Liquefaction is a very interesting, and earthy, problem. The word is usually connected to earthquakes, with a dirt and water mixture shaken to produce a slime. But it happened the other day in California. They called it a mud slide, but the result was the same -- vehicles encased in solid dirt.
See some amazing photos at Dailymail.co.uk in 'A raging river of mud': Hundreds of cars and trucks completely CONSUMED by 6ft-deep California mudslide. My favorite is the one showing two guys standing on solid soil looking down at a tractor trailer half consumed by the earth.