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Fresh Geologic Froth

Foamy digital flotsam for me and you

Random shots in Piute Valley, Nevada.

       

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Posted November 18, 2009
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Mud curls in Piute Valley, Nevada

     

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Posted November 17, 2009
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Turns out that graphs in ArcGIS are pretty damn handy.

It was recently brought to my attention that the graphing tool in ArcGIS could be really useful if you had the right type of data (thanks to ND at UO). Well, I spent most of today trying to refine a longitudinal profile of the Owyhee River from my coveted LiDAR data set, and it occurred to me that I had some useful data. 

My goal beyond just examining the profile was to indicate the locations of major landslide complexes along the river corridor to investigate how they may influence the river's gradient.  I actually extracted the profile data from the data using a tool in GlobalMapper which I like. I converted the data to an excel spreadsheet, opened the sheet in Arc and then exported it into my Geodatabase as a feature dataset. Once it was in there, I created a graph of the data (basically the profile) and began to select points on the profile along key reaches that I had mapped. Lo and behold, those points i selected on the map lit up in the profile graph. Sweet. This was huge. It goes both ways as well. Select points on the graph, and they light up on the map. 


Restrict the displayed points on the graph to those selected on the map and you can export them as a subset of the data. This step comes in really handy for plotting the exact position of the landslide complex-reaches on the overall profile figure. Previously, I had stupidly brute-forced this process. Typical. The result is below:


Also very useful is to plot the profile data in the form of cumulative distance vs. slope of channel segment. This graph immediately indicates important trends and anomalies in the data. Turns out that the anomalously high slope values and negative slope values relate, in this case, mainly to inadvertently collected data from vegetated bars, extremely coarse gravel bars, and even wave trains at some of the rapids. Thus, an important and informed QA step can be taken to clean out the riff-raff. In general, though, you can see how useful this method is for zeroing-in on areas of key interest. For example, many of the points on the map below correspond to rapids

 

 

 

 

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Posted November 13, 2009
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Lyell was a closeted catastrophist?

A recent (re?)-discovery by fellow Yeehow JEO:

Not so fresh geofroth, but insightful nevertheless:

Our historical figure states thusly...

"The power which running water may exert, in the lapse of ages, in widening and deepening a valley, does not so much depend on the volume and velocity of the stream usually flowing in it, as on the number and magnitude of the obstructions which have, at different periods, opposed its free passage."

which follows upon...

"It is evident, therefore, that when we are speculating on the excavating force which running water may have exerted in a particular valley, the most important question is not the volume of the existing stream, nor the present levels of the river-channel, nor the size of the gravel, but the probability of a a succession of floods, at some period since the time when some of the land in question may have been first elevated..."

Who is our extrafluvial catastrophist?

None other than Charles Lyell!

Lyell, C., 1830, The Principles of Geology, vol. i. John Murray, London.
The first quote is from page 192, and refers directly to floods resulting from breached obstructions as key to forming valleys. The second quote is from page 188.

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Posted November 13, 2009
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Near-death experience of the Lower Walker River map, November.

Just had to post this one. While heading out to the field for a map review, this gem from a co-worker appeared on my Blackberry:

"...as I was trying to copy files into a subset archival folder...I ...managed to delete nearly all of the Lower Walker River work order folder."

This really happened, and yes, it involved every shred of data I had pored over while killing myself to get the map done. Thankfully, we actually have a fairly new system that reliably backs our data up.

All is well, now. Not sure what would have happened had the data been lost.  I managed to remain calm until I got the word that the data were revovered. Not sure how I managed that.

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Posted November 12, 2009
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Critics are everywhere

I was in the field yesterday doing some mop-up following a field review of a map. While checking a contact I had mapped that was queried by one of the reviewers, I happened upon this blunt assessment of my interpretation rolled up in a desert shrub.

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Posted November 11, 2009
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Flash Earth and Geohacks...Who knew? Not me.

Just happened upon a sweet and simple geobrowser called Flash Earth...very smooth and easy to understand. Added bonus for me is that it links to high-res images of my favorite field area that are available only in Yahoo and Virtual Earth / Bing Maps:


Seems my pals at Google still just don't care about SE Oregon. Anyway, I found the site by perusing the details in an exif header in one of my geotagged photos. Was checking that out in Irfan View, a program I was aware of but hadn't tried yet. Turns out, it is well worth a look:

Which led me to the GeoHack wiki:

The internets are amazing, no? Totally cool.

 

 

 

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Posted November 2, 2009
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Mapping yet another tortured river...the Mighty Bill Williams River, AZ

It is tortured river season in my office. Lately, I have been tackling Nevada's mighty Walker River and its shrinking terminal lake (new term is terminus lake...but that is a bit soft); and Oregon's Owyhee River and its travails with lava and landslides; but now I am back on to the Mighty Bill Williams River of Arizona. You know, the Bill Williams River.

Included below is a snippet of the map I am working on. Shown are 6 generations of lines that document major changes in the channel, most since a dam was finished in the late 60s. One day soon, this map will actually make sense, I promise.


The BWR is a special case. It is a roughly 35 mi stretch of river that traverses the hot desert below the confluence of two rivers that collectively drain more than 5000 square miles of western Arizona. Alamo Dam sits just below the confluence and traps essentially all of the sediment that would otherwise have gone down the BWR and to the Colorado River (well, at least to Lake Havasu). Also important to note is that the pre-dam BWR could attain peak discharges ranging up to 100,000 cfs, whereas the post-dam BWR can hardly exceed 7000 cfs owing to the outlet works of the dam. Thus, large runoff events that would have otherwise blasted through the system in a week or less (Spikes) are now converted to protracted, flat-topped hydrographs that lumber through the channel for up to several weeks to months (Bricks). Recall that these bricks are also sediment-free except for the sed picked up in the channel below the dam.

The result is an interesting experiment in channel change, sediment budgeting, and inadvertent (or otherwise) tamarisk farming. 

I won't be posting daily updates of this map, so don't worry. Be assured, however, that I will make a lot of noise when I finally finish it. This one is a long, long, long, time coming. Just ask the sponsors.

Some other BWR info: 

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Filed under  //   arizona   bill williams   mapping  
Posted October 30, 2009
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Holy crap, it's a map! Lower Walker River Map, October 28, 2009

Today, the preliminary map was finally finished. It will be delivered tonight or tomorrow AM. Too bad I can't take a break and bask in its preliminary glory.

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Filed under  //   mapping   Walker Lake   walker river  
Posted October 28, 2009
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State of the lower Walker River Map, October 27, 2009

The current 'Dead Tree' version...damn it is small.

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Filed under  //   mapping   Walker Lake   walker river  
Posted October 27, 2009
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