The Cascades

1. The Cascades By: Theresa Zajac & John Solder

2. Geography & Climate • Extends 700 miles N-S • Lassen Peak to Lytton Mountain • West Slope – 150 inches • East foothills – 9 inches • Temperate rain forest to alpine • Mount Rainier 14,411 ft http://www.skimountaineer.com/CascadeSki/Images/CascadesMap.jpg

3. Geology • Cascades- volcanics • Western Cascades • Eocene & Miocene • High Cascades • Pliestocene • North Cascades • Western • Greenschistfacies Meta-sedimetary &Meta-volcanic (Paleozoic to Mesozoic formation and Paleogene metamorphism) • Metamorphic Core • Epidote-Amphibolite facies meta-volcanic and meta-sedimentary (Mesozoic) • Methow • Oceanic sandstones and shales (Mesozoic back-arc basin)

4. Tectonics • Juan de Fuca and Gorda plate subduction is source of modern volcanism and seismic activity. • N. Cascades trisected by N-S running faults. • Paleomagnetic data suggest rotation and northward movement of Cascades.

5. Crust and Lithosphere • Oregon- high heat flow, >80 mW/m^2 • Wash.- low heat flow, <40 mW/m^2 Gao, 2011

6. Chronology • 500-200 m.y.a - North Cascades plutons implaced • 100 m.y.a –Farallon Plate begins subducting beneath N. America • 90 m.y.a. –Terranes accreted onto N. America • 36 m.y.a. - Cascade Range volcanism begins • 5-7 m.y.a. – After lull in activity, Cascade volcanism resumes, forming High Cascades. • 4-7 m.y.a – Juan de Fuca separates from Explorer plate, steeping subduction angle of Juan de Fuca, prompting the folding of the N American plate and uplifting of North Cascades • May 18, 1980 – 31 years ago – Mt. St. Helens ERUPTS!!!!