Professor George Walker FRS was a principal pioneer of modern quantitative volcanology and widely regarded as one of the foremost volcanologists of the twentieth century, or, as he was also described, one of the fathers of modern volcanology. His special expertise was in explosive volcanology, and particularly pyroclastic deposits generated by volcanic explosions. This eminence was based on an interest and expertise, as well as a considerable enthusiasm for fieldwork, which took him all over the world, and which sprang from his teenage interest in geology and mineralogy, which originated in his teenage years in Ulster, fascinated as he was by the volcanic mineralogy of County Antrim.

Though born in London he moved at the age of 13 to Northern Ireland where he was educated at Wallace High School, Lisburn; he spent a lot of time in the quarries and outcrops of Antrim collecting minerals, making his own maps and geological sketches, and studying minerals in the Ulster Museum. After Wallace, he entered Queen's University, Belfast, where he graduated BSc in geology (1948), followed by an MSc, also in geology and also at Queen's (1949). In 1951 he was appointed Assistant Lecturer at Imperial College London, and promoted Lecturer in 1954. During this time he was working on his doctoral thesis at the University of Leeds; this was based on his study and knowledge of secondary zeolite mineral zones in the basaltic lava flows of County Antrim - in fact, he discovered several new minerals - and his PhD was duly conferred in 1956. Throughout the 1950s, a series of articles on the burial and alteration of lavas cemented his reputation as an exceptional mineralogist.

He then turned his attention to what became seminal studies of the geology of east Iceland. Starting with his interest in zeolite minerals, which often grow in the interstices of lava flows, his method, which was thoroughly practical and quantitative and involved a lot of fieldwork, which he carried out with considerable energy and enthusiasm, he mapped the entire geological structure of much of the east coast of Iceland. He found that distribution of zeolite minerals was directly related to the depth of lava flows. His research here brought him to study sea-floor spreading, then a new field, and plate tectonics; he revolutionised understanding of Icelandic geology.

Already in the 1960s, he was becoming interest in volcanoes, beginning with lava flows. Ever the fieldworker seeking quantitative data, he went to Italy to study the rheology of lavas (that is, lava flows) of the live volcano, Mount Etna; and to India to the Deccan Traps, one of the world's largest volcanic regions. During the 1970s, he concentrated more and more on younger active volcanoes, in the area known as explosive volcanism, widening and deepening understanding of the morphology of volcanoes, the relationship between the geology of pyroclastic deposits (that is, cooled lava) and the eruptions which formed them, and suggested new methods of assessing volcanic hazards.

In 1978, although by now Reader at Imperial College, he resigned to take up a Captain James Cook Research Fellowship of the Royal Society of New Zealand, based at the University of Auckland. These Fellowships are designed to allow outstanding scholars to "concentrate on their chosen research for two years without the additional burden of administrative and teaching duties", a special attraction for Walker, the dedicated and highly assiduous fieldworker, as he was not at all interested in administration (although as a teacher he was held in the highest regard). He made a special study of young volcanic rocks in the Taupo Zone, central North Island, especially regarding the what he found to have been the particularly violent volcanic eruption which occurred in recent geological time under present-day Lake Taupo. Such explosions are known as Ultraplinian (that is, even more violent than the eruption of Vesuvius which caused a pyroclastic flow to smother Pompeii in 79 AD, as described by Pliny; a modern example was the famous Krakatoa eruption of 1885). Walker found evidence of low aspect-ratio ignimbrites, by studying deposits from such enormous explosions.

In 1981, he became the first occupant of the new Gordon MacDonald Chair in Volcanology at the University of Hawaii. He reverted to his interest in lava-producing volcanoes, particularly the evolution of basaltic volcanoes and the dynamics of basalt lava flows. In 1996 he retired and settled in Gloucester, though his was a retirement of the Active type, and he continued research as a visiting professor at the University of Bristol.

Walker was, academically, very much a field geologist, interested in simple though systematic field observations and logical deduction from these. He covered a lot of ground, travelling all over the globe: his carefully maintained records showed that he visited 30 volcanoes in 15 countries. A man who prioritised work, even over food and sleep where required, he was supremely fit, and could out-hike groups of students on field trips - and there very many of these - into his seventies. He was a brilliant and devoted teacher, respected and held in great personal affection; not just at University or other specialist levels - in Hawaii, for example, he frequently visited schools, where he would attempt, often successfully, in imbuing pupils with some of his profound interest in his subject. He was encouraging also of upcoming professional geologists and volcanologists, not least those in developing countries, where most volcanoes are found. His scholarly legacy, in terms of publications, was considerable, including a stream of academic papers.

His awards and distinctions list was second to none: Fellow of the Royal Society, 1975; an honorary Fellow of the Royal Society of New Zealand. He was awarded the Icelandic order of the Falcon (the Hin íslenska fálkaorða), Knight's Class, conferred on him by the President of Iceland. Also in Iceland, in 1988, he was awarded an honorary doctorate from the University of Iceland and made an honorary professor in the University. This was quid pro quo, in a way, as the citation stated that he had done more for the study of Earth Sciences in Iceland than anyone else, while Walker for his part declared that Iceland taught him geology and that the eruption of Surtsey (1963-1967) was the main influence in turning his interests to volcanology.

He won the Thorarinsson medal from the International Association of Volcanology and Chemistry of the Earth's Interior (the IAVCEI, the highest award in volcanology) and the Wollaston Medal, the highest award of the Geological Society of London. And not least, the highest esteem of his professional peers: his obituary issued by the Geological Society described him as "one of Britain's most outstanding geologists of the last few decades and one of the world's most influential volcanologists." The Hawaiian Volcano Observatory obituarised that "such was his impact that the majority of volcano scientists refer to some fundamental aspect of his work in almost every piece of research they carry out."

He died at Gloucester, survived by his wife Hazel, who was also his devoted assistant throughout his career.

Born:	2 March 1926
Died:	17 January 2005