In 1991, while conducting avalanche research on Mount Unzen in Japan, Glicken and fellow volcanologists Katia and Maurice Krafft were killed by a pyroclastic flow.

Despite a long-term interest in working for the United States Geological Survey, Glicken never received a permanent post there because there was a hiring freeze for federal agencies when he graduated with his PhD.

While conducting research from sponsorships granted by the National Science Foundation and other organizations, Glicken accrued expertise in the field of volcanic debris avalanches.

[12] After the eruption, Glicken went to Toutle High School, the center for relief efforts, where he joined Air Force Reserve Rescue Squadron officials in a helicopter to look for Johnston or any sign of his post.

[18] Glicken and a team of geologists mapped the debris field left over from St. Helens's structural collapse, which consisted of roughly a quarter of the mass of the volcano.

Through extensive, meticulous analysis, the team traced the origins and the means of movement of each piece of debris, ranging from blocks 100 yards (91 m) in width to mere fragments.

[19] With his group, Glicken compiled a landmark study in the field of volcanic landslides, establishing the principle that tall volcanoes have a tendency to collapse.

[19] The study garnered praise for its unique conclusions and attention to detail, [20] inspiring volcanologists to identify similar deposit mounds at volcanoes around the world.

After the findings from his dissertation were published in several shorter articles throughout the 1980s,[21] Glicken earned recognition as the first geologist to explain the creation of hummock fields near tall volcanoes.

[20] In the years following the eruption, activity at Mount St. Helens diminished, prompting USGS to reduce CVO's budget and contemplate closing the station.

[23] From 1989 to 1991,[24] Glicken continued his volcanological studies in Japan as a postdoctoral fellow at the Earthquake Research Institute of the University of Tokyo, supported by grants from the U.S. National Science Foundation.

He had already defined the criteria for debris avalanches on the slopes of volcanoes, and authored several publications on the subject; Swanson named him one of the foremost experts in the field.

It was later published in 1996 as a single report by his acquaintances Carol Ostengren, John Costa, Dan Dzurisin, and Jon Major, among others, at the United States Geological Survey.

[3] United States Geological Survey co-worker Don Peterson adds that Glicken was keen in his enthusiastic approach to observation, and praises his accomplishments throughout his career and as a graduate student.

[21] Reflecting on Glicken's body of work, USGS employee Don Swanson names him as "a world leader in studies of volcanic debris avalanches".