Sample Emit on Collision Procedure

Create this in the expression editor (filtering by script Node).  It's what I used for my avalanche.

global proc mySnowProc(string $particleName, int $particleID, string $objectName)
{

//float $pos[] = `getParticleAttr -at position $particleName.pt[$particleID]`;
float $pos[] = `particle -at position -id $particleID $particleName -q`;

//float $vel[] = `getParticleAttr -at velocity $particleName.pt[$particleID]`;
float $vel[] = `particle -at velocity -id $particleID $particleName -q`;

//print($pos[0] + " " + $pos[1] + " " + $pos[2] + " " + $pos[3] + " " + $particleID);

int $i;
int $MaxNumParts = 4;
float $velScale;
float $posScale;
string $emitCmd = "emit -object snowDust ";
for ($i=0; $i<=$MaxNumParts; $i++)
{
$velScale = 1;
$posScale = rand(-.3, .3);
$emitCmd += "-pos " + ($pos[0]+abs(3*$posScale)) + " " +($pos[1]+$posScale) + " " + ($pos[2]+$posScale) + " ";
vector $v = $velScale * << 2*$vel[0]+$posScale, $vel[1]+$posScale, $vel[2]+$posScale>>;
$emitCmd += "-at velocity ";
$emitCmd += "-vv " + $v + " ";
}
eval($emitCmd);

//print $emitCmd;

}

}