Abstract
We modeled pressure sources under Mount Ontake volcano, Japan, on the basis of global navigation satellite system (GNSS) observations of ground deformation during the time period including the 2007 and 2014 phreatic eruptions. The total change in volume in two sources below sea level in the period including the 2007 eruption was estimated from GNSS network observations to be 6 × 106 m3. Additionally, data from a GNSS campaign survey yielded an estimated volume change of 0.28 × 106 m3 in a shallower source just beneath the volcanic vents. The 2007 eruption may have been activated by magmatic activity at depth. During the 2014 eruption, the volume change at depth was very small. However, tiltmeter data indicated inflation from a shallow source that began 7 min before the eruption, representing a volume change estimated to be 0.38 × 106 m3. We infer that the potential for subsurface hydrothermal activity may have remained high after the 2007 eruption.
Highlights
Mount Ontake volcano, a 3067-m volcano in central Honshu Island, Japan, has had two phreatic eruptions in recent years that were accompanied by ground deformation
The volume of the eruptive products was estimated to be 0.3–0.5 × 106 m3 dense rock equivalent (DRE) from a field survey conducted after the 2014 eruption (Maeno et al 2016), but no obvious ground deformation was detected on the day of the eruption
The global navigation satellite system (GNSS) observations indicate that deep magma migration was not associated directly with the 2014 eruption, but that existing magma under the volcanic edifice reactivated the shallower hydrothermal source that was responsible for the 2007 eruption and subsequently led to regional ground deformation
Summary
Mount Ontake volcano, a 3067-m volcano in central Honshu Island, Japan, has had two phreatic eruptions in recent years that were accompanied by ground deformation. We analyzed the changes in these geodetic positions at five sites with respect to JMANET station JMA510 and found evidence of regional extensional ground deformation in the summit area We accounted for this deformation with a shallow spherical pressure source at 1700 m above sea level (1000 m below the surface) with a volume change of 0.28 × 106 m3. This position is just beneath the Jigokudani valley south– southwest of the summit (Fig. 6), where volcanic vents were active during the 1979 phreatic eruption (VEI 2), the first eruption in recorded history. Because the results included aftereffects of the 2011 off the Pacific coast of Tohoku Earthquake, it was difficult to estimate how much of the deformation was
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
