Issue 46: Landslides
October 6, 2022
Researchers use Earth observation data to track and analyze catastrophic landslides; and we take a look at some scenic braided rivers in New Zealand and Iceland.
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Feature Story: Landslides
Certain events are so intense that they rewrite landscapes in a single stroke and make us question the solidity of the earth beneath our feet. There are a number of geomorphological processes that fall into this category, but perhaps none are more sudden, destructive, and unpredictable as landslides. Broadly speaking, they’re what happens when a destabilized mass of rock, soil, and debris moves rapidly down a slope. With the inexorable pull of gravity as its engine, landslides transform Earth’s surface and serve as a stark reminder that the land beneath and around us is not solid, it’s fluid.
Landslides are a global threat that claim the lives of thousands each year and cost billions in damages. They occur when slope stability is compromised, but some of their common triggers are heavy rains, erosion, earthquakes, volcanic eruptions, and anthropogenic disturbance. In short, their causes are numerous and their effects horrendous. Oh, and they’re getting worse.
Climate change is aggravating some of these causes. Extreme rain events — a catalyst for landslides — are increasing in number. And while the hydrological cycle dumps more rain in some locations, it dries out others. Places burdened by drought are more prone to wildfires, which burn away an area’s vegetation and roots. This turns the soil from a sturdy sponge to a nearly-impenetrable surface, increasing the likelihood that rainfall turns into hazardous debris flows. This is what happened when an inch of rain fell within 15 minutes on the burn-scarred-mountains above Montecito.
Alright, let’s zoom back out. Landslides happen on every continent, and even every US state. Unfortunately, landslides are largely unpreventable. As long as slopes and gravity exist, landslides persist. But their hazards can be minimized. And that’s exactly the type of problem that geomorphology researchers are working on.
“We can do things now with rapidly evolving phenomena that we simply couldn’t dream of in the olden days.” That’s Dan Shugar, an Associate Professor of Geoscience and Director of the Environmental Science Program at the University of Calgary. He’s also the Director of the waterSHED Lab, which works at the intersection of climate change and high altitude/latitude landscapes. We spoke with him last week about his research and where satellites fit into the picture.
* This interview has been edited for length and clarity.
When there’s a landslide, chances are you’ll hear about it first from Dan’s Twitter account. Dan and his team rapidly assess events through a network of different satellite operators and data sources, an arsenal that allows them to be as effective and quick as possible.
“Daily revisit with high-res optical? Amazing. But in areas where I often work, like southeast Alaska, we sometimes can’t get a good view for a few days or longer due to cloud cover. But now we are absolutely spoiled for choice when it comes to different kinds of imagery, at different resolutions, and at different cadences.”
Part of his research is studying landslide’s cascading effects, like damming rivers or triggering tsunamis. During the catastrophic 2015 Gorkha earthquake in Nepal, Dan and a global network of volunteer scientists had their academic training tested in real-time.
“We were using satellite imagery from a variety of sources to map secondary and tertiary hazards, such as landslides triggered by the shaking. This was especially useful for response efforts, since we could see what was happening in otherwise inaccessible valleys. So for example, a series of landslides had partially blocked the Marsyangdi River in Nepal, and some of the satellite analysis from our group was used to brief the authorities so they could mobilize a team to investigate on the ground or by helicopter.”
Dan’s team also does post-event analysis to retrace a landslide’s course and figure out exactly what happened. “Within days of the Chamoli disaster in India last year, we were able to use sub-meter resolution satellite imagery from Planet, Maxar, and CNES to produce a really detailed geomorphic map of where the landslide and resulting debris flow had eroded and deposited material — in other words a map of the path that the flow took as it traveled down the valley. We could then compare those satellite observations to model runs using different parameters to determine what was happening inside the flow itself in terms of its physical properties.”
“The Feb 7 Chamoli landslide really drove home the point, for me, of how important daily imaging as well as pure luck can be in a disaster situation. In the mountains where the weather can change pretty quickly, having lots of images can be really important. For example, we had Planet imagery from both Feb 6 and 7, so we could begin to think about whether rapid snowmelt might have added a lot of liquid water to the slopes, effectively predisposing them towards failure.”
“But the really critical piece of the puzzle was the timing of one Planet SuperDove scene at 5:01 UTC on Feb 7, which showed a plume of dust like a snake traveling down the Ronti Gad valley. This dust train looked pretty similar to some of the videos I had seen on Twitter that morning, and I was able to piece things together, back to the landslide source. Only later did colleagues confirm the timing of the landslide as 4:51 UTC from seismic data. In other words, Planet just happened to catch the landslide in action, which was incredibly lucky. Another image from 5:28 showed the valley after the dust had mostly settled.”
There’s little you can do once a landslide gets going, so detecting at-risk zones and implementing early warning systems is crucial. Dan believes that with new Earth observation tech and digital elevation models, “we can move towards better hazard assessments that incorporate a wide area view of potentially unstable slopes. We won’t ever be able to catch them all, since slopes fail without notice, but hopefully we can identify at least some that are giving off warning signs.”
Like a number of Earth’s processes, landslides are an unavoidable part of living on the planet’s surface. But that doesn’t mean we have to sit idly by. Through researching these events we can better understand, anticipate, and react to their inevitable return. And that sounds like a logical plan to us. Because any force that can literally move mountains is one to be reckoned with.
Braided Rivers
Across the world are rivers that display braids so impressive they put the likes of challah bread and Rapunzel to shame. Braided rivers, as they’re called, contain multiple river channels with bars in between. Plus they’re usually faster, steeper, and have more sediment than your run-of-the-mill meandering rivers.
Braided rivers are often found in mountainous regions near glaciers and areas without much vegetation. Take a look at Thjóres River crashing through the Icelandic Highlands like a crack of lightning.
