OSO, Wash. (AP) — Landslides occur around the world and have helped shape the Earth as we know it. They tend to garner little notice when they strike in remote, unpopulated areas, but they also have the potential to cause immense catastrophes.

Ten years ago on Friday, a landslide in Oso, located northeast of Seattle, destroyed a rural neighborhood and resulted in the loss of 43 lives. This tragic event holds the record for the highest number of fatalities caused by a landslide in U.S. history. However, it is not uncommon for landslides around the world to have devastating consequences.

Numerous fatalities have occurred this year due to landslides in Colombia, China, and Indonesia. In 2020, a landslide in Guatemala claimed the lives of over 100 people, while a previous one five years prior resulted in a death toll of at least 280. Earthquakes and volcanic eruptions have also triggered thousands of deaths from landslides.

The threat of intensified storms and wildfires caused by climate change has led to destabilized soil, heightening the risk of landslides. Unfortunately, it often takes a tragedy such as deadly landslides in California, Washington, or Alaska to bring attention to these dangers and inspire actions towards improved preparation.

Landslides refer to the downward displacement of earth and rock. They can either be triggered by natural disasters like earthquakes or can happen independently.

The type, severity, and frequency of landslides differ. Landslides are commonly classified as shallow or deep-seated, depending on whether they originate in the surface soil or deeper layers, such as the Oso slide.

Landslides, such as debris flows, are often caused by excessive rainfall. The removal of trees due to logging or fire can lead to a loss of root structure, weakening the soil. In the absence of plant absorption, rain can saturate the ground, increasing the likelihood of a landslide. Other forms of landslides include creeps, which move down slowly, and rock falls.

The state of Alaska is experiencing several triggers for landslides, including melting permafrost, shrinking glaciers, seismic activity, and heavy rains. The authorities are particularly concerned about the potential of the Barry Arm landslide to cause a tsunami in Prince William Sound if it were to occur.

According to the U.S. Geological Survey, the 1980 Mount St. Helens eruption in Washington caused the largest recorded landslide, sending out debris that could fill 1 million Olympic-sized swimming pools.

Lidar is a significant technique used for mapping, typically from an aircraft or drone, which utilizes lasers to capture an image of the Earth’s surface. This method is effective in removing any vegetation that could block the view.

The analysis revealed that the Oso landslide affected an area where previous large landslides had taken place in ancient times.

After the Oso tragedy, Washington state has recruited several staff members to focus on the mapping and examination of landslides. The geologists are sent to the field to verify the findings from aerial mapping.

“Are the trees curved or contorted? Are there fissures in the earth?” asked Mitch Allen, one of the workers in a government-owned forest near Olympia, Washington, as he and his colleague Emilie Richard carried out their duties. “It is crucial to ensure that your vision is synchronized not only with the lidar, but also with the movements of the ground surface.”

One can consult the USGS national landslide inventory to determine if their residence is located in a region that has had previous landslide occurrences. It is also advisable to confer with state authorities to inquire about any comprehensive mapping or research that has been conducted. However, landslides have the potential to affect regions that have previously been unaffected.

“We may not have enough information to accurately predict which slope will fail and which one will not,” stated Ben Mirus, a geologist from USGS.

High inclines are typically more prone to damage following a wildfire or when the soil is completely saturated.

The National Weather Service collaborates with the US Geological Survey in the western region to issue notifications when rainfall increases the likelihood of debris flow in regions affected by wildfires. A primary objective of a newly implemented federal legislation on landslide preparedness is to strengthen these types of collaborations.

Predicting landslides is considerably more challenging in unburned regions.

After landslides from Hurricanes Frances and Ivan two decades ago, North Carolina produced a map depicting areas at elevated risk of landslides during heavy rain.

In response to a landslide that claimed three lives in Sitka, a temperate rainforest in southeast Alaska, researchers created an accessible online dashboard to provide forecasts and measure rainfall intensity. It displays the level of risk for landslides in the community as low, medium, or high.

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Bohrer reported from the city of Juneau in Alaska. The Associated Press journalist Manuel Valdes contributed to the article from Olympia, Washington.

Source: wral.com