Sunday, November 30, 2008
If you are not up on the evolution of the Western Snake River Plain (WSRP) and the timing of the cutting of Hell's Canyon in relation to the Owyhee intra-canyon lava flows then consider reading a paper by BSU Emeritus geomorphology professor Spencer Wood and his colleague Drew Clemens, "Geologic and Tectonic history of the Western Snake River Plain, Idaho and Oregon" Find it at:
Among other things, the paper discusses where and when Lake Idaho existed and how and when Hell's Canyon was cut. It refers to work done by Kurt Otherberg, who Jim had mentioned before in the context of Hell's Canyon.
Two years ago I asked Peter Wigand for some direction in
searching for papers that might help us understand the
paleoclimate (and therefore perhaps river discharge and
stream power) of the Owyhee River basin. He replied to
me but I never was able to track down all the papers he
suggested. I am providing his suggestions here in the
hopes that we can improve our understanding of what the
Owyhee River might have looked like during the existence
of the lava dams. He said to start with the first one
which had an extensive bibliography that would
lead to some of the others.
Wigand, P. E. and D. Rhode. 2002. Great Basin
Vegetation History and Aquatic Systems: The Last
150,000 years. Pp. 309-367. In Hershler, R., D. B.
Madsen and D. R. Currey (eds.), Great Basin Aquatic
Systems History. Smithsonian Contributions to Earth
Sciences 33. Smithsonian Institution Press,
Mladen Zic, Robert M. Negrini, Peter E. Wigand. 2002.
Evidence of synchronous climate change across the
northern hemisphere between the north Atlantic and the
northwestern Great Basin, USA. Geology 30(7):635-638.
Cohen, A. S., M. Palacios, R. M. Negrini, P. E.
Wigand, and D. B. Erbes. 2000. A paleoclimate record
for the past 250,000 years from Summer Lake, Oregon,
U.S.A.: II. Sedimentology, paleontology, and
geochemistry. Journal of Paleolimnology 24
Negrini, R. M., D.l B. Erbes, K. Faber, A. M. Herrera,
A. P. Roberts, A. S. Cohen, P. E. Wigand, and Franklin
F. Foit, Jr. 2000. A paleoclimate record for the past
250,000 years from Summer Lake, Oregon, U.S.A.: I.
Chronology and magnetic proxies for lake level.
Journal of Paleolimnology 24 (2):125-149.
Mehringer, P.J., Jr. and P.E. Wigand. 1990. Comparison
of Late Holocene environments from woodrat middens and
pollen, Diamond Craters, Oregon. In Martin, P.S., J.
Betancourt and T.R. Van Devender (eds.), Fossil
Packrat Middens: The Last 40,000 Years of Biotic
Change. University of Arizona Press.
Wigand, P.E. 1987. Diamond Pond, Harney County,
Oregon: Vegetation history and water table in the
eastern Oregon desert. Great Basin Naturalist 47
Friday, November 14, 2008
Here are two photos--long overdue--that show the contact relations of the WC lava where I collected sample OWY-19. One shows the modern swale that has eroded around the WC lava that filled the paleo-swale. The other photo shows the nature of the contact between WC and lava flows within the Tertiary section: the WC lava sits on top of the Tertiary section there.
Wednesday, November 12, 2008
The results are in. Nick Foit's lab at WSU has analyzed some Owyhee tephra samples with a new probe. The delay in getting the data owes to the time it takes to set up such a device. Turns out that it was worth the wait. The tephra id's match Yeehow conventional wisdom in so much as they match the most likely candidates at each site.
I don't have time to work up anything fancy for this post (leaving for different field area in AM...not ready yet, but here is the dirt:
Mt. St Helens Set C, approximate age 47.2 ka found in lacustrine seds on river right and left above West Crater flow (image above is from sample on river right). These are the samples that we both related to OSL ages of approximately 20 ka. The occurrence of this tephra on both sides of the river and at disparate elevations is interesting and is evidence for sedimentation at two different levels here. One associated with the Owyhee, and one associated with the perched paleo Ryegrass Creek.
Mazama Tephra was found in auger holes in depressions on the Bogus Point landslide and on one of the Heaven's Gate landslides. The Trego Hot Springs tephra was also found deep in the core of the Bogus Point landslide sag. This bed (from Newberry Volcano, I believe) dates to approximately 23.2 ka.
We also found Mazama (6850 c14 yrs BP; ~7600 real years) tephra in an arroyo cut formed in a breached sag on a landslide on river left in Heavens Gate.
View Larger Map
Tuesday, November 4, 2008
Today, I finally began to georectify O'Connor's field maps to cross-check against and augment my mapping. Using GlobalMapper this process takes only about 1 minute per map. Love that program. As expected, Jim's mapping is good. Take a bow. Our overlapping mapping only differs by refinement owing to more overland work and hi-res imagery. Of course, the man found some things I missed under both of those circumstances. Don't worry Cooper, your mapping is next. Will pay attention to your paleochannels on West Crater, relax.
While compiling Jim's compilations, I noticed a couple of intracanyon flow remnants in the gorge that I had forgotten about. They are labeled as Lambert (West Crater) but are most likely Clark's Butte given their elevation. I believe that the northernmost one is in the Tertiary section...but am not sure.
Any clarification / confirmation / elevation/ consternation that any Yeehow may have about these blobs would be appreciated. Photos would be super neato.
The area marked by a question mark on the image you posted could certainly contain sediment from the Owyhee River as the river flowed over the top of the WC lava. I have been there and was impressed by this expansive, low relief area made mostly of silts. I will review my notes at home tonight on the matter. I do recall also acknowledging that the area could easily be a depocenter for Bogus Creek. The road that you can see in the upper right corner of the image is built on a ~1.5-2 m high (man-made) berm (levee!!) that ensures all of Bogus Creek flows north rather than between some tumuli down to the low relief silty area as it clearly could do in the drop of a hat (or a March rain-on-frozen-ground event).
Yes, there are some large gravel/cobble bars along the lower reaches of Bogus Creek near the kipuka. If i recall correctly, these happen to be low enough in elevation and downstream enough to be within reach of overflows from the Owyhee River passing through the possible depocenter but also from other overflows further downstream. (Having said that, there are some sizable ephemeral channels that pour off the Bogus Rim directly to the east of the kipuka and these could contribute a lot of discharge in a large convective event or spring rain on snow.) It may be worth considering auguring this silty depocenter or digging some test pits there to understand the deposits or find some datable material.
And yes, there are several different lobes and inflationary flow fronts to the WC lava flow that wrap around Bogus Point and create some unique positive and negative relief. I looked at these in stereo many times and walked around on the ground there with an eye towards assessing the timing of these lava pulses and the potential interaction with the river. After a lot of back and forth, I continue to return to my original interpretation that there is only one lava flow in the area--the WC-- and that water flowed through a narrow gap between several tumuli far more upstream than the rounded boulders on the edge of the modern cliff of WC adjacent to Chalk Basin show. I am pretty sure that this nascent paleo channel is the upstream-most one shown on my maps of several years ago. Furthermore, there probably is a complex set of damming and overflow events because even though there is probably only one lava flow there, it probably made several surges or advances in its battle with the river and rising lake.
I sure wish I could have come to Bend!
I recently re-read Howard et al.'s paper. The difference I see is that they stop short of going into detail about the impact of the lava dams on the geomorphic evolution of the canyon. Their paper provides a great basis of comparison for ours, but we can take ours much further with our more extensive dating, mapping and our possibly greater interest in the river canyon geomorphology. The Howard et al. paper was not that long, and mainly focused on the description of the lava flows and dams. We have more controls on incision rates through different lava flows at different times and places on the river, which I think will lead to interesting discussion.
I've sent away for a few more references to lava dams in the last couple of days. I'll circulate them when I get a chance to look them over. Quite a few on the Snake River, some in Canada, one in China.
Now that I have finally read Keith's Boise River lava dam paper, I can understand why he was skeptical given the striking parallels between the Boise River story and the Owyhee River story. (thanks to Lisa for sending the pdf). Moreover, the Howard and Fenton abstract (that, admittedly, I was not aware of) reads just like the thoughts I had in mind while thinking of the Owyhee while floating the Colorado. Some of the differences are profound.
Admission of guilt: I am truly embarrassed that I had not read the Howard et al. paper years ago, as it would have made it far easier and faster for me to understand the history of the Owyhee River. Oh well....As for the more recent abstract...no excuses there either.
We should really consider checking out the Boise River sites sometime.
LAVA DAMS COMPARED IN BOISE RIVER CANYON AND GRAND CANYON
HOWARD, Keith A., U.S. Geol Survey, Menlo Park, CA 94025, firstname.lastname@example.org and FENTON, Cassandra R., U.S. Geol Survey, 1675 W. Anklam Rd, Tucson, AZ 85745
Pleistocene intracanyon basalt flows that dammed the Boise River, Idaho offer comparisons to those that dammed the more powerful Colorado River in Grand Canyon. In both canyons, olivine basalts erupted several times from vents near canyon rims, and flowed down steep canyon walls into the rivers and onto thick gravel beds. The multiple lava dams in Grand Canyon exhibit many stratigraphic complexities as compared to the simpler stratigraphic structure of the dams built on the Boise River, best exemplified by the Steamboat Rock Basalt and the Smith Prairie Basalt on the Boise River’s south fork. These two dams were each constructed to heights of 150 m from multiple flow units of basalt, which flowed tens of kilometers downstream while building lava deltas into the growing reservoirs on the dam’s upstream faces. Paleowater levels in the lava deltas, where lava flowed into rising reservoir waters behind the dams on the Boise River, are easily recognized as passage zones where topsets of subaerial pahoehoe pass abruptly downward into upstream-dipping foresets of pillows and hyaloclastite. Successive flow units entering a rising reservoir resulted in an asymmetric dam, much longer on the downstream face, and cored by massive subaerial basalt that interfingered upstream with a series of upstream-thickening wedges of pillow basalt. Grand Canyon lava dams also show evidence of upstream deltas where lava interacted with dammed water (described by Hamblin), but coarse hydroclastitc breccia dominates over pillows and foreset-bedded hyaloclastite; the deltaic structures are complex. Whereas several dams in the Grand Canyon failed catastrophically to produce outburst floods (described by Fenton and colleagues), the dams on the Boise River were incised gradually. Their long downstream lengths contributed stability. The long flows and abundant pillows relative to breccias suggest fluidity of the lavas, and suggest rates of eruption and lava flow that were high relative to the discharge of the river that they entered. The Colorado’s discharge is twenty times that of the Boise River South Fork.
Rocky Mountain (56th Annual) and Cordilleran (100th Annual) Joint Meeting (May 3–5, 2004)
Funny aside: at the meeting in Bend, I 'independently' developed a diagram for how we could graphically convey the last 1.8 my of the persistently interrupted incision history of the Owyhee. Much to my dismay, within minutes of touting the merits of my exmple figure, I was faced with a nearly exact example prepared by Howard et al. Lisa had the paper with her and I read it for the first time right then and there. In addition to the figure, many of the concepts presented in the paper were identical to discussions that we always have and were having that day. We then became concerned about how we could distinguish our study from theirs beyond just stating that it also happened somewhere else not very far away. I keep verging toward a discussion of the differences between landslide dams and lava dams with interesting counterpoints from the Colorado River and the Rio Grande.
For the past few days, I have begun to compiling mapping using vr...the 3d visualization and digital mapping tool I mentioned last February--(http://yeehowcentral.blogspot.com/2008/02/virtual-reality-on-owyhee-almost.html). This has been very illuminating because it allows for me to zoom in to key areas in very clear 3D. Since I have already done so much flat-mapping (heads-up digitizing on NAIP images with stereopairs nearby) I have opted to focus on only key and slippery contacts or particularly complicated areas (i.e., the Hole in the Ground). I spent most of yesterday gawking at the Lambert Rocks, Bogus Point, and AM-PM areas.
In conjunction with recent field work (which was, in hindsight, inadequately thorough) I began to recall / notice that the low-relief area in the middle of Qbw is a likely depocenter for overflow related sedimentation by the Owyhee before it cut a canyon through the area. I traced rounded basalt gravel and sand through a sinuous tract across the lava flow toward that area but, alas, opted to head to my vehicle instead of trapsing (yet again) across the lava flow surface. It seems that all of my traverses on the flow have missed this key area. Anyone in the group happened to have been here?...Cooper?
Also, there are some fairly large gravel bars evident in parts of the Bogus Creek course near the large kipuka that are curious as well. Anyone been there?
Have also noticed that there are at least 3 conspicuous flow fronts of Qbw lobes in the Lambert area and am wondering if there is a more complex damming and overflow story there than it appears at first glance.