Mount Lancia Eruption

The eruption of Mt. Lancia was one of the most devastating events in the history of the island currently known as Liraj A'Talvo. The volcano spewed not lava and ash, but a massive, heavier-than-air cloud of toxic gas across the city and the neighboring islands. Animals and people on the surface perished almost instantly, depopulating the city in a few short hours and leaving the magical research on modern-day Kanan A'Talvo unattended.
Like so much on Plavithen, the gas was supernatural in nature, as is the volcano. The gas was the same type that is summoned by a cloudkill spell, but there was much, much more of it. It covered the entire island and an area hundreds of miles out from shore. The gas slew the crews of ships in the harbor and people on nearby islands before it dissipated enough to be survivable.
The worst of it was that the residents of the island new it was coming, or at least some of them did. The magical and scientific advancement of the age was able to tell that the volcano would erupt. What they got wrong was the when of it. When the mountain erupted with its lethal vapors, a set of massive warding glyphs to keep the volcano from doing exactly what it did, each over 30 feet high, were over 75% completed.
Nobody currently is sure why the estimates proved so inaccurate - Stelavorn explorers found detailed notes from the operation to ward the volcano along with estimates calling for the eruption to happen two years from the date when all of the journals in the city ended at once. The residents should have had ample time, but the volcano erupted early.
Since the Stelavorn Empire resettled the island, the volcano has "erupted" twice, and the glyphs worked perfectly, immediately dissipating the toxic gas into harmless steam. The threat is neutralized as long as the glyphs stay where they are.

Type

Metaphysical, Elemental