Fires and Landslides
Thursday July 17, 2008
Not long ago, the mountains of California were on fire. This week, they're sending mudslides down on the villagers. Those two things are not always just a coincidence, because fires strip the ground of the shrubbery, duff and undergrowth that protect the soil from rain and runoff. Unprotected, those soils wash away when rains do come. It's all part of the great cycle, but that is scant comfort for anyone close to the mud or, in the case of Independence, California, anyone trying to drive US route 395 through town. In any case, the link of fire to flood is illustrated in the Landslides Gallery. Geology Guide photo
Comments
Fire & landslides are more intimately linked than simply removing the plants which hold things together.
I remember being taught in an undergraduate geology course that fire often alters the clay minerals present in the soil. Alas, I don’t recall which minerals are involved, but I do remember the fact that the one which forms in response to the heat of the fire is *far* more likely to cause slope failure if it gets wet soon after the fire–something about the crystal structure…
Apparently the minerals which undergo this change are prevalent in Southern California soils. As I recall, we even watched a film on the topic, so it should be easy to look up which minerals are involved if anyone is interested.
Andrew, Nice illustrations and photos of landslides. And I’m glad the fires are easing off.
R.M., I remember hearing something about clay mineralogy, also, can’t remember which clays are involved.
10 years ago or so, there was a big fire near highway 50 on the way up to Lake Tahoe. Some of the homes along the highway were burned. The owner of one of the houses rebuilt the house only to have it ddestroyed by a mud slide the next year.