By background Lionel is a physicist; his doctoral thesis was concerned with the load-bearing properties of the surface of the Moon just prior to the Apollo landings. When ancient lava flows were detected on the Moon in images taken by the astronauts he was amazed to find that there was essentially no literature on the physics of volcanic eruptions that he could use to analyze these flows; as a result he has spent the last 50 years developing mathematical physical models of all types of volcanic eruption. Spacecraft data have shown that all of the silicate planets - Venus, Mars, Mercury, our Moon, Jupiter's satellite Io, and even some asteroids - have been volcanically active at some point in their lives. Comparing eruption deposits on these bodies, which differ as a result of differences in the acceleration due to gravity and the presence or absence of an atmosphere, has been a major spur to Lionel's research.