I also assumed there was a layer of ice below the rocks; between the rock and the dirt which then became mud. Not exactly close! It's taken over 60 years but some guys have now recorded (video taped) the actual movements! Ice had nothing to do with making the mud slick!
Very funny, John! This is a serious scientific matter! Highly technical! I'm surprised and disappointed at the lack of respect for the ability of these men to secure funding! 
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cool story
Yes, right around 32°F, ±2°, depending on the salt content...
->Two can play this game!<-