What industries or government departments hire volcanologists and igneous petrologists/geochemists in the United States?
The first department that comes to mind is obviously academia, i.e. faculty or research positions at universities. However, there are many other career paths available (hopefully: there are not enough academic positions for every student completing a Ph.D...). For volcanologists, there is actually a nice site called volcanologists outside academia. As the name suggests, it compiles various testimonies about people who got a Ph.D. in volcanology but now work outside academia. They have also conducted a survey to gather more data. The results show that there are very diverse employment possibilities, including (but not restricted to):
- Outreach/science communication
- Academic publishing
- Data analysis
- Material science
- Instrument companies
I'm not sure for igneous petrologists/geochemists, but I think the possibilities are pretty close.