Thursday, April 23rd, 2009
So, while much of the world was going about its business, I was cooped up inside an architecturally insipid hotel downtown listening to interesting and not so interesting papers on archaeology. Last night’s crop was really good, today’s more mundane….
The picture is of a “slide” someone put up (in these days of Keynote and it’s awful MS imitator, they’re no longer slides, but what to call them?), showing a huge erosional gully. The ladder is 4 m tall—that’s 13 feet. And the soil at the height of the guy standing on the ladder was deposited maybe AD 1400, so all that soil above his head was deposited in the last 500 years, then the whole mess suffered the erosion that made the eroded face we’re looking at. If that makes sense. (The soil at the bottom dates to about 7500 BC or so. That’s one heck of a lot of soil when you consider there’s a whole modest valley with this kind of deposition!)
Lesson: if you’re going to take away the vegetation in a mountainous region with friable soils, either maintain the ground surface or watch it wash away. There’s no middle ground.
*…and somewhere nearby I’m sure there’s plenty of red soil eroding (whosh!), too….