Thomas Augustus Jaggar Jr. (January 24, 1871 – January 17, 1953) was an American volcanologist. He founded the Hawaiian Volcano Observatory and directed it from 1912 to 1940. The son of Thomas Augustus Jaggar, Jaggar Jr. graduated with a PhD in geology from Harvard University in 1897. In 1902, he was one of the scientists that the United States sent to investigate the volcanic disasters at La Soufrière volcano, St Vincent, and Mont Pelée, Martinique, which he credited with inspiring him to make a life's work out of geology. He became head of the department of geology at Massachusetts Institute of Technology in 1906. Jaggar traveled to Hawaii in 1909, where he began fundraising to establish the Hawaiian Volcano Observatory (HVO). Jaggar became the first director of HVO in 1912, and remained at HVO until 1940, when he retired and became a research associate in geophysics at the University of Hawaii. Jaggar married twice in his life, and had two children. He died in 1953 in Honolulu, Hawaii. Biography Thomas Augustus Jaggar Jr. was born on January 24, 1871, in Philadelphia, Pennsylvania to Thomas Augustus Jaggar and Anna Louisa (née Lawrence). Growing up, Jaggar Jr. hiked with his father, and in 1875 climbed Mount Vesuvius. His father was the first Bishop of Southern Ohio. Jaggar Jr. graduated with a baccalaureate degree in 1893 and a master's degree in 1894, both in geology and both from Harvard University. After studying petrography and mineralogy at Ludwig Maximilian University of Munich and Heidelberg University, he graduated with a Ph.D. in geology from Harvard in 1897. Jaggar was named an associate professor of geology at Harvard in 1903, and, during summers, worked for the United States Geological Survey (USGS). He felt strongly that experimentation was the key to understanding earth science. Jaggar constructed water flumes bedded by sand and gravel to understand stream erosion and melted rocks in furnaces to study the behavior of magmas. As he matured as a scientist, he began to feel the increasing need for field experimentation. Jaggar wrote: Whereas small scale experiments in the laboratory helped me to think about the details of nature, there remained the need to measure nature itself. In May 1902, he was one of the scientists sent from the United States to investigate the volcanic disasters at Soufrière and Mont Pelée. With the help of the U.S. Navy and the National Geographic Society, Jaggar