GEORGE WALKER was an internationally renowned geologist whose discoveries underpin much of our modern thinking about the function and structure of volcanoes.

He was born in London in 1926, and brought up mainly in Northern Ireland. He took a BSc and MSc in geology at Queen’s University Belfast, and a PhD in mineralogy at Leeds University in 1956, by when he already had a lectureship at Imperial College, London for two years.

Walker’s earliest scientific achievements were in mineralogy but related to volcanic rocks. As part of his doctoral studies he recognised and mapped secondary mineral zones in the lava flows of northeastern Ireland. Apart from discovering several new minerals, his research yielded a series of papers on the burial and alteration of lavas, published in 1951-1960. Through this he developed a reputation as an outstanding mineralogist.

In the 1960s he worked for many years on the volcanic rocks of eastern Iceland. Having established a link between the concentration of different zeolite minerals in basalt rock and the depth at which it had been laid down, he mapped a considerable portion of Iceland, showing the structure of the upper parts of the Earth’s crust. He showed how dyke swarms in eastern Iceland were produced during crustal spreading, a discovery which lent weight to new ideas about plate tectonics. His research greatly advanced understanding of the geology of Iceland, which awarded him the Order of the Falcon in 1977.

By the mid-1960s he was also working on Mount Etna in Sicily, a frequently active, lava-producing volcano, and proposed radical views on the importance of viscosity to flowing lava, including the first attempt to explain what processes limited the length of flows.

A lengthy visit to India in 1969 to study the much older Deccan Trap lavas led to the concept of compound lava flows, which was adopted as a major concept in volcanology.

About 1968 Walker began to expand his interests to explosive volcanism. It is perhaps in this field that he made his greatest contribution. His classic papers on the fundamentals of modern quantitative volcanology are numerous, and from 1971 he revolutionised the understanding of explosive volcanism by moving away from qualitative and descriptive analyses, making it instead a quantitative science.

In 1978 Walker left Imperial College and took up a Captain James Cook Research Fellowship of the Royal Society of New Zealand based at the University of Auckland, from where he began his work on the young Taupo Zone volcanic rocks. He discovered evidence of low aspect ratio ignimbrites — deposits of particularly violent eruptions. He also uncovered evidence for ultraplinian eruptions, the most explosive volcanic events.

In 1981, Walker accepted the new Macdonald Chair in Volcanology at the University of Hawaii, and in that decade his interests returned to lava-producing volcanoes. He continued his highly innovative research, focusing on the evolution of basaltic volcanoes and dynamics of basalt lava flows. He retired in 1996 and returned to the UK to live in Gloucester. He also held an honorary professorship at the University of Bristol.

Walkerwas elected a Fellow of the Royal Society in 1975, and an honorary Fellow of the Royal Society of New Zealand. He also received an honorary doctorate from the University of Iceland. He won the Thorarinsson medal from the International Association of Volcanology and Chemistry of the Earth’s Interior (the highest award in volcanology) and the Wollaston Medal, the highest award of the Geological Society of London.

He was a brilliant teacher and devoted much time to nurturing young scientists. His first love was for field geology, and he liked nothing better than to show students how to read the rocks on field classes. He was supremely fit, and carried on fieldwork into his seventies. In Hawaii he spent considerable time at schools talking about geology and volcanoes, and leading field trips for many non-specialist groups.

He trained many distinguished volcanologists and petrologists and he encouraged many scientists from the developing world, where most active volcanoes are located. Walker was devoted to geology and much of his work was done on a tight budget, sometimes at his own expense.

He was a quiet man, who never sought the limelight, and a devoted husband and father. He leaves his wife Hazel, one daughter and one son.

Professor George Walker, FRS, volcanologist was born on March 2, 1926. He died on January 17, 2005, aged 78.