May 7, 2018 update: No eruption since April 27th, per JMA, but volcanic activity continues and the crater perimeter warning is still in place.
For the first time in centuries, a small, unassuming member of the Kirishimayama Volcano group erupted this week.
No one is apparently threatened by this (in fact, another member of this group has been active for a while now). Here is more information on Ioyama and the Kirishimayama Group:
Smithsonian’s Global Volcanism page for the Kirishimayama group.
Japan Meteorological Agency page with activity updates. (I ran the JMA page in Japanese, which is updated more frequently than its English page, through a machine translator for this link, which is now in English.)
H/T to UPI