Sorry Yeehows, Our Secret is Out

The hydrograph above effectively encapsulates the ambient conditions of field camp. The overall wetness was pretty freaking shocking.

The field camp experiment is over. It was a muddy success. The region was (and still may be) under the influence of a persistent cutoff low pressure system that delivered record amounts of rainfall. It is true that the roads on the rim become somewhat challenging when they get wet, but we did manage to get seven vehicles all the way in and out to the Artillery Rim camp site (eventually). The first night at Rome launch, it rained nearly 1.5 inches. A record for Rome. It was truly disheartening. While lamenting my plight at the Rome Cafe very early on Saturday, the woman in charge at the time offered up access to the Grange building in Arock for us to use while we waited out the rain. Once in Arock, we were given access to the Arock School by an extremely gracious host. The school was a perfect fit for us...hot water, bathrooms, class rooms with high-speed internet, a playground, etc.

While at the school waiting out the rain, I gave a marathon lecture (with playground breaks) about the study area, the Quaternary, surficial geologic mapping, and of course provided various demonstrations about geotagging photos, how the gigapan robot works, how I make a map in ArcGIS, and how the magic pen works.

Thankfully, Duane and Caitlin were also there. Duane gave a lecture about the history of paleomagnetism and described how it works in the case of correlating basalt units in the field area.


Caitlin gave a lecture about her project. That night it rained like hell and we enjoyed watching a major thunderstorm plow through Arock. All the more enjoyable because we had a dry place to sleep.

The next day, we had a foreshortened tour of the field area (mud concerns) and made it to the Coffee Pot lava field and the vent by way of the Rockhouse Coffee Shop...all great places to take students.


The road to Birch Creek was in good shape so we peered over the rim. The students were moderately amazed because all they had seen of the river so far was the boring reach at Rome. We then headed out through JV and actually made it to Artillery Rim with only minor mud delays.

Once at the camp site, we approached the rim on foot as a group, and it was the perfect field camp moment. Everyone was awestruck by the view from there.


What then ensued were two perfect field days in the Artillery Rim landslide complex...full of ticks and snakes (lots of snakes), but the weather was perfect. The students had never faced such a complex array of landforms and deposits. Rest assured they have newfound respect for rivers, canyons, and Quaternary geology (and rattlesnakes).

The field camp mascot...saw 9 or 10 rattlesnakes in two days.

Here's an idea. Bring the girls from the Mackay School of Mines Mining Team into the field to dig for you. Next year, the augering competition. In less than 15 minutes they created the best exposure of the Qfl that any of us has ever seen.

The last day ended with an all night soaking rain, and we (the TAs, the cook, and I) were concerned that we may be stuck for a day. It was extremely wet that morning. But, alas, Duane (who proved various times on the trip that his last name is no fluke) and his field assistant Nicole showed up at our camp around 8 AM proving that the roads were viable. As we then rapidly started to take the camp down, it started to rain very hard and things were horribly wet. As we pulled out of the camp, there was a lot of water running down the rocky road past the gate. The rim roads were muddy as hell in the immediate area and one van got mired. It was a relatively easy extraction and we were again on our way through the mud. As we approached the (once-named) veneers of dreaded rim gravel, we changed the name to the sanctified rim gravel. The roads were fine and we proceeded out of the field with no incident.

Looks like my UNR field camp session will hit the Owyhee every year. It remains an amazing place worthy of sharing.

A beautiful evening looking north over the Artillery Rim landslide complex. Worth the trip.

Trip re-cap: The Boulders

This year's group trip to the Owyhee was a great success. I, with much help from everyone, filled in some gaps in the map and the stratigraphy; we all found some new stuff; explored some new areas; acquired valuable field data; and met some very cool people. I am madly compiling the gigpans I took and just remembered that I needed to reduce the GPS data for the boulder measurements. Just got that done. Here are some screen shots:

Bunny's Bar:

Artillery bar:


Look at each and note the very high correspondence between the two types of data--LiDAR and High-Precision GPS. It is a whole new world. Don't fall off.

Imbricated thoughts on gravel, pt. 2

Now the high gravels. Maybe I haven't shared this with the entire group, but there are very, very sparse gravels in very few locations near the western edge of the Bogus Rim lava (Qbbr). Cooper and I spotted some in October 07 and I saw them again in Oct 08 and got a precise GPS reading on them of 1194 m. This is the level of the highest gravels upstream (skirting Little Owyhee Butte), but I haven't gotten a gps reading on them to really pin it down yet (May trip). Thus, these most likely represent the effect of damming by the Qbbr. The edge elevation of the Qbbr approaches 1204 m at the narrowest gap between it and the west edge of the Gorge at Iron Point. Note that the copious (6 m thick) volcanic-clast dominated overflow gravel appears downstream from the likley point of blockage at an elevation of 1160 to 1140. Suggests clearwater pour-over of the blockage to me.

Other high gravel elevations of note include the gravels on the Ice-Axe (1148 m), the low Rim Gravels on the tip of Bogus Point ( 1114 m), and the lone gravel deposit on the West Crater Kipuka (1050 m). More on them later.

Imbricated thoughts on gravel, pt. 1

Have lately been thinking about gravel deposits along the Owyhee. Using the LiDAR data, it is possible to rapidly extract precise elevation data from any point within the swath. This allows for a quick appraisal of the potential significance of the positions of various gravel deposits. In this image, I have highlighted some interesting spots. Of particular interest here are the gravels at the 993-995 m level ('perimeter gravels'). These are roughly concordant with the height of the west edge of the the West Crater flow and probably define the position of the first established channel of the river on its way through the lava. These surfaces stand well above the highest gravels at Dogleg, but that gradient is controlled by the gradient of the lava flow. What of the large difference between the elevation of the perimeter gravels and the next level down at Dogleg...a 33 m difference over only 3 km? Steep.

Also of note in the figure are the gravel deposits in the 1017-1025 m range (need to step on these sites before too long). These deposits must pre-date the West Crater flow and would have flanked the paleochannel that it followed. I was pleased to notice that the 1017 m gravel coincides with a prominent scarp-ish feature that is fairly obvious on the east side of the valley. Suggestive of gooey paleovalley margin for sure.

More posts on other gravel issues to come. Feel free to participate.

Bogus Rim lava now ~solidly in Quaternary!

According to the new geologic time scale being promulgated by GSA as well as the IUGS:

Double Spring Landslide Complex (with nod to G.G.)

Maybe it has all been virtually fake?

Well, the LiDAR has shown us that a digitally rendered landscape offers, in some ways, more insights into the geology than a picture, a hike, or a stereo model. Of course, the field observations are the most fun and provide the true context that allow us to gain those epiphanic insights. But...have we ever done any real field work? After going through some old photos I started to wonder if the whole thing has been a synthesized digital construct fed into my brain from some inscrutable computer network. I believe these are KC's photos.

Bullseye Bar in Surfer

Surfer is an old favorite of mine...it is good for quickly displaying the data and creating intuitive views. I think that this perspective clarifies the geometry and orientation of the landslide.

Dogleg Bar in Quick Terrain Modeler

Just fired up QTM today to see what it is all about. I can tell it is powerful, but am not yet qualified to use it. Working on it.

Profile Prototype

Here is a first stab at a simple, annotated profile from the LiDAR data. It is a very slightly smoothed curve. I used a 50 point weighted average to get the smoothest profile that clearly mimicked the more data-rich version. 

Have not yet gotten to extracting the lava flow profiles, but have added their longitudinal extents. Also added the main landslide complexes and some key sites to enable yeehow orientation. Overall the profile is pretty good. The only aberrant points show up where I tried to 'drive around' some of the no-data points and ended up treading on a terrace, so to speak. Next example will be the longitudinal changes in local gradient.

Olivine Separates: 051107-2(3)

Here are some images that show that status of the olivine mineral separation efforts. This sample contains the most olivine so far. It is one of two samples from the upstream end of T4 in The Hole in the Ground. Can someone tell me if two samples were collected from the same rock?

Anyway the point of this post is to show Cassie the status of our efforts to separate and clean the olivine crystals. On several crystals you can see some adhering matrix crud. We know we need to get that off. As for the black specks...?

Whatever, dude...

Like we didn't already know there were boulders on Bullseye Bar...

Yawn...

Big Deal

Big deal, so we got freakin' LiDAR for the Owyhee

Cosmic Mineral Separation Initiative

The cosmic mineral separation directive has officially been implemented at NBMG. I now actually understand what we are doing and learned how a microscope works. Turns out looking for olivine makes my hair grow. 

I have received much help from colleagues Nick (of previous 3D mapping fame) and Bret (shown in photo). Bret is doing nearly all of the work. Nick is providing more guidance than I am because he separates minerals for Ar-Ar all of the time. I (we) am (are) paying Bret for all of this work. Have also gotten some billets for thin sections out of the deal.

Can you guess where this is?

Hint: SWA Flt 2268







You can clearly see the RB, CB, WC, BR lavas in this one.


Here you can see the WC vent and the main lava tube. Rad.


-Spud

Dave's landslide blog: The Tennessee flow slide accident - what went wrong?

Dave's landslide blog: The Tennessee flow slide accident - what went wrong?

Geologic Froth: Geofroth at AGU 2008

Geologic Froth: Geofroth at AGU 2008

I'm done with the map, I'm done with the map, etc.

Finished just in time to attend a meeting about heavy budget cuts at UNR. Check the earlier entries to see how far this came. On this version, the lava dams are indicated and I have exercised my urges to name stuff.

I will only change something if it is factually and not only aesthetically erroneous.

I'm sick of the map, I'm sick of the map, I'm sick of the map, etc.

Here is one version...had some plotter problems (shocking, no?) and dumbed the base down a little. This one is about 24 by 28.

I'm the map, I'm the map, I'm the map, etc.

This is what I came up with for a draft layout for the map. I will add the base material images when back at my office computer. Any votes for shaded relief vs topo or some other possibility (e.g. a combination of those, the NAIP imagery, satellite imagery)? I am traveling after noon tomorrow and will be unavailable on Thursday and Friday. Weekend is possible, but I have a talk to prepare for AGU and haven't started that yet.

The draft above shows some labels on the lava flows. I could add more or delete the ones on there. Anyone have a preference? Let me know soon.

Owyhee Map for AGU...almost there

I have reached a point of no return on the map and have gotten close to a final draft for inclusion on AGU poster(s). In this version, a lot of the detail is left out:

no bedrock older than Bogus Rim flow
undivided landslides,
undivided mainstem fluvial deposits (active channel is divided),
undivided lacsutrine deposits.

Reasons: map is too complicated for showing everything and too many loose ends in some units (mainly generalized bedrock) to build polys.

The colors are chosen to highlight the various features and are obviously not conventional geologic map colors. Mainly, those conventions are a real annoyance when you map detailed surficial units anyway. The snippets in this post should give you a good idea of where things stand. I am leaving town tomorrow afternoon and cannot have this map hanging over my head...and I bet that spud is tired of waiting.

It will be pretty easy to create a basemap using these data as the 1:250,000 version indicates. I need some feedback on where to go from here.

Cool Tangent...Rocky Butte and Jordan Creek

I have been mapping the Q basalt flows that didn't make it to the Owyhee and have learned that the lava v. water situation on Jordan Creek is exceptionally cool and interesting. We should really check this out this spring if time permits. The photo here shows a very well developed overflow channel. It appears to have filled in and then incised some depressions on the flow surface. Lots of interesting features associated with this flow.

Map-tacular Effort

Great job on the mapping Kyle! I am looking forward to seeing it on our poster.
-Spud

Miraculous Late Night Recovery!

GeoMap-a-thon, Day 6. The curse of Topology

Put in 7 hours on map today to find an inexplicable topology error that precluded building polygons. I was so excited for this to happen. After lengthy consultation with local GIS supergeek, turns out that exporting feature dataset as shapefile and then reimporting it as feature dataset worked. Took 1.5 hours to figure that out. If you get this error in your life, don't panic like I did, it is not worth it (just follow the steps above):


Despite this roadblock, I made alot of progress. Will post map tomorrow AM...can't work on it much at all beyond tomorrow.

Holy Crap, day 5 was a bad one

Lots of tedium, lots of cursing, lots of computer problems. Nonetheless, I made a lot of progress. Here is a snippet of the Bogus Rim / Lambert Area. Don't be alarmed...there are still some tiny holes that lead to bleeding polys. This does show my interp of the landslides vs. in situ rox in the Bogus Rim area. Until Monday....

Yeehow GeoMap-a-thon, Day 4

I don't have a particularly meaningful map to post today. Have been mired in correcting imported linework from the vr...topology issues. However, did spend a lot of time mapping in the landslides coming off of Bogus Rim and had a good online chat with Spud about some contentious mapping calls of mine. Worthy of a group discussion in the field for sure.

Using the vr is instructive, but it is most useful in topographically complex areas. Many of the lines I added were redundant with respect to prior flat mapping and field mapping. By placing the vr lines on high-res imagery using ArcExplorer (get it now) also proved just how useful it would be to be able to directly edit arc-ish linework. The screen shot below is what my computer looked like most of the day. The area is the large foundering slab of Qbw above Dogleg. Check the killer perspective on the right vs. the flat map perspective on the left. Note also that the overprinted lines on the left are the imported vr lines and the prior flat mapping lines. My goal is to now find out why I can't place vectors on precisely georeferenced images draped on topography.

Check out ArcExplorer. It is free. Not as good as Google Earth, but possibly more functional? At least it has the high-res imagery for our area. Lastly, it cannot adequately render the gorge because of the extreme relief and some bad orthorectification inthe NAIP data. Turns out that careful orthorecitification of high-res photo scans in the vr has some (but less) trouble here. If we can drape images on the LiDAR and map on that....

Yeehow GeoMap-a-thon Day 3-D

No map to post today, instead here is a shot of me totally geeked-out (electric glasses, mp3 player, Blackberry) working away on the map. The 3-D mapping is great, but it takes some serious time. Since it allows you to check the elevation of any point in the image, it allows for some checks of in situ vs. landslide strat...this has led to some significant reinterpretations of the suite of landslides off of Bogus Rim...lots to talk about. Lots more in situ rock there than appears at first, second, and third glance.

Yeehow GeoMap-a-Thon day 2

Good progress today despite interminable interruptions. Heather (NBMG Yeehow in training...YIT) set up Rome Valley on the VR today...the 3-D computer mapping device. I will get to mapping that in more detail tomorrow AM. 3-D will help immensely in that reach. Have relied on much of Cooper's mapping to get the lava flow extents. Some refinement added. Some questions about where some begin and where some end still remain. Anyway, here it is:

A big week for the Yeehow GeoMap

Howdy. Here is a 1:200k version of the map as it stands at the end of the day today. I will commit to updating this image via blog entry each day through Friday as a form of personal motivation. Many of the color bleeds will go away with some topology corrections and some additional lines. Yes. I did start mapping the Q lava flows to their sources. At some point, I need a little help from Cooper with this. Note the major league lava-water interface in the Danner area (east of Arock)...yowza. Looks like a good side trip for Yeehows. Totally cool and unexpected (by me, at least). Sometimes it is good to look beyond the map area, no?

Incision of Hell's Canyon

Hi again,

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:
http://earth.boisestate.edu/home/swood/WOODCLEM-2002.PDF
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.
-Spud

Paleoclimate of northern Great Basin and Owyhee area

Hi folks,

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.
-Spud




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,
Washington, D.C.

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
(2):151-182.

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
(3):427-458.

OWY-19, river left outcrop of WC between Bogus Falls and Dogleg

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.
-Spud

Cascadian Pyroclastic Goodness

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

Geologic Compilation Celebration

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.

Reply to depocenter in middle of WC flow

Yes, the comment fcn on the blog seems to be out of order--this post is in regard to Dr. Jerque's post of WC in VR hindsight, etc. etc.

Dr. Jerque,

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!
-Spud

Ouch. I missed these... comment by Lisa

Lisa e-mailed a nice comment that I have placed on the blog for the record. I agree with her points. Something appears to be wrong with the commenting function in blogger...not with Lisa.

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.

Ouch. I missed these...

On my (not so) recent trip down the Grand Canyon, I had a lingering memory of Cassie suggesting that Keith Howard had been a little hard to convince as to the reality of lava dam failure and catastrophic flooding there, but that some of the field evidence finally convinced him. I had that lingering memory because I was weakly skeptical based on the lack of such evidence on the Owyhee, but was confused because I had read (and reviewed) a couple of her papers. Turned out that I really needed to see the stuff in person with a better backlog of personal observations. As I noted in a previous post, some of the flood evidence was (to me) hilariously clear and my skepticism was baseless for the most part.

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, khoward@usgs.gov 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.

West Crater flow (Qbw) in VR...old new insight

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.