Supervolcanic Eruption

Volcanic eruptions are dramatic events in which magma erupts from a planet's mantle onto its surface. They're often preceded by earthquakes and the opening of fissures in the ground that vent toxic gases. These initial signs can occur months or even years in advance, making it difficult to predict the eruption's timing. While the intensity, features, and progression of eruptions vary, this hazard represents the most dangerous variety of eruption, one that can swiftly overtake cities with rapid tides of superheated gas and rock and spew out enough ash to affect the climate for years. When these sorts of eruptions are also supervolcanos, eruptions with the highest degree of explosive force, they cause unparalleled transformation to the landscape and alter climate on a planetary scale.

If you're looking for something more supernatural, it's a relatively simple change to adjust the energy damage caused by a supervolcano's pyroclastic flow to something else—for example, a cloud of ghosts erupting from a long-lost city might inflict mental, spirit, or void damage instead of the fire or electricity damage a normal pyroclastic flow brings. Just be sure to give the new event a suitable description that matches the new type of damage!