How to create a "scorched area" on a 3D terrain?

i'm experimenting a bit with C# and XNA. Going through the advanced "Riemers tutorials" helped me a lot, but i want to make my terrain even better. I have a simple game where player controls a tank and destroys other buildings and tanks. I would like to somehow draw the effects of the explosion on the terrain. The effect i want can be seen in many new games, for example HERE in the lower right corner you can see two dark spots on the ground (some explosion occured there a while ago probably). This is exactly what i want to achieve.

Could someone point me in the right direction?开发者_运维问答 I think multitexturing will be needed, but when it came to this i found myself a little bit lost (all the stuff with pixel shaders...). Is this the only way? And if so, could someone help me understand how can i make it to work? Or are there other approaches? Thanks.

EDIT: Forgot to say that i'm not familiar with 3d graphics theory. Everything i know is based on brief tutorials, so a more detailed explanation might be needed. Currently i have no idea how would i draw something on an already textured surface.

You may want to check out this blog, it goes hand-in-hand with the Riemers tutorials. http://allenwp.com/blog/2010/05/06/simple-fast-gpu-driven-multi-textured-terrain/. Hopefully this can get you pointed in the right direction, there is a pretty good walkthrough here.

I haven't used XNA, but I believe what you're looking for is covered in this forum thread http://forums.xna.com/forums/p/34339/198791.aspx