Gas extraction to the north the Frisian Islands The question In the Dagblad van het Noorden (Daily newspaper of the North) it said that subsidence caused due to gas extraction to the north of the Frisian Islands has no negative effects on the Wadden Sea. The sand replenishment is such that there are no consequences. I am a mudflat hiking guide and observe that channels in certain areas, north of Uithuizen, north of Broek, change drastically within a short time frame, in fact in such a short time that I feel that these changes would previously have needed many years, whereas now they take place within a relatively short time frame, 2 or 3 years. My question is this: Is the statement made in the newspaper correct: can we assume that gas extraction north of the Frisian Islands has no negative effects on the Wadden Sea, especially in the long term, when this area will subside further. A. Van der Kloet, Groningen The answer Gas extraction in and around the Wadden Sea consists of different parts: the Ameland gas field where gas has been produced since 1985 and the so called ‘Wadden Fields’ Moddergat, Nes and Lauwersoog. When you mention the locations Broek and Uithuizzen you must be referring to the gas extraction to the north of Schiermonnikoog. You won’t find any gas extraction taking place here yet, but there is a small field N7-FA, about 5 km to the north of Schier, with oroved gas supplies. There are plans to develop this in the future, but it concerns a very small field with an expected subsidence of a mere few centimeters. This won’t have any influence on the plates / channels in the Wadden Sea. The current gas extraction at Moddergat, Nes and Lauwersoog has resulted in subsidence, but this is compensated by 1) Sand supplementation and 2) A limited production (‘hand on the tap’) allowing the dynamic tides system in the Wadden Sea to keep the channels and the plates intact. Now, in fact what is involved isn’t so much the absolute subsidence in centimeters but the speed of subsidence (millimeters per year). Previously, the RIKZ (nowadays Deltares) had calculated that if in the Lauwersoog field (the easternmost gas extraction location) the subsidence 6mm/year is not exceeded, the system can still tolerate it. If you notice changes in the channels (I assume that you meant the location of the channels) near Uithuizen and Broek, then this takes place outside the influence of the current gas extraction and my conclusion is that this involves a natural process. This is dependent on the tides, sedimentation and coastal currents in the North Sea. Sincerely, Prof. M.A. Herber Geo-Energy University of Groningen Translated by Anniversary Project Group .