Hey Gamers! Welcome to the beautiful Summerset of Elder Scrolls Online!
Video below will show locations and discussion of the achievement!
For Abyssal Devastator you will need to tackle 50 of the abyssal geysers which are only found in the Summerset region of Tamriel, and are similar to the Dolmen's in the rest of the game (in fact they are indicated on the map with the same icon).
There are a total 6 abyssal geysers in Summerset (areas shown in the video) and entail killing several waves of enemies prior to a boss being spawned (just like the dolmens, but a different look to them). Now, whats different than the dolmens is that the bosses are actually pretty tough and difficult to solo so you will most likely need at least another person to finish these off. The number of adds depend on the number of people within the area of the geyser during its spawn.
You will need to finish 50 total abyssal geysers and then BLEEP BLOOP, achievement unlocked.
-Damron Out