By: Theresa Zajac & John Solder
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Transcript of By: Theresa Zajac & John Solder
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!!!!