The X-Files: Season 2, Episode 9

2 - 9: Firewalker

With Scully back in the X-Files, Mulder and her flies to the site of an erupting volcano in Oregon to investigate the mysterious disappearances of several scientist who were studying the volcano. Mulder and Scully discover a deadly life form that can survive in the searing heat of the crater and is killing the scientists to avoid being discovered.