ontake japan eruption case study

japan’s tectonic setting / causes

• Mt Ontake has been dormant for many years

• over 100 active volcanoes - accounts for aboit 10% of all active volcanoes in the world

• subduction zones of the pacific plate beneath continental and other oceanic plates along its margins

• junction of 4 plates - the pacific, phillipine, eurasian and north american plates. mainly located on 5 subduction-zone related volcanic arcs

• affected by frequent large earthquakes and vulnerable for tsunamis

• september 27, 2014 - the eruption was small and terminated with a short period

• on october 6, typhoon phanfone came near to the Ngano prefecture, where ontakesan is located

• volcanologists have pointed out that this was a relativley small eruption that was driven by super-heated steam and ash, rather than by lava being ejected from the magma chamber

• this made it more difficult to predict.

• there were also no signs of an imminenet eruption, such as eart movements or changes on the mountain surface.

• while some seismologists noted increased seismic activity on Mount Ontake ahead of teh eruption, they waere still unprepared for what followed and teh devastation it caused

what type of volcano is Ontakesan?

• strato-volcano

• 200km west of Tokyo

• 3000m tall - summit nearly always covered in snow

why do people live near mount Ontakesan?

• folklore associated with volvanoes - immportant to culture and tradition

• popular for tourists

responses

• rescue and recovery missions began on 28 september deploying more than 500 japenese military adn police.

• metal and landmine detectors played a role in locating victims buried under ash

• halting of some initial search and recovery efforts on 30 september owing to increased tremor the night before raising concerns then about the return of volcanic activity

• typhoon - heavy rains, a mixture of volcanic ash and rain formed into mud, making it harder for large helicopters to land near the summit

• rescure missions were halted on 15 octover due to teh wintery conditions despite people still missing.

impacts

• more than 60 fatalities including missing people - maily climbers and hikers

• pyroclastic flows extended approximatkey 2.5km along the valley at an average speed of 32km/h - the absense of burning or fallen trees in this areas indicates that the temperatures and destructive forces associated with the flow were both low.

• falling ash and boulders sufficient density to cause several minutes of total darkness

• air space in the vicinity of the eruption was closed as a precaution