Ed: All this week Massive is marking Halloween with stories of scary, witchy, and downright ghastly stories from nature. 

If you walk around an old cemetery, you might notice tombstones that have sunk into the dirt, tilted to the side, or even appeared to move across the ground since they (and their owners) were first placed. This is because these gravemarkers are heavy and the dirt under our feet is often unstable over long time periods. The tread marks left behind have inspired spooky urban legends.     

Unfortunately for those that love ghost stories, there’s a scientific explanation behind the phenomenon of moving tombstones. It’s  got the wonderfully spooky name of "downhill creep" (or soil creep), and also explains natural phenomena such as bending trees on a hillside or depressions in mountainsides. 

There is even a physics formula that explains downhill creep. Called diffusional sediment flux, this is calculated as the product of hill-slope and a value called the diffusion constant. Those values multiplied together yields the speed at which a given tombstone (or any physical object on a hill) moves over time. In addition to just modeling tombstone movement, this formula has also recently been used to calculate how erosion rates change with precipitation. 

So if we calculated this value for the average tombstone on a hill, it is pretty clear that it will always be gently moving, tombstone owner beneath be damned.