapted to the natural site itself. However, once discussion is opened between private owners and the authorities, and with pressure from local inhabitants, compromises and acceptable solutions can be found. The integration of the inventory into the city plans will help in creating awareness of the benefits that result from applying more inventive strategies to secure unstable slopes. But the role of individual citizens is vital as well.

Participatory mapping is not the only way to promote the active participation of city dwellers in geoconservation. A number of outcrops in private gardens are already well integrated into the microlandscape as they are used as elements of decoration, and some outcrops are even preserved within building walls. Recognition of these in the inventory can reward the owners and help them further value this geoheritage.

Local communities could help in the daily management of some public geosites as well, maintaining vegetation and regularly supervising the cleanliness of the sites, especially if they are used as recreational sites. The park of Creux de l’Enfer (geosite CF1217) would be a good site to develop this type of initiative.

Privately-owned geological outcrops or cavities could be opened and showcased for visitors on dedicated days, following examples of cultural heritage such as the project Budapest 100, which is a yearly Hungarian civil urban initiative that gives people free access to 100-year-old buildings (Budapest 100 n.d.). The journées du patrimoine (heritage days) that take place one weekend a year in France is a similar event during which heritage sites with normally restricted access (mostly historical buildings) can be visited. The success of such initiatives promotes its growth every year, and in 2019, the ACAVIC association organized a visit for members of the general public to selected caves of the Butte de Clermont.

The aesthetic value of specific geosites can also be amplified and used to drive local businesses. A good example of this is the CF1210 geosite (Rue Desdevises du Dèzert 20) that is located in the backyard of a 3-storey building constructed along the walls of an ancient quarry in the Grave Noire lava (carrière de Mourlevat, Glangeaud 1901). The owners of the building, an architectural firm, adapted the former garage to provide a view of a spectacular ca. 10 m-high lava outcrop with a pond at its base fed by a natural spring, converting it into an attractive place that they use as an art gallery.

Cultural connotations of the presently inventoried geosites should be examined in more detail as well, by local history experts. Examples are the strategic importance of positive landforms such as Montferrand raised platform, the Plateau of Côtes de Clermont with the oppidum (ancient Roman settlement) of Augustonemetum, the Butte de Clermont with the medieval constructions and ancient uses of the caves, and the Creux de l’Enfer (Hell’s Hollow) park, where there are legends and stories relating to the spiky reddish lava outcrops.

A future phase of the inventory and the geodiversity action plan of the city municipality could also deal with what represents a close connection between cultural and geological heritage, namely the heritage stones (Brocx & Semeniuk 2019). The Base Mérimée, the national architectural inventory of France, currently contains 123 sites for Clermont-Ferrand (POP n.d.). An over-whelming number of them, 101 sites, use an iconic dark trachyandesitic, finely-vesiculated rock that was quarried from the neighbouring town of Volvic. It is planned to nominate this rock, locally known as Volvic stone, to the Global Heritage Stone Resource. Volvic stone is used either as a construction material or an ornamental stone. Several buildings, such as the famous black cathedral of Clermont-Ferrand or many houses in Montferrand, are entirely constructed from this light-weight, and hence, malleable rock. The Basilica of Notre Dame du Port, which is part of the World Heritage Sites of the Routes of Santiago de Compostela in France (UNESCO 1988), also features local building materials, such as the arkose of the Plateau des Dômes. In addition, modern 20^th century buildings, such as the Galeries de Jaude or the former hospital-sanatorium of Sabourin, use imported sedimentary stones that have not yet been described. Considering such potential, the historic areas of Clermont and Montferrand should be examined in detail from a heritage stone viewpoint and the most representative buildings could be included in geotours of the city.

The Chaîne des Puys-Limagne Fault Tectonic Arena encompasses two world-renowned examples of geosciences education, the Vulcania theme and adventure park on volcanism, and Lemptégy, a quarried-out volcano turned into a unique, open-air educational site. Both are situated only 15 km from Clermont-Ferrand. They are often frequented by local and national school groups, as are the exhibitions of the Henri Lecoq museum in the city that contain a variety of examples of ex-situ geoheritage in its geological department. However, the local geosites of the city, such as lava outcrops and nationally important sites like Puy de Crouël or Puy de la Poix, are generally overlooked by the public education system; geography students seldom visit them, and information about the geology of the city is not included in the curriculum.

As the city hosts a major university, which includes one of the largest European research institutes in volcanology and geoscience, some geosites such as the Saint-Astrimoine outcrop of the Grave Noire lava flow (CF1219) or the quarry of Gandaillat (CF1102) are regularly visited by university students. On the other hand, other sites were not well-known or described before the present inventory due to the existence of other representative examples, and the limited studies that exist on the specific geology of the city. The inventory will allow local outcrops to be more widely used for high-level education, with the city itself being viewed as a field site.

The general geological description of a geosite is a requirement for the INPG during the inventorying and assessment process. University courses could help add material to the sites and students could help with the monitoring as part of their training. A more detailed description of outcrops, paleontological examination of less known outcrops such as CF1002 at Rue de Cheval or smallscale research projects on the paleotopography of landforms, such as that of Montferrand, could easily be integrated into the inventory.

Twenty of the more than fifty geosites have received high or the highest scores in the evaluation of pedagogical interest (2–3 points). Not all of them are easily interpretable at the level of elementary or secondary education, but a collection of sites should be selected that could give an excellent tool for teachers to illustrate the basic phenomena of Earth processes at easily accessible examples: the sites are often only a short tram or bus ride away from schools. Such sites include the Quarry of Gandaillat (CF1102) for sedimentation and fossils, Puy de Crouël (CF1101) for Miocene volcanoes (offering a wide panorama for the Quaternary volcanism of the Chaîne des Puys as well), Plateau of Côtes du Clermont (CF-1501) for geomorphological inversion and outcrops of the Grave Noire lava flow (e.g., CF1207, CF1219, CF1220) to illustrate effusive volcanism.

Geosites can be used to improve the resilience of people to natural hazards and improve environmental awareness as well. The lava flow outcrops of the Grave Noire lava flow through the city, and together with its clearly visible source, the Puy de Grave Noire scoria cone, provide a good illustration of the eruption of a small, monogenetic volcano, a hazard scenario that is still possible for Clermont-Ferrand. Tens of schools are built on the lavas or near to their front, and this can be used to raise awareness about the local geology and related volcanic hazards. Renewal of activity in the Chaîne des Puys is possible, and future eruptions could affect the city (Latutrie et al. 2015). The current position of the Grave Noire lava as a topographic high, while it originally filled a valley, also indicates the scale of changes to a landscape (driven by erosion) that can take place in just 50,000 years. Inverted relief is a key element of the nearby UNESCO site’s story, and is also perfectly represented in Clermont-Ferrand.

The anthropogenic site of Puy Longue (CF1103) is the landfill site for Clermont-Ferrand, and could also be used for educational purposes. It has become an iconic, visible part of the city landscape, after only several decades of use, thus showing the large-scale environmental effects of human consumption and waste deposition. With dedicated tools of interpretation, such as guided tours for citizens to selected sites, information panels, thematic exhibitions, awareness about these issues could be raised.

Clermont-Ferrand is the tourist hub of the Auvergne, a region to which many visitors come for its beautiful landscape, which is strongly linked to its geoheritage values. The city is a gateway to the countryside, especially the Chaîne des Puys, a popular national destination since the 19^th century that has gained increasing international recognition, especially since the 2018 World Heritage nomination. It is part of the Regional Natural Park of Auvergne Volcanoes as well, together with Puy de Sancy, a popular ski resort, and Monts du Cantal, both built on large, highly eroded stratovolcanoes. The iconic landscape of Puy-en-Velay, with its exhumed volcanic necks, is also often visited from a base at Clermont-Ferrand.

Several considerations that have been discussed above about geoconservation and geoeducation also apply to geotourism. The caves of the Butte de Clermont have a huge geotouristic potential for their high historical and cultural values, which could be developed through the creation of a visitor centre and organised tours on a more regular basis. Heritage stones could easily be integrated into cultural tourism, especially at the Basilica of Notre Dame du Port and the Cathedral of Clermont-Ferrand, which are World Heritage sites along the Routes of Santiago de Compostela.

Urban geoheritage can be promoted through geotours offering a dedicated tourist (and educational) package. Inspired by examples in London (Robinson 1982), São Paulo (del Lama et al. 2015) and Rome (Pica et al. 2018), we propose four initial itineraries (Fig. 10) that provide an overview of the geodiversity of Clermont-Ferrand and could be included in the tourist strategy and promotion of the city. –

The Grand Geotour of Clermont-Ferrand gives a complete overview of the geodiversity of the city, with the best examples of different geological-geomorphological phenomena. It is subdivided into two sections. –

The Grand Geotour North section that starts at Montferrand and ends in Clermont historic centre gives an overview of sedimentary landforms (Montferrand and Montjuzet), inverted relief (Plateau of Côtes de Clermont), mass movements (Puy de Chanturgue landslide), Oligocene sedimentation in the Limagne basin (e.g., Rue Nohanent 184), travertines (Saint-Alyre) and heritage stones in central Montferrand and Clermont.

Fig. 10

Starting points are defined for all these geotours except for the circuit of Go with the Flow. However, the easy accessibility by public transport of almost any section of these routes (Fig. 10) means that they could be cut into multiple segments, or only selected sections could be visited by (geo)tourists. The southern section of the Grand Geotour is possible to do on foot or by bicycle while the northern section and the Inversion Ideas are more easily done on foot due to the steeper topography. The Go with the flow circuit is ideal for running, jogging or cycling, which could make this long loop more enjoyable.

So far, the only interpretation panels about geological importance are placed at Puy de la Poix and on the western edge of the Plateau of Côtes de Clermont. There are a few other sites with panels on biodiversity (Montjuzet, Creux de l’Enfer) and history (Plateau of Côtes de Clermont – oppidum of Augustonemetum). Permanent panels could be installed, especially at the sites with highest significance (3-star), but a viable alternative is the integration of these routes into a mobile application similar to the GeoGuide app that is available in Lausanne and Rome (Pica et al. 2018). These routes, or their edited forms, should also be published in the Balades Géologiques series of the Geological Society of France (de Wever et al. 2015).

Previous work on urban geoheritage (e.g., del Lama et al. 2015, Pica et al. 2016, Zwoliński et al. 2017) concentrated on large cities with populations of several hundred thousand to several million, whereas this work addresses a smaller, provincial city (ca. 140,000 inhabitants). Urban geoheritage inventories and geodiversity action plans can be implemented in smaller urban centres (towns) as well as for rural areas (villages). Besides complementing the city’s inventory, another objective in the future should be its geographical expansion, by incorporating the surrounding administrative units as well. Such inventories would be especially valuable in the case of Clermont Ferrand for the villages that are located within the neighbouring World Heritage site.

Clermont-Ferrand is the centre of the Clermont Auvergne Métropole that includes neighbouring villages and towns such as Royat, Aubière and Saint-Genès-Champanelle, which are undergoing rapid growth and urban sprawl. The Métropole has already asked if this inventory can be expanded to cover the whole of the area under their administration. Some of these communities lie partially within the protected areas of the UNESCO World Heritage site of the Chaîne des Puys – Limagne Fault or within those of national designations such as the Regional Park of the Volcanoes of Auvergne. While the elements of geoheritage that are located within these protected areas should be effectively conserved, geodiversity often overlaps into adjacent urbanized areas, where it is threatened with destruction. Conversely, urban growth can sprawl into the UNESCO site, through the villages that lie in the buffer zones, or even within the site, and these areas are in need of dedicated geoheritage inventories to deal with this. Geosites have already been destroyed or damaged in the UNESCO territory, though a lack of such an inventory (Petronis et al. 2019, van Wyk de Vries et al. 2019).

A good example of shared geoheritage around the borders of Clermont is the scoria cone of Puy de Grave Noire and its lava. The cone itself and the proximal part of the lavas are located at the very edge of the core zone of the World Heritage site, but most of its lavas are located within the city limits. Therefore, some of the most representative outcrops are located in the dense urban areas and they are highly vulnerable. Actual preservation of these geosites should be based primarily on the geoheritage management strategy of the corresponding municipality, but there should also be an effort to synchronize geoconservation efforts with all adjacent municipalities and with the authorities in charge of protecting the designated natural areas as well, such as representatives of the World Heritage site.