Tuesday, July 31, 2018

Iceland Circumtransit With Yavapai College Begins August 1

I am going back to Iceland! This time with Yavapai College EdVentures. I will be blogging from there so watch Earthly-Musings for stories and photos in the next few weeks. Here are some teasers from some of my previous trips to Iceland.

Looking south along the Mid-Atlantic Rift at Þingvillar National Park (pronounced Thing-vadth-leer). The Eurasian plate (left) is being pulled away and collapsing downward adjacent to the North American plate (right). Þingvillar Lake is resting in the downdropped basin.

Pahoehoe lava textures at Þingvillar.

The gorge at Gullfoss (Golden Falls).

At Geysir, and the namesake for all the world's geysers, the Strokkur geyser erupts about every 6 minutes. I caught this boiling bubble just as it was about to explode.

The southern coast of the Snæfellsnes Peninsula at Arnastapi Beach.

This valley near Dettifoss Falls was carved by a catastrophic outburst flood let loose from beneath a glacier within the last 10,000 years. We are hoping for weather like this!

Monday, July 23, 2018

Green River Geology - Echo Park, Whirlpool Canyon and Split Mountain Gorge

Continuing on our rafting trip just past the mouth of the Yampa River, we entered Echo Park, a lovely glen that is perched slightly on a Pleistocene (Ice Age) terrace along the Green River.

The mature Fremont cottonwood trees (Populus fremontii) that line the river are lovely but are losing their foothold here as the river cuts into the terrace on its outside bend. We saw large tree trunks that were undercut by the river. Additionally, prior years grazing caused the young shoots too be trampled and eaten by cattle. The National Park Service has established a cottonwood nursery back up against the wall in the distance, and is replacing the trees on the terrace.

This is our lunch stop across from Steamboat Rock. J.W. Powell camped here between June 17 and June 21, 1869 and named the promontory Echo Rock. I found myself wanting to call it that as well on this trip. The rock was the site of a well-known incident from the trip. Powell and George Bradley climbed the rock to obtain a reading with their barometer. As they scrambled upwards Powell leaped across a gap into a small crevice and found himself unable to move forward or back. He called to Bradley for help, who then climbed above the crevice. Powell then explains, "The moment is critical. Standing on my toes, my muscles begin to tremble. It is sixty or eighty feet to the foot of the precipice. If I lose my hold I shall fall to the bottom...At this instance it occurs to Bradley to take off his drawers, which he does, and swings them down to me. I hug close to the rock, let go with my hand, seize the dangling legs, and with his assistance am able to gain the top. Then we walk out on the peninsular rock, make the necessary observations... and return finding an easy way down." 

The Mitten Park fault has upturned the once flat-lying beds of the Morgan Formation. When the crust began to be compressed and squeezed in a mountain building event known as the Laramide orogeny, the rocks were first bent. Then, as the pressures became too great, the rock layers broke and were faulted. The actually trace of the fault is in the canyon on the far left, where our guide is pointing. A few things to keep in mind - when all this occurred, the rocks seen today were buried by about 5,000 to 10,000 feet of additional strata that have since been eroded away. When rocks are buried that deep, they are hot and can bend more easily. And, it all happened between about 70 and 40 million years ago. The nondescript looking rocks on the left are older and uplifted higher than the colorful rocks seen on the right.

After leaving Echo Park and crossing the fault, we entered Whirlpool Canyon. In the downstream view is the site of the Echo Park Dam. In the 1950s this area almost became inundated in water by a reservoir. You can read about the controversy and its rather happy ending here.

Gloria in fine form on the stand-up paddle board.

Whirlpool Canyon is cut into rocks of the Uintah Mountain Group, the dark knob on the left. This knob was in existence - much as we see it today - some 500 million years ago! How do we know? The whitish, flat-bedded Lodore Sandstone on the right has been dated to this time and it pinches out and laps onto the older Uintah Mountain Group. A similar relationship between what are essentially the same rocks in the walls of the Grand Canyon, occurs farther south about 500 miles.

Close-up view of the onlap relationship of the darker Uintah Mountain Group and the lighter-colored Lodore Sandstone. This relationship reveals that there was an undulating, hilly plain in existence when the sea began to encroach upon and bury it. The Green River has exposed it all once again.

View upstream in Whirlpool Canyon to Harpers Corner viewpoint. Before the river trip, Ed, Howard, and I drove out there. Our camp next to the river is located near the Colorado/Utah state line.

My bed for the night. I love to have these little perches next the beach and the water.

These pictographs were seen on our hike up Jones Hole and are likely from a cultural group called the Fremont.

Stylized bighorn sheep.


This is Ely Falls, a tributary of Jones Hole. We sat in the shade here and watched the earth turn for about two hours. Nice spot.

The north facing wall of Whirlpool Canyon. I was intrigued by the sharp buttresses that separated the rills in the hillside. It made me wonder if some peri-glacial conditions might have caused this?

J.W. Powell called this Mt. Hawkins, located across from our last nights camp. The Pennsylvanian Morgan Formation is tilted down to the west. This alternating grey limestone and red sandstone reflects the fluctuating sea levels around 300 million years ago, when ice caps in the southern hemisphere waxed and waned, changing the level of the sea, and thus the sediment types worldwide.

Aptly named Rainbow Park, an open expanse formed within the Island Park syncline.

Note the vegetation-covered slope between the two sandstone buttresses. This is likely a former channel of the Green River that was filled with sediment during a prior aggradation event. Later downcutting bypassed the former channel and into the present one, which curves to the right.

A huge bison petroglyph left by Ute Indians.

While taking a picture of this large raptor (immature Golden eagle?), I accidentally caught an accipiter (?) fluttering nearby. Can any of my knowledgable bird friends identify the two?

Floating towards the Split Mountain anticline.

Entrance to Split Mountain Gorge. Amazing how the river enters this uplifted "barrier."

This single feature caused J.W. Powell to speculate on the history of the Green and Colorado rivers. In fact, his observations here were later used to also explain the Grand Canyon. Trying to come to terms with a river entering the uplift, he proposed a new process known as antecedence, whereby the river(s) was/were in place before the uplifts occurred. Later uplift proceeded slowly so as not to alter the course of the river, thus cutting into the rock mass like a saw working on a piece of lumber. Other geologists weren't so sure and the first "controversy" regarding the origin of the river was born.

Inside Split Mountain Gorge, we saw this most interesting fault and fold. During uplift, a wrinkle formed in the strata which began to bend the layers. Then the stress became too great and the upper portion slid over the lower part toward the left. Wow!

Samuel F. Emmons had also completed work in this area around the same time as Powell and found evidence that the uplift was actually older than the course of the river (thus opposed to Powell's interpretation). Envision the upwarp already in place when it gradually was buried in lake sediments of the Green River Lakes. The lake sediment ultimately formed a subdued surface with the uplifted rocks buried and encased within. Then the rivers' course was established on top of the subdued surface and only coincidentally on top of the buried uplift. As the river cuts down, it encounters the fold and begins to slice through it. This process is called superposition and it is the likely explanation for these spectacular canyons. Archibald Marvine, who also worked in the Rocky Mountains along with Powell, found the same evidence for superposition.

Exit of Split Mountain Gorge. What a great trip with a great group of people! I may be doing another one of these five-day rafting trips on the Yampa River next year. Write to me if you are interested.

Monday, July 16, 2018

Rafting the Geology of the Canyon of Lodore, Colorado

The Set-Up - Dinosaur National Monument and the Douglass Quarry 'Wall of Bones'

Use this map to orient yourself. The monument is located in northeast Utah and northwest Colorado near Vernal Utah. You can also access this map online here to view at a larger scale.

Dinosaur National Monument was created in 1915 because of an upturned bed of rich, fossil-bearing sandstone discovered by paleontologist Earl Douglass in 1909. The monument was enlarged in 1937 to include two long sections of impressive river canyons along the Green and Yampa rivers. I recently led a group of 24 people on a five-day raft trip through Lodore, Whirlpool and Split Mountain canyons along the Green River. My explorations began at the Quarry Exhibition Hall near Vernal Utah, where this life-size model of a Stegosaur is on display.

Visitors take a shuttle bus from the Visitor Center to the recently renovated Quarry Exhibit Hall. Along the way, exposures of the Morrison Formation are evident and this is the rock unit that holds the fossils here. The Morrison Formation is a fluvial (river) deposit from the Late Jurassic (160 to 145 million years ago) with the bone bed having been dated precisely at 149 Ma.

The upturned bed of sandstone is within this building, housing one of the more unique fossil sites in the world.

The discoverer of the bone bed was very keen that the site could be made into a public display and his wishes came to fruition by the National Park Service.

Here is a small section of the wall which stretches over 100 meters in length and 15 meters in height. Twenty complete skeletons were found, along with nearly 1500 individual bones. In 1909 when the site was first discovered only eight bones at the top of the ridge were exposed. As layers were peeled away downslope, more bones came into view. The site is a mass grave of animals!

Many of the bones belong to the huge Sauropods that dominated Late Jurassic landscapes. The climate was semi-tropical and humid but subject to drought and even wildfires.

Allosaurs are also well-represented at the site. This animal is the state fossil of Utah.

An artists scientific take on how the bone bed came to be. The sediments that contain the fossils are known to be fluvial in origin and the direction of the rivers can also be known using the architecture of the sediment body. Using modern coordinates, the rivers flowed northwest to southeast. Since both complete skeletons and disarticulated bones are found here, geologists suggest that during an extreme drought, the river may have gone dry with animals dying next to the drying waterhole over a period of time. Then a large flood moved the bones a short distance downstream where they piled up on the outside bend of the river in a giant bone jam (similar to a log jam after a flood).

The Big Picture - Harper's Corner Road and the View from the Top

A 26-mile long road takes one from the valley floor to the top of Blue Mountain (actually a plateau). With friends and fellow river runners Howard and Ed in tow, we head up the road to see the canyons and landscapes we will be floating through for the next five days. This view is to the east along a fault-lined valley.

Looking down into the canyon of the Yampa River from the Harper's Corner Road.

On top, we found exposures of the Bishop Conglomerate, a course boulder and cobble deposit that accumulated between 25 and 30 Ma on top of a nearly flat, eroded surface. The conglomerate is extensive in this area but is now only found as remnants on top of plateaus. Note the flat-topped surface in the background - it too has the conglomerate on top. The ancient surface is known as the Gilbert Peak erosion surface and was a region-wide erosion surface before the cutting of the canyons commenced.

I couldn't resist and hollered tot Howard to stop the car! A herd of cows were wallowing lazily next to a restricted watering hole. The present-day drought does not allow them to venture too far away. I could not help but think of our morning visit to the quarry, where a similar scene played out 149 million years ago, only with large reptiles instead of large mammals. It seems, the more things change, the more they stay the same!

The Canyon of Lodore - To the Confluence of the Yampa River

This is northwest Colorado and it is BIG country with very little population. The Gilbert Peak erosion surface is clearly seen in the distance. The valley is called Browns Park and formed about 20 million years ago when the crest of the Uintah anticline collapsed into a graben. The Green River likely followed this down-dropped depression east toward the North Platte River and onto the Great Plains before it attained its present course. This is then, an abandoned river valley.

When the Green River abandoned its easterly course through Browns Park, it instead was directed to the south. At the time of the drainage readjustment, the rocks shown in the distance were buried within the Brown's Park Formation. The river at that time had no idea it was being directed on top of a resistant quartzite rock. But as the river whittled away at the Browns Park Formation, it slowly encountered the buried Uintah Mountain Group rocks. It then carved the Gates of Lodore, the site of our river put-in!

After passing the Gates of Lodore, we entered the Canyon of Lodore. The walls were spectacular!

The Uintah Mountain Group is composed of sandstone, quartzite, and minor conglomerate, all fluvial in origin. Detective work reveals that these ancient rivers delivered their load of debris from north to south, during the break-up of the supercontinent Rodinia. This supercontinent began to fragment about 1,100 Ma. A reconstruction of Rodinia is shown below.

Note the positions of the various continents at this time, with eastern Australia right next to western North America, known as Laurentia for this time period. The Uintah Mountain Group was deposited just above and to the left of the letter "L" in Laurentia. (1.1 Ga means 1.1 Giga-annum or 1.1 billion years ago; belts means mountain chains; craton means an undisturbed continental center).

Running Winnie's Grotto Rapid.

Running the upper part of Disaster Falls, where the John Wesley Powell party lost a boat in 1869.

 Lower Disaster Falls.

The Uintah Mountain Group is on average between four and seven kilometers thick! That's about 24,000 feet. It certainly was a consistently subsiding basin during this time, likely the result of Australia pulling away from Laurentia.

As we progressed downstream, younger rock units descended down toward us. Our river journey was across the southern flank of the east-west trending Uintah upwarp. About midway through the red cliff is the contact with the Lodore Sandstone. This unconformity represents about 600 million years of time where no rocks are preserved. Unconformities are like pages ripped out the center of a book.

The upper part of Hell's Half Mile, a rapid also named by John Wesley Powell.

A stately juniper tree with its roots firmly set in the Uintah Mountain Group.

Although very similar in color, note the difference in bedding characteristics between the lower Uintah Mountain Group (blocky) and the overlying Lodore Sandstone (horizontally bedded). The next day, we would climb to the top of the back side of this cliff for a view upstream on the river.

There were dozens and dozens of Bighorn sheep seen on our trip and this individual was found resting in the sun next to our camp.

Sunset on the limestone cliffs above our camp at Limestone Draw. The upper cliff and intermediate slope are part of the Pennsylvanian age Morgan Formation (about 300 Ma) and the lower, partly shadowed cliff is in the Madison Limestone.

Bioturbation in the Lodore Sandstone looks similar to vertical worm burrows observed in the Tapeats Sandstone farther south. In fact, the Lodore Formation is a dead ringer for the Tapeats Ss. and in fact the two units are correlative, meaning they are the same age and deposited in the same depositional setting.

Note the angle of the beds in this north view, exposing the southern flank of the Uintah upwarp.

We are now almost on the brink of the overlook at the north end of the Limestone Draw campsite.

Voila! The Green River in all of its glory inside the Canyon of Lodore. Note the erosional remnant of Lodore Sandstone making a rectangular cap on top of the underlying Uintah Mountain Group just below and to the right of the photo center. This was an awesome hike!

On the way back someone found a coral fossil, likely eroded from the Madison Limestone above.

Nearing the Mitten Park fault, where beds of the Morgan Formation are upturned against the upthrown side (right). This signals our imminent arrival to Echo Park.

John Wesley Powell named this monolith Echo Rock, composed of Permian age Weber Sandstone. Today it is called Steamboat Rock. Desert tapestries cascade down the rock surface, forming when water drips down from above causing bacteria and lichens grow on the watered surface.

The confluence of the Yampa River, looking east. We were supposed to float the Yampa on this trip but the lack of a winter snowpack made the river unrunnable for our 18-foot rafts. This concludes the first half of the river trip.