Month: March 2018

11-12-2011 Ray Wells: Revolutionary tectonics

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About the Talk

Ray Wells of the U.S. Geological Survey presented a lecture on the Revoluntary Tectonics in the Pacific Northwest.

Rotational History of the Pacific Northwest

Crustal deformation and paleomag-netic rotations over the past 50 million years indicate that the Cascadia forearc is moving northward along the west coast and breaking up into large rotating blocks. Deformation occurs mostly around the margins of a large, relatively non-seismic Oregon coastal block composed of thick oceanic crust. This 400 km-long block is moving slowly clockwise with respect to North America about a rotation pole in eastern Oregon, thus increasing convergence along its leading edge near Cape Blanco and creating an extensional volcanic arc on its trailing edge. Northward movement of the block breaks western Washington into smaller, seismically active blocks and compresses them against the Canadian Coast Mountains. Movement of these blocks may be up to 9 mm/yr, sufficient to produce damaging earthquakes in a broad deformation zone along block margins.

Recent GPS data show that clockwise rotation of Oregon continues today, and rotation rates from GPS studies are similar to older paleomagnetic rates. Northward moving Oregon is currently squeezing Washington against slower moving Canada: this constriction has produced the Yakima fold and thrust belt and its analogs, like the Seattle fault, in the forearc. Locally, right lateral shear in the forearc is apparent in the GPS data, consistent with recently discovered right-lateral faults in the Portland area that may be seismically active. In a broad sense, the smaller, clockwise rotating blocks of the Pacific Northwest appear to be caught like a giant ball bearing between the much larger Pacific and North American plates.

About the Speaker

Dr. Wells has been a research geologist for almost 30 years, concentrating on the use of field geology, magnetic rock properties (paleomagnetism), and GPS to solve large-scale problems in the Earth’s on-going structural evolution. Ray has produced a simple, hands-on block model of the Pacific Northwest, which he will demonstrate at the talk. Today, 165 of the models are used in classrooms around the Pacific Northwest.

03-03-2012 Hugh Shipman: Bluffs and Beaches

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About the Talk

Bluffs and Beaches:  Geology on the edge (of Jefferson County)

Puget Sound is best distinguished from other large American estuaries by the pervasive influence of the last glaciation.  This glacial legacy includes a steep, irregular coastline, an abundance of coarse-grained sediment, and a shoreline dominated by coastal bluffs.  These bluffs are inherently erosional landforms, although the rate and character of this erosion varies greatly.

Bluffs are a key component of a dynamic beach system that supports an incredible array of coastal landforms and environments, including spits and small estuaries.  This talk will draw on local examples to show how geologic processes have shaped the modern shoreline and how they continue to do so – sometimes with significant implications for people who live near the shore.  The talk will also include observations on how geology is becoming increasingly important to our thinking about how we protect Puget Sound’s shorelines.

About the Speaker

Hugh has been a geologist with the Shorelands Program at the Washington Department of Ecology since 1989.  His interests include coastal erosion, geologic hazards, and the environmental impacts of shoreline modifications. Hugh grew up near the coast of Maine but moved to the Puget Sound region in 1983.

Visit Hugh’s blogs at:

Gravel Beach – http://gravelbeach.blogspot.com/

Washington Coastal Hazards Resilience Network – http://www.wacoastalnetwork.com/blog

 

04-28-2012 Dave Montgomery: DIRT

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About the talk

Dirt, soil, call it what you want—it’s everywhere we go. It is the root of our existence, supporting our feet, our farms, our cities. This fascinating yet disquieting book finds, however, that we are running out of dirt, and it’s no laughing matter. An engaging natural and cultural history of soil that sweeps from ancient civilizations to modern times, Dirt: The Erosion of Civilizations explores the compelling idea that we are—and have long been—using up Earth’s soil. Once bare of protective vegetation and exposed to wind and rain, cultivated soils erode bit by bit, slowly enough to be ignored in a single lifetime but fast enough over centuries to limit the lifespan of civilizations. A rich mix of history, archaeology and geology, Dirt traces the role of soil use and abuse in the history of Mesopotamia, Ancient Greece, the Roman Empire, China, European colonialism, Central America, and the American push westward. We see how soil has shaped us and we have shaped soil—as society after society has risen, prospered, and plowed through a natural endowment of fertile dirt. David R. Montgomery sees in the recent rise of organic and no-till farming the hope for a new agricultural revolution that might help us avoid the fate of previous civilizations.

About the speaker

David Montgomery is a Professor of Geology at the University of Washington’s Department of Earth and Space Sciences. He was selected as a MacArthur Fellow in 2008, based on his exceptional creativity, significant accomplishment and potential for subsequent creative work.