Jaggar, Thomas Augustus, Jr.

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Jaggar, Thomas Augustus, Jr.

(b. Philadelphia, Pennsylvania, 24 January 1871; d. Honolulu, Hawaii, 17 Junuary 1953)

geology, volcanology.

Jaggar was the son of the Reverend Thomas Augustus and Anna Louisa (Lawrence) Jaggar. As he later wrote, a love of the outdoors was instilled in him by his father, and at an early age he was tramping the backwoods of Maine and the Maritime Provinces. At fourteen, while in Europe with his family, he was schooled in French and Italian, climbed Vesuvius, and became committed to natural science. Jaggar earned three degrees (B.A., 1893; M.A., 1894;Ph.D., 1897) at Harvard University, and spent two postgraduate years in Europe at the University of Munich, with K. A. von Zittel (1894), and at the University of Heidelberg, with K. H. Rosenbusch, V. Goldschmidt, and E. Osann (1895). In 1903 he married Helen Kline, later marrying, in 1917, Isabel P. Maydwell, a valued assistant and companion throughout his career.

The need for careful field observation was impressed upon Jaggar at Harvard by Nathaniel Shaler, and also by Arnold Hague, with whom Jaggar worked as an assistant in the Rocky Mountain volcanic province (1893). The latter experience introduced Jaggar to volcanology, the field of geology that was to dominate his scientific career. While a graduate student, he studied intrusive rocks with R. A. Daly, and for his doctoral dissertation he invented a “mineral hardness instrument”(microsclerometer0 and studied the xenoliths in the dikes in Boston.

After completing his formal education Jaggar worked for the U.S. Geological Survey (1898-1901) He participated with S. F. Emmons, J. D. Irving, Bailey Willis, and N. H. Darton in studies on the laccoliths and economic resources of the Black Hills in South Dakota, and with Charles Palache on the geology of the Precambrian granites of the Bradshaw Mountains in Arizona. In 1899 Jaggar provided for Charles D. Walcott, director of the survey, the first estimate for a geological survey of Hawaii, a project which eventually led Jaggar to that area of the Pacific. During the next several years Jaggar and his associates in Boston and at Harvard experimented with various devices, including stream tables and model geysers. The experimental geyser was in effect a miniature “Old Faithful,” yielding (although scale was not a serious consideration) some mechanistic understanding and, by application, more knowledge of phreatic volcanic eruptions. In addition, squeeze-box experiments by Jaggar and his associates extended the earlier work of Bailey Willis, and experiments by the team on the crystallization of basalt melts and artificial mixtures of their constituent minerals yielded observations on textural variations and on the rate of cooling.

In 1901 Jaggar left the U. S. Geological Survey to become an assistant professor at Harvard and in 1906 head of the geology department at the Massachusetts Institute of Technology, where he remained in close association with the survey until 1910. It was during this time (1901-1912) that Jaggar began to make his volcanic expeditions to the island of Martinique after the Mount Pelee eruption (1902); to Vesuvius, where he became acquainted with F. A. Perret (1906), the noted volcanic photographer and volcanologist; to the Aleutian Islands (1907); and ultimately to sixty of 450 still-active volcanoes.

In 1911, with financial help from the Massachusetts Institute of Technology and the Volcano Research Association of Honolulu, Jaggar established what was to become the Hawaii Volcano Observatory. He served as director until 1940. Under his charge all measurable parameters of Hawaiian volcanic activity were recorded—shape, character of flow, height of lava in craters (particularly Halemaumau, since this crater remains filled for extended times during eruption), temperature (his early attempts used pyrometer, iron pipe, and immersed thermocouples), and eruptive periods. Seismic data (some recorded on Jaggar’s “shock recorder”) and accurate surveying yielded important evidence of swelling of volcanic edifices and the first hints of eruptive predictability. The cyclic nature of volcanism was substantiated by the continuous, careful records kept by Jaggar and his associates. The work at the Hawaii Volcano Observatory and Jaggar’s experience at other volcanoes culminated in the publication of “Origin and Development of Craters” (1947).

Jaggar was responsible for a classification of volcanoes by viscosity (1910) and for early direct temperature measurements of basaltic lava. He also formulated nomenclature, although it is not used frequently today, for specific lava conditions. “Pyromagma,” for example, referred to hot, gas-charged lava in lakes; “epimagma” to partially solidified and crystallized lava; and “hypomagma” to the subsurface source magma. Much of Jaggar’s work, based on firsthand observation and experience, was qualitative. He made significant contributions on the development of volcanoes and on the role of groundwater in explosive eruptions. He always demonstrated concern for the people who lived in volcanic areas. In 1936 he recommended a plan of bombing from aircraft that succeeded in diverting the flows endangering Hilo.

After Jaggar retired from the Hawaii Volcano Observatory in 1940, he became a research associate in geophysics at the University of Hawaii. Up to his death he continued to impart his knowledge of volcanology through travels with his wife and through his writing.


I. Original Works. A large number of Jaggar’s works, including his early publications and important journal articles through 1945, are listed in the reference section of his major work “The Origin and Development of Craters,” Memoirs. Geological Society of America, 21 (1947). Significant among these are “Japanese Volcanoes and Volcano Classification,” in M. I. T. Bulletin of the Society of the Arts (Feb. 1910); “Seismometric Investigation of the Hawaiian Lava Column,” in Bulletin of the Seismological Society of America, 10 (1920), 155-275; and “Protection of Harbors From Lava Flows,” in American Journal of Science,243A (1945), 333-351, with reference to a number of reports written by Jaggar for the Volcano Letter of the Hawaiian Volcano Research Association, published by the Hawaii Volcano Observatory.

Additional works include “The Mechanism of Volcanoes,” in Volcanology, National Research Council Bulletin no. 77 (1931), 49-71; Volcanoes Declare War (Honolulu, 1945); Stream Blast Volcanic Eruptions, Hawaiian Volcano Observatory, 4th spec. report, a significant work; and My Experiments With Volcanoes (Honolulu, 1956), an autobiography that provides an interesting look into Jaggar’s experiences through 1952 and contains information on his early inclination toward natural science and his developing interest in Hawaii.

II. Secondary Literature. A brief but important sketch of Jaggar’s life is found in F. M. Bullard, Volcanoes &in History, in Theory, in Eruption (Austin, 1962), pp. 27-30; and in World Who’s Who in Science (Hannibal, Mo., 1968), p. 870. Reference to much of Jaggar’s professional work is in A. Rittmann, Volcanoes (New York, 1962), pp. xiii, 18 55, 63, 167, 188; F. A. Perrett, “Volcanological Observations,” in Publications, Carnegie Institution of Washington,549 (1950), 50, 133; and most recently in G. A. MacDonald, Volcanoes (Englewood Cliffs, N.J., 1972), pp. xii, 37-39.

Wallace A. Bothner