[*Cloudkill*](https://www.dndbeyond.com/spells/cloudkill) has an interesting property where the area of effect moves on its own. The spell states:

> 
> The fog moves 10 feet away from you at the start of each of your turns, rolling along the surface of the ground. The vapors, being heavier than air, sink to the lowest level of the land, even pouring down openings.
> 
> 
> 

However, we do not receive any direct ruling on what occurs when the effect encounters a solid obstacle. I can think of a number of possible rulings:

1. The effect stops and the radius remains at the point until dispersed
or the obstacle is removed
2. The gas bunches up along the obstacle leaving a line against
the wall instead of a circle.
3. The fog just disperses itself by trying to force its way
through, ending the spell.

**Are there any RAW answers to what happens when Cloudkill encounters a wall that the gas could not move through?**