I'll be working on the 2nd image. Base on that image, I start a new document 640x480.

Now open the mud image up, on the dirt image, do a CTRL+A to select all, then go to the new document you just created and press CTRL+V to paste the image.

The cracks are dark, so we'll invert the image so it becomes white, this will give it a better explosion effect. so go to Image->Adjustment->Invert (or press CTRL+I).

Now use the eliptical marquee tool and make a large round selection on the image. Hold SHIFT while you create the selection to make a perfect round circle.

Click to view larger image

Now go to Select->Inverse,
Then hit Delete so you are left with a circle from the mud image. DO NOT DESELECT YET.

Click to view larger image

Now, while you still got your selection, go to SELECT->INVERSE again to select the shape.

Now go to Filter->Distort->Spherize. Set amount to 100%. Then do it again, this time, 50%. You can now deselect.

Now, lets fill the background layer (the layer underneath the mud layer) with black.

Then go to Layer->Flatten Image

Now go to Filter->Sharpen->unsharp Mask.
Amount: 500%. Radius: 1.7px. Threshold: 122 levels

- Go to Filter->Distort->Polar Co-ordinates.
Options: Polar to Rectangular. VIEW

Go to: Image->Rotate Canvas->90CW. VIEW

Apply: Filter->Stylize->Wind
Method: Wind. Direction: From the right. Hit CTRL+F to reapply. VIEW

Go to: Image->Rotate Canvas->90CCW. VIEW

Finally, apply Filter->Distort->Polar Coordinates.
Options: Rectangular to Polar.

There you go, now all you do is just play around with colors, by either using Image->Hue and Saturation, or Image->Color Balance.
I use color balance in the image below.

This tutorial will work for basically and image with textures such as cracks. Here are a few variations.
Before                   ----->                        After.