The northrend trees are nice, but the trees would be more skeletony the closer they are to the area of eruption, you have a lot of northrend trees in areas that would have just been touched by the lava, which doesnt make complete sense
(I worded that in a wierd way, sorry if its confusing)
There are also a lot of custom tree models you can download to give it more of an island-ish feel, such as palm trees and the like. There are also a lot of dead leafless tree models that can be downloaded to replace the northrend trees.
I also agree on the use of smaller doodads to make it look like the area has jungles and not just an assortment of trees. You can look at Karzvitch's island for a good way to do this:
http://123pichosting.com/viewer.php?id=8678Island.jpg
This is just something i thought of that you could try, is add a small (really small, but still present) terrain elevation around the lava tiles. This might make them appear more like theyre spreading over the ground than being the ground. (This may not work, it is just something i thought of)
Dont forget to use Ctrl+Page Up and Ctrl+Page Down to get rid of those floating objects (adjusts the the flying hieght of the doodad, not the size).
You can use spell models as well to enhance the terrain. Dont hesitate to look through spells, buffs etc to find a good doodad model to work with.
Also, the fire seems a big too large and overtaking in the picture. Im not sure if thats how it is in a real volcano but i dont think the fire spawns out of nowhere and reachs 5 feet high
. I think it usually burns it up really fast and really quick and moves on, so the fireswould be smaller in height.
Overall, great start