There's more than just snow that can disrupt travel on the North Cascades Pass. The North Cascades receive frequent storms moving in from the Pacific Ocean. Because of these storm events, the peaks, deep valleys, streams and rivers receive large amounts of rain and snow. Since the Cascade Mountain Range is composed of numerous materials from volcanic rock, ocean sediments and pieces of the earths subcrustal mantle, some rocky slopes are unstable. The constant freezing and thawing of these geological formations, combined with its unique weather system and naturally occurring erosion, can cause natural forces to collide into events that are destructive to the highway.
Below are stories of natural occurring events that closed the Cascades Highway in the past.
Flooding - October 2003
The week of October 16 through 21 is on record as one of the wettest weeks ever in Western Washington history. The large amount of water overwhelmed the roads, creek beds, culverts, drainage systems, and ultimately proved to be more water than the Cascade Mountains could absorb.
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Rockslides - November 2003
Without warning, a rockslide of gigantic proportions thundered down the mountainside Sunday, November 9, 2003 at 6 a.m., just east of Newhalem. The size of the landslide was estimated at two to three million cubic yards.
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Mudslides - August 2004
Sometime after 6:00 p.m., mud began sliding down the steep hillsides west of Rainy Pass on SR 20, the North Cascades Highway, blocking the roadway in three places and trapping some 65 people.
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