erupting volcano
A volcano that is currently erupting or in a state of eruption. Used in geology and news reports.
A large amount of volcanic ash is erupting from the erupting volcano.
休火山 is a dormant volcano, not currently erupting but could become active again, contrasting with 噴火山 which is actively erupting.
Compound of 噴 (ふん, 'erupt') + 火 (か, 'fire') + 山 (ざん, 'mountain'). The reading ざん is a rendaku form of 山 (さん).