This is a fun bit of video on a landslide at Snake River Canyon, Wyoming. Watch until the DOT workers show up with their orange coats to give you a better sense of the speed of the mudslide:
This flow of dirt is moving down a hillside and across a highway at a rate of 50 centimeters per hour, says Dave Petley on the American Geophysical Union's Landslide blog.
The Snake River Canyon landslide is slow enough that Wyoming Department of Transportation workers can climb around on it, as it's moving. In fact, they took a video of themselves doing this. When the film is sped up, you can see the landslide in action—and see that it is actually two separate landslides moving alongside each other!
The final result...