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Vening Meinesz

Vening Meinesz

F.A. Vening Meinesz (1887-1966) is especially known from his gravity measurements at sea. He devised the Vening Meinesz pendulum apparatus by which it became possible to measure gravity at sea with comparable accuracy as on land.

Starting in 1923 he conducted several global gravity surveys on voyages on submarines, particularly to and in the Indonesian Archipelago. He detected strong gravity anomaly belts running parallel to the Indonesian deep sea trenches. He explained these Meinesz belts as sites of downbuckling of the Earth's crust. He introduced the concept of regional isostasy taking flexure of an elastic crust into account. He also contributed to physical geodesy: The Vening Meinesz formula connects the deviation of the vertical from the plumbline to gravity anomalies.

At the beginnings of space age the problem of the Earth's external gravity field received his attention.

His work connected with geodynamics, and in particular with mountain building, epeirogeny, and graben tectonics, did not receive much of the interest it certainly deserves. The present paper deals in particular with the geodynamic concepts which were developed by Vening Meinesz as a consequence of his observational work, already from an early time onward. The evolution of these concepts, from the possibility of a contracting Earth to the hypothesis of convection currents in the Earth as underlying causes of mountain building and other geodynamic processes, are presented in retrospect. Special attention is devoted to the connection between Vening Meinesz' ideas and their relevance for the plate tectonic hypothesis.

Vening Meinesz stood at the threshold of modern Earth science. Many of his ideas have not yet lost their validity. Many problems he addressed still await their solution. The social and scientific environment in which he worked enabled individuals like him to pioneer pathways into the future.

Measuring Gravity at Sea

Felix Andries Vening Meinesz was born on July 30, 1887, as the youngest of four children of S.A. Vening Meinesz and C.A.C. den Tex. He descended from lines of Dutch gentry and patriciate. His father was mayor of the city of Rotterdam and later of Amsterdam. His background, stately appearance, and distinguished manners would, in his later scientific career, open many doors and give access to the highest authorities.

The choice of his high school education indicates that he destined himself for a profession in science, technology, or commerce. This was quite unusual in his family. A career as magistrate or lawyer would have been more in line.

He graduated from Delft Technical University in civil engineering in 1910 and found his first occupation with the Netherlands State Committee on Arc measurements. He was assigned to measure gravity in the Netherlands. One of the main concerns of the international geodetic community at the beginning of this century was to determine the Earth's shape, not only by arc measurements, but also by means of the gravity field. Measuring the gravity field in the Netherlands would be decisive for Vening Meinesz' future career.

Like for the other famous Dutch geodesist, Snellius, some centuries before, the peculiar geography of the low countries would prove to be the incentive for some of their most important contributions to science. The flat landscape, together with the many church steeples to act as reference points, induced Snellius to become the founder of geodetic triangulation. Vening Meinesz designed his famous pendulum apparatus in order to eliminate the noise of the unstable and shaky soil. The principle of the apparatus was based on using two pendulums swinging in a common plane with equal amplitudes and opposite phases. Thus their relative motion eliminates the motion of their common support. Later he perfected his instrument by adding a third pendulum.

The theory of his apparatus was subject of the thesis, which, in 1915, earned him the doctors degree, cum laude. Up to 1921 gravity in the Netherlands was measured at fifty localities. The precision of the measurement was shown to be considerably increased relative to single pendulum observations and this success induced Vening Meinesz to investigate the feasibility to use the instrument at sea. Gravity at sea, which covered the larger part of the Earth's surface, was not yet possible with the same precision as on land. Earlier measurements at sea by Hecker of the Berlin observatory, who used an instrument based on barometric principles, did not achieve a precision comparable to on land measurements. He succeeded in finding large gravity variations over the Tonga-Kermadec trench.

Vening Meinesz had to employ his apparatus on board a submarine in order to eliminate as much as possible unwanted wave motion. In 1923 he took his instrument on a voyage of one of the submarines of the Dutch Navy, H.Ms.K2, sailing from the Netherlands to Indonesia -- the former Dutch East Indies -- through the Suez Canal. Several submarines had to be brought to the East Indies in order to strengthen the Dutch fleet in the area. Vening Meinesz was granted to exploit this opportunity for scientific purposes. His primary goal was to test his instrument. After some initial misfortune he arrived at measuring absolute gravity with an accuracy of the order of 1 mgal, hence, at the epoch, comparable to measurements at land.

Several voyages aboard submarines to the far East were to follow. In 1926 with H.Ms.K13 through the Panama Canal, and in 1935 around the Cape of Good Hope. In 1937, Vening Meinesz participated in a voyage to the United States aboard the submarine H.Ms.O16. He also took part, taking his pendulum apparatus along, in submarines of the U.S. and of the Italian Navy, for the purpose of studying the gravity field in the Caribbean and the Mediterranean seas, respectively.

Being of tall stature, about two meters tall, life on those early small submarines must have meant hardship for Vening Meinesz. Adding to this the heat, either of the tropical sun when at the surface, or of the batteries which powered the ship under water, great sacrifices had to be made during the more than 100.000 nautical miles totalling the voyages to the East Indies.

Though the primary purpose was to take the submarines to the overseas territories, the scientific goals also were considered to be of great importance. After arrival in Indonesia, the K18 was put to Vening Meinesz' disposal for half a year, solely for the purpose of measuring bathymetry and gravity in the Indonesian waters. The cooperativeness of the Dutch admiralty was set as an example by the international scientific community to other seafaring nations. Of course, showing the flag, and trying to place orders for submarines in overseas countries also played their role. The combination of naval and scientific achievements came in as an extra argument. In that sense Vening Meinesz could play a part in public relations! The O16 trip to the U.S.A. in 1937 even gave rise to being received by President Roosevelt.

The unescorted voyage of the K18 in 1926 of over 20.000 nautical miles was the largest ever made by a submarine and resulted in a book written by two officers of the crew (Klaar voor onder water, by commanding officer Mr. Hetterschij).

The 1930's were a time of records, and the combination of science, technology and travels to far away beaches stirred the imagination. In 1936, the voyage of the K17 was made subject of a movie picture, featuring the crew and Vening Meinesz. For the older generation in Holland, the K17 still rings a bell.

Vening Meinesz designed his instrument, to become known as the Vening Meinesz pendulum apparatus, and undertook personally to measure gravity at sea. Notwithstanding the elaborate measurements and corrections, hundreds of pendulum observations over the world oceans, and particularly in the Indonesian Archipelago were made. These achievements must be esteemed as highly outstanding contributions to geodesy and geophysics at that time. It would take another 35 years after its invention before the Vening Meinesz apparatus could be replaced by a more modern instrument for measuring gravity at sea with the same accuracy: the Askania spring gravimeter placed on a stable platform aboard a surface ship.

The Meinesz Belt and the Buckling Hypothesis

The first aim of measuring gravity at sea was to have more pertinent data in order to determine the shape of the Earth. A particular issue was whether the Earth's equator would deviate from the circle. From his observations, at equatorial latitudes circumpassing the globe, Vening Meinesz found no evidence for such a deviation. He found, however, that like on the continents, also on the oceans Airy isostasy prevailed, thus confirming the existence of a thin low-density crust which floated on a high-density yielding mantle. Knowing that the continental topography could give rise to deviation from isostatic equilibrium, he was intrigued by the gravity effects of the deep sea trenches in the Indonesian Archipelago, and gravity was measured more densely in this area. This led to the discovery of belts of strong negative isostatic anomalies running parallel to the trenches. These belts were to become known as the Meinesz belts. He found that these belts were inherent to deep sea trenches in general. The negative anomaly belt could only be explained by assuming that the elastic crust was held down in the trench by external causes, maintaining deviation from isostatic equilibrium. A second, parallel belt of positive anomalies, discovered more seaward from the trench, could be explained in terms of the upward flexure of the elastic crust being pushed down at the trench. The theory of the flexure of a thin elastic plate gave a thickness of 35 km for the crust. This is still, at present, a valid figure for the thickness of the mechanically strong part of the oceanic lithosphere. Vening Meinesz indeed distinguished between the chemical crust, which in general was subject to Airy isostasy, and the "elastic" crust, which was defined rheologically. The flexure of the elastic crust made him to broaden the concept of isostasy. Whereas Airy isostasy departed from purely local density compensation at depth, Vening Meinesz introduced regional isostasy and compensation, taking into account the flexure of the elastic crust when loaded. Regional or Vening Meinesz isostasy was to become a useful concept in connection with mountain building and loading of the oceanic lithosphere by volcanic edifices.

As early as 1930, Vening Meinesz casts his findings in a more general framework. He was aware of a connection of the Meinesz belts, deep sea troughs, seismicity, volcanism, and mountain building. Realizing that strong isostatic anomalies could only be supported by forces acting on the elastic crust, he suggested that these forces, acting in the plane of crust, should give rise to linear features of local plastic yielding, This then should lead to local thickening and downbuckling of the crust. Relaxation of the acting force fields would restore isostatic equilibrium and uprising of the downbuckled crust would lead to the formation of a mountain belt. He had found that the Meinesz belts occurred generally on the Western Pacific rim. Being aware of the large forces involved and the large regional extent of their action, he speculated that downbuckling should be the result of compression between large, and more or less rigid, crustal blocks. In 1931 he regards contraction theory as most plausible generation cause for the large compression required, and also mentions Wegener, without, however, coming to conclusions concerning a causal mechanism. His views found support in the ideas living among contemporary Dutch geologists and engineers.

The geologist Umbgrove (The pulse of the Earth) proposed that mountain building periods were episodically occurring during the Earth's history. This confirmed Vening Meinesz' hypothesis that mountain building was the effect of forces on the Earth's crust, which, after a period of action, would relax. The sedimentologist Kuenen would later provide scale experiments by which the downbuckling process was vividly demonstrated.

In 1935, the engineer Bylaard published an article in which he associated the theory of plastic buckling of an elastic plate with the findings of Vening Meinesz in the East Indies. When an elastic plate is subject to increasing in-plate compression, instability will occur, giving rise to large displacements perpendicular to the plate, and along in-plate lines perpendicular to the direction of compression. However, if the plastic yield limit is reached before elastic instability, plastic thickening will take place along a line making an angle of 55E with the direction of compression. Applying this to the Earth's elastic crust should lead to thickening and downbuckling in the plastic substratum and thus to crustal shortening and the formation of a root as depicted in Kuenen's experiment.

Later, following David Griggs (1939), he also distinguished the case of plastic shear along a crustal fault, taking place without plastic thickening, and allowing movements such as along the San Andreas fault. Theory predicted that this should take place under an angle of 23E with the direction of compression. The angles of 55E and of 23E, in Vening Meinesz' later work, were almost to become magical. He found these angles clearly demonstrated along the troughs south of Java and south-west of Sumatra by assuming a pressure field which was aligned N.W.-S.E., comprising the Australian-Indian Ocean and the Asiatic block. Whereas south of Java plastic thickening and downbuckling was supposed to take place, Sumatra was to move laterally by "pseudo-viscous" shear with respect to the Indian Ocean. The latter shear movements, in a compressive regime, could cause overriding of one crustal block over the other and thus also could result in a form of mountain building. Indeed, already in 1898, J.J.A. Mulder, by geodetic triangulation near Bengkulen, Sumatra, had observed lateral off-sets of 2 meter along a fault directed parallel to the coast. Mulder, as president of the Dutch State Committee an Arc Measurements, would later be the first employer of Vening Meinesz.

The Convection Hypothesis

The first time that Vening Meinesz made mention of the possibility of convection currents in the Earth is in a highly remarkable paper which appeared in 1934 in the proceedings of the Royal Netherlands Academy of Science entitled: "Gravity and the Hypothesis of Convection Currents in the Earth." Referring to the hypothesis as being put forward by Arthur Holmes some years earlier for explaining the driving mechanism of mountain building, Vening Meinesz states that thermal convection may well be causally related. The motivation for accepting the hypothesis, however, is not ad hoc, but is based on clever reasoning departing from some peculiarities of the observed gravity field. He knew that large "fields" of anomalous gravity existed, both over continental areas and deep oceanic basins which up till then deferred being understood in terms of Airy isostasy. In order to explain the isostatic anomalies by anomalous density distributions, the Airy isostatic hypothesis, applied to the crust, did not give satisfactory answers, and subcrustal density anomalies had to be inferred.

Earlier, Vening Meinesz had suggested that upbending of the elastic crust by compression on a curved Earth would lead to subcrustal mass excess and thus to positive isostatic anomalies over deep sea and sedimentary basins. This suggestion fitted well in the hypothesis of a shrinking Earth. However, he found that the stresses involved should exceed 10 kilobar, and hence far beyond the yield limit of crustal materials.

Subcrustal mass excesses under deep ocean basins and mass deficiencies under large continental areas he now explained by temperature gradients from the continents to the ocean basins which by their inherent perturbation of hydrostatic equilibrium would give rise to subcrustal mantle currents from the continents to the oceans. These currents were then supposed to be part of a convective upper mantle circulation which was triggered by the horizontal temperature and associated horizontal pressure gradients. The temperature difference could be ascribed to blanketing by the continental sialic crust having a larger concentration of radioactive elements relative to basaltic oceanic crust. A consequence of this scheme was episodicity of convective circulation which was in line with the ideas of geologists like Umbgrove, who advocated the idea of episodic mountain building. A further consequence was rapid uplift and subsidence as was evident in epeirogeny.

Simple calculations, using a viscosity as deduced from postglacial Fennoscandian uplift (in 1934!) confirmed, in a quantitative way, the picture of subcrustal upper mantle convection currents being episodically triggered by temperature gradients form the continents towards the oceans. Associated gravity anomalies were in good agreement. Convection currents were supposed to be rising under continents and sinking under oceans. The Earth's crust suffered drag at its base exerted by the subcrustal currents. When in a compressive regime the crust could be subject to downbuckling.

Later, during the forties, contrary to Bullard's hypothesis of compression, Vening Meinesz explained continental graben formation as being due to tension in the crust caused by upwelling and diverging hot material in a convective subcrustal regime.

Heat flow measurements in the ocean floor would only emerge after 1950. Had Vening Meinesz known modern oceanic heat flow data, his hypothesis would have predicted upwelling limbs of convection cells beneath the oceanic rises, and downwelling ones at the continent-ocean transition beneath the deep oceanic basins. His deduction of absence of Airy isostasy under the latter would be completely in accord with the modern concept of a spreading and cooling oceanic lithosphere. It would then have been one step more to involve the oceanic crust as part of the convective system. Subduction or ongoing downbuckling of oceanic lithosphere at deep sea trenches could have completed the cycle of creation and subduction of the oceanic crust as manifestation of thermal convection in the Earth. Lacking observational evidence on oceanic heat flow, Vening Meinesz had to assume that subcrustal currents were flowing from the continents towards the oceans, subjecting the Earth's crust to compression or tension.

Being aware of the strong deviations of hydrostaticity as expressed in gravity anomalies and most probably caused by horizontal temperature differences in the subcrustal "plastic layer", Vening Meinesz concluded that flow was a necessary consequence for readjustment of equilibrium. However, still in 1939 he states on the subject of the hypothesis of convection currents in the Earth: "For the time being it is nothing but a speculative hypothesis". His scepsis will turn into a belief, and even a faith in the hypothesis of thermal convection in the Earth, in his later years.

Already in the thirties it had been proved by Pekeris and by Hales that convection in a homogeneous layer with the thickness of the Earth's mantle subjected to a slight superadiabatic gradient and with a viscosity deduced from postglacial rebound a Rayleigh number which was far beyond the critical one.

Vening Meinesz adapted Rayleigh's theory to a spherical coordinate system and found also in this case thermal convection throughout the mantle was feasible. His theory was intrinsically departing from the assumption of stationarity, notwithstanding that he took convection in the Earth as an intermittent process. He assumed that convective motion which was supposed to be triggered by horizontal temperature gradients, could only take place when gravitational instability of the Earth mantle from cooling from the Earth's surface downwards, was restored by overturning of the mantle. This should take place episodically in the Earth's history leading to periods of geosynclinal formation and mountain building, separated by long intervals of tectonic quiescence. We should now find ourselves in the decline of the Alpine period.

During the early forties Vening Meinesz used his theory to demonstrate that third order tesseral spherical harmonics would lead to the peculiar ocean-continent distribution which was known as the "tetraeder theory". Convection had to be mantle deep and was assumed to have taken place early in the Earth's history, having fixed the relative position of continents and oceans. Apart from localized downbuckling and rifting, the Earth's crust was supposed to remain a strong shell. Shrinking of the Earth was not any-more accepted, as graben structures proved to be tensional features in the crust. Wegener's theory of continental drift was only acceptable in as far as it explained the continent-ocean distribution being frozen-in already during the Earth's early existence. During the early period, the oceanic crust might have been still sufficiently weak by the prevailing high temperatures. Continents could drift in it, be swept together, or torn apart. Vening Meinesz rejected the notion of continental drift in more recent geological periods. Altogether, until the advent of the plate tectonics era, he stuck to this concept.

Following Prey (1922), who expanded the Earth's topography in spherical harmonics of lower order, Vening Meinesz extended the expansion to order 31. The spherical harmonic spectrum of the Earth's topography appeared to confirm his views that these features were caused during a period of thermal convection in the early stages of the Earth. In this context, also the oceanic rises were to be the frozen-in product of early geodynamical processes! However, admitting mantle convection to exert a net torque on the crust, he concluded that true polar wander would be well possible. He calculated the stress field in the thin crust generated when the latter shifts over the ellipsoidal mantle, and attributed large crustal fault systems to this mechanism. Later he will explain the results of palaeomagnetism which indicate continental drift, in terms of true polar wander. Refinements of the concepts of thermal convection constitute the acceptance, apart from whole mantle convection, of smaller scale convection on an upper mantle scale. Whereas whole mantle convection appeared to be necessary for the explanation of large-scale compressive phenomena over the Pacific and South-East Asia, small-scale convection was required by the existence of small regional oceanic basins in Indonesia and the Mediterranean. It was known that these basins were rapidly subsiding.

During the fifties, inspired by the work of Meyering and Rooymans of Philips Physical Laboratories, and earlier suggestions by Bernal and others, he includes the olivine-spinel phase transition - supposedly present in the upper mantle - into his considerations. He concludes that this transition should enhance gravitational instability and thus whole mantle convection. Also, rapid basin subsidence could be fitted in the scheme of upper mantle phase changes. Whole mantle, or upper mantle convection, combined with downbuckling and shear failure of the elastic crust, enabled Vening Meinesz to set up a grand scenario for geodynamics. His approach should be characterized as speculative, but turns out to be a prelude to plate tectonics.

Mountain Building and Epeirogeny

In geology it was observed that the initial stage in an orogenic cycle was the formation of a geosyncline. A geosyncline resulted from the subsidence of a sedimentary basin. After deposition of thick piles of sediments the sedimentary layering was folded and faulted. Subsequent uplift resulted in a mountain range above sea level.

Vening Meinesz regarded the orogenic cycle to be caused by plastic thickening, downbuckling and uplift of a narrow zone in a compressed elastic crust. The initial stage of plastic thickening and downbuckling resulted in a sagging depression in which sediments could be deposited. The unstable state of the crust resulted in accelerated downbuckling and collapse of the crustal layering. Whereas the lower part of the crust was to form a deep root penetrating the mantle, the more shallow crustal layering was compressed, faulted and folded.

This conception was in agreement with crustal shortening as observed in fold belts, for which the Alps stood as an example. Also, the existence of a "Verschluckungszone" (Swallowing zone) in the Alps as put forward by geologists was in agreement with the downbuckling hypothesis. A major difficultly, however, was posed by the amount of crustal material which had to be downbuckled into the mantle in order to be compatible with the amount of crustal shortening of the shallow crustal layering in the fold belt. The amount of downbuckled material, should, after restored isostasy as observed at present, have produced much higher mountain ranges. Vening Meinesz solved this problem by "subcrustal erosion". The light root material, after having been reheated to ambient mantle temperatures, would have been partly transported away by subcrustal currents. Adding this lighter material from below to the crust at distance, should then give rise to uplift of the crust and the formation of the German and French "Mittelgebirge".

Vening Meinesz distinguished between continental and oceanic geosynclines. He assumed that a mountain range like the Alps was the result of the collapse of a continental geosyncline. Due to the lack of a light sialic layer in the oceanic crust, mountain building should only be minor as only a small amount of light root would be available to produce large topographic features upon isostatic readjustment. In how far deep sea trenches at the margin of continental areas, like those in Indonesia, conform to this distinction, was not explicated. Island arc volcanism, however, was cast in terms of "subcrustal erosion" of a root containing more acid crustal material and producing magma.

A major difficulty, already in the first years of Vening Meinesz' involvement in Indonesian geodynamics, was posed by the presence of deep earthquakes in the Archipelago, which were detected by the seismologists Berlage, Vissers and Koning. Assuming subcrustal plasticity, the occurrence of these earthquakes could not be explained. The rheological model of "pseudo-plasticity" used by Vening Meinesz for the mantle, in which an initial small elastic strain had to be surpassed before plastic yielding occurred, enabled him to find an explanation. He argued that shallow earthquakes would trigger deep earthquakes when at depth the resulting deformation was too rapid to be relaxed by plastic flow.

Vening Meinesz distinguished three types of mountain ranges. Firstly, those associated with plastic downbuckling of the crust leading to Alpine type foldbelts. Secondly, mountain ranges which were supposed to result from overriding of one crustal block over the other on a "pseudo-viscous" shear fault in which the large pressure required for plastic downbuckling would not be reached. This mechanism of mountain building was in favor among American geophysics. Its modern version is named transpression. Vening Meinesz attributed oceanic escarpments, which are now known to be associated with transform faults, to the latter mechanism. A third type of mountain ranges were constituted by the submarine oceanic ridge systems. At the time, he was not able to give a satisfactory explanation of their existence. However, by assuming that the ocean-continent distribution was generated in an early stage of the Earth's history, he speculated that they should be associated with true polar wander.

Plate Tectonics

During most of his speculative involvement with geodynamics, Vening Meinesz was only a few steps away from the hypothesis of plate tectonics. The phenomena he tried to explain were mostly the same as those which confirmed the spectacular breakthrough of plate tectonics. Vening Meinesz' model of the Earth's dynamics, however, appeared to be founded on so solid ground that he rejected the necessary notions inherent to plate tectonics.

As the Earth's crust and the continent-ocean distribution in his view originated in the existence of the planet, continental drift would not be possible in later periods. He disregarded geological evidence and also the findings of palaeomagnetism which were emerging from the early fifties. The mobility of the Earth's crust he understood as local yielding phenomena in an otherwise static crust. This "fixist" view of the Earth's crust was counterbalanced by assuming episodic convective overturning of the Earth's mantle, a "mobilistic" principle. Episodicity, however, excluded continuous relative motion of parts of the crust with respect to each other. Stationarity of the Earth's internal dynamics should have made ongoing downbuckling and thus creation of new crust necessary. In his episodic scenario there was no need for a crust which was part of the convective cycle. His notion that convection currents were upwelling under the continents and sinking under oceanic basins, was just the opposite from the findings which proved to be instrumental to the success of plate tectonics.

A few years before the beginnings of the plate tectonic era, influenced by the ideas of Hess and others, he embraced the notion that convection currents should be uprising under oceanic ridge systems as well as under continents.

His book, "The Earth's Crust and Mantle" appeared in 1964, just prior to the breakthrough of the plate tectonic hypothesis. The last two pages must be considered quite remarkable, particularly in the light of plate tectonics yet to come. He writes that Runcorn's palaeomagnetic findings are in complete accord with Wegener's theory and that continental drift therefore is well possible. He argues that downbuckling of the oceanic crust -- because of the small density difference between oceanic crust and mantle -- is easily to accomplish, and thus could go on indefinitely. This must be appreciated as the first statement concerning the possibility of subduction of oceanic crust. However, he fails to create necessary new oceanic crust elsewhere, otherwise plate tectonics possibly could have been born a few years earlier. Nevertheless, he still concludes that continental drift could only be possible during orogenies which he supposed to be episodic.

Vening Meinesz and Geology

In the early years Vening Meinesz found much appreciation for his ideas in geological circles. On the other hand, geology was very much in need of basic concepts which could explain mountain building, and he offered these concepts, firmly based on geophysical observations and theory. The geologists Umbgrove and Kuenen wrote articles on the geology of Indonesia in Vening Meinesz' "Gravity expeditions at sea, Part II" which appeared in 1934. However, this would be his last scientific cooperation with geologists.

Geologists amongst each other remained divided on tectonic issues for several decennia. Geology remained in a descriptive and naturalist state for many following years. Conflicting ideas and observations could only result in a chaotic presentation, not very much in according with a schematic approach as advocated by Vening Meinesz. The distance between his approach and geological reality would remain too large to gain the sympathy of all geologists. As W. Nieuwenkamp once put it: "An extreme standpoint is to appreciate Vening Meinesz' work as an underhand attempt to torpedo the efforts of geologists from a submarine". Others understood the significance of geophysics at an early stage and encouraged Vening Meinesz to become a professor in geophysics -- on a part time basins -- at Utrecht University, already in 1937. His teachings would remain of limited significance as his courses had to cater to an audience with a poor background in mathematics and physics. Also, his approach stood far away from the ambitions of an average geology student who planned a career in industry. Studying the Earth as a physical system, even still at present, has not gained large popularity in many geological circles. Vening Meinesz always worked as an individualistic scientist. Also, geophysics had not evolved to the level of an indispensable tool in exploration and did not have the practical significance as it has at present. Probably all these circumstances together did not favor that a distinctive geophysical school around Vening Meinesz came into being. Vening Meinesz, being a professor in a geological department, showed his interest by participating in geological excursions. The students could not avoid the impression that professor Vening Meinesz admired the landscape and old village churches more than geology. On the other hand, the views on mountain building as developed by Vening Meinesz, particularly in connection with the geology of Indonesia and the Alps, were not always in agreement with geological interpretations.

The transport over large distances of nappes in fold belts like the Alps, was often accredited to gravitational sliding. This, of course, did not conform to the concept of the collapse of a zone of downbuckling.

Van Bemmelen, an authority on the geology of Indonesia, teaching at Utrecht University about contemporary with Vening Meinesz, held different opinions on the subject. Being an adept of Haarman's "undation theory" he thought to see this theory confirmed in the geology of Indonesia, demonstrating in his views an orogenetic wave travelling South East. Moreover, he ascribed orogeny in general, and nappe transport in particular, to gravitational sliding. Gravitational sliding was supposed to result from upbuilding of the crust ("geoblisters", "geotumors"), due to upwelling of mantle material, which, in turn was mobilized by "physico-chemical processes". The latter process had the character of a "deus ex machina", not unlike present day "hot spots".

Van Bemmelen tried to proof his point in the field. Vening Meinesz could baffle his mostly geological audience with spherical harmonics and other mathematical intricacies. Discussions between those prominent scientists could run high. The atmosphere was not very encouraging for students to become dedicated to the problems of mountain buckling otherwise than by descriptive geological fieldwork.

Vening Meinesz was known to be a very amiable and courteous person. However, like many great men, he appeared to be blind for arguments which were not in line with his own views. He even could react with a certain intolerance towards unbelievers.

In the fifties and sixties, instigated by Martin Rutten, a professor in geology, the development of palaeomagnetism was strongly encouraged in Utrecht. Vening Meinesz never referred to this work. The idea of continental drift taking place in recent geology times, did not appeal to him.

Epilogue

The first part of Vening Meinesz' career was marked by the great discoveries of his pendulum apparatus, the Meinesz belts, the concept of regional isostasy, and the downbuckling hypothesis. To this list we also should add the Vening Meinesz formula, connecting the deflection of the plumbline from the vertical to gravity anomalies. He devoted his later years to find a unifying theory for global tectonics. His lifework was ahead of his time. His background in civil engineering gave him the ability to regard the Earth as a mechanical system. Towards the end of his life he complained that he considered himself to be a failed civil engineer. He could permit himself this modesty as by then he was one of the greatest geophysicists to life. He truly was a great scientist.

Looking back, one feels great respect for his achievements and is impressed by the firmness and originality of his conclusions which were based on such a limited set of data. This then, compared to the present time, when data are drowning the world, science is managed by bandwagonry, and originality is often suppressed. Vening Meinesz was one of the last gentleman-scientists who were not bothered by collectivism and red tape.

In the meantime, plate tectonics has taught us a great deal about the evolution of the oceanic lithosphere, and insight has been gained in many geodynamical issues which were already addressed by Vening Meinesz.

Plate tectonics even appeared to confirm the convection hypothesis and has set the pace for a strong emphasis on the subject of convection in the Earth as an explanation for geodynamics. It may be that this emphasis may have reached the state of a paradigm, and even may hamper further developments. Plate tectonics yet did not contribute considerably to the subjects of Vening Meinesz' interest: mountain buckling and epeirogeny. Our state of knowledge of the continental evolution has hardly increased in a conceptual way since his days. Data and description have accumulated exponentially, but out understanding has not kept pace.

The subject of heat transfer in the interior of the Earth is interesting in its own right and of great importance for the evolution of our planet. However, this evolution cannot be understood properly without taking into account the growth and structure of the continental masses. Geophysicists should learn more from geological evidence, and geologists should be more aware of the possibilities and limitations of geophysics. The no man's land between the disciplines of geology, geophysics, and geodesy should be conquered by cooperation and not by domination.

Vening Meinesz stood high above his environment, physically, scientifically, and socially. He also stood out as a leader in scientific management: he was one of the founders of the Dutch counterpart of the National Science Foundation, and he was General Director of the Royal Netherlands Meteorological Institute (KNMI) in de Bilt. He held memberships of the Royal Netherlands Academy of Science, and also of several foreign Academies. He received many distinctions, both royal and academic. He was awarded the Bowie Medal in 1947, and the Vetlesen Prize in 1962. From 1933 to 1945 he was president of the International Association of Geodesy, and from 1948 to 1951 president of the International Union of Geodesy and Geophysics.

His life was devoted to science. He was a man with strong religious beliefs. Vening Meinesz died on August 10, 1966, leaving us a rich scientific heritage.

N.J. Vlaar
University of Utrecht, The Netherlands
Honorary Member of the EGS
Article copied from
AGU Geophysical Monograph 60
IUGG Volume 10
pages xi-xvi

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