Wednesday, June 26, 2013

West Fork Complex fire

from 40 miles away.



Spent the day up high yesterday (much cooler!) and watched the afternoon heat amp up the West Fork fire. It was barely visible in the morning but as the afternoon wore on we could watch the cloud grow larger. What is needed is a good rain storm and the forecast doesn't look all that favorable just yet.

Thursday, June 6, 2013

Studying stream velocity in the Grand Canyon

How much fun is a Grand Canyon raft trip for a geologist? Well...plenty! I had the opportunity to float the Colorado River through the famous canyon a few weeks ago. I had plenty to look at and to explore but one thing literally took the oar right out of my hand. 

While rowing even the easy sections I could easily feel the current push and pull my oar with practically every push I made.  Frankly I am used to sections of the upper Colorado where there is much less force.  Was I being just lazy, or was there something else at work? 

The week we were on the river, the discharge at Lee's ferry, (mile 0 of the Grand Canyon) was a steady 8,000 cfs (cubic feet per second) for a study the NPS was conducting. Discharge is simply a measurement of how much water is flowing past a certain point. here in the US we measure discharge in cubic FEET/second, while the rest of the world measures cubic METERS pr second...oh well.

Often when I am on the upper Colorado, the discharge is similar 5,000-9,000 cfs. This could account for some of the extra force I was feeling on the oars, but not all of it. 


 Rowing through the Muav Gorge, looking serious and trying to avoid obstacles.


 Navigating the famous "Black Rocks" of the upper Colorado River, again looking serious and trying to avoid obstacles.



The diagram below, borrowed from California State University, shows that the velocity is some how proportional to the wet area (depth times width).  Looking through some old notes when I would have students measure the width and depth of the upper Colorado to calculate discharge, I could see that there is little appreciable difference in these two physical parameters between the upper Colorado and the Grand Canyon.

Thank you CSU Long Beach


However, the one physical parameter I found that was different was river gradient. Looking through my river guides and doing some simple math I found that the upper Colorado stretch has a gradient of 3+ feet/mile while the section of the Grand Canyon has a gradient of almost 7.5 feet/mile.

Could this be the reason I found the oars being snatched out of my hands?



Thursday, May 16, 2013

yet another example of a cap rock


Last week we were camping along the Colorado River above Moab Utah when we saw these pillars showing how a more resistant chunk of sandstone will protect the less resistant shale below. The last blog post showed how the more resistant White Rim sandstone was left standing even after the softer Organ Rock shale had all eroded away leaving a really fun arch to visit.




Differential erosion of the Cutler formation along the Colorado River

Wednesday, May 8, 2013

Regime change

What a fun place, Musselman Arch in Canyonlands National Park.  The arch is composed of the White Rim sandstone a Permian aged wind blown classic sandstone in a near coast environment. Sandstone is fairly well cemented together making a rock unit somewhat resistant to erosion. Right below the White Rim you can see a reddish (isn't almost everything in the Canyonlands red?) brown silt-mud stone formation. This shaley material is poorly cemented making it fairly easily eroded. You can see how the sandstone in the arch is lasting much longer than the missing shale/silt/mud stone found below the arch. 


So the White Rim sandstone is acting as a cap rock to the softer Organ Rock found below.

Musselman Arch is found along the White Rim mountain bike trail. You can ride down the Shafer trail to the arch and back in a day, but the 1300 vertical foot climb back up is an interesting way to end the day's ride.

Thursday, March 28, 2013

Joshua Tree boulder factory


Spent some time in Joshua Tree last week. It has been a long time since I have played in so much granite. In fact it was way back in grad school and we had a professor who always brought the freshman students up to his idea of a "boulder factory" We would spend a little time discussing chemical weathering and then let the students climb around a little bit to experience the sharp quartz minerals left behind.

This was the same thing...only I was the one climbing around. You can clearly see how the once monolithic rock has jointed to make very regular blocks with the resulting acidic water rounding the blocks into spheres. In some cases, you would swear these were very large river rocks eroded down by the movement of water.



 Eroded monoliths with quartz intrusions. These intrusions are harder than the surrounding country rock. In some cases the intrusions were vertical making a quartz wall.
Very spherical boulders. These boulders were once part of a larger monolith similar to the image above.   A series of joints, both vertical and horizontal made regular shaped cubes of granite. Acidic water running through the cracks chemically eroded the feldspars into clay minerals that have since been flushed out leaving behind very smooth spherical boulders.

Friday, March 15, 2013

Did you see it?


4 days camping in the desert
4 days with great open views to the west
4 days with clouds in the west right at sun set and lasting most of the night


Comet Pans STARR borrowed from the NASA.gov web page

Sunday, March 10, 2013

Where is all the snow?


Anyone who has looked through my past blog posts have seen my fascination with our snow pack, whether how big a year we are having or how low a year we are having or about its ability to slide.

This year, like last year is all about how little we have. The graph below, courtesy of the NRCS, shows  the snow totals for the Gunnison River drainage in Western Colorado. The line in the middle is average. The dark line that ends suddenly is this year. Not only are we below average, but we are below last year, a bad year. Note how the slope of the two lines are almost parallel. This suggests that the winter storms are in line with normal. But, look at when we started accumulating snow. The new snow year started last October 1. It took until mid December before any appreciable snow covered the ground. Look at last years graph. It was about this time last year when the snow started to melt. Way ahead of schedule. 

I know that two years do not make a trend. I hope that the next two years will be as high as these years are low, just look at two years ago with a record breaking snowfall. But looking at these past two years with everything else happening around the planet, I wonder if we are starting to see the new normal. Time will tell.