Here is the ability description:
Creates a Fire Rune at target location for 30 seconds, dealing 18 Fire Damage when an enemy enters the area of effect. Affected enemy takes 8 Fire Damage over 10 seconds.
So, if I cast it once, does it always stay on the ground for 30 seconds? Or does it disappear once it has hit one monster? If a monster stands in the rune, does it continue to take both the area of effect damage and the DoT?