The Slowest Avalanche |
 Dave Thurlow, Host |
John Wayne may have talked kinda slow and walked kinda slow, but you still didn't want to get him riled up. Some avalanches are like John Wayne: they move at a leisurely pace but can pack a mean punch. Hi, I'm Dave Thurlow and this is The Weather Notebook.
The speed of an avalanche depends mainly on the slope and size of the mountain it's on. The steeper and longer the slope, the more a sliding slab of snow will accelerate. A big avalanche may cruise downhill at more than 100 miles an hour. But the speed of an avalanche also depends on the friction it encounters as it goes down the slope.
One famous avalanche slid into a ski area at only a couple of miles per hour, fast enough for a brisk walker to stay ahead of it. This bizarre snowslide happened at the Alyeska ski area just above Anchorage, Alaska, on April 12, 1969. The area had gotten two feet of wet snow that week, priming it for an avalanche. The ski control crew decided to trigger an avalanche after skiers were done for the day on the 12th. The idea was to safely release the unstable snow near mountaintop level, but things got more complicated than expected.
The avalanche encountered a mass of wet snow halfway down the mountain. It slowed to a crawl and piled up almost three stories high. The snow mass then oozed down the slope, destroying a ski lift in slow motion while dozens of people watched in amazement. The avalanche inched it's way toward the ski area's ticket office, coming to not-so grinding halt at the front door.
Robert Henson is today's writer. Georg Brandl performs the music you hear creeping like a slow avalanche into your ears. Our show is underwritten by Subaru, the beauty of all wheel drive with major support provided by the National Science Foundation.