4. Geology of Corvallis Area Today.
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4. Geology of Corvallis Area Today. Eugene, Spencer, Yamhill, and Flournoy formations are the remnants of the ocean sediments that once covered the area. Gravel pushed down by glaciers forces Willamette River to west side of valley. Ocean sediments.

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Eugene, Spencer, Yamhill, and Flournoy formations are the remnants of the ocean sediments that once covered the area.

Gravel pushed down by glaciers forces Willamette River to west side of valley.


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Ocean sediments remnants of the ocean sediments that once covered the area.

Faults caused by collision of the Juan de Fuca plate with North American plate. Pressure of collision cause rocks to move along fault lines (weak places in rock). Faults cause formations to displace.


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Area between the Corvallis and King’s Valley faults is uplifting, exposing 54 million year old Siletz Volcanics.


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Cartoon by Sidney Harris uplifting, exposing 54 million year old Siletz Volcanics.


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Source: uplifting, exposing 54 million year old Siletz Volcanics.

Earthquake Hazard and Risk Assessment and Water-Induced Landslide Hazard in Benton County, Oregon

Final Report

Wang, Graham, and Madin Oregon Department of Geology and Mineral Industries, June 2001


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Corvallis Fault uplifting, exposing 54 million year old Siletz Volcanics.

Lewisburg


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The Corvallis Fault uplifting, exposing 54 million year old Siletz Volcanics.

Although the fault is not currently active, in the past land to the west of the fault was rising and land to the east was sinking.

Timberhill

Walnut

Witham Hill


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54 Million Years Ago uplifting, exposing 54 million year old Siletz Volcanics.

Vineyard Mountain

Pacific Ocean

Ocean sediment

Siletz River Volcanics - Basalt

The geologic history of the Mt View area begins 54 million years ago with formation of an undersea mountain range, the Siletz River Volcanics. Vineyard Mountain is one of these peaks which are made of Basalt, an igneous rock. At this time the Oregon Coast was far to the East.


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30 Million Years Ago uplifting, exposing 54 million year old Siletz Volcanics.

Rivers dump sediment

Vineyard Mountain

Pacific Ocean

sediments

Ocean sediment

Siletz River Volcanics - Basalt

After millions of years, the undersea mountains are covered with marine sediment including sediment deposited by ancient Oregon rivers.


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20 Million Years Ago uplifting, exposing 54 million year old Siletz Volcanics.

Vineyard Mountain

Western Cascades

sediment

Pacific Ocean

SRV SRV SRV

Subduction Zone

SRV = Siletz River Volcanics

By 20 million years ago, the sediment covered mountains were “Uplifted” above sea-level by an ocean plate colliding with the North American Plate. The Oregon coast was now close to where it is today.

Melting of subducted rock leads to volcanic activity in what will become the Cascades.


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5 Million Years Ago uplifting, exposing 54 million year old Siletz Volcanics.

Vineyard Mountain

SRV = Siletz River Volcanics

Pacific Ocean

sediment

SRV SRV SRV

Corvallis Fault

Subduction Zone

King’s Valley Fault

By 5 million years ago, sediments covering the Siletz River Volcanics had eroded away – the hard basalt is more resistant to erosion than the soft sedimentary rock. The collision of the two plates results in many “faults” . The area between the Corvallis Fault and the Kings Valley Fault is uplifted, while the areas to the West and East are forced down.


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Geology of the Mt View School Area uplifting, exposing 54 million year old Siletz Volcanics.

Vineyard Mountain

Newport

Mt View

Mt Jefferson

Cascades

Coast Range

Pacific Ocean

North American Plate

Corvallis Fault

Juan de Fuca Plate

At this depth rocks melt

Subduction Zone – Place where two plates collide. Major earthquakes occur every 300 to 600 years. Last quake in 1700.

Mt View School is just East of the Corvallis Fault. The area to the West of the fault is being “uplifted” including Vineyard Mountain. The area to the East of the fault is moving down.


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The Willamette Valley is Wine Country uplifting, exposing 54 million year old Siletz Volcanics.

The most complex wines come from vineyards at the boundary between old volcanic soil and glacial deposits or old sandstone.

Siletz River Volcanics

Good vineyards require good drainage, the correct growing season, and nutrient rich soils.


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Quiz uplifting, exposing 54 million year old Siletz Volcanics.

3. Why are vineyards planted on slopes on low hills?

3. Answer: Drainage, self watering, cold air flows down, best soils are associated with weathered volcanic geological features.


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5. Collision of tectonic plates – geology in action today! uplifting, exposing 54 million year old Siletz Volcanics.


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The earth’s crust is composed of a patchwork of “plates” that move!!

Most volcanoes are located close to where two plates collide


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Quiz “plates” that move!!

4. True or False? Most volcanoes are located near two colliding plates.

4. Answer: True


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Subduction zone “plates” that move!!


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Axial Seamount “plates” that move!!

Seafloor spreading

Seafloor spreading

Juan de Fuca Ridge


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Juan de Fuca Ridge “plates” that move!!

Juan de Fuca Plate

Pacific Plate

Pacific Plate

Juan de Fuca Plate

An Ocean Ridge is where two plates are separating. At the Juan de Fuca Ridge , the Pacific plate is moving West and the Juan de Fuca Plate is moving East.


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Quiz “plates” that move!!

6. What causes the collision between the Juan de Fuca plate and the North American plate?

6. Answer: Seafloor spreading


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( like Mt Saint Helens) “plates” that move!!

Subduction

The roots of Mt Saint Helens are up to 100 km deep!

Magma comes from the Mantle which is 3000º C


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What happens at the boundary between plates when subduction occurs?

Ocean sediment scraped off the Juan de Fuca Plate by collision with the North American Plate

North American Plate

Subducting Juan de Fuca Plate



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Source: occurs?

Earthquake Hazard and Risk Assessment and Water-Induced Landslide Hazard in Benton County, Oregon

Final Report

Wang, Graham, and Madin Oregon Department of Geology and Mineral Industries, June 2001


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Source: occurs?

Earthquake Hazard and Risk Assessment and Water-Induced Landslide Hazard in Benton County, Oregon

Final Report

Wang, Graham, and Madin Oregon Department of Geology and Mineral Industries, June 2001


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Unusual earthquakes measured off Oregon occurs?

Scientists Baffled by Unusual Swarm of Hundreds of Earthquakes Off Oregon Coast

JEFF BARNARDAP News

Apr 12, 2008 16:06 EST

Scientists listening to underwater microphones have detected an unusual swarm of earthquakes off central Oregon, something that often happens before a volcanic eruption — except there are no volcanoes in the area.

Scientists don't know exactly what the earthquakes mean, but they could be the result of molten rock rumbling away from the recognized earthquake faults off Oregon, said Robert Dziak, a geophysicist for the National Oceanic and Atmospheric Administration and Oregon State University.

There have been more than 600 quakes over the past 10 days in a basin 150 miles southwest of Newport. The biggest was magnitude 5.4, and two others were more than magnitude 5.0, OSU reported.




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