Geology of the Northwest

NW Stories in Stone Glacier National Park, MT North Cascades NP

NW Stories in Stone John Day Fossil Beds National Monument Gingko Petrified Forest State Park

NW Stories in Stone Columbia Plateau Mt. St. Helens

NW Stories in Stone Dry Falls State Park Puget Sound

NW Stories in Stone 1700 Quake Portland Volcanoes

James Hutton “The Father of Geology” Uniformitarianism “The Present in the Key to the Past.”

Geology of the Northwest

Scientific Method Raise question Gather data

Scientific Method Raise question Gather data Form hypothesis Test and modify hypothesis Scientific Theory Scientific Law

1.Earth’s “surface” is broken into rigid plates 2.Plates move 3.“Geology happens” where the plates interact with one another Basic Plate Tectonics

What do we mean by the Outer Part of the Earth?

Three Layers: Based on Composition LayerComposition CrustRock: Felsic & Mafic MantleRock: Ultramafic CoreMetal: Iron & Nickel

Crustal Properties CrustDensityCompositionThicknessAge Continental ~2.8 g/cm 3 Felsic (High in Silica) Thick: km Old: up to 4 Byrs Oceanic ~3.2 g/cm 3 Mafic (Low in Silica) Thin: 2-10 km Young: <200 Mys

Five Layers: Based on Physical Properties Layer“State” LithosphereSolid / Rigid AsthenospherePartly Liquid / “Plastic” Lower MantleSolid Outer CoreLiquid Inner CoreSolid

Part #1 of Plate Tectonics Definition Earth’s “surface” is broken into rigid plates Surface = Lithosphere (includes Continental Lithosphere and Oceanic Lithosphere)

The Major Plates

Part #2 of Plate Tectonics Definition Plates move… …on the “plastic” Asthenosphere

What Drives Plate Tectonics? Internal Heat

How do we Know How Fast Plates Move? One Method: Mantle Hot Spots

Volcano Forms Above Hot Spot Hot Spot

Plate Moves Hot Spot Age in Million Years (Myr)

Plate Velocity Plate Velocity = Distance Traveled / Age of Volcano Age in Million Years (Myr) Distance Moved = 1000 km Hot Spot

Hawaiian Islands

Part #3 of Plate Tectonics Definition “Geology happens” where the plates interact with one another How do they interact? 1.Pull Apart from one another (Diverge) (New rock is formed) 2.Push into one another (Converge) (Rock is destroyed) 3.Slide past one another (Rock is conserved)

Divergent Boundary Results in the formation of Oceanic Crust

Examples:

Transform Boundary

Transform Example

San Andreas Fault

Convergent Boundary: Subduction Results in the formation & growth of Continental Crust and destruction of Oceanic Crust Melting Produces More Felsic Magma

Example: Pacific Northwest

Example: Andes Mountains

Convergent Boundary: Collision Results in the growth of Continental Crust

Note Alternative Names: 1. Divergent (also called Spreading Ridges, Rifts, and Mid-Ocean Ridges) 2. Transform (also labeled as Strike-Slip Faults) 3. Convergent: Oceanic-Continental (also labeled as Subduction Zones) 4. Convergent: Continental-Continental (also labeled as Collision Zones and Thrust Faults)

Volcanoes

Earthquake Distribution

Topography

Rock Age

1.Earth’s lithosphere is broken into rigid plates 2.Plates move about 1-10 cm/yr on the plastic Asthenosphere 3.“Geology happens” where the plates interact with one another along Divergent, Transform, Subduction and Collisional Boundaries Basic Plate Tectonics - Revised