Friday, November 26, 2021

End Cretaceous Tsunami Event Recorded in Rocks on the Tora Coast in New Zealand

 

This one from my colleague and good friend Jack Share. Watch this five minute video here to understand how a deep sea rounded conglomerate was formed. And be sure to check out Jack's blog, Written In Stone: Seen Through My Lens.

Monday, November 15, 2021

Salvage Geology in Cataract Canyon

Aerial view of the confluence of the Green (light brown) and the Grand (darker brown)
that formed the Colorado River (left) prior to 1922 . (Image taken May 25, 2015) 

I've run the rapids through Cataract Canyon in Canyonlands National Park and Glen Canyon National Recreation Area a few times and marveled at the exquisite geology exposed there. In fact, I believe that the country surrounding the confluence of the Green and Grand rivers is the quintessential location of the heart of the Colorado Plateau. Names like the Orange Cliffs, the Land of Standing Rocks, and Island in the Sky evoke images of stratified terrain that may be equaled elsewhere nearby but never surpassed. You can see some of my past blog postings of trips through the canyon here, here, and here.  

Image taken May 25, 2015

The ongoing drought in the American Southwest has caused the level of the Powell reservoir behind Glen Canyon Dam to drop 156.5 feet from its full pool elevation of 3,700 ft. (above mean sea level). This has caused the once drowned channel of the Colorado River in Cataract Canyon to slice through over 35 years of sediment within a narrow, confined channel. In the photo above, you can see part of this great sediment pile directly above the boat and in the shadowed bank on the right. The Powell reservoir once inundated  these terraces but the lower level of the reservoir causes the river to slice through them.

The Powell formation. Image taken May 25, 2015

Now, the Returning Rapids Project is documenting the scientific and social significance of this sediment excavation event. You can read an article from the Salt Lake Tribune here about some of the results. 

For the Edward Abbey that resides in many Southwestern souls (and I proudly proclaim my fondest affection for the anticipation of the demise of the unneeded reservoir), this is an exciting moment in time. It is an opportunity for scientists to monitor both the deposition of the Powell beds for the mid-1960s to about 2000, and the erosion of this sediment pile as the level of the reservoir drops. 

In the linked article, the author refers to the sediment body as the Dominy formation, after Bureau of Reclamation Director Floyd Dominy, who essentially spearheaded the drive to construct Glen Canyon Dam in the 1950s. However, all rock units in geology must be named after a geographic location where they are first studied and described (called the type section). Until someone names a feature after Dominy, a better name for unit might be the Powell reservoir formation, or simply the Powell formation (both names in a rock unit are capitalized if the name has been formalized with a scientific description; if it has not yet been described then the suffix name is lower case, signifying that it is an informal name).

Monday, November 08, 2021

My First Grand Canyon Backpack Since Knee Replacement Surgery

Well, it is nice to have this goal finally achieved! 23 months after having two total knee replacements, my wife and I headed back down to the bottom of the Grand Canyon on a six-day backpack. While rehabbing after surgery in December, 2019, a photo of me hiking the Tonto Trail in 2017 was placed on the wall of my hospital room to serve as inspiration to see my recovery through. It worked!

And I owe it all to this lovely lady, who was by my side these whole 23 months and made the necessary arrangements for my volunteer lectures at Phantom Ranch! Thank you Helen from the bottom of my heart (and knees).

To say I was bit uneasy to see if my knees could withstand the steep descent of the Bright Angel Trail doesn't convey fully my concern. 

Within 50 meters, my left knee began its odd pain. But after the Mile-and-a-Half House, I took a break and upon beginning again, the pain was gone for the rest of the trip. It apparently was just warming up.

And then it was like the other hundreds of hikes I have completed here such that the beauty and scale of the Grand Canyon took over! This is Jacob's Ladder through the Redwall Limestone.

This is the view from Plateau Point across to Zoroaster Temple. The weather could not have been better for hiking the entire six days.

I had never before noticed these detailed trilobite appendage traces in the Tapeats Sandstone near Plateau Point. The critter was swimming in shallow water but pushing across the bottom sand.

At Plateau Point proper, these trilobite "landing" scours have always impressed me. Imagine the swimming sea creature coming down to the shallow sea floor and scooping out a place for itself. Note also in the upper left a trace known as Corophioides, paired holes at the top of the bedding planes that transition to concave-upwards scours at their base. These are interpreted as dwelling structures for suspension-feeding organisms such as annelids.

One of the trail guides we met out at the Point told me of a trace fossil he has stashed (people steal these things) so that he can continually show his guests trip after trip. I used this technique myself when I was a trail guide. This is a trace known as Rusophycus, a resting or predation escape structure for a trilobite.

A beautiful sunset was seen from Plateau Point toward Dana Butte. Horn Creek Rapid at relatively low water can be seen (and heard!) from Plateau Point.

The Tapeats Narrows along the lower Bright Angel Trail is one of my favorite places in all of Grand Canyon.

Beautiful Buddha Temple framed by Fremont cottonwoods.

Finally, the bottom of the canyon and the Colorado River was achieved.

This was our home for 4 nights - Bright Angel Campground site 17.

I gave a geology lecture to guests at the Ranch each afternoon at 4 PM. I talked about Grand Canyon rocks and how the canyon was carved.

Rocks and resources for the talk were available.

The lectures were well attended and appreciated by tired hikers and sore mule riders.

An outcrop of boudinage in Bright Angel Campground was nearby.

The most beautiful view I know of is located here along Bright Angel Creek.

Thanks for believing I could do this Helen! Let's do it again soon!