Ash Cloud?
 

Is this causing any problems?

Volcanic Ash Advisories: RJJJ FUKUOKA FIR / KT AIRSPACE VA ADVISORY DTG: 20120410/2014Z VAAC: TOKYO VOLCANO: SAKURAJIMA 0802-08 PSN: N3135E13040 AREA: JAPAN SUMMIT ELEV: 1060M ADVISORY NR: 2012/341 INFO SOURCE: JMA AVIATION COLOUR CODE: NIL ERUPTION DETAILS: EXPLODED AT 20120410/2007Z VA CLD UNKNOWN OBS VA DTG: 10/2000Z OBS VA CLD: VA NOT IDENTIFIABLE FM SATELLITE DATA WIND FL180 260/52KT 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 IM AGERY NXT ADVISORY: NO FURTHER ADVISORIES=

I am not an expert or anything but here is what i think is happening.. hehe

I think it "might cause" cause it clearly states: COLOUR CODE: NIL ERUPTION DETAILS: EXPLODED AT 20120410/2007Z VA CLD UNKNOWN : So volcanic cloud unknown and as it is written it is still not identifiable... but it is to be "aware"
but untill +6 +12 +18 they dont expect it. but you will have to wait if volcanic ash is surely detected on IM.

I dont know if I am saying it right.. correct me if wrong..

best regards,

Australia Significant Weather (SIGWX)

Check the SIGWX chart 18z, download as pdf and enlarge to japan...

You will see the warning...

Been erupting for several weeks at least. No effects at high altitude when I've been through there.