(b. Magdeburg, Germany, 8 November 1885; d. Bonn, Germany, 26 September 1951),
Cloos’s father, an architect, died young, leaving the upbringing of the three children to their mother, a highly gifted woman who contributed greatly to her son’s intellectual development. Upon completing his secondary studies at Saarbrücken and Cologne, Cloos began to study architecture at the Technische Hochschule in Aachen but soon became interested in geology. After a short period of study in Bonn and Jena he went to Freiburg im Breisgau, where he received his doctorate under Wilhelm Deecke. Between 1909 and 1913 he did work in applied geology in South West Africa and Java. In 1914 Cloos qualified as a lecturer at the University of Marburg, and in 1919 he was appointed professor of geology and paleontology at the University of Breslau (now Wroclaw, Poland). He was called to the University of Bonn in 1926 to succeed Gustav Steinmann. He married Elli Grüters, the daughter of an orchestra conductor, who bore him four children.
Cloos was a corresponding member of the Academy of Sciences of Berlin and of Göttingen and an honorary member of the geological societies of Germany, Finland, London, Sweden, the United States, and Peru and of the Natural Science Society of Schaffhausen, Switzerland.
In his dissertation, in which he examined the tectonic relationships between the folded mountains and plateaus of the Jura south of Basel, Cloos treated subjects that appeared in his later work: tectonics, structural geology, and internal dynamics. His stay in South West Africa presented Cloos with problems involving the mechanics of magmatic intrusion when he investigated the granite massifs in the Erongo Mountains. As a petroleum geologist in Java he was able to study active volcanoes and their structure.
During his years in Breslau, Cloos developed the field that became known as granite tectonics, the reconstruction of the dynamics of emplacement of a mobilized pluton from its internal structure (1921, 1922, 1925). Its basis was provided by the great granite massifs of Silesia. Cloos discovered that the granite, considered until then as massive and essentially structureless, bears clearly oriented features gained during or directly after its intrusion. These include the linear or laminar flow textures of the solidifying magma, the regular relationship of the joint and vein systems to the flow textures, and the cleavage of the granite (well known to quarry men). Cloos applied granite tectonics to the Bavarian forest near Passau, and in Norway and North America (1928). The results obtained during the years at Breslau are among Cloos’s most significant achievements.
At the same time that Cloos developed granite and magmatic tectonics, still another procedure for investigating similar problems was discovered by Bruno Sander—structural petrology, which examines, among other things, adjustment and behavior of mineral granules in a solidifying, magmatic liquid solution under tectonic influence. For a time there was sharp opposition between the two lines of inquiry. This resulted in scientific polemics between Cloos and Sander, which are now settled.
When Cloos moved from Breslau to Bonn in 1926, he turned his attention to other tectonic problems: jointing and cleavage as typical of the deformation of solid rocks, especially in the Paleozoic formations of the Rheinische Schlefergebirge (the area around Bonn) folded and faulted in the Hercynian orogeny, as well as the reproduction of tectonic phenomena and processes in the laboratory. He may have been the first to make extensive use of wet clay. His experiments on rift valley formation using wet clay (1931) have found a place in the literature and are particularly impressive, Many trips, including those to Africa and North America, widened his knowledge and experience and enlarged his view. The results can be seen in his outstanding textbook on internal dynamics (1936). Moreover, the years in Bonn witnessed more new knowledge: the division of the old continental masses into polygonal fields, the existence of Grundschollen (ground blocks) and Erdnähten (geofractures) which put Cloos in opposition to Alfred Wegener (1947)—the significance of the buckling processes in the earth’s outer crust, the mechanics of volcanic processes in the so-called” embryonic volcanoes” in Württemberg (1939), and many lesser studies on the mechanics of folding and faulting.
Cloos always placed tectonic considerations foremost, regarding the earth’s crust as an architectonic edifice. In his view the significance of the structural form and its analysis were primary: the investigation of the historical development of the mechanical processes that led to this structural form were of lesser interest. In many respects Cloos had an artistic temperament, filled with passion and enthusiasm for his science; and he knew how to convey this feeling to his students. His popular book Gespräch mit der Erde (1951) is a further expression of this ability. Through his tectonic researches, especially those concerning the relationship between tectonics and magma, Cloos provided geology with new knowledge and methods.
I. Original Works. Cloos’s writings are “Der Mechanismus tiefvulkanischer Vorgäng,” in Sammlung Vieweg (Brunswick), 57 (1921), 1–95; “Tektonik and Magma. Untersuchungen zur Geologie der Tiefen; Band I Einleitung: Über Ausbau and Anwendung der granittektonischen Methode,” in Abhandlungen der Preussischen geologischen Landesanstalt, n.s. 89 (1922), 1–18; Einführung in die tektonische Behandlung magmatischer Erscheinungen (Grnittektonik), I, spezieller Teil: Das Riesengebirge in Schlesien (Berlin-Bonn, 1925); “Bau und Bewegung der Gebirge in Nordamerika, Skandanavien and Mitteleuropa,” in Fortschritte der Geologie and Palaeontologie, 7 , no. 21 (1928), 241–327; “Zur experimentellen Tektonik II. Brüche and Falten,” in Naturwissenschaften, 19 (1931). 242–247; Einführung in die Geologie: Ein Lehrbuch der inneren Dynamik (Berlin, 1936; repr. 1963); “Hebung—Spaltung—Vulkanismus; Elemente einer geometrischen Analyse irdischer Grossformen,” in Geologische Rundschau, 30 , special no. 4A (1939), 405–527; “Grundschollen and Erdnähte Entwurf eines konservativen Erdbildes,” ibid., 35 (1947), 133–154; and Gespräch mit der Erde, 3rd ed. (Munich, (1951), Trans. by E. B. Garside as Conversation with the Earth, ed. and slightly abr. by Ernst Cloos and Curt Dietz (New york, 1953).
II. Secondary Literature. See also r. Balk, “Memorial to Hans Cloos (1886–1951)”, in Proceedings. Geological Society of America (1963), 87–94, with portrit; Erich Bederke. “Hans Cloos,” in Zeitschrift der Deutschen geologischen Gesellschaft, 104 (1953), 553–557; S. von Budnoff, “Requiem auf Hans Cloos,” in Geologische Rundschau, 41 (1953), 1–10, with complete bibliography and portrait; and E. Hennig, “Cloos, Hans,” in Neue deutsche Biographie, III (Berlin, 1957), 294.
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