Landslides are among the least sexy disasters. Mud and rocks are less photogenic than lava, a single event usually impacts fewer people than an earthquake, hurricane, or tsunami, and anyone who lives in big, flat places will probably never encounter one (I’m looking at you, central Australia and central North America). Yet landslides are closely tied with living somewhere with a great view, crashing down mountainsides, wiping out infrastructure, destroying homes, and killing people. The risk grows ever more problematic as more people crowd into marginal land, increasing the likelihood of landslides impacting settlements. The way around this is to prevent landslides from happening, or prevent people or structures from being destroyed by a landslide when it does happen.
At its most technical, landslides are an erosional process of solid-liquid mixtures of (spatially and temporally) variable composition engaged in gravity-driven motion with free upper surfaces and potentially erodible basal surfaces. In normal language, that means a landslide is anything that falls down slopes.
The basic requirements for a landslides are absurdly simple: a slope and gravity. Landslides may be triggered by anything (rain, earthquakes, human blasting, or even nothing!), but the basic driving force is gravity pulling material down a slope. Water increases the probability of a landslide occurring, reducing cohesion holding everything together, increasing weight, and possibly lubricating the failure surface, but a landslide can happen in totally dry material on a sunny day. Wet, rainy British Columbia with its young, spiky mountains is highly prone to landslides.
A landslide can be all one material, or a mix of rock, debris, sand, dirt, trees, boulders, telephone poles, cars, pebbles, and anything else that gets caught up in the event. The composition of a landslide can be uniform, or it can change with both space and time as more materials are scooped up and incorporated (entrained) into the flow .
The trouble with landslides is that aside from killing people and destroying things:
- Landslides are tricky to identify; and once you do,
- Landslides are tricky to prevent; and if you can’t,
- Landslide motion is tricky to predict.
Each of these aspects is interesting enough that I’ll devote future posts to summarizing the problem. Links will be added retroactively as future posts are written.