This effect has a lot in common with the icesheet one. The differences mostly come down to hotspot motion, source art, blend modes, the scrolling parameter for the bitmapdata, and the filter used to erase the effect over time - which might sound like a lot of parameters, but they're just that, parameters.

Download the source for this file here. You might need to right click and select "Save As". This file was saved in Adobe Flash CS5, and uses Actionscript 2.