4. Geology of Corvallis Area Today.

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

Eugene, Spencer, Yamhill, and Flournoy formations are the 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.

Ocean sediments

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

Cartoon by Sidney Harris

Source: 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

Lewisburg

Corvallis Fault

The Corvallis Fault

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.

Walnut

Timberhill

Witham

Hill

Siletz River Volcanics - BasaltOcean sediment

Vineyard Mountain

Pacific Ocean

54 Million Years Ago

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.

Siletz River Volcanics - BasaltOcean sediment

Vineyard Mountain

Pacific Ocean

30 Million Years Ago

sediments

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

Rivers dump sediment

SRV SRV SRV

Vineyard Mountain

Pacific Ocean

20 Million Years Ago

Subduction Zone

sediment

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.

SRV = Siletz River Volcanics

Western Cascades

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

the Cascades.

SRV SRV SRV

Vineyard Mountain

Pacific Ocean

5 Million Years Ago

Subduction Zone

sediment

SRV = Siletz River Volcanics

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.

Corvallis Fault

King’s Valley Fault

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

At this depth rocks melt

Newport

Coast Range

Mt Jefferson

Cascades

Vineyard Mountain

Mt View

Geology of the Mt View School Area

Corvallis Fault

Pacific Ocean

Juan de Fuca Plate

North American Plate

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.

The Willamette Valley is Wine

Country

Siletz River Volcanics

The most complex wines come from vineyards at the

boundary between old volcanic soil

and glacial deposits or old sandstone.

Good vineyards require good

drainage, the correct growing season, and nutrient rich soils.

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.

5. Collision of tectonic plates – geology in action today!

Most volcanoes are located close to where two plates collide

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

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

4. Answer: True

Subduction zone

Juan de Fuca Ridge

Axial Seamount

Seafloor spreading

Seafloor spreading

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.

Juan de Fuca Plate

Pacific PlateJuan de Fuca PlatePacific Plate

Juan de Fuca Ridge

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

6. Answer: Seafloor spreading

Magma comes from the Mantle which is 3000º C

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

( like Mt Saint Helens)

Subduction

What happens at the boundary between plates when subduction occurs?

North American Plate

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

Subducting Juan de Fuca Plate

6. Earthquakes

Source: 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

Source: 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

Unusual earthquakes measured off OregonScientists Baffled by Unusual Swarm of Hundreds of

Earthquakes Off Oregon Coast JEFF BARNARD

AP NewsApr 12, 2008 16:06 ESTScientists 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.

Convergence of three tectonic plates: Juan de Fuca, Pacific, and North American

Cartoon by Sidney Harris

“I guess we shouldn’t have built on the San Andreas Fault!”