At 09:59 on May 29, Mt. Shintake (626 meters) on Kuchinoerabujima Island in Kagoshima Prefecture erupted.

すごい噴火　#噴火 #口永良部島 pic.twitter.com/mzWPhmqHnc

— チクモ (@chikumo3) May 29, 2015

I immediately rushed to check the Volcanic Ash Advisory Center website, which I introduced before. The volcanic ash reached an altitude of 32,000 feet / over 9,000 meters; this eruption was indeed powerful. Consequently, the Japan Meteorological Agency raised the volcano alert to the maximum level of 5, requiring all residents on the island to evacuate to safe zones outside the island.

http://ds.data.jma.go.jp/svd/vaac/data/TextData/2015/20150529_28205000_0001_Text.html
Volcanic Ash Advisory Text
FVFE01 RJTD 290113
VA ADVISORY
DTG: 20150529/0113Z
VAAC: TOKYO
VOLCANO: KUCHINOERABUJIMA 282050
PSN: N3027 E13013
AREA: JAPAN
SUMMIT ELEV: 657M
ADVISORY NR: 2015/1
INFO SOURCE: MTSAT-2 JMA
AVIATION COLOUR CODE: NIL
ERUPTION DETAILS: EXPLODED AT 20150529/0059Z OVER FL320 STNR
OBS VA DTG: 29/0100Z
OBS VA CLD: VA NOT IDENTIFIABLE FM SATELLITE DATA WIND FL400 330/45KT
FCST VA CLD +6 HR: NO VA EXP
FCST VA CLD +12 HR: NO VA EXP
FCST VA CLD +18 HR: NO VA EXP
RMK: WE WILL ISSUE FURTHER ADVISORY IF VA IS DETECTED IN SATELLITE 
IMAGERY.
NXT ADVISORY: NO FURTHER ADVISORIES=

Afterwards, the volcanic ash moved southeast. According to the Volcanic Ash Advisory Graphic (VAG), looking at SkyVector, there are quite a few Airways near Kuchinoerabujima, such as Y45-A582, Y25, and Y532, but fortunately, they did not affect the flights on that day.

目の前の屋久島で口永良部島噴火した。噴火警戒レベル5。ドーンって地鳴りがすごかった pic.twitter.com/nhzESpWJJE

— Oh!kawa@カムバックパラダイス (@TAKUYAbluewhale) May 29, 2015

Looking at the photo taken from a distance above, the eruption was primarily white smoke. It feels like there wasn’t much volcanic ash; it was likely mainly condensed high-temperature water vapor in the upper atmosphere.

Looking at another photo taken by a passenger from the air, the height of the smoke indeed seemed to have little impact on flight.

#飛行機 から　噴火の瞬間 #鹿児島　#口永良部島　#新岳　#爆発的噴火　#火砕流 #防災　#火山　#番屋ヶ峰　#本村港　#屋久島　#宮之浦港 pic.twitter.com/EWxHgoyNDp

— mikiya itou (@mickey228) May 29, 2015

On May 30, the RJJJ NOTAM was as follows. With an altitude of only 3,000 feet, it looked even less of a problem. 300021 RJAAYNYX (7307/15 NOTAMN Q)RJJJ/QWWXX/IV/NBO/EW/000/030/3027N13013E120 A)RJJJ B)1505300021 C)1505300620 E)VOLCANIC ACTIVITY INFO KUCHINOERABUJIMA PSN/302636N1301302E(REF AIP ENR5.3-23) VA CLD OBS AT 0000 VA CLD TOP:FL030 DRIFT DIRECTION:N F)SFC G)FL030)