What causes landslides?
EarthSky spoke with Scott Burns. He’s a geologist and landslide expert at Portland State University. He said:
It’s just like a baseball analogy. Three strikes and you’re out. Generally you’ll have a fairly steep slope. That’s strike one.
Then you have weak soils, weak geological units, rocks. And so the site is prime for failure. All you have to do is add that trigger. The third strike is generally a lot of water that has fallen rainfall in a very short period of time, or an earthquake. Three strikes, you’re out – and you have a landslide.
Burns said landslides happen all over the world.
But most of the time, people are not prepared for them. And so we get a lot of loss of life that we are just not wanting to have.
In the U.S. each year, landslides cause an average of 25 deaths and 1 to 2 billion dollars of damage, according to the U.S. Geological Survey. Burns told EarthSky:
For instance as homeowners, generally the biggest item that you own is going to be your house. And if your house if hit or slides down the hill, you lose everything.
Burns said that the next frontier in landslide science is mapping where landslides have struck in the past, because that’s where they’re more likely to strike again. He gave some advice for homeowners looking to lower their risk from landslides.
Before you build, before you buy, get a registered geologist or a registered geotechnical engineer to come out and take a look at the piece of property. Ask the question, have there been landslides before? But then also, if you’ve got a house, and it is on the side of a hill, the big thing is controlling the water. Every time it starts raining, ask, where’s the water going for my property? Where’s the water coming from your driveway or from your patio? Where is all of the storm water that’s getting collected in your gutters? Is it going into a system and then being taken away, either into a storm sewer or to the bottom of the slope?
Dr. Burns said he and other scientists are working on maps that identify areas prone to landslides.
One of the things that we would absolutely love to be able to do is produce hazard maps, to be able to show people where landslides may be happening in the future. We have an old adage. If it’s moved once, it has a higher potential for moving again. We’ve done a pretty good job in figuring out where landslides have occurred in the past. But then, what is that trigger? When is that landslide going to move? A lot of the research that is going on right now in the United States and around the world is focusing in on what causes those landslides.
Our thanks today to The Geological Society of America – where geology and people come together.