In 1906 he became head of Massachusetts Institute of Technology's department of geology. The next 10 years of Jaggar's life brought expeditions to the scenes of great earthquakes and eruptions in Italy, the Aleutians, Central America, and Japan. With each trip, Jaggar became increasingly concerned that his field studies were but brief, inadequate snapshots of long-term, dynamic, earth processes. After the 1908 Messina earthquake killed 125,000 people near Mount Etna in Italy, Jaggar declared that something must be done to support systematic, ongoing studies of volcanic and seismic activity. He traveled to Hawaii in 1909 at his own expense, and determined that Kilauea was to be the home of the first American volcano observatory. He would work on that project the rest of his life.