History of Geophysical Research in The Netherlands ... - DWC - KNAW

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geomagnetic poles have changed several times. Moreover • he found that at least during the Miocene the mean geomagnetic ,pole practica11y coincided with the geographic pole. M . G . R utten, professor of geology at Utrecht, recognized an agreement between the result of investigations by Hospers on the polarity of lavas on Iceland and those in the Plateau Central in France, found by A. Roche . For example, both investigators dated the latest period of reversed polarity at the beginning of Pleistocene. M. G. Rutten and J. C. den Boer (1954) realized that palaeomagnetism can be used for correlating lava flows over large distances. The outcome of Hospers' research was that, at the instigation of M. G. Rutten, a beginning was made in 1955 into the investigation of the magnetism of rocks. This took place under the guidance of Veldkamp • professor of geophysics at Utrecht from 1955 ti11 1974. Because Veldkamp was at the same time director of the geophysical dep art ment of the KNMI (from 1945 till 1972) this research was conducted for the first years in the seismograph pavilion of the KNMI. The instruments and measuring methods we re developed by J. A. As (KNMI) and the first results were found there. This was the beginning of a very fruitful development in cooperation bet ween geophysicists and geologists at Utrecht University. On the one hand the geologist could provide rock samples whose orientation was observed and measured in situ, on the other hand the geophysicist could measure the direction and the intensity of the magnetic components in the rock sample. This made possible in favourable cases determination of the direction of the local geomagnetic field at the time of the formation of the rock. From this direction conclusions could be drawn about the former positions of continents or of parts thereof. This cooperation bet ween geophysicists and geologists has resulted in a series of publications and theses produced at Utrecht University. In total no less than 18 dissèrtations and a number of papers were produced under the supervision of M.G. Rutten, R.W. van Bemmelen, J. Veldkamp and J.D.A. Zijderveld. The contents of these publications were to a considerable degree based on the study of palaeomagnetism . J.A. As (1960) developed the instruments necessary for measuring the magnetism of rocks. These instruments (astatic magnetometers and A. C. -demagnetization coils) were constructed at the KNMI and set up in the seismograph pavilion. As and Zijderveld (1958) designed methods for analyzing the magnetism of rocks. by means of heating as we11 as by demagnetization step by step in alternating magnetic fields. These methods made it possible to separate the fossil magnetism in a rock sample from recent magnetizations (see also: Zijderveld , 1967. and R. O. van Everdingen • 1960). Whereas origina11y demagnetization was applied only to test the stability of the remanent magnetization of rocks. the step-wise demagnetization developed by As and Zijderveld became important for separating vectorially the magnetizations present in the rock samples. In many cases the direction of the original magnetization could be derived with reasonable accuracy. This allowed calculation of the position of the geomagnetic po Ie at the time of the formation of the rock , and from this the geographic latitude of the country where the rock sample was taken. In favourable cases even the intensity of the fossil geomagnetic force could be found. In 1963 the magnetometers and demagnetization instruments were transferred to the former Fort Hoofddijk , which was rebuilt by Utrecht University especia11y for magnetic measurements. The research in rock magnetism has continued there under the leaders hip of Zijderveld . The Palaeomagnetic Laboratory contains now, in addition to the astatic magnetometers and the demagnetization apparatus, a spinner magnetometer, a cryogenic magnetometer , a magnetometer for 38
Figure 19. The Palaeomagnetic Laboratory of the State University at Utrecht. formerly Fort Hoofddijk (Photo e.G. Langereis) .
Page 1: History of Geophysical Research in
Page 4 and 5: ISBN 0-4448-5615-3 Author's address
Page 6 and 7: Section 11.3.3.1 Southeast Asia and
Page 8 and 9: Preface During the Congress of the
Page 11 and 12: CHAPTER I Research in Geomagnetism
Page 13: intensity at more than 300 places i
Page 16 and 17: .... Ol Figure 4. The KNMI during t
Page 19 and 20: Geomagnetic Observatories and Surve
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Page 26 and 27: Ftgure 13. The changing ionosphere
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Page 40: low and high temperatures, an elect
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Page 49 and 50: Hilten, D. van, and J.D.A. Zijderve
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Page 55 and 56: CHAPTER 11 Seismological Research 1
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Page 81 and 82: Visser, S.W. (1937) - Aardbevingen
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the oceans. This is a consequence o
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shaped when a southeasterly crustal
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- - o - .tJ_- 7
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Veldkamp, J. (ed.) (1969) - Gravity
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a year at Angmagssalik (East Greenl
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Outside the Netherlands geophysical
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Figure 47. Launching of a meteorolo
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means of data from both seismology
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IV.6. WIND MEASUREMENTS IN THE IONO
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y W. Bosrna, S. B. Kroonenberg, R.
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Holland in 1953 to 1958. Only after
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depth of 250 to 350 meters, under t
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A major improvement in the method w
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T I M E I N 5 E C o N D 5 l2t 381 2
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tally in a processing centre. The w
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Dijkstra, J. en A. Volker (1957) -
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Koefoed, O. (1968) - The applicatio
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Veldkamp , J. (1951) - Geomagnetic
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versity of Toronto. There he was su
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