Tuesday, June 13, 2023

The 4th NAU Geology Alumni River Trip in Grand Canyon

In May of this year, 19 alumni of the Geology Program at Northern Arizona University gathered in Flagstaff for the 4th-ever alumni river trip in Grand Canyon. What a wonderful time traveling with old and new friends. Many of the participants this time were from my era at NAU. Some were from the 2000s and we had three from the 1970s. NAU Geology Rocks!

Dr. Jim Gaherty of NAU was along as faculty along with his wife Dr. Donna Shillington. Here Jim is talking near Sunset Crater and the San Francisco Peaks about the migration of volcanism in the region.

Two dear friends from NAU Geology in the 1980s - Ralph Hopkins (center) and Mike Darr (right). We are at the Desert View Watchtower on the pre-river trip field trip.

At Lees Ferry getting ready to depart.

Reptile trackway in the Coconino Sandstone. Avalanche features are also present on this surface.

Vasey's Paradise is back after a bountiful snowpack on the Kaibab Plateau this past winter. This voluminous spring was virtually dry the last few years due to a lack of precipitation.

The "hump" of limestone seen in the photo center is a mud mound within the Redwall Limestone. Algae likely was growing here on the seafloor some 340 million years ago, trapping silt and clay size particles.

Rafting past Grey Castle carved into the Bright Angel Shale in Marble Canyon.

Garnets found in the Vishnu Schist give an indication at what temperatures and pressures the schist was metamorphosed from shale or sandstone. This species of garnet forms at temperatures and pressures that today, are about 10-15 miles below the surface. Incredible to think that these rocks, now returned back to the surface, were once buried in that amount of crust! Where did it all go? Not to outer space - it was eroded onto the ancient landscape somewhere. But so much time has passed, who knows where it is now.

A typical camp scene - this one at the lower Garnet Camp near river mile 114. The Powell Plateau is on the top left skyline.

The oldest rock in the canyon is the Elves Chasm Gneiss, dated at 1.84 billion years old. This makes it 90 million years older than the Vishnu Schist.

I am enamored with cavitation pits that form on limestone near the rivers' edge. As fast moving river water encounters a tiny protrusion on an otherwise smooth boulder surface, it hydraulically forces the water away from the rock surface, creating a vacuum between water and rock. When the vacuum collapses, the concussive force pops off a piece of the boulder creating the scalloped pits.

I can never say it again - no one ever photographs this site - and landslide composed entirely of limestone debris. Fellow river runner Jon Hirsch was the first person to notice and describe this landslide.

Our group - what a wonderful trip. So many memories and new ones made on the river in Grand Canyon!