Sunday, August 22, 2010

Oregon Trip Day 7: A Volcano Observatory

Photo from Windy Point: I'm standing next to 50,000 year old basaltic andesite from Black Crater (foreground, age approximate), looking across a 2,900-year-old basaltic andesite flow from Little Belknap (dark flows beyond the foreground trees), at the snow-capped peak of the 300,000- to 35,000-year-old Mt. Jefferson stratovolcano (Windy Point location, MSRMaps).

(If you don't know what observatory I'm speaking of, then you need to read on — and then you need to go there: you go down there — I mean, up there.)
Our third stop on the seventh day (after the rock garden stop) was in the town of Sisters, Oregon, where we had lunch indoors, and ice cream outdoors. The clouds were threatening when we arrived. They had cleared some by the time we left, but had regrouped before our fourth stop... the Dee-Wright Observatory on top of McKenzie Pass (Google Maps). That's a view of Black Crater behind the sign — it's a partly glaciated shield volcano that extruded basaltic andesite flows about 50,000 years ago (see Cashman et al, 2009*).
At Dee Wright, you either climb steep stairs made of basalt (or basaltic andesite) or you walk a paved, gentle incline.
More than half way up, you come to a circular room with windows looking off in several specific directions. Each window frames a particular volcano; this is Mt. Jefferson.
It's worth going all the way to the top of the observatory for the view, and also to see this bronze "peak finder." According to long-time residents, this compass — which points to many but not all of the volcanoes visible from the top — has had to be replaced more than once. If you read the arrow in front of the snow-covered mountain on the horizon, you'll see that it's pointing to the North Sister, 6.6 miles distant, 10,094 feet elevation (according to the bronze plaque; according to the Dee Wright Observatory page at the CVO , the elevation is 10,085 feet). The Middle Sister, youngest of the three, is just right of the North Sister; Little Brother (the oldest) is on the right edge of the photo.
The Dee Wright Observatory is built on basaltic andesite flows that erupted from the base of Yapoah Crater, a 2,000 year B.P. cinder cone on the north flank of the North Sister (Cashman et al, 2009). The cone is visible but hard to point out from this angle.
Off to the northeast, the light brown volcano on the left is Belknap Crater, a basaltic andesite to andesite shield volcano that erupted 2,635 to 1,500 years B.P. Little Belknap is the dark point right of Belknap near the right edge of the photo. It erupted basaltic andesite about 2,900 years B.P. (these dates are from Cashman et al, 2009). The dark flows in the distance, behind a narrow swath of trees, are from Little Belknap; they flowed around a patch of older volcanic material (green area roughly in the center), forming what is called a kipuka (as seen in Cashman et al, 2009; USGS definition).

UPDATE: Read more about kipukas at Geotripper, who is currently in Hawai'i!
On the way down, a flock of small brownish birds with yellow colorings — possibly pine siskins — were hanging out amongst the basaltic flow rock.
If you drive a little ways to the west, you can look up toward the North Sister along a treeless flow from Yapoah Crater, the relatively barren cinder cone that barely sticks up above the mostly tree-covered skyline on the left side of the photo. It appears to have a white patch of snow on it's north side. In this Google Street View, Yapoah Crater is just left of the centered tree.

And you already know what we did after the field trip: we went to the Terrebonne Depot, had a great meal and good ale.

Main References:
Cashman, K.V., Deligne, N.I., Gannett, M.W., Grant, G.G., and Jefferson, Anne*, 2009, Fire and Water: Volcanology, Geomorphology, and Hydrogeology of the Central Cascades and Adjacent Areas, Oregon: Geological Society of America, Field Guide 15 (field trip no. 409).

*Anne Jefferson, who blogs at Highly Allochthonous, sent me a copy of this field guide, which I used extensively during this portion of our road trip. Thanks, Anne!

USGS Cascades Volcano Observatory.

Trip report to be continued... not necessarily in a timely fashion.


Gaelyn said...

I love the roughness of the youthful North Cascades. Nice to see geologic events so visual. I've never been to that observatory. Really like the construct, and the compass.

Lockwood said...

Apparently, I forgot to hit "post comment," but this may be redundant.

Check the date on the Little Belknap flow; there isn't much in Oregon that's 2900 Ma in age.

I've been up to this pass more times than I can count, but many people find its starkness off-putting. For a geologist, though, it's truly amazing and beautiful. For biologists, the stages of succession on display are awesome. For photographers, the landscapes, textures and tonal variations are unlimited.

I agree: everyone should have the opportunity to experience this special place at least once.

Another interesting thing to see here is the trace of the southern branch of the Oregon Trail excavated into the flows across the road from the observatory. Every time I'm up there, I can't help but wonder at the reactions of settlers as they confronted the last two major obstacles on their trip to the Willamette Valley: the rugged lava flows and the long steep decline into the deep valley leading to the McKenzie River. I wonder if any of them finally gave up, so close to their goal.

Blue Sunflower said...

Oh, I *loved* this place. Ended up there on one of the windiest days of the year, plus it was snowing and beyond foggy! And this IIRC was in September. Terrible drive. :D Still impressed how you can see the flow as it went around the hills.

Silver Fox said...

Lockwood, thanks for catching that - too much writing, not enough editing.

I've never thought of the area as stark, with so many volcanoes around - a new perspective. Another neat thing about the area, is driving up the old highway from the McKenzie River side - the narrowness and tight curves are fascinating, although I understand they may widen or straighten some.

Silver Fox said...

Gaelyn, next time you go to Fossil Beds or go agate hunting in Oregon, drive up the pass to see the observatory.

And maybe when you go, the Lava Trail will be open - it's been under re-construction the last two times I went. It has signs pointing out a few volcanic features in the Yapoah lava flow.

Silver Fox said...

Blue Sunflower, it sounds like you missed some of the views because of fog, but the lava flows are always there, right under foot.

Did you come up from the McKenzie side (possibly closed?), or from the Sisters-Bend side? (Just curious - I usually come in from the east, but used to come in from the west whenever possible.)

Silver Fox said...

(Yeah, how did that "Ma" get in there?)

Lockwood said...

The difference between the approach to the pass from either side is astonishing. From the west, you come up the cirque wall of a valley glacier, with, as you point out, narrow switchbacks and blind corners. There's some great exposures of the volcanic stratigraphy, but god help you if you actually want to stop and get out to look carefully. From the east, it's a long, almost imperceptible grade, and quite straight until you are almost to the pass. As I remember, the first major curve is there at Windy Ridge (which lives up to its name).

Regarding "stark," it's the apparent barrenness and lack of life on the fresh lava. It's like desert: the first time I was actually out in it, I found it off-putting and threatening. It takes time to accept it on its own terms, and to recognize that there is life there... it's just not as obvious. When you learn to see the beauty there, you never get over it. Some people I've taken up to McKenzie pass have just never had the opportunity to see the beauty of that kind of volcanic landscape. It feels threatening to them.

Silver Fox said...

Desert, and any place without vegetation (like the Big Island in the basalt flows) is something many people don't like. I have found wide views of any kind quite refreshing (mostly)for a long time. Rainforests used to give me claustrophobia! (I've gotten over that a bit.)

One thing great about deserts and other "barren" areas: not as many people! :)

I don't know when I first went to McKenzie Pass, but I suspect it was before I turned 10.

Blue Sunflower said...

Silver Fox - Yeah, came from Bend side. And yes, clouded view. Still awesome though!

Dan McShane said...

Whenever I have been in that area I come away thinking, When will one of these volcanoes erupt again? Thanks for posting the references and the great trip write up.

Silver Fox said...

Any day now? :)

Alaska Al said...

I grew up in the McKenzie valley and the volcanic view of the volcanoes and flows is one of reasons I chose geology. In 1942 I was one of a small group of Boy Scouts that hiked from the Scott Lake camp and climbed Belknap Crater. The falling-down run from the top down through the cinders was a hoot and a half. In the spring of 1951 your mother and I, and a couple of other graduate students, helped on a freshman geology field trip up to Collier Glacier on the North Sister. The last mile was steep and without a trail. A friend and I dragged your mother up by her armpits to a moraine ridge where we could look down on the glacier. What a view!

Silver Fox said...

Alaska Al, glad you wrote this story down!It's one I haven't heard before, and I've already had confirmation of it from the other party mentioned. :)

Silver Fox said...

P.S. I did know about the McKenzie River part!