Urban geology: A failed example of gabions as false urban geology from the Netherlands

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Stephen K Donovan (The Netherlands)

The provinces of Noord and Zuid Holland, including much of the Dutch North Sea coast and adjacent inland areas, are devoid of rocky exposures. In a region of flat-lying Pleistocene siliciclastic successions (Burck et al, 1956), there are no quarries, cliffs or other man-made or natural exposures of lithified rocks. The topography is slight, with the highest natural structures being the coastal sand dunes, in part preserved as a national park (Jelgersma et al, 1970).

To offset this lack of geological ‘furniture’, the Dutch have enterprisingly imported and installed sundry rocks that fill what may be an unattractive void in the environment. These rocks vary from the minimalist, such as roadside boulders (in part, possibly erratics) (Donovan, 2015), to reconstructions of structures such as a replica of a natural bridge in Mississippian limestone slabs (Donovan, 2014). But, in some instances, reconstructions are unsuccessful or, at least, inaccurate, such as the false (Pennsylvanian) Coal Measure strata without identifiable coal beds in the national railway museum (Het Spoorweg Museum) in Utrecht (Donovan, 2018a). In this article, I describe further mock geological structures that fail in the details.

Gabions are tools of the engineering geologist. Yet, when packed with cobbles of imported, grey Mississippian limestone, they may make convincing false sedimentary ‘beds’, at least from a distance, and are a not uncommon feature of the environment of Noord and Zuid Holland (Donovan, 2018b). (Vertical, dyke-like structures are rarer and are less successful as false geology; Donovan, research in progress.) The example of gabions imitating geology described below fails, because it is a ‘mirror-image’ of the field relationships seen in many real situations elsewhere.

Locality

The locality (Fig. 1) is close to Bijlmer Arena station in southeast Amsterdam, Noord Holland. This station is served by mainline rail services (Nationaal Spoorweg or NS) on the Amsterdam Centraal to Utrecht Centraal line. It also has regular NS services from Amsterdam Schiphol Airport station and is on various Metro lines and bus routes.

Fig. 1. The southwest side of the railway embankment, south-southeast of Bijlmer Arena NS/Metro station, southeast Amsterdam, in December 2017.
(A) General view showing extent of distribution of gabions; Bijlmer Arena station in distance, on top of the embankment. The gabion baskets are limited to about five levels and over only a limited length of the railway embankment.
(B) Close-up of gabions at north-northwest end (left) of (A). The lower baskets might be popular as benches for weary walkers, but not those higher up the slope, which would be more overgrown in spring and summer.
(C) The view of the gabions from high on the embankment; the picnic table (upper, centre) is apparent in (A) far left.

Leave the station by the main bus station exit and walk south-southeast on the southwest side of the NS/Metro, towards the next station, Bullewijk. The locality is just a few hundred metres away, on the other side of the main road and across the canal from the Courtyard by Marriott Amsterdam Arena Atlas Hotel.

Description

The gabions are situated on the side of the railway embankment (Fig. 1). They are elongate metal baskets filled with cobbles of Mississippian limestone and topped by wooden planks/seating(?). Baskets are arranged end-to-end, with gaps between them, but at recurrent elevations, thus imitating gaps due to natural processes, such as erosion, between exposures of the same beds. Therefore, the gabions are not laterally continuous, but are spaced like a natural rock exposure.

Discussion

These gabions satisfy no obvious engineering purpose. But am I over-interpreting them; are they merely benches (utilitarian), not false geological phenomena (environmental)? I am strongly inclined to say no, for three principal reasons.

  1. There is a more traditional picnic table and seats adjacent to the gabions (Fig. 1A and C), which seems incongruent if the latter structures were mainly intended as seating.
  2. If the gabions were intended as seating, then spacing them up the side of the embankment was a poor option, as accessibility decreases up the slope. In spring and summer, this area is more overgrown than in Fig. 1 (the photographs are taken in mid-December); and the slope is muddy and slippery in the wetter months. Furthermore, the lateral distribution of the gabions is limited: there are no other gabions between Bijlmer Arena and Bullewijk stations. They are unlikely to represent an amphitheatre-like arrangement, as there are no facilities for performance, apart from a narrow strip of grass (Fig. 1C).
  3. This is not a residential area. The gabions are situated close to a major railway station, on an embankment and facing a canal, cycle- and footpaths, and offices and hotels. If they are primarily benches, who might they serve? It is no more than a local thoroughfare, within a few hundred metres of cafes and shops.

Thus, these gabions appear to be mainly for ‘show’ rather than utility. Assuming this pseudo-geological interpretation is correct, then why is this is a poor representation of a real situation? Quite simply, it is inverted from a real exposure. Where they are present, bedded rocks are likely to be exposed in a railway or road cutting. However, any embankment is going to be made ground. The only way that real, horizontally-bedded rocks could be exposed in such a situation would be if the entire surrounding land surface was removed by quarrying. This is certainly possible, such as the Thornton Quarry in Illinois (https://en.wikipedia.org/wiki/Thornton_Quarry), but it is likely to be rare.

The significance of this contribution is that such a simple structure has been reconstructed, erroneously and without adequate, most probably any consultation with knowledgeable geologists. This may be because geologists are perceived to be too expensive or rare or uncooperative or just plain unnecessary. I am sure that this perception is inaccurate; I would happily have commented on this idea at the proposal stage for free. Donovan (2018a) charged geologists to get involved with such restorations and ensure their scientific accuracy. This is a plea that I repeat here.

Other articles in this series include:
Urban geology: Productid brachiopods in Amsterdam and Utrecht
Urban geology: The Boxtel wall game
Urban geology: A failed example of gabions as false urban geology from the Netherlands
Urban geology: The strange tale of a windowsill
Urban geology: Gabions in the Dutch townscape
Urban geology: A rostroconch in Hoofddorp
Urban geology: The Worsley Park wall game, Manchester
Urban geology: New Red Sandstone at Amsterdam Airport
Urban geology: Monumental geology
Urban geology: A sunny Sunday in Hoofddorp
Urban geology: Two granites
Urban geology: Boulders and the Dutch
Urban geology: Palaeontology at the Wagamama restaurant, Amsterdam
Urban geology: An inselberg in Rotterdam
Urban geology: brush up your neoichnology
Urban geology: The battery on the Sloterweg

References

Burck, H.D.M., Van Eerde, L.A.Æ., Harsveldt, H.M., Van der Heide, S., De Jong, J.D., Pannekoek, A.J., Van Voorthuysen, J.H., Ter Wee, M.W., Zagwijn, W.H., Zonneveld, J.I.S. 1956. Geological History of the Netherlands: Explanation to the General Geological Map of the Netherlands on the scale of 1 : 200,000. Staatsdrukkerij- en Uitgeverijbedrijf, ‘s-Gravenhage.

Donovan, S.K. 2014. An unnatural bridge in an artificial limestone environment, the Netherlands. Cave & Karst Science, 41: 118-119.

Donovan, S.K. 2015. Urban geology: Boulders and the Dutch. Deposits, 42: 8-9.

Donovan, S.K. 2018a. Urban geology: Modelling Coal Measures strata in the 19th and 21stGeology Today, 34: 26-30.

Donovan, S.K. 2018b. Urban geology: Gabions in the Dutch townscape. Deposits, 53: 14-16.

Jelgersma, S., De Jong, J., Zagwijn, W.H., Van Regteren Altena, J.F. 1970. The coastal dunes of the western Netherlands: geology, vegetational history and archaeology. Mededelingen Rijks Geologische Dienst (nieuwe series), 21: 93-167.

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