How on earth did Seattle’s train tracks wind up in mudslide zones?

After a lot of rain, you might be used to hearing us say something like this on the air: “Amtrak has canceled passenger train service from Seattle to Everett for the next two days …”

Landslides on railroad tracks along Puget Sound frequently delay trains. That made KUOW listener April Isenhower curious: Why were train tracks between Seattle and Everett built in areas prone to mudslides?

“I keep hearing the reports about the tracks being shut down, and I’m like, “Man, what is the answer to this?” Isenhower said.

So, I set out to find the answer on a bridge over the train tracks at Carkeek Park in North Seattle. The wheels of a freight train squealed against the tracks as a black lab named Loki hesitantly peered on.

“Loki didn’t seem too impressed by the train," said Dave Montgomery, a geologist at the University of Washington and Loki’s owner. "If it was a Milk Bone, it’d be a different story."

On one side of the tracks is a beach. On the other side are steep slopes along the shoreline. These coastal bluffs, as they’re called, have been moving away from the water for almost 15,000 years at a rate of about one foot every 100 years, Montgomery said.

When railroad executives built these tracks in the late 1800s, they were inserting themselves into the path of a geological process that long predated them.

Part of the blame for the erosion comes from what’s in the hills: sand, boulders, clay — sediment left by glaciers.

“The nature of the materials are fairly weak,” Montgomery said. “We’re in a pretty wet region and there’s steep slopes. Those three factors are what really conspire to make the bluffs potentially unstable.”

Since 2015, landslides have disrupted or canceled passenger trains along Puget Sound on the Amtrak Cascades and Sound Transit Sounder routes over 540 times, according to data from Sound Transit and the Washington State Department of Transportation.

Around this time last year, a landslide sent dirt and some trees onto the tracks near the place where Montgomery and I stood. It covered a few feet of tracks and canceled train service.

These slides are not like the 2014 Oso landslide, a massive tragedy that swallowed a neighborhood. But they’re not always benign. Occasionally they hit a train, like in 2012 near Everett when a bystander caught a video of a lump of earth sliding down a hill and pushing freight train cars off the track. No one was hurt.

The BNSF Railway owns the tracks and doesn’t allow passenger train traffic for 48 hours after a slide. Freight trains get running again sooner.

In the past 10 years, mudslides caused five train accidents and one injury in our region, according to accident data from the Federal Railroad Administration.

Back to our listener’s question, though: What were railroad builders thinking when they put the tracks here?

I turned to historian Kurt Armbruster, who set the scene. Seattle and Tacoma were booming mill towns in the late 1800s, and Everett was getting into lumber too. Businessman James J. Hill spied an opportunity.

“(Hill) saw that the Pacific Northwest was poised to be a real economic center,” Armbruster said. “He saw that Seattle and Puget Sound would be the major gateway to the Far East.”

Hill wanted to connect the cities west of the Cascades with a railroad, Armbruster said. But, you’ve probably noticed, we have a lot of hills and it would take too much energy, machinery and people to carry all that freight up and down such steep slopes. The most efficient route would have to be flat.

“The easiest, cheapest, most efficient way to connect those cities was right along Puget Sound,” Armbruster said.

That's where the Great Northern Railway began to run in 1893. ​Armbruster said historical records don’t show the kind of frequent landslides we have now, probably because more trees anchored down the soil.

Yes, we humans are making landslides worse through development. To see an example of the problem, Montgomery and I went up the hill from Carkeek Park to a busy street, a spot once covered in trees. Clearing old-growth forest causes more landslides, Montgomery said.

“We've paved over a good portion of the upland surface,” he said. “And what happens when you pave over a surface? Rain that falls on that surface is going to run off quickly and go wherever the pavement directs it.”

Including down a steep, muddy slope and onto train tracks.

We’ve made this naturally unstable terrain a lot more unstable, Montgomery said.

Railways and government agencies are trying to make up for that. The BNSF Railway invests in preventing landslides from hitting the tracks, spokesperson Gus Melonas said. In the 1980s the company focused on Carkeek and Golden Gardens parks by increasing drainage and changing the contour of the steep slopes adjacent to the tracks. BNSF also installs walls to stop falling debris before it hits the tracks, including two such projects in Everett this year.

In 2014 and 2015, the Washington State Department of Transportation spent $18 million in federal grants to prevent landslides and protect train tracks around Mukilteo and Everett.

The state says the construction worked for those areas. In other places, the slides continue.