The Ancients specifically designed their shield to be used intermittently. Continued use would reawaken the volcano. The Taranians who settled did not correctly interpret the Ancient machinery they were accustomed to using and kept the shield on continuously, causing the volcano to increase in activity until it eventually exploded.
With help from the Atlantis expedition nearly the entire settlement of Taranis was evacuated before the planet's super-volcano generated an extinction-level event.
HOME TO - Uninhabited
FIRST APPEARED - Inferno
Inferno - The Atlantis expedition answers Taranis's distress call, where the people require assistance with their Ancient devices.