noun
volcanic cone
Geological term for a cone-shaped hill or mountain formed by volcanic material around a vent.
富士山は典型的な火口丘です。
Mount Fuji is a typical volcanic cone.
この地域には小さな火口丘が点在している。
Small volcanic cones are scattered in this area.
火口 means 'crater' or 'vent', the opening itself; 火口丘 is the hill or mountain formed around it.
Compound of 火口 (crater, vent) and 丘 (hill), literally 'crater hill'. The reading is on'yomi for both characters.