Alexander R. “Mac” McBirney, a pioneer in the application of physical reasoning and fluid dynamics in physical volcanology and igneous petrology, passed away on 7 April 2019. During a scientific career that began at the dawn of plate tectonic theory and spanned some 50 years, he played a key role in our understanding of the physics of magma chamber evolution and the volcanism characteristic of hot spots and subduction zones.
Mac grew up in California and attended the U.S. Military Academy at West Point, N.Y., for his undergraduate studies. He had a great sense of humor and a wry wit and always prided himself on having been in the last West Point class that, to graduate, had to demonstrate its prowess leading a cavalry charge while wielding a sword on horseback.
From West Point, Mac took his young family in 1950 to Nicaragua, where he tried his hand running a coffee plantation that he and his crew hacked out of the jungle.
It was in Central America where Mac happened upon University of California, Berkeley, volcanologist Howel Williams, who convinced Mac to leave the coffee plantation and join him in the Bay Area for his doctoral studies in 1957. Upon completing his dissertation in 1961, Mac joined Scripps Institution of Oceanography in the earliest days of the study of plate tectonics.
An Original Thinker
When the University of Oregon came looking for the first members of its newly conceived Center for Volcanology, Mac answered the call, becoming the center’s first director in 1965 and remaining at this institution for the next 5 decades. Under Mac’s leadership, the center’s research soon put the University of Oregon on the global map of volcanology and petrology research powerhouses. Among Mac’s best-known work in the center’s early years were experimental studies of the physical properties of igneous rocks and their melts and classic field studies of the Skaergaard layered mafic intrusion in East Greenland. His investigations of the volcanoes of the Galápagos Archipelago, an outgrowth of a 60-scientist expedition to the Galápagos Islands in 1964, resulted in the publication of Geological Society of America Memoir 118 [McBirney and Williams, 1969], a classic study of ocean island volcanism and petrology. Mac was a brilliant and original thinker and was ahead of his time in many ways. He was among the first to interpret heat flow observations at mid-oceanic rises in terms of magmatic intrusion [McBirney, 1963] and to propose that dewatering of subducting slabs likely fluxes melting in the mantle wedge overlying subduction zones [McBirney, 1969].
In the 1960s and early 1970s, Mac recognized the lack of good data available to describe key physical properties—like viscosity, surface tension, density, and thermal conductivity—of igneous rocks and their melts. His 1973 paper with T. Murase [Murase and McBirney, 1973] reporting their laboratory measurements went a long way toward rectifying the data shortage and remained very influential throughout the 1970s and 1980s.
Mac was particularly well known for his recognition that geochemical stratification could develop in magma chambers via sidewall crystallization, thus initiating doubly diffusive convection—an understanding he developed using the Skaergaard intrusion as his type example. He built on this work in proposing that such crystallization could result in fractionation of liquid from crystals at a time when more scientific attention was given to the opposite scenario [McBirney et al., 1985]. Indeed, he played a major role in fostering recognition of the importance of fluid dynamics in igneous petrology, well illustrated in his landmark and paradigm-changing paper with R. M. Noyes [McBirney and Noyes, 1979].
Contrary and Controversial
Mac enjoyed a good argument and was sometimes a contrarian, often delivering his views tongue in cheek with a twinkle in the eye. Many igneous geochemists will remember his fictive 1973 manuscript poking fun at trace element analyses, “The Holmium-Thulium Ratio of Kuselite and Seafloor Spreading,” written under his nom de plume, Derek Bostok, and published in Transactions of the Philosophical Society of Agua Blanca, an imaginary society inspired by a night Mac and Howel Williams spent in a dingy Central American jail cell after being detained for lacking proper identification.
On a more serious note, Mac provoked enormous controversy with his later studies of the Skaergaard intrusion, pointing out [e.g., McBirney and Sonnenthal, 1990] that many of the outcrop- and grain-scale features appeared inconsistent with crystal fractionation by settling or gravity currents, upending a generational paradigm. Instead, he proposed that many of those features were created by near-solidus material transfer (metasomatism) and self-organization.
Mac was of another generation and will always represent for many of us one of the last members of a golden age of exploration. He was a man of many talents and wide-ranging interests. Outside of science, Mac was a skilled cabinet maker, a model train enthusiast, and an accomplished bookbinder well versed in the old ways of the craft. His facility with languages—English, French, German, and Spanish—enriched his travels and led to many international collaborations and several highly regarded translations, including F. A. Fouque’s 1879 book on Santorini: Santorini et ses Eruptions [Fouque, 1999].
Mac’s influential textbook, Igneous Petrology, now in its third edition [McBirney, 2006], introduced generations of students to his insightful approach to igneous processes. He was the founding editor of the Journal of Volcanology and Geothermal Research and was a fellow of AGU, the Geological Society of America, and the American Academy for the Advancement of Science. In 1990, he was awarded the Bowen Award of the Volcanology, Geochemistry, and Petrology section of AGU.
Mac is survived by his wife, Carmen, and daughters, Anne and Christine.