Published by the American Geophysical Union as part of the Special Publications Series.

The various disciplines of geodesy and geophysics grow so rapidly that it is difficult to follow recent developments outside one's particular field of research. For this reason the Union Lectures were established, in which prominent speakers review various topics in geodesy and geophysics in a way that should be understandable to their colleagues from other geophysical and related disciplines. Union Lectures, usually five at each General Assembly, were first introduced at the XVII General Assembly of the International Union of Geodesy and Geophysics (IUGG) held at Canberra in 1979 and since then have enjoyed considerable interest. To underline their importance, no other scientific events of IUGG are permitted during the time of a Union Lecture.