I am not totally sure i understand what it is you are trying to do here. So this might be way off <img src="smileys/smiley1.gif" border="0" align="middle" />
But if you want to destroy the lava(if it is a sprite or something) you can make an invisible bar where you want it destroyed, and then destroy the lava when a collision with your invisible bar is detected.
or you can use the fade behavior to fade it out.
Or use a timer and destroy it after a given time period.