Wednesday, December 21, 2011

AW #41 a significant geologic event

From Ron: What we seek for Accretionary Wedge #41 is an account of a geologic event that you experienced firsthand. It could be an earthquake, a landslide, a flood, a volcanic eruption, etc. (but don’t feel compelled to stick to the biggies – weathering, anyone?) – some geologic process that you were able to directly observe and experience. The event itself need not have been dramatic or life threatening, or it may have been.

It has been said that as we grow older our tendencies to be high in the mountains change into spending quality time in the desert. I am in that stage where my summit time is being eclipsed by my canyon time. So it was just last summer on a blue sky day that I saw the very beginnings of a flash flood coming down the canyon.

Lucky for us, the catchment basin was small and so was the run off amount, but the idea to see the very tongue of red frothy water coming down the once dry stream bed was enough to make us sit up and take notice.

We were actually between two choke points of narrow slot canyons. So it was easy to step up and out of the way of the water. If we had been up or down stream just a little it would have been harder to get out of the way.
I have taught classes about the bed load and suspended load of streams. I have had my students put pfd's on and act as particles as we float down the Colorado River, but to see the red mud flowing around the corner where there was no water just moments ago was pretty cool. It was so cool, that we just watched and didn't take as many pictures (or video) as you might imagine.

The last part of the canyon, where we would rather not be during any water event flashing or not.

Sunday, December 11, 2011

A mid-continent shallow snowpack

Went snow shoeing this weekend near the summit of Red Mountain Pass where we were a bit disappointed with the snow depth and quality of the snow. However, I admit that I am a snow snob and expect quite a bit when I am recreating on snow.

The snow is always dry and light here, but today it was dry, light and bottomless. Any step off of the packed trail would send our snow shoes to the ground (albeit that was not far away). The snow crystals looked very much like the image below, large facets not anything like their original snow flake self. This is what happens with a shallow snowpack.

Snow crystals on a pine tree after a little bit of metamorphism.
This winter saw a very nice snowfall of at least 50 cm, a few weeks ago, but since then hardly anything. The weather, clear and cold each day and it can get cold at 10,000 feet. In fact, when we started that morning the temperature at the car was 9 F.

The metamorphosis of snow crystals depends on a few factors, not the least of them is the temperature gradient through the snowpack. What we were seeing was a large gradient. The bottom of the snow pack at the ground is usually thought to be at 0 C while the top of the snowpack is equal to the air temperature. Lately we have seen temperatures approaching -25 F or -31 C. Making a gradient of 32 C over the depth of the snow which originally was 50 cm. It seems that if the gradient is smaller than 10 C/m then the metamorphosis of snow will lead to a more rounded grain of snow that can connect with its fellow snow grains easily making for a more stable snow pack while gradients greater than 10 C/m will result in a more faceted grain which will not connect all that well with its fellow snow grains. Our gradient of 32C/0.5 m is certainly within the this-snow-grain-does-not-play-well-with-others category.

A fantastic picture of a snow flake "growing" a large facet. Image courtesy of the Utah Avalanche Center
It seems that the newly fallen snowflake will sublimate small amounts of water vapor from the tips of the crystal arms (where the vapor pressure is greater) . If the temperature gradient is small enough (<1 C/cm) then the vapor will re-condense in the areas between the arms (where the vapor pressure is less) effectively making the snow flake into a round snow grain. If the temperature gradient is too large (as in the example) then the water vapor will sublimate from the tips of the crystal arms and re attach onto a cold region of a nearby snowflake creating the large faceted crystal. These crystals will not connect with its fellow snow grains well creating an unstable snow pack.

This is the problem with the early season snow followed by a week or so of good weather. The snow pack is now made of a bunch of grains that will make a poor base for the coming winter.

Stay tuned for any avalanche reports as the snow pack starts to pile up. But, perhaps the La Nina will keep the snow depths to a minimum and we can worry about drought instead of snowslides.

Saturday, December 10, 2011

A tortured inner canyon

I accept the blame that my Grand Canyon trip was in early October and we are currently observing early December.

I think what impressed me the most about the Grand Canyon was the tortured rocks in the inner canyon. I am used to being around 1.7 billion year old gneiss and schist while floating the upper stretches of the Colorado River. The Vishnu schist and Zoroaster granite exceeded my prior experiences greatly.

Putting my hand on the Great Unconformity. An amazing amount of missing earth history under my hand.
An old river runner told me that most river guide books will identify any crystalline rock as schist so I wanted to visit the bottom of the Grand Canyon to see what was there. Take a look at the folding!
An intrusive Zoroaster vein. There are so many times I wish I had normal color vision to see these outcrops as others can. It is pretty vivid with my red/green problems.
The dark inner gorge

Friday, October 21, 2011

Trilobites before lunch

The last time I tried this blogger decided to stop working.

Earlier this month I had the opportunity to hike across the Grand Canyon from rim to rim. Wow! what a trip. I went with a group from the Grand Canyon Field Institute taking a geology class (of course) The trip met all of my expectations both as a backpack trip and as getting to know the geology of a part of the Colorado Plateau I am not familiar with. Most of my time is spent around Canyon lands where I am quite familiar with the Mesozoic sedimentary sequence. This Paleozoic stuff was all new to me. Hence the title of this post. We started with the Kaibab limestone and ended in the Cambrian Tapeats sandstone where we spent some quality time during lunch looking for trilobites. This is just the trip down. It gets better!

Looking over the edge the night before our descent into the canyon.
The Coconino sandstone. A layer that scares the hikers traveling back up to the rim. This Permian aged sandstone creates a 300 foot cliff with some great cross bedding showing the "petrified" sand dunes .
Lots of chert nodules throughout the Redwall limestone, another formidable cliff former!
Ribbon falls, notice the travertine dome at the base of the falls. Calcium carbonate rich water has created a fantastic dome similar to a stalagmite in a cave.
Next will be about time spent at the bottom of the canyon.

Monday, September 19, 2011

A new campsite for geology field class

Last week I spent an enjoyable 4 days floating down a nearby stretch of the Colorado River looking for new places to take my geology-by-canoe class. There is a campsite almost 1/2 way down this particular stretch that has a name made for a geology field class. "Fault Line".

These images show the Kayeta-Wingate combination being bent downward by the actions of the fault. The canyon just to the left of the fold continues upward right along the fault. It is an easy hike with the exception of minor 15 foot pour over that requires a touch of scrambling.

How easy is it to find this fault line? The BLM post identifying the campsite. Unfortunately the site is found on an outside bend and with the fast water of last week the landing was not pretty. We stayed dry but just barely.
The view across the river from the campsite. Although not as dramatic as the big fold in the first image, I think the fault line is easier to see. The right side (upriver) shows the mid-Jurassic Entrada sandstone. Just downstream from the fault is the early-Jurassic Kayenta formation.
As an added attraction, the cobbles on the gravel bar encompass examples from all directions in the Colorado Rockies. And, if that wasn't enough the channel in the fore ground makes for an awesome float. I love having my students become particles and float down stream.

It truly doesn't get any better

Wednesday, September 7, 2011

Serendipitous geology

I can't believe it has been over a month since I last posted anything...well I can believe it I guess. It is a combination of it being summer and constantly on the move and being a bit lazy when it comes to posting.

Last week I was poking around an un-excavated Pueblo III site in the Montezuma Valley near Mesa Verde NP. I am quite used to looking at cliff dwellings all around the 4-corners area, this was the first Pueblo aged, non-cliff dwelling that I had spent any time in. What struck me first was that the Mancos shale does not have much of the favorite building materials- sand stone blocks. The Mancos shale is an incredibly deep layer of marine sediment left over from the Cretaceous Seaway. It is not known for it's sandstone building blocks. However, as the inland sea retreated somewhat, there were deposited three units that can be used for building blocks: the Point Lookout sandstone was deposited followed by the Menefee formation, a coastal plain region and a local source of coal and lastly the appropriately named Cliff house sandstone. The Cliff house is where most of the famous cliff dwellings are found.

However, the Montezuma Valley is dominated by the Mancos shale.

Lucky for the former inhabitants of this little pueblo the Menefee formation, is not only rich in sandstone but has a habit of slope failure creating sandstone deposits on the valley floor. The search for local building materials just got easier. A little bit of driving around the nearby county roads found a potential sand stone quarry.

To be a more complete geology day and completely overshadow the archeology was the discovery of fossil shells in the sandstone building blocks. My knowledge of paleontology is quite limited and I won't even hazard a guess at the names of the fossils we found.

A section of wall peeks out from beneath some vegetation with Mesa Verde in the background.

Some of the pottery shards found near the site.
A chunk of ancient building materials complete with even more ancient fossil evidence.
...and more
A close up of the surviving Pueblo wall.

Friday, July 29, 2011

Summer, a time for roving bands of geologists

We just returned home from a spontaneous road trip to the Pacific Northwest. While traveling through the Inter-mountain West we saw many a van load of students standing along side the road with notebooks at the ready with an older guy in front waving his arms around. The only part of the scene that changed was the rock cut, sometimes flood basalts (and some cool columnar basalt) sometimes river terraces and often rock units known for their fossils.

Field Trip Season!

Unfortunately I never had a camera ready when we came across a group of geology students learning the ways of rock cuts. And, only once did we have the chance to talk with any of the groups. A group from the University of Kentucky were on a western National Park tour after spending some quality time in a field camp near Gunnison Colorado.

It is good to see the tradition continues.

Sunday, July 3, 2011

First summit of the year

It really is a testament to the amount of snow and the cold spring that our first summit (and it really wasn't a real mountain) was on July 1st. Even now, many trailheads are not open and if they are the amounts of snow, especially in the sub-alpine forest is still pretty deep. We had tried other peaks earlier and were unsuccessful on everyone. So Twin Peaks right outside of Ouray was our first summit of 2011.

The summit rock is part of the San Juan formation or just the San Juan Tuff a volcanic-clastic sedimentary rock. Within this impressively thick formation (3000 feet in places) , you can identify breccia clasts from long ago pyroclastic flows and thick welded tuff segments resulting from falling ash. A cool place!

The "little sister" right before the last big climb. Even without zooming in you can see the brecciated surface.
There is still a bit of snow in the high country
A long way down to the City of Ouray CO. This was a fun 3000 foot climb.
An close up showing the volcanic-clasts within the matrix. Unfortunately there is quite a bit of biology hiding the rock details.

Thursday, June 30, 2011

The only geologist on an archeology trip

Way back in graduate school my emphasis was on the glacial history of the Colorado Rocky Mountains. At the time, I loved the alpine environments, the cold temperatures and the climbing associated with glaciers. However, as I have grown older I have found that I enjoy the warmer climate of the desert southwest. Please don't get me wrong, I still spend time in an alpine environment, but the desert places have captured a big part of me.

While exploring the canyons found in the southwest I have changed my geology interests from glacial episodes of the Quaternary to the ergs of the Mesozoic. With more and more time spent in the canyons, I have found a strong interest in the previous occupants of the canyon country. You can only look through so many ruins and see so many rock art panels before you are just driven to know more.

So, a few weeks ago I joined a group of both professional and amateur archaeologists on a float down the San Juan river in SE Utah. What fun! What great examples of rock art. And, I was able to explain how some of the geology happened to be. The story in the rocks actually started 350 million years ago...not just 1100 years ago

Chert nodules
iron concretions. Many of my fellow explorers were not ready for a little chemistry lesson at river side to explain the origin of either the chert or the concretions.
The rock art was tremendous

The Mexican Hat. What a great example of the more resistant cap rock
The Raplee anticline

Friday, June 17, 2011

Where did the Wingate go?

If you have read this blog for any amount of time, you have already gathered that my favorite formation on the Colorado Plateau is the Wingate sandstone. In fact, the cover photo of the blog is of the Wingate sandstone along the Green River. It is a late Triassic- Jurassic aeolian sandstone. The grains are very uniformed in size making fantastic conchoidal fractures when blocks fall from the cliff face. Making a very nice cap rock on top of the Wingate is the Kayenta formation. The Kayenta, an early Jurassic siltstone-sandstone showing evidence of mid energy stream action is cemented very well and acts as an excellent cap rock. The top most component of this group (the Glen Canyon Group) is the Navajo Sandstone. This sandstone is another Jurassic aeolian sandstone that hints at being one of the largest sand islands ever seen on planet earth.

But...back to the missing Wingate.

Most of my play area is in Southeast Utah along the Colorado and Green Rivers. This past month we have spent some serious time in South central Utah in the Paria drainage. Here we see the familiar Glen Canyon Group wit the navajo sandstone along the horizon, the Kayenta formation directly below but instead of another aeolian sandstone there the Moenave Formation with reddish siltstone and pinkish sandstone showing clear evidence of water deposition. What a difference from the windblown Wingate.

The story in the rocks suggests that perhaps, in the early Jurassic we would have been in a desert resort area with ponds and streams with a large desert just to the east. A paleo-Palm Springs?

Canyon cliffs of Navajo sandstone with the Kayenta formation making the canyon bottom
Canyon walls of Wingate sandstone
And 100 miles to the west... the high white cliffs of Navajo sandstone, the reddish ledges of the Kayenta formation and the reddish-pink slope forming Moenave formation near the bottom.

Wednesday, June 1, 2011

high water

Last weekend while exploring different parts of the Uncompahgre Plateau we came across an unfortunate place to leave a truck. With the recent warm weather (and the extra long cool spring) the rivers are coming up high and fast.

Its not only the rafters that need to be careful around rivers.

Monday, April 25, 2011

History lesson turns to a chemistry lesson

A few weeks ago I described a snowshoe history field trip of the Red Mountain Mining District. This area took out millions of dollars of metals in the late 19th century and early 20th century. Unfortunately the profits are long gone and we are left with the clean up. There was lots of evidence of iron in most every mine in the area. Obviously, the RED in Red Mountain is due to iron mineralization in the rocks.

What hard rock mining did was increase the air and water exposure to the iron pyrite found naturally in the geology of Red Mountain Pass. Iron pyrite (FeS2) reacts with the water and oxygen to form sulfate (SO4). which combines readily with water to form sulfuric acid and ferrous iron.

FeS2 + O2 + H2O = Fe2+ + SO42- + H+

The ferrous iron reacts with the air and water to create ferric iron. The ferrous ions are soluble in water while the ferric ions are not. The ferric ions precipitate out of the water coating the entire substrate with an almost impervious layer of iron. No matter the water chemistry, this iron pavement alone signals the end for any biology in the water, there is no place for macroinvertebrates to live, no place for aquatic plants to take hold. The food chain dies at the lowest trophic levels.

Fe2+ + O2 + H+ = Fe3+ + H2O

However, the water chemistry is not normal. Most biology needs a near neutral pH to live. The sulfate ions reacting with water results in the formation of sulfuric acid, lowering the pH to extreme acidic conditions. I have measured the pH of alpine creeks down to 2.0.

FeS2 + Fe3+ + H2O = Fe2++ SO42- + H+

Part of trying to fix the Uncompaghre water shed is to determine how bad was the water prior to mining. At the time, the miners did not do any environmental impact studies before they started digging. The best we can do are some anecdotal comments about catching fish just outside the mining camps- an impossibility today. It is obvious that there was natural mineralization present before the advent of mining. So, how much can be cleaned up today?

Do we have the will to clean up seriously degraded waterways way up in the headwaters?

Red Mountain #1
Looking for red rocks next to the channelized and embedded Red Mountain Creek
Part of an old tailings slurry pipeline. The miners used wooden flumes because the metal corroded to quickly with the acidic water.
Red Mountain Creek in the winter. The yellow water stands out nicely against the white snow.

Wednesday, April 13, 2011

feng shui on the trail AW 33

This month, John in the Taconic Mountains has asked about how we incorporate geology into our homes. I was thinking about some landscaping we had done in the backyard or about the fireplace in Ed Abby's old home in Moab UT where the rocks represent the stratigraphic column of the Canyonlands. BUT

I didn't have any pictures. I know that this isn't exactly what John had in mind, but it sure beats the shelf with my "prettiest" hand samples.

Last week I was visiting Zion National Park and hiked up the West Rim Trail past the infamous Angels Landing. While walking up "Wally's Wiggles" we saw this fantastic example of a Navajo sandstone iron concretion used in the retaining wall. Whoever was trail crew leader had a great eye for aesthetics and incorporated some fun geology in the trail.

Looking way down at Wally's Wiggles. Click the image for a larger version.

the concretion in the wall
up close

Monday, April 11, 2011

A history lesson

A few weeks ago I attended a ski/snow shoe tour of the Red Mountain Mining District courtesy of the Ouray Historical Society and the Uncompahgre River Project. The area I took the most pictures was the picturesque Yankee Girl mine.

The Yankee Girl was discovered in 1881 and by the time most mining had ceased in 1896 over 3 million dollars of gold, silver and lead had been brought to market (while leaving tons of debris on he ground near the mine). The Yankee Girl. like most mines in the district took advantage of several volcanic breccia chimneys, a result of the creation of the Silverton caldera. The most productive ore seems to be associated with the quartz porphyry found in the chimneys. Lead and zinc ore paid he bills, the silver provided the profit and the little gold that was found provided the headlines.

lunch at the Guston mine

The Yankee Girl headframe
The Yankee Girl up close. The main mine shaft dropped over 1000 feet from this point.

Monday, March 21, 2011

windy spring= disappearing snowpack

The snowpack in the northern San Juan mountains is still looking pretty good at 113% of normal. However, every spring we get these nice breezes that move the red dust from the desert landscape of Utah and Arizona to the mountains of SW Colorado. Between the sublimation of snow in these warm winds and the decrease in surface albedo from the dark dust, we can lose a large portion of our snowpack in just one wind event.

This "weather story" is courtesy of the National Weather Service explaining what we have in store for today and tonight. The first major wind event of the new spring. Notice how the SW winds come from the deserts right onto the southern mountains. Through most of the winter much of the west was damp, but now it seems that the snotel sites in New Mexico and Arizona are showing snowpack percentages in the single digits. Not a good sign at the END of winter.