The real voyage of discovery is not seeking new landscapes, but having new eyes. (Proust)
Oregon & PNW Geology: A Quick Introduction.
About PNW Geology: For geologists, the Northwest’s essential DNA is volcanic. Its basement is a collage of exotic, accreted terranes, mostly volcanic islands, welded to the Archean edge of the continent by repeated episodes of volcanic eruptions, and now pulled asunder by faulting. The Northwest’s iconic High Cascade Mountains are only the most recent episode in a long history of eruptions. They are built on a foundation of older Cascade volcanoes that date back to 40 million years ago. And these rest upon accreted volcanic islands and oceanic plateaus that were erupting when dinosaurs munched cycads in Kansas.
Whitebark Pine stump left by Mt. Hood's last major eruption in 1790.
From the Introduction of the forth-coming book:Living with Thunder. (Oregon State University Press, 2014) The Pacific Northwest is a region defined as much by its geology as by its drippy or dry landscapes, its threatened salmon, its picked-over forests, and its and proclivity for environmental activism. In general parlance, the northwest includes the states of Oregon and Washington , although geology has never learned to color strictly within state lines. Geologically, the Pacific Northwest is more defined by its ranges and rocks, its heritage of volcanoes and accreted terranes, its flood basalts and subduction zones. We are Mount St. Helens. We are the Columbia River Gorge. We are sea-stack, Haystack, tide-pool-festooned coastlines, bombastic volcanoes, basaltic outpourings, and a collage of ancient, exotic islands, seamounts, and ocean bottoms that have created North America’s newest land. Our landscapes are scions of the seafloor and they represent the ultimate in recycling. The Northwest’s environmental passions could well be rooted in this landscape. Tom McCall’s beloved bottle bill may have come to pass because, viewed from his ranch beneath the rimrock, a distant Mt. Jefferson presented a looming message: All matter, even rock, is re-used, reformatted, and reborn. And of such rebirth comes greatness.
Our landscapes prosper on reusing, reformatting, and remanufacturing. Cascade volcanoes recycle small amounts of time-worn sea floor sediments, dragged down a subduction zone, melted and re-invented as tiny, molecular components of new lavas. The ancient sea floor appears in our Cascade lavas as invisible, chemical components. We cannot pick up a chunk of Cascade lava and actually see a fragment of sea floor basalt or a smudge of bottom ooze, any more than a remnant of plastic milk jug can be seen in an Olefin carpet. These components are entirely recombined. But we can detect their presence through traces of chemistry—a few extra parts per million boron, a bit more beryllium, than magmas that come purely from the mantle. In many Cascade lavas, there are tiny, chemical remnants of sea floor, caste back into daylight as volcanic rock. We build cities on it. We build cities of it. We crush it for roads, and then follow those roads to trails that lead us to intimacy with the great peaks, with South Sister, North Sister, Mount Rainier, Crater Lake. All supreme recyclers. All giants with lessons to teach.
Every rock, with the possible exception of meteorites, is a chunk of reformatted or remanufactured planet. The bedrock of the Northwest is dramatically associated with this geologic recycling. Seattle rests on glacial till gleaned from more ancient North Cascade rocks. Tacoma and towns to its east lie astride volcanic debris—mudflows that brought chunks of domes and lava flows from Mt. Rainier. Spokane nests in channels carved and gravels abandoned by the great, ice-age Missoula floodwaters, and straddles the northern fringe of Columbia River basalts (lavas purged from the mantle, 10 miles beneath the city,) and the much older granitic rocks of the Spokane dome (remelted, remastered volcanic rocks of ancient, accreted terranes.) Portland sits atop debris from the same floods of lava and water. Bend’s foundation is the ashy residue of hot-breathed Cascade volcanoes, a fluffy concoction of molten mantle and sea floor coughed up violently by a vanished Cascade volcano some 3 million years ago Eugene is buttressed by older, more staid Cascade lavas that form Skinner and Spencer Buttes—but share the history of recycled and reformatted material with their Cascade kin.
What makes the Pacific Northwest geologically distinct from the neighboring Rockies, or Great Plains or other western geographies, is this emphasis on re-birth and re-invention. We are a landscape of exotic terranes, of once and future volcanoes, of new starts for old things, of reconstitution and rebirth. Of Westside rainforests, yes. Of Eastside bluebunch wheatgrass, of canyons and powerful rivers. But we are also the landscape where geology does not take life sitting down. Where being run over, scraped off, and dragged into the mantle energizes uplift, eruptions, and mountain-building. This is not the flattened landscape of Kansas, or the tired hills of Pennsylvania, or Florida’s passive margin. There is hope here, rebirth and recycling. It is in our landscapes as much as within us.