I took a couple of stabs at this, but I'm still not sure the best way to go about it. I thought maybe using Don't Erase would be best, because that would let the particles leave a trail behind as they fell. That attempt ended up looking like a big brown blob. Then I tried a super emitter, but it ended up looking more like a muddy firework than anything.
Here's the "muddy firework" one if you want to have a look. The graphs I played around with most were the f-velocity over life graph, and the f-weight over life, basically trying to get the motion of a quick burst, a momentary stop, and then making the free emitters fall and leave a trail.
http://pi.shockingtales.com/ipf/mudTest.zip
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Elvis Deane!
The particleIllusion FAQ
particleIllusion Resources and tutorial CD
Astounding Adventures