Geology of Washington A very interesting state, indeed!

Earth Basics Planetary Structure Lithosphere (Crust) Mantle (Liquid) Outer Core (Liquid) Core (Solid) Lava Lamp Convection style currents within mantle

Tectonics Geology’s Unifying Theory

Continental Arc Subduction zone is close to continental crust (21 to 30 miles thick)

Island Arc Subduction zone is beneath ocean crust (4 to 5 miles thick)

Building Blocks of Washington Timeline approximately 200 million years Terrane Belts: Small crustal plates that combine with larger crust These belts are exotics— they have come from far away. Some are ocean belts of plate raised up, and others are volcanic island chains that were added to N. America Each addition created subduction and continental arcs

Intermontane Volcanic Island Chain A series of volcanic islands, like Hawaii or Japan were forced onto the North American plate around Spokane These islands are welded on, and end about where Twisp and the Methow valley is today

Insular Belt Insular Island Chain This island chain was too big to subduct, so it just welded on to Washington This chain makes up western BC, Vancouver Island, and Washington north of the Skagit River Coast Range Arc built many of the North Cascade volcanoes

Melange Belt French word for a mixture or medley of vegetables Broken Plate The plate responsible for the Insular islands broke up Plate from N. California broke and moved north Melange belt is jumble of rock scraped north by the moving plate Jumble of rocks were scraped on top of Insular Belt by passing plate

Crescent Basalt 50 million years ago Massive ocean lava flow off coast of WA and OR Tectonics jam it into area as Olympic peninsula and Western OR

Almost Modern Times 5 to 7 million years ago Cascade/Olympic Mountains The Cascades and Olympics are fold mountains They are created by the tremendous pressure caused by subducting the Juan de Fuca plate off the coast Eastern OR and WA will be flooded with lava flows as well

Today Juan de Fuca plate is being over-ridden by N American plate Subduction zone is off the NW coast Responsible for volcanoes and earthquakes Major danger of tsunamis

Mt Rainier North America’s most dangerous volcano Active hydrothermal system vents sulfer—with water forms H 2 SO 4 25 glaciers on Rainier Lahars—60 large in 10,000 years (500 years since last major) Osceola took off top, went 100 miles to Sound (5,600 years ago) 150,000 people live on mudflows atch?v=N_cyG2dJPpc atch?v=N_cyG2dJPpc

The Ice Age Cometh

Puget Lobe

Puget Lakes Light Blue (Fresh Water) Dark Blue (Salt Water) The Sound was not open to the ocean Whidbey Island was much larger and blocked ocean water from entering the area Fresh water lakes filled the area of the Sound today You could walk from Tacoma to the coast

Extent The Puget Lobe was about 3000 feet thick Extended from Cascades to Olympics Went as far south as Centralia

Aftermath The enormous ice sheet became a very effective bulldozer, scoring out the Sound The ocean connected with the Sound after chunks of Whidbey were ground away Glacial lakes spread a layer of clay throughout the Sound Retreating glaciers left a layer of till, many feet thick

Soil Composition Till on Clay Clay (superfine soil with low permeability) above bedrock Glacial till (loosely packed, highly permeable) over the top Water soaks through till, collects and runs down clay Creates slip zones (wet clay acts like a lubricant) Washington leads the nation in mudflows or slides Till is very unsteady in earthquakes (turns to jelly) Glacial Till

Glacial Floods

Lake Missoula

Polson Lobe This lobe covered the mountain valleys of western Montana Clark Fork river drains western Montana— with the block, a lake the size of two Great Lakes formed Ice dam breaks and greatest recorded flood flows across ID, WA, OR

Missoula Floods Harlen Bretz wrote in the early 20’s, but unproven until the 50’s The water was 400’ tall, moving at least 45 to 80 mph Floods west to Wenatchee and south to central OR

Results E WA scoured like a beach Dry Falls largest we can find Erratic's all over water’s path Provides perfect template for study of Mars