Cascade Volcanism Is Back I The New Cascade Arc The Shutdown 1618 Ma Western Cascade Group volcanism stopped CRBs start up Why I The New Cascade Arc B Cascade subduction renewed ID: 530382
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Slide1
The High Cascades
Cascade Volcanism Is BackSlide2
I. The New Cascade Arc
The Shutdown~16-18 Ma
Western Cascade Group
volcanism stopped
CRB’s
start up
Why?Slide3
I. The New Cascade ArcB. Cascade subduction renewedJuan de Fuca plate (old
Farallon) subducts~2-3 Ma
Juan de Fuca Ridge offshoreSlide4Slide5
I. The New Cascade ArcC. Evidence for subduction?
Volcanoes & volcanic rocksYakima Fold & Thrust BeltSlide6
Yakima Fold & Thrust Beltseries of ridges in central & south central WashingtonRattlesnake Hills, Saddle Mtns
., Horse Heaven Hills, Umtanum Ridge, Manastash Ridgeseries of broad folds (anticlines & synclines)
a
nd thrust faults
p
ost basalts!Slide7Slide8
Yakima Fold Beltfolding & thrusting after the CRB’suplift ~3000 ft. So! What does that have to do with the price of rice?
Compressional stresses due to ?plate convergence!Slide9
I. The New Cascade ArcD. Quaternary Eruptionsbegan in Oregon & southern Washington
dominated by dark andesites & basaltsevolved into more typical
andesites
oldest ?
2-3 MaSlide10
I. The New Cascade Arcmost flows & volcanoes <700,000 years olddeep erosion by glaciers
most Cascade volcanoes 700,000-15,000 yearsSlide11
II. High Cascades Group
Snow Conesseries of isolated composite cones stratovolcanoes
defined alignment N-SSlide12Slide13
The Snow Cones
so prominent because they are built on the old WCG
also continued uplift of modern rangeSlide14
II. High Cascades Groupvolcanic histories of each
http://vulcan.wr.usgs.gov/home.html
low viscosity to high viscosity
become more
felsic
with younger eruptions
quite variable eruptive materials
tephra
/ash – lava flows – lahars
http://vulcan.wr.usgs.gov/Volcanoes/Cascades/volcanoes_cascade_range.html
Slide15
II. High Cascades GroupB. Present Day Tectonic Setting
continental volcanic arc subduction of oceanic crustJuan de Fuca &
Gorda
platesSlide16Slide17Slide18
II. High Cascades GroupC. Hazards: historic & future
Volcanic eruptionslava-steam-ash-pyroclastics
Nuee
ardents
(pyroclastic flows)
Example
: Mount
Mazama
~6950 BPSlide19
Mt. Mazama
~6950 years agoLarge eruptionCaldera collapseSlide20Slide21Slide22
HazardsExample: Mt. St. Helens youngest of High Cascades
most active last 4000 yearsSlide23Slide24
Hazards2. Lahars
volcanically related mudflowsmelting glacial ice or rainfallExample:
Mt. RainierSlide25
Mt. RainierOsceola flow ~5000 years agoEruption – crater collapse
HUGE lahar flow all the way to Kent & south Puget Sound
~70 kmSlide26
Mt. RainierElectron flow~600 years agoPuyallup -
Summner50-60 kmSlide27Slide28Slide29Slide30