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Aug 22, 2023 45 likes •295 views

Columbia Gorge Geology and the Ice Age Floods Columbia River Gorge Near Perfection... And Only 40+ Million Years in the Making Lloyd DeKay, Ice Age Floods Institute - Columbia Gorge Chapter GorgeFloods.org Geologic Time If 1 MY = 1

SLIDE 1

Columbia Gorge Geology and the Ice Age Floods

Columbia River Gorge Near Perfection... And Only 40+ Million Years in the Making

Lloyd DeKay, Ice Age Floods Institute - Columbia Gorge Chapter

GorgeFloods.org

SLIDE 2

Geologic Time

Geology has a very long time to do its work

If 1 MY = 1”

Dinosaurs Gone = 65in Columbia River trough = ~50in Columbia River = 20in Columbia River Basalt = 17.5-14in Ice Age Floods = .018in Earth formed = 125yd BIG BANG = 1/4mi

SLIDE 3

~50-20 MYA – Oldest Gorge Records

An offshore volcanic arc, west of present-day Cascades, spewed ash eastward toward John Day Fossil Beds

John Day Fossil Beds National Monument

SLIDE 4

Proto-Cascades 50-20 MYA

Volcanic ash from these proto-Cascade volcanos blowing eastward repeatedly buried the John Day area, preserving the world's most complete record of Miocene life

John Day Fossil Beds Natl Monument

Meanwhile weathered volcanic debris washed down the arc flanks into the Columbia trough

Eagle Creek Debris Flow ~20MYA

John Day Area ~30 MYA

SLIDE 5

Columbia River Basalt 17.5-6 MYA

About 17.5 MYA volcanism shifted east to the Idaho border area, burying the Columbia Basin in 1000’s of feet of basalt

They covered 81,100mi2 to 16,000' thick
Could cover Cont. US 12'+ thick
90% erupted in first 2 MY
21 poured thru Columbia River “Gorge”
Flowed at up to 9mph
Took ~1 week to the coast

There were over 300 MASSIVE fissure eruptions that poured extremely fluid basalt from 20,000 vents, up to 30' wide and 10mi long

SLIDE 6

Stacked Basalt Layers – Horsethief Butte

Local Columbia River Basalt Features

Pillow Basalt - Hwy 197, I-84 exit south

Basalt Pillows Basalt Columns

Curved Columns Horsethief Butte Basalt Arch – Catherine Creek

SLIDE 7

Rise of the Cascades <3 MYA

Volcanism shifted west again ~5+ MYA

Columbia River downcut as the Cascades slowly rose

SLIDE 8

Shield Volcanoes Began <1MYA

Mt Defiance @ sunset Frosty Underwood Mtn

These were broad, low relief volcanos, similar to Hawaiian Island volcanos

SLIDE 9

Strato-Volcanoes Began ~500,000 YA

Mt Hood Mt Adams

Their stiffer lavas tend to build upward

SLIDE 10

Local Cascades Features

Collapsed Lava Tubes – White Salmon River

Folded CRB – Coyote Wall, SR14 east of Bingen

Lava Tubes – Guler Ice Caves, Trout Lake Bird Crk Meadows – Mt Adams

SLIDE 11

Missoula/Spokane/Bretz Floods

At the end of the ice ages,18-12 KYA, ice dams repeatedly blocked the Clark Fork River creating Glacial Lake Missoula

When the ice dams broke they released massive floods across central WA and all the way to the Pacific Ocean

SLIDE 12

Release of Cataclysmic Floods

The lake floated and undermined the ice dam, causing catastrophic collapse The floods swept away icebergs carrying encased rock that later melted out downstream as erratics.

Maybe 120 times (~every 50 years) these Ice dams broke catastrophically, releasing huge floods up to 1000' deep that raced at up to 60 mph across central WA, through Wallula Gap, the Gorge, and on to the Pacific Ocean

SLIDE 13

Floods Across the Landscape

Dry Falls

Stev Ominski

140 mi3/day poured across the eastern WA landscape It striped sediment and plucked massive blocks of bedrock behind a wall of water up to 1000’ high. It could have been felt 2 hours beforehand. It left behind massive coulees, scablands, mega- ripples and bars, even lake deposits.

SLIDE 14

Touchet Lake Beds Deposited inTemporary Lakes Huge Coulees and Scablands Mega-Ripples 30+ ft high (Camas Prairie) Massive Rolled Basalt Boulders

Evidence Left Behind

SLIDE 15

Through Wallula Gap

Wallula Gap only allowed ~40 mi3/day, forming a large temporary Lake Lewis behind it reaching into the Yakima Valley Narrower channels downstream caused more temporary

lakes. Modelling

shows it took a month for each flood to fully drain

SLIDE 16

Stev Ominski

And On Through the Gorge

Columbia River Gorge

Peter Marbach

Remember, the Gorge was already here… for the past 20 million years The floods swept away the erosional debris, leaving behind the majestic palisades and waterfalls of the Columbia Gorge National Scenic Area

SLIDE 17

Kolk Pond at The Dalles Discovery Center

Some Local Features

Whirlpools plucked bedrock

SLIDE 18

Erratics and Huge Gravel Deposits Mark Hatfield, Mosier

Streamlined Bedrock Outcrops Horsethief Butte, WA Turbulent Water-Cut Benches opposite Dalles Discovery Center

SLIDE 19

Scablands at Columbia Hills State Park, WA

Upstream Dipping Foreset Beds (Canyon Road, Lyle)

Hanging Valleys with Spectacular Gorge Waterfalls like Multnomah Falls off I-84

SLIDE 20

Missoula/Spokane/Bretz/Ice Age Floods

Challenged by Six Geology Elders

W. C. Alden

Henry Ferguson Oscar E. Meinzer

E. T. McKnight

James Gilluly

G. R. Mansfield

James Gilluly Oscar E. Meinzer

The Elders fought Bretz’s “heretical” neo-Catastrophist explanation until Joseph T. Pardee’s 1940 Glacial Lake Missoula presentation that provided the source for the floods and ended the debate

J Harlan Bretz Neo-Catastrophist in 1923

Joseph T. Pardee Proposed a megaflood explanation, but not where floods came from

A MAJOR Geologic Controversy

SLIDE 21

Landsat Confirmation

Landsat Image (1970s) Bretz Map (1930s)

Bretz’s theory was fully confirmed on Landsat images

SLIDE 22

Bonneville Landslide ~1450 A.D.

More Recent Gorge Geology

Bonneville Dam

SLIDE 23

Bridge of the Gods Indian Legend

Wy’east (Mt Hood) Pahtoe (Mt Adams) Loowit (Mt St Helens)

SLIDE 24

40+ Million Year Recap

Proto-Cascades Cascades, Ice Age Floods, and Columbia River Gorge

Mt Washington

Columbia River Basalts

SLIDE 25