The Cascades

By: Theresa Zajac & John Solder

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

Geology• Cascades- volcanics

– Western Cascades• Eocene & Miocene

– High Cascades• Pliestocene

• North Cascades– Western

• Greenschist facies 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)

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.

Crust and Lithosphere

• Oregon- high heat flow, >80 mW/m^2• Wash.- low heat flow, <40 mW/m^2

Gao, 2011

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!!!!