Today marks the 25th anniversary of the pyroclastic flow from Mount Unzen which claimed the lives of 43 people.
Mount Unzen is actually several over lapping volcanoes on Japan’s island of Kyushu. It was the cause of Japan’s largest ever volcanic disaster in 1792 when a lava domed collapsed and caused a mega tsunami which killed nearly 15,000 people. After this even the volcano lay silent until beginning to stir in 1989.
Seismic swarms began in the November of 89 about 10 km west of the summit and gradually migrated eastward until the first phreatic eruption a full year later in November 1990. By May 20th 1991 fresh lava began to flow from the highly inflated summit area prompting the evacuation of almost 12,000 locals.
The threat of another eruption to the scale of 1792 brought journalists and scientists alike flocking to the surrounding area to monitor the activity of Unzen and its potential threat. Sadly this curiosity resulted in the deaths of 43 when on June 3rd activity peaked due to a possible lava dome collapse. This sent a huge pyroclastic flow surging down its flanks and funnelled in to a valley point in the direction where volcanologists and journalists had set up a base at what was thought to be a safe distance, over 4.5 km, from the summit.
Activity continued well in to 1995 and over 10,000 pyroclastic flows were recorded over this period. By the end of the eruption a new lava dome was in place 1.2 by 8 km wide. Its volume was approximated at 0.1 cubic km. In total, about 0.21 cubic km of plagioclase-phyric dacite magma was erupted over the course of the eruption at peak effusive rates of 7 cubic metres per second in 1991. Over 2000 buildings were destroyed by these flows in Shimabara City alone. Matters were further complicated between August 1992 and July 1993 when heavy rains caused multiple lahars destroying a further 1300 homes along the Mizunashi and Nakao Rivers, requiring the sudden evacuation of several thousand residents.
Mount Unzen has been placed on the official decade volcano list and is one of Japan’s most highly monitored areas.
Maurice and Katia Krafft
The Krafft’s were French volcanologists and soul mates who met at the University of Strasbourg. Their love for volcanology almost reviled their love for each other. The specialized in documenting eruptions as best and often as close as possible, their end was almost inevitable.
Their most famed contribution was the documentation of Nevado del Ruiz which when shown to the Phillipine president Corazon Aquino who was then convinced to evacuate the area surrounding Mount Pinatubo before its catastrophic 1991 eruption almost certainly saving hundreds if not thousands of lives.
Over a 20 year period, when volcanology was still a relativity young science, the married couple documented hundred of eruptions. They fillmed over 300 hours of footage, took thousands of photos and published multiple books.
While in the Philippines during Pinatubo’s early stages, Maurice was interviewed by a local news agency where he told the journalist “I am never afraid, because I have seen so much eruptions in 23 years that even if I die tomorrow I don’t care.” From here they flew out to Japan where activity was picking up at Unzen. The pair perished together when they were overcome by the pyroclastic flow on June 3rd.
Harry was an American volcanologist who although was based at USGS was funded by outside organisations. He specialised in volcanic debris flows and was closely involved with research on St Helens with his doctoral thesis ‘Rockslide-debris Avalanche of May 18, 1980, Mount St. Helens Volcano, Washington‘ being recognised as a leading paper on the event.
Glicken cheated death on St Helens as he was meant to be the volcanologist on duty May 18th however swapped with his then mentor David Johnston who was killed by the blast.
Figure 1; http://raredelights.com/top-28-worlds-important-volcanoes/mount-unzen-in-japan/
Figure 2; https://curiousmatters.wordpress.com/2014/05/23/curious-facts-31-of-the-strongest-volcanoes-known-to-man/
Figure 3; https://en.wikipedia.org/wiki/Mount_Unzen
Figure 4; https://volcanogeek.wordpress.com/2011/09/20/maurice-and-katia-a-love-story/
Figure 5; https://en.wikipedia.org/wiki/Harry_Glicken
Figure 6; https://www.youtube.com/watch?v=Cvjwt9nnwXY