subterranean
A dormant volcano is a volcano that is "sleeping," for lack of a better term. It is a volcano that is not currently active.
a dud
EROPSHIN
Crypt.
aquifer
Crypt.
vulcanologist which is a speciality of geology
A Den. Cave. Underground lair
The matter thrown out of a volcano while it is erupting is called lava, and it consists of melted rock matter. Before erupting, the lava moves underground towards the opening of the volcano. When it is underground like this, it is called magma.
Lava, which is melted solids from the underground
No mines. But there is an underground chamber in Arturus. And the volcano passages are underground. (see related questions)
The underground pressure inside of the volcano built up and finally exploded. It was looking for a pathway with the least resistance and the volcano's central lava tube was it.