Mentolat is a stratovolcano which has erupted lava flows and pyroclastic flows, and covers a surface area of . The total volume of the edifice has been estimated to be about , or . A wide caldera is filled with ice, which covered a surface area of in 2011. In 1979, the glacier covered a surface area almost 2.5 times larger. Alternatively, the caldera may be filled with a lava dome, or an ice covered lava dome. The caldera may have formed during one of Mentolat's large explosive eruptions.