Continuing on...

So, I take a copy of this layer:
Click image for larger version. 

Name:	quick volcano-step4.jpg 
Views:	91 
Size:	2.5 KB 
ID:	4675

to work on.

First thing I did was play with the color curves. The previous bumpmap had a steep drop-off at the outside edge of the cone, and I wanted to soften that up. To do that, I wanted to move the blacks mostly toward grays, which means making the left-hand side of the color curve go more flat looking. I also rounded out the tip of the right-hand side of the color curve, but left most of the rest a straight line.

Then, I used the smudge tool and rubbed in and out rapidly along the ouside edge of the cone, bringing some of the lights down and the darks up, as before, but breaking up the edge of the cone as much as possible.

I also decided I wanted lava spilling out one side of the volcano, so I picked a likely spot based on the lights and darks (remember, darker is lower on the bumpmap) and made sure to smudge and blur one edge of the crater edge. I did some more clean up work around the crater. It's probable I also did some more noise>spreads and gaussian blurs for a few pixels. I didn't keep a full accounting of these. The result:

Click image for larger version. 

Name:	quick volcano-step5.jpg 
Views:	135 
Size:	2.4 KB 
ID:	4676

Then, I created a new layer filled with 50% gray, a ran a bumpmap filter using the previous result:

Click image for larger version. 

Name:	quick volcano-step5-1.jpg 
Views:	72 
Size:	4.2 KB 
ID:	4677

This layer will be set to overlay.

Next, I took another copy of the original gray blob, created a new layer and filled with Render>Clouds set to maximum detail and X&Y and created a bumpmap layer (with a lower depth than the previous bumpmaps) on to the gray blob using the noise.

Click image for larger version. 

Name:	quick volcano-step6.jpg 
Views:	77 
Size:	2.7 KB 
ID:	4678

This is also set to Overlay.

To get the original image, I had all three bumpmap layers set to overlay showing visible (I decided i needed both cone bumpmaps to make the volcano really pop) with the color layer and the green background layer all showing. The color layers need to be below the overlaying bumpmaps in the layer stack.

To finish, I create a new transparent layer above the other color layers but below the bumpmaps. I pulled up the plasma palette that comes pre-installed with GIMP, and I used this to select reds, oranges, and yellows for lava. So, using a small fuzzy/soft brush, I paint in yellows and oranges and reds in places I like (yellow toward the center, radiating outward toward reds). I do this will all the other layers showing, but on my new transparent layer. That way, I get the lava where I want it in the crater and running down the mountain. Once I have these colors in place, I do a tiny gaussian blur.

And that leaves us with the previous finished product.

To work on this a little, I went back to the mountain color layer and smudged and blurred the dark bottom edge of it. I also changed the mountain color's layer to "lighten only", which seemed to help get rid of the dark ring near the bottom.

Click image for larger version. 

Name:	quick volcano-step3-1.jpg 
Views:	85 
Size:	1.9 KB 
ID:	4680