EVERETT, Wash. — As commutes go, the 59-minute train trip from this suburb into downtown Seattle can be pretty sweet. The tracks, first laid in 1873, swerve between the scenic eastern edge of Puget Sound and the steep bluffs increasingly covered with houses overlooking the water.

“And this time of year” said Steve Pratt, a regular rider, “the sunsets are great.”

When you can see the sun, that is.

As Mr. Pratt knows, this time of year it often rains — a lot. And those pretty bluffs get wet — really wet. Eventually, all that water changes the alluvial soil from relatively stable to completely sodden. It also transforms Mr. Pratt and his fellow passengers. Instead of train riders, they become bus riders.

Sometimes those bluffs become so saturated that they collapse, sending earth, trees and more down onto the tracks. That halts passenger train service and forces Mr. Pratt and his fellow passengers to transfer to express buses, to once again endure (and mostly shrug off) a topographical drama less spectacular but far more common than the potentially deadly earthquakes, avalanches and tsunamis that loom in anxious minds across the Pacific Northwest: mudslides.