Since last Friday, the Netherlands has a new geological map for the first time in 43 years. What is on such a card, what should you do with it, and why would you renew it? NEMO Kennislink attended the unveiling at the anniversary of the Geological Survey.
Do you want to gain energy, find drinking water, build a house, or build a road? Then first familiarize yourself with the composition of the substrate. Where are the strata that harbor oil, gas or (warm) water? Where is the peat where roads and houses sink, and where is the much firmer sandy soil? Which underground water flows pass polluted locations and pick up the pollutants?
Without that information, many projects are much more expensive than necessary, or even doomed to failure. That was the message that was delivered on Friday at the symposium of the Geological Survey of the Netherlands of TNO in Utrecht, which was celebrating its centenary.
Models
The Geological Survey of the Netherlands collects data from the subsurface and makes maps and models of it. Nowadays, these are three-dimensional computer models that become more and more detailed towards the top, and consist of voxels (pixels in 3D, so a kind of digital Lego blocks).
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The most accurate is the top of the model. It shows the earth's surface on which we walk, but without the blanket of agricultural land, meadows, forest floors, asphalt, construction sand and tiles. The Geological Survey presented a brand new geological map of this top last Friday. The old one dated from 1975.
Why?
Nobody will argue that a road map needs regular updates. Many a person has driven desperately in circles through a newly constructed neighborhood, sternly ignoring the voice of the navigation device ("try to turn around"). But why refresh a geological map every few decades? Wasn't geology a process of thousands to millions of years?
Not always, says Michiel van der Meulen of the Geological Survey of TNO when he is allowed to give the Staring Lecture of the KNGMG that afternoon. Peat can perish, the coastline can move. “And after the Noordoostpolder was built, stickers were made to expand your map yourself.” But the most noticeable change you see on the successive cards is the increase in knowledge about the subsurface.
Color
In 1822, the Netherlands had only one color on the geological map. The entire subsurface was simply referred to as Terrain Mastozootiques – which means ‘ground with mammalian bones’.
In 1844, the first map of the Netherlands that actually showed anything, was made by soil scientist Winant Staring. He divided the subsoil into eight types, with names like dune deposits, layers from the third epoch, and seawater base layers. This eventually resulted in the first official map in 1852, which was more detailed and distinguished between the Diluvium (deposits of the sea, or literally:the Flood), and the Alluvium (washed up ground).
A quick glance at the map of 2018 is enough to see that a lot of work has been done since then. Not only our country, but also the North Sea has a cheerful mix of many shades of gray, red, green, blue, yellow and purple, containing all kinds of sand (yellow), river deposits (blue), tidal deposits (green), peat ( brown) and ice age phenomena (pink), with very detailed boundaries. For those with an eye, the map gives a glimpse into history – showing the former tidal areas, river courses and coastlines.
The making
Where Staring did his work traveling through the country on foot and on horseback – although he also had a network of correspondents – earth scientists today increasingly use technical methods to make their models, such as satellite data, gravity measurements and seismic (a kind of echo of the substrate).
The most important turning point for the map and model makers was probably the discovery of the Groningen gas field in 1959. In order to be able to extract the gas, a detailed knowledge of the subsurface was required, and for this purpose boreholes were drilled. There was also oil and gas in the ground elsewhere, making the Netherlands one of the most pierced pieces of land on earth. Half a million times a drill or probe went into the ground. The data are in the archive of the Geological Survey, partly in the form of (more than 6,500) drill cores.
Volcano eruptions
The increasing understanding of how the country came to be has also influenced the map. Where a layman may only see sand and gravel, the earth scientist sees river deposits, tidal areas, or dune formation from the past. There will also be another map, assures Tirza van Daalen, director of the Geological Survey, because the agency will continue to gather knowledge.
The map provides insight into the possibilities for using the subsurface as a storage location, source of raw materials or foundations, and into risks such as flooding and subsidence. But also earthquakes and volcanic eruptions, Van der Meulen emphasizes – because the Netherlands does not only consist of our little country on the North Sea. The Caribbean also has Dutch municipalities, and these too are now, for the first time in history, on the Geological Map of the Netherlands.