noun
igneous activity
Geological term referring to processes related to the formation and movement of magma, including volcanism and plutonism.
この地域では過去に激しい火成活動があった。
There was intense igneous activity in this region in the past.
火山活動 specifically refers to volcanic activity (eruptions, lava flows), while 火成活動 is a broader term encompassing all igneous processes, including those that occur underground.
Compound of 火成 (igneous) and 活動 (activity). The term is a direct translation of the English geological term 'igneous activity'.