It is with much sadness we record the passing on 23 June 2022 of friend, colleague and mentor Peter Molnar.
Peter Molnar
Peter Molnar. Photo credit: Roland Bürgmann

Peter was born August 25, 1943 in Pittsburgh. He attended Oberlin College, where in 1965 he obtained a degree in Physics, and Lamont-Doherty Geological Observatory where he obtained a PhD in Geophysics from Columbia University in 1970.  He followed this with a postdoc appointment at the University of California at San Diego and an exchange scientist position in the USSR before being appointed in 1974 a Professor at MIT.  He resigned from his faculty position at MIT in 1986, remaining a senior research associate there until 2000.  He enjoyed several visiting appointments at Grenoble, Montpellier, Oxford, Caltech and Santa Barbara before in 2001 accepting an appointment as a Professor in the Department of Geological Sciences and Fellow of CIRES, University of Colorado at Boulder.

Fluent in French and Russian, Peter had a legendary command of numerous displines related to the physics of the solid Earth, its oceans and atmospheres and how they influence each other.  He was one of the pioneers of Plate Tectonics close to the time of its formulation.  In 1969 and 1970, using the distinctive teleseismic signatures of major earthquakes, he and his colleagues published several data-rich articles that for the first time detailed the tectonics of the Caribbean plate, the stress changes in the lithosphere, and the state of stress in descending plates as they sank deep into the Earth’s mantle. These meticulous and lengthy articles set the scene for many of his future publications.  He went on to refine the mechanics of mountain building processes in the Andes and the Himalaya, initially using patterns from earthquakes, but increasingly from the magnetic anomalies on the sea floor and calculations of the fluid mechanics of flowing rocks deep in the Earth’s crust and mantle.  

Peter possessed an exceptional ability to learn new techniques to solve hitherto insoluble problems, not only in developing new mathematical approaches, but using new data as and when they became available.  For example, the collision velocity of India towards Asia required detailed analysis of the magnetic lineations of the Indian Ocean floor imprinted by sea floor spreading volcanism.  He and his colleagues’ analyses of these were responsible for the iconic image of India’s northward passage at rapidly declining speeds from south of the equator to the collision 50 million years ago with what is now Tibet, with the consequent formation of the Himalaya.  But the present day, much slower, rate cannot be established from these magnetic lineations. Very-long-baseline-interferometry and GPS provided him with the tools to determine not only the present day collision rate but the internal rate of deformation of Asia.  Shortly before these data had become available, he and Paul Tapponnier had examined a mozaic of early Landsat satellite imagery of Tibet and Mongolia and had recognized the exciting details of the splintering of Asia into a series of giant crustal blocks whose movements were facilated and recorded by enormous earthquakes.  

Following this Peter turned his attention to calculations of the fluid dynamics of the thickened crust of Tibet and the implications that the blocks were being translated and jostled by these slowly flowing rocks. This research direction has inspired numerous other scientists to interpret the rise of plateaus elsewhere (e.g. here in Colorado), and earned him in 2014 the prestiguous international Crafoord Prize in Geosciences.

Shortly before joining CU Boulder, Peter had realized that the “sudden” appearance of the 5 km elevation Tibetan plateau (a few tens of millions of years ago) must have changed wind patterns on the Earth and hence its weather.  Could a study of changing plants and past climates tell us about the timing of the growth of the plateau; and could Tibetan tectonics tell us about climate change? Climatologists acknowledge that their pivotal new understandings of the dynamics of the Asian monsoon are the result of Peter’s innovations. In a 2010 review paper, he and his colleagues quantified these ideas. The key was to focus on the total energy content (moist enthalpy), a simple and powerful idea that dodged the numerous variables that bogged down many climate models, which Peter disliked for their potential ambiguity.

His modus operandi was always to identify the next most important problem perceived to be arresting the future progress of Earth science.  He instilled this notion in his students and in his colleagues. He had an extraordinary ability to identify talented young scientists and to gather them together to thrash out the details of what solutions were needed to understand new geodynamic, climate or geomorphological problems.  Peter’s grasp of the big-picture was of such breadth that he could often recognize the significance of a colleague’s work better than they themselves, and could contextualize their contributions to others in a way that was both understandable and compelling. Often, he would energize colleagues to organize international meetings to get people to think about these issues. These conferences occurred in South America, in New Zealand, in China, in India and in Tibet, and they were frequently followed by week-long field trips and multipage reports that formed the basis of future collaborative proposals.

He did this with humor and with a wit and intelligence that few could match.  Young scientists in awe of his reputation soon learned that he was just a regular bloke who was really interested in them as people and was encouraging them to excel.  He would launch them in the right direction with an equation and the need to understand its solution, and he would regularly discuss their ideas and difficulties.  His office door was always open.

He seems to have read everything there was to read in numerous disciplines.  His file cabinets were full of reprints with underlined phrases and comments. His computer files were full of digital reprints with yellow highlight and if deemed of sufficient interest, often with a one or two paragraph summary of the article.  Colleagues used him as a google search engine, long before google had been established.

His home with Sara, his wonderful wife, was always open to visitors.  Very often he would invite visiting lecturers to stay with them, and there he would host generous dinners to encourage further discussion with colleagues invited to join them.  Many of our most prestiguous lecturers over the last two decades came to Boulder because of invitations from him, or for a chance to discuss science with him.

He loved walking in the mountains, in snow or sunshine.  He loved music.  He loved science.  We all loved him for all of this, and we shall miss him.

Roger Bilham 23 June 2002, with input from Philip England, Gerard Roe, David Battisti, Marin Clark, Carmala Garzione, Zhang Peizhen, Bob and Suzanne Anderson, Anne Sheehan and Craig Jones.