So here is a very simple method to create craters and explosion effects. I do warn you, though, the tissue paper takes FOREVER to dry completely so if you need a piece of terrain immediately, look elsewhere. Otherwise if you have about ten or fifteen minutes to kill in a day and don't mind leaving it to sit for a few days, this method is ace.
Step one, cut out a frame. It can be anything. I suggest foamcore, but I use posterboard here. You're just using it so you can place the wet paper down and be able to move it around so the material isn't a huge deal.
Step two is to mix some Elmer's Glue with water (it should be mostly water. I'd say about at least 5:1 water:glue)and gather your materials. I have my paste mix, some Toilet Paper, some paper clips, an old pen shell and some super glue.
First I'll start with the crater. Simply tear of lines of toilet paper, dip in you paste substance, and create a circle with them on your base. Be sure to slope the outer edges!
Next, if you want, sprinkle on some sand to give it an extra texture.
Bam! Done with the crater construction. Now onto...
First glue your pen shell upright. This will be the main debris flying from the impact of the exploding shell on the ground.
Next, bend your paperclips and glue them around your pen shell. These will be the debris strands flying outward from the center of explosion.
Now dip small strands of Toilet Paper into your paste substance and begin to wrap it around each debris strand. Make sure you fiddle with it to make it look chaotic (like an explosion) and be sure if you have any loose strands that they point up in the direction of the debris. It is inevitable that some will fall off and some will need to be adjusted, but if you are patient it's not a big deal. The beauty of the long dry time of this paste is that it directly results in a longer work time meaning you can change anything you want for a long time after the original build.
The next step i don't have a picture for, but just like the "Crater" part of this tutorial, create a small crater directly around the debris strands. It will produce an effect as if a shell just hit the ground causing a crater and all the crap flying upwards is the displaced ground.
Now sprinkle sand on it. This will further add to the effect of ground being blown upward.
Part Two can be found here!