Ring Mountain, also known as Crucible Dome, is a flow-dominated tuya (a type of volcano erupted through glacier ice). It is located at the north end of the Mount Cayley volcanic field (MCVF), between Little Ring Mountain and Slag Hill. It is a cylindrical, flat-topped volcano with nearly vertical sides at least 500 m high, and includes at least five stacked andesite lava flows sitting atop a non-volcanic topographic high. The huge slope of volcanic scree (rubble) that surrounds it makes it impossible to tell its precise base elevation, or how many flows are present. Ring Mountain formed from successive pulses of lava melting a hole through a glacier and then repeatedly flooding this hole, impounding against ice on all flanks. Based on the summit elevation, Ring Mountain’s final eruptions probably took place at or near the height of the Fraser Glaciation (25,000-10,000 years ago). A small discrete andesite lava flow lies to the northwest of Ring Mountain. It is slightly different in chemical composition from the other Ring Mountain flows, but it likely originated from a volcanic vent on or in the vicinity of Ring Mountain. It has some features indicative of eruption in contact with ice (cooling joints indicating very rapid cooling from vertical surfaces) at high elevations, but at lower elevation has features more typical of subaerial eruptions (no ice). Thus, this small lava flow probably erupted after the main Ring Mountain pile but at a time when ice cover was more extensive than today.

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