Introduction

Volcanoes and eruptions are dramatic manifestations of dynamic processes within the Earth, mostly but not exclusively localized along the boundaries of Earth's relentlessly shifting tectonic plates. Anyone who has witnessed volcanic activity has to be impressed by the variety and complexity of visible eruptive phenomena. Equally complex, however, if not even more so, are the geophisical, geochemical, and hydrothermal processes that occur underground -- commonly undetectable by human sense -- before, during, and after eruptions. Experience at volcanoes worldwide has shown that, at volcanoes with adequate instrumental monitoring, nearly all eruptions are preceded and accompanied by measurable change in the physical and (or) chemical state of the volcanic system. While geochemical methodologies of volcano monitoring have shown increasing sophistication and promise in recent decades, seismic and geodetic (ground-deformations) techniques remain the most widely used tools in volcanic surveillance. These two geophysical workhorses have proven to be robust and, generally, the most diagnostic and reliable techniques for volcanologists.

In the early 20th century, systematic measurements of ground deformation were initiated at few active volcanoes in Japan and the USA. Since then, VOLCANO GEODESY -- a specialized field of the still-young science of volcanology --  has come along way, not only in term of greatly increased diversity and precision of measurements, but also in the number of volcanic systems being monitored worldwide. There has been a virtual explosion of volcano-geodesy studies and in the modeling and interpretation of ground deformation data over the past three decades. Nonetheless, other than selective, brief summaries in journal articles and general works on volcano-monitoring and hazard mitigation (e.g., UNESCO, 1972; Agnew, 1986; Scarpa and Tilling, 1996), a modern, comprehensive treatment of volcano geodesy and int applications was non-existent, until now.