Who is the volcanologist known for analyzing the eruptions of Vesuvius and Mt. Saint Helens?

The correct answer identifies Haraldur Sigurdsson, a contemporary volcanologist renowned for his expertise on volcanic eruptions, including those of Vesuvius and Mount Saint Helens. Sigurdsson's research and analysis provide critical insights into the behavior and impact of these volcanoes, utilizing modern scientific methods to understand their eruptions and potential hazards.

The other figures mentioned, while notable, do not fit the criteria of volcanologists focused on such analyses. Pliny the Elder, for instance, is historically significant for documenting the eruption of Vesuvius in 79 AD but did not have the formal training or contemporary scientific background that characterizes modern volcanologists. Vitruvius, primarily known for his works on architecture and engineering, and Pliny the Younger, who also recorded the eruption events but in a literary context, do not align with the specialized field of volcanology that Sigurdsson represents.