Swift Creek Landslide facts for kids

The Swift Creek Landslide is a large, slow-moving landslide in western Washington, USA. It's located near Everson on Sumas Mountain. This landslide is special because it contains asbestos, a natural mineral that can be harmful if its tiny fibers are breathed in. Asbestos can cause serious health problems, like cancer.

Scientists have found asbestos in the dirt and water of Swift Creek and the Sumas River, which flows downstream. The amount of asbestos found in the creek's sediment is often higher than what is considered safe for people working with such materials. This makes the Swift Creek Landslide an important area for scientists and local communities to watch closely.

What Causes Landslides?

Landslides happen when a large amount of earth, rock, or debris moves down a slope. In the Pacific Northwest, several things can cause them.

One big reason is the type of ground. Imagine layers of loose material, like sand, sitting on top of harder, less absorbent layers, like clay. When a lot of rain falls, the loose top layers can get very wet and heavy. This makes it easier for them to slide over the slicker, harder layers underneath.

Washington state gets a lot of rain, which adds to these conditions. Earthquakes can also trigger landslides, especially in areas like the Puget Sound. Other activities, like logging or waves eroding the land, can also play a part.

The Swift Creek Landslide might be a smaller part of a much older, larger landslide that started moving again. Perhaps an earthquake long ago caused this older landslide to become active once more.

How the Landslide Moves

The Swift Creek Landslide is quite large. It's about half a kilometer (about 1,640 feet) wide and 1.5 kilometers (about 4,920 feet) long. It goes down about 100 meters (about 328 feet) deep into the ground.

The speed of the landslide changes, but the fastest part is at the bottom, called the "toe." This part can move more than 10 meters (about 33 feet) every year!

You won't see many trees growing on the toe of the landslide. This is because it's always moving and too steep for plants to get a good hold. Trees on the sides and front of the landslide often look tilted or disturbed. This shows how much the ground is constantly shifting.

However, some trees in the middle of the landslide seem to be moving together as one big block. At the top of the landslide, there are clear cracks and steps in the ground, called "scarping." On the sides, you can see "transform faulting," which is like cracks where the land is sliding past itself.

If you look closely at the soil under the trees in the middle of the slide, it looks firm. But just outside the tree roots, you can see cracks. These cracks show how fast the landslide is moving. If it were moving very slowly, rainwater would fill these cracks. But even after rain, the cracks can be up to 1 centimeter (about 0.4 inches) wide, showing how quickly the ground shifts.

What the Landslide is Made Of

The main rock type in this landslide is called serpentinite. This rock forms when other rocks from deep inside the Earth change due to water and heat. The asbestos found here is a type called chrysotile, which comes from serpentinite.

Millions of years ago, as the Cascade Mountains were forming, glaciers or rivers might have deposited loose rocks and soil. Later, the North American and Pacific plates of the Earth's crust collided. This collision pushed up the land, forming Sumas Mountain. As the mountain slowly wore down over time, the landslide began to slip from the mountain's face to its current spot.

Around 45 million years ago, the Chuckanut Formation (a group of old rock layers) stopped forming. At the same time, volcanoes in the North Cascades were just starting to become active. This area was also greatly changed by the Pleistocene ice age, which left behind a lot of loose, unstable soil on top of the Chuckanut Formation.

Because there isn't a strong connection between the hard bedrock and the serpentinite above it, the Swift Creek Landslide can move much faster.

Environmental and Community Challenges

Every year, over 120,000 cubic yards (about 92,000 cubic meters) of dirt and rock from the landslide fall into Swift Creek. This huge amount of sediment can make the creek overflow its banks, flooding roads and homes.

To prevent flooding, the creek used to be "dredged." This means machines would dig out the extra sediment. This dredged material was even given away for free to be used in building projects, like making driveways or filling in land.

However, in 2006, the United States Environmental Protection Agency (EPA) tested the dredged material. They found that it contained up to 4% asbestos, with an average of 1.7%. Because of the possible health risks from the asbestos, the EPA suggested that the dredged material should no longer be removed and given away as it had been. They also recommended that people living nearby be taught how to avoid or reduce their exposure to the asbestos.

Some of the dredged material that was left along the creek banks was sprayed with a special green liquid called a "tackifier." This spray helps to keep the asbestos from blowing away in the wind.

There's a growing disagreement between the government and the people who live near Swift Creek. The sediment will continue to build up, eventually causing the river to flood and damage nearby properties. But because of the health risks from the asbestos, it's very expensive and difficult to safely remove and store the material.

Different government groups, from local to federal, are working together to figure out what to do. They are talking to the public about the health risks and looking for money and ways to manage the situation. Natural asbestos is found in other places in the United States, and in some areas, it affects how land can be used for building. The Sumas Mountain landslide is especially challenging because it combines flooding and sediment problems with the fact that the asbestos can move around.

Health Concerns for People

In 2006, the EPA did a study to see how much asbestos people might breathe in while doing common activities near the dredged material. They had people rake, run, bike, and dig in the material while measuring the asbestos in the air.

Using this information, the EPA estimated the risk of cancer for adults and children doing similar activities. In some cases, the risk was higher than 1 in 10,000. Many health agencies consider this level of risk serious enough to require action.

In 2008, the EPA collected samples outside some homes where people had used Swift Creek dredged material for driveways or pathways. They found asbestos levels as high as 6% in these areas.

Because of these findings, in September 2008, the Whatcom County Health Department and the Washington Department of Health issued a health warning about Swift Creek.

In January 2009, during heavy rains, the Sumas River flooded. After the floodwaters went down, they left behind sediment. The EPA tested this sediment, as well as streamside dirt and water, in 14 different places. Some sediments contained up to 27% asbestos, and the amount of asbestos in the surface water was higher than federal drinking water safety standards.

That July, the Whatcom County Health Department and the Washington Department of Health updated their health warning to include the northern part of the Sumas River.