Thursday, May 06, 2021

Nevada's Valley of Fire State Park - A Tortured and Beautiful Landscape

There is not much going on with the travel restrictions for Covid still in place. So here is a reminiscence of a trip completed eight years ago in April, 2013, with friends and former students of mine at Yavapai College Prescott and Sedona. Enjoy!

I just finished a fantastic four-day exploration of Nevada's Valley of Fire State Park. The trip was a reunion of sorts with past students and friends from my teaching days at Yavapai College in Prescott and Sedona. They scouted the trip, planned the itinerary, and executed a fine geology program. I am so lucky to have such wonderful alumni and friends! They are awesome.

I had driven through the area briefly in the 1970's and knew the area would be a good one to visit. But I had no idea that it would be OUTSTANDING!! The geology is "off the charts" fantastic and we visited during the spring wildflower season.

East entrance to the park

The main story here is that during the Early Cretaceous (145 to 100 million years ago), western North America was subjected to compression from the west when gray Paleozoic limestone was shoved horizontally to the east over Jurassic sandstone. In this overview shot, you can see the result. In the foreground is the Jurassic Aztec Sandstone, while in the background are the Paleozoic limestones. The thrust fault that created this inverted relationship is known as the Muddy Mountains thrust fault.

First, let's describe the Aztec Sandstone, the rock unit that gives the park its name. It is time equivalent to a common Colorado Plateau unit known as the Navajo Sandstone. They are one in the same but when they were named no one knew that. Geologists could attempt to remedy the discrepancy but they are not generally "lumpers". The Aztec and the Navajo are one in the same.

The Aztec has beautiful eolian textures like these wind ripple marks

Another set of ripple marks located on the lee side of an ancient dune. Note how the ripples appear to climb up the lee face of the dune. I have seen this occurrance on modern dunes in India and the Middle East.

Close-up of the ripple marks

Balanced Rock shows that the Aztec Sandstone has experienced many episodes of deformation. Here the beds dip steeply to the left (north) recording an anticline that overprinted the thrust.

Balanced Rock framed by a Beavertail cactus in bloom. The flowers on the trip were spectacular.

Petroglyphs on the Aztec near Mouse's Tank

Although the plane of the Muddy Mountains thrust fault is not directly visible here, the result definitely can be seen. The limestones are 500 to 300 million years old and the red sandstone beneath is only 180 million. Imagine the first geologist to ponder this odd relationship and the wonder they must have felt when they realized what this represented. If that is not enough, later studies showed that the limestone here traveled more than 50 miles along the thrust!

From our camp we could look to the Virgin River Valley to the east, known locally as the Overton Arm of Lake Mead (the reservoir has backed up into the valley of the Virgin about 35 miles). The rocks in the distance contain an almost complete section as seen in the walls of the Grand Canyon. The cliff-top unit is the Kaibab Limestone and the prominent cliff in the middle is the Redwall Limestone. I always love seeing the Grand Canyon section of rocks outside of its "normal" home. 

A camp scene in Group Site #3

On the second day we explored the northern part of the park to Rainbow Vista. It is aptly named.

Desert marigolds in bloom

The colors in the Aztec Sandstone are a big part of the geologic story here but involve groundwater fluids that remobilized certain iron oxides within it. First the sandstone was colored red by the dissolution of iron rich minerals within it such as mica or hornblende. The iron coated each grain of sand. Then fluids traveled along faults and fractures and removed some of the iron oxide to make the rocks white. Then a third period of groundwater movement brought in purple and yellow staining (limonite and goethite). Thus was formed the rainbow colors of the park.

In some areas the colors blend wildly

Groundwater fluids also hardened the cement within fractures and joints in the rocks

A geology talk in the field is worth five talks in the classroom. I did  not have to lead this trip - some of the students did the research and presented to the group

We next took a hike into a fantastic area that is reminiscent of Coyote Buttes in the Vermilion Cliffs

Along the way, the Chinle Formation made an appearance. It is seen as the drab gray claystone in the foreground at the base of the red sandstone.

Fantastic colors

Eroded into wonderful shapes

Valley of Fire reflection time

At the end of the hike we could see the Cretaceous Willow Tank Formation, an assemblage of coarse rocks that unconformably overlie the Aztec

The deposit contains some well rounded quartzite clasts as well as clasts of the Aztec. Hmm?

The lower part is colored red with an upper part that is more gray. This color difference likely reflects what kind of rocks were eroding with the lower, redder beds derived from areas of Aztec Sandstone and the upper grayer lenses from Paleozoic limestone terrain. The interpretation is that this unit is the debris being shed off of the thrust front a few miles west of here. Imagine a highland to the west that originated when limestone deposits were being thrust up to the east over the Aztec Sandstone. As erosion attacked the thrust front, gravel was washed to the east over the Aztec. That is what is exposed here.

Brittlebush in bloom on the conglomerate

We next hiked to the White Domes. Primroses were in bloom along the way.

View into the slot canyon area at the White Domes. Note the dark wall of adobe near the sandy patch on the floor of the canyon?

It is the remnants of a Hollywood set for the 1966 movie, "The Professionals". The movie starred Lee Marvin, Burt Lancaster, and Jack Palance and many scenes were filmed here and in Death Valley. Ironically, Helen and I watched the movie last night, just days after returning home! I can highly recommend the movie for southwestern scenery.

Many scenes in the movie were filmed in this slot canyon, carved in the Aztec Sandstone

Sandstone, fractures, and light

On the third day, we drove to the Lake Mead National Recreation Area and hiked to the Bowl of FIre. Here Dennis gives the group a short lecture. But this blog is long enough and its time to end.

Sunset on the Muddy Mountains from camp

The group photo at Frenchman's Mountain. Thank you everyone for this wonderful trip!

Wednesday, April 28, 2021

Day 30 of the Iceland Volcanic Eruption

 It just keeps on going! This photo from 15:30 MST on April 28. Watch the continuous live ffed here.

Tuesday, April 13, 2021

To the Rim of SP Crater

Of the more than 600 scoria (or cinder) cones within the San Francisco Volcanic Field, SP Crater stands out as the steepest of them all! One reason for this  is that its final eruptive phase delivered molten lava that welded into dense agglutinate that caps its rim. This hard carapace protects the top and steepens its sides. SP Crater is likely the second youngest crater in this volcanic field (Sunset Crater is the youngest) and has recently been dated at about 55,000 years old. On April 7, I visited and climbed this unique cone, located about 35 miles north of Flagstaff.

A Google Earth image of SP Crater. The image clearly shows the crater and its spectacular set of lava flows that erupted from its base and flowed downhill to the north (top). Note the variations in color on top of the lava flows - the older (and broader) of the flows are weathered and support grasses that appear as green-gray patches. These are seen mostly around the flow margins where the quenching of the lava produced lava levies. There are two lava lobes on the west (left) margin that spilled over these natural levies into a low-lying valley. Younger flows on top of the older flows are not weathered enough to allow for grasses and they appear jet black on top of the older flows. There are least eight other scoria cones in this image that are much older and much more weathered that SP Crater. Some of these have elongate rims suggesting structural control of the vents. The light color in the upper left is the Kaibab Formation bedrock.

SP Crater from an earlier trip in January, 2011 shows the steep sides of the scoria cone.

The hike I undertook with friends began on the west side SP Crater (left) and generally switchbacked up to its western rim. Then we hiked around to the south side of the rim. 

This is where the young rubble from SP Crater rests on the older material of an older cone.

Brad and Dawn on the indistinct social trail that climbs the west slope.

Volcanic bombs are seen on the slopes of the volcano. One would not want to be hit by one of these dense blobs of 1000°C  lava.

When hot spatter lands on the ground, it tends to squash and flatten out into distinct layers.
After achieving the top of the cone, a fantastic view to the south is obtained. In the far distance is the San Francisco Mountain stratovolcano. In the middle distance with a deep shadow in Colton Crater. It is a next on our tour of craters in Northern Arizona.

Close-up view of the agglutinate rim of the volcano. This hard carapace protects the unleaded scoria that lies beneath it. Through time the slope beneath this likley becomes oversteepened.

The agglutinate likely once completely covered the surface of the inner crater. It is now being undercut as scoria slips downward, causing the agglutinate cap to collapse. A possible sequence of events at SP Crater would be construction of a cone, possible phreatomagmatic eruption to create an inner crater, then fountaining of lava to produce agglutinate, and finally a lava leak in the north side of the cone to produce a lava flow.

More volcanic bombs lying on the rim.

Beautiful clear skies in an enchanted landscape.

Shadows begin to creep in from the west across the volcanic landscape.

On the way down and toward the lava flows.