Saturday, December 27, 2008

No Passing

(map and road cams from the ODOT TripCheck page)

So today we need to get back across the Cascades, and of course the weather is being uncooperative. Here it's a mix of snow and rain, with the temperature around 35. Up on the Route 20 passes (Santiam and Tombstone) it's snowing heavily. Throughout the region, the wind is gusting up to 30 miles per hour. It's been howling all night.

And the cables that my sister and brother-in-law bought for their rental van are not fitting well. Each of them have broken a link. We've wired down the loose pieces, and they seem to be working well, but none of us are experienced with chains/cables.

We're considering driving up to the Gorge (I-84), which goes through the Cascades at just above sea-level. The problem there is that we've got to get to the gorge, which might also require chains.

So our choices are 1) Head straight over the mountains, and hope that the chains hold for an hour to an hour and a half. If they break we may have to come back to Sisters or Bend to find traction options, and waste several hours. 2) Take the chains off, and head north on 97 toward the Columbia River Gorge, hoping we don't hit areas where chains are required (more importantly, truly needed). And if we have to waste time putting them back on, will they hold? Not only does the latter option add 115 miles to the trip, we might end up in exactly the same position as we could by just trying to dash through the Cascade passes.

As I've commented several times, Corvallis has spoiled me. It's mild and we just don't get winter weather, with unusual exceptions. The temperature there now is low forties, with a predicted high of 47 degrees today. I have enjoyed the snow here in Bend, and taken many pictures of it over the last few days, some of which I will post sooner or later. But I've had my fill, and snow is great as long as you're just admiring it. Actually dealing with it is a pain in the butt.

Thursday, December 25, 2008


Inches of snow Portland has seen this month as of late Thursday, according to the National Weather Service. That's the most in December since the state started keeping records in the 1880s.
(From Oregon Live)

And according to the Mt Bachelor website (as of this writing), they have had 168 inches of snow this season. Less than two weeks ago, I was worried they might not have enough by Christmas; there were only 8 inches on the ground, and 18 are required to open. So 160 inches- over 13 feet- have fallen in the last two weeks or less. (In fairness, that has packed down to only 67 inches.)(picture from the Bachelor website photo album, Christmas day)

I'll bet Corvallis has set a record too, though from what I saw on OSU webcams today, it didn't look like they had a white Christmas there.

And the Bend area is expecting more snow tonight. Hope we can get home safely Saturday.

Merry Christmas!

Can you say it too many times?
Christmas sunrise over Newberry Volcano, moments ago, from our porch.

No Sign of Santa

But Merry Christmas anyways! You all have been a great gift all year (I started reading blogs regularly in late '07, but didn't start blogging myself until May), so I don't really need to wait up for the jolly old elf. Have a good one!

Wednesday, December 24, 2008

The Growth of Continents

This month's Accretionary Wedge topic is "What recent geological advance has been most important to your geological work?" I'm paraphrasing, but that's basically my understanding. I had been thinking about writing on paleomagnetism, but the roots of that sub-discipline go back to (if I remember correctly) Cox in 1956- please don't quote me on that: I'm trying to dredge up memories from 20 years ago. (Late Note: See this article excerpt- I have a little more confidence now. Note particularly, "Paleomagnetic results for the Mesozoic and early Tertiary might be explained more plausibly by a relatively rapidly changing magnetic field, with or without wandering of the rotational pole, than by large-scale continental drift.) So the early work in that area predates my birth. Furthermore, the results that have been most important and, yes, inspiring, to me all focus on a particular topic: accretionary tectonics, or as we used to call it when I was an undergrad, "flake tectonics."

Oregon is composed of a fairly large number of discrete terranes, or "flakes" that have distinct and different histories up to a certain point in time. After that point, the geologic history of a particular terrane and its neighbors are congruent and coherent.

As a brief aside, note that "terrane" refers to a particular tectonostratigraphic unit, while the word "terrain" refers to landscape.

So to choose an imaginary but typical example, picture an island arc volcanic system. In the above cartoon, subduction is under the arc to the left, and is consuming oceanic plate between the arc and the continent to the right. Sediments (in tan/greenish?) are accumulating in the basin between the continent and the arc.

The volcanic arc continues to approach the continent, and the basin accumulates more sediment.

As the arc approaches the continent, the sediments continue to accumulate; thrusting and folding start to thicken the sequence. Ultimately, when the oceanic crust is consumed, subduction ceases.
The overlying sediments are severely deformed; while not of the same magnitude as the India/Asia continental collision, the processes are similar. The now accreted island arc and the continent to which it is attached will henceforth share the same sedimentary and tectonic history. In a practical sense, that means events and sediments can be correlated between the blocks. And in reference to my first idea for a topic, they will share similar (basically identical) paleomagnetic histories. Often, subduction will resume on the outboard of the newly accreted block in an opposite direction. This has been called a "polarity reversal," but with a very different meaning from a magnetic polarity reversal.

Geologists will immediately see that I have grossly simplified the diagrams above. For example, the magma rising in the subduction zones that does not reach the surface will crystallize to granitic rocks. Much of the sediment and volcanic rock will be metamorphosed. Faulting and folding will jumble things terribly. A further complication is that an accreted terrane may itself be composed of two or more terranes with independent histories up to a certain point, but share discernible spans of history prior to continental accretion. This is the case in terranes of the Klamath Mountains of southwestern Oregon and northern California. Back arc spreading following a polarity reversal in a subduction system (as happens between the second and fourth cartoons above) can emplace ophiolites- again, this can be seen in the Klamaths.The above diagram shows schematically the kinds of terranes that have formed much of western North America. The article in which I found it has a larger version, and discusses some of these ideas with respect to the Klamaths.

I had the privilege to take a field trip to the Snake River Canyon area with Tracy Vallier toward the end of my undergrad years; the geology there is somewhat less complex than the Klamaths (at least it seems that way to me), but is still best described as "a mess." This article focuses primarily on Idaho, but provides plenty of insight into northwestern Oregon as well.

The accreted terrain with which I am most familiar was referred to as "Siletzia." I say "was" because I haven't really followed the professional literature; I'm not certain that it still is. Actually, quick check, it does look as if it still is- see here and here. This block extends from approximately Coos Bay, Oregon northward to the southern end of Vancouver Island, British Columbia. The eastern margin, as far as I know, has not been tightly constrained, but probably lies along the eastern edge of the Cascade forearc basin, or along the western edge of the Cascade arc; in either case it is buried in basin sediments and older Cascade volcanics. At a first level of approximation, it consists of oceanic crust, apparently thickened by hot-spot volcanism, overlain by a thick sequence of turbidites (the Tyee Formation, correlates, and similar units of slightly different ages), then a shallowing sequence of marine sediments. During the time I was getting my degree, extensive research into the provenance of these sediments, along with paleomagnetic analysis of units of varying ages, showed that the history of this block was far more complex than the essentially simple sequence of rocks would suggest. Paleomag showed that the oldest rocks were oriented about 90 degrees counterclockwise from their modern orientations- that is, this block, approximately 150-200 km by 700-800 km, originally had its long axis in an east-west orientation. It now has its long axis in a north-south orientation. Progressively younger rock units show progressively less deviation from the modern orientation. Provenance analyses of the sediments suggest that the bulk of the Tyee turbidites were derived from the Idaho Batholith or chemically and isotopically similar granitic rocks, since hidden, further south. Given the age of the Tyee (Eocene), and hypothesized drainages in the northwest, it has been suggested that the drainage from the Green River Basin (home of the marvelous fossil fishes, and an enormous amount of petroleum reserves in the form of oil shale) was the stream that carried these sediments to the head of the Tyee fan.

When I was doing some volunteer teaching for OSU's experimental college, the way I explained this to (non-science) students was that the rock sequence is easy to describe and understand, but if you want to describe where the rocks came from and how they got where they are, it gets very messy very fast.

So even though I don't consider myself a professional geologist, and can't claim that there's any particular breakthrough or advance that has had great implact on my career, my avocation for the last few decades has been to try to make sense out of Oregon geology. When I started my education, tectonics was used primarily to describe the cause of the Cascade arc. By the time I finished my education, accretionary tectonics was considered fundamental to making any sense at all out of Oregon's geologic history.

Tuesday, December 23, 2008

C'est Moi

My mom gave me an early Christmas present: a digital camera! A pretty nice one, too. It's the one she's had for a while, so there's been some confusion over the manual (found it online), the camera to computer data transfer (couple of trips to Wal-Mart- or as my brother calls it, Wally World, and a little common sense), and coming up to speed on digital vs. film technology (mostly I've just used auto-everything so far; as I have more time, I'll play with other variables and learn how to take advantage of them). But I have managed to get a not-too-flattering self-portrait, which I have now loaded.

I've been spending most of my time with my family, several of whom are also not skiing, so posting has been light, but I'll try to get up some pictures and descriptions of the magnificent vacation area soon. Since all my family is on the eastern part of the continent, I don't see them too often, and they're my first priority right now.

Sunday, December 21, 2008

Only Oregon

Well, here I am in Bend. We do have wifi here and I'm showing my nephews, Kris and Garette, how to write a blog entry. Maybe soon I'll show them how to start their own blog. My other nephews and I went over to the coast yesterday. It was rainy and stormy, but we had a good time. We got to Florence, and I was reminded of this video from about 1980.

Yeah. Only in Oregon