Weird Geology: Accretionary Wedge #34...Our Human Nightmares

Well, how about that? I was trying to figure out how to squeeze in a bizarre shot from my recent trip to Joshua Tree National Park, and the 34th Accretionary Wedge announcement drops in my mailbox, courtesy of Dana at En Tequila es Verdad:

Geology can be strange. Outrageous. Bizarre. I'm sure you've all run into formations and landscapes and concepts that have left you scratching your head. Maybe they got less weird later. Maybe they stayed strange. But however transient or permanent that weirdness was, it got weird.

So tell us about it. Hit us with the strangest stuff you've got.

I'm late to the party, but what's new?I see a lot of weird stuff in my travels, but what strikes me isn't so much the geology, but our weird response to the geology. Can you look at the rock in the picture at the beginning of the post and not see the face of monster trying to emerge from the ground? The rock results from a random process of weathering and erosion, but see it from the right angle, and the rock becomes of mythical story of beasts and human nightmares and heroes on quests. Perseus fought Medusa, who turned men to stone. Tree molds in Hawaiian lava flows were people turned to stone (above). The volcanic necks of the Four Corners region were the monsters who were vanquished by the Navajo Twins Monster Slayer and Child-Born-of-Water (below).Pareidolia is a psychological phenomenon "involving a vague and random stimulus (often an image or sound) being perceived as significant. Common examples include seeing images of animals or faces in clouds, the man in the moon or the Moon rabbit, and hearing hidden messages on records played in reverse". It's part of being human, the recognition of human faces being one of the most important skills of a newborn baby.

Of course, such things can get out of hand when we start seeing Jesus on tortillas, or faces on Mars that are obviously signs of Martian civilization (I thought it was Elvis myself). Or the Devil smiling in the smoke and ash of the Twin Towers burning (wasn't there enough evil in the hearts of the terrorists?).

Fire Down Below III - a Geological History of the Colorado Plateau

Another couple of perspectives of the volcanism that effected the Colorado Plateau between 20 and 30 million years ago.

A very accessible view of a classic volcanic neck can be had from Highway 163 a few miles south of the Utah-Arizona border near the town of Kayenta, Arizona. Agathla Peak (sometimes called El Capitan) is almost 1,500 feet high, and as can be seen in the photo on top is not composed solely of dark volcanic rock. Instead, much of the prominence is composed of large fragments of the surrounding sedimentary rock, shot through with dikes of darker volcanic rock that have more or less welded the pinnacle together. The surrounding rocks are shales and siltstones of the Chinle Formation.

The second photo is of Navajo Mountain, described at the end of yesterday's post. I had intended to include a photo, but to my surprise found very few of them in my archives. It strikes me that as I travel through the plateau country that the mountain looms in the background of nearly every part of our route. It comes into view soon after we leave Grand Canyon National Park out to the east. We drive south of the mountain as we approach Navajo National Monument and Cedar Mesa. It rises to the south when we drive through Escalante-Grand Staircase National Monument. And yet for all that, I hardly ever snapped a shot! But here is one from Cedar Mesa. The mountain is covered by sedimentary rock that has domed up over the volcanic rocks underneath.

Fire Down Below - a Geological History of the Colorado Plateau

I've been seeing a fair number of geobloggers giving apologies for not blogging recently, and then I notice I haven't posted anything in nearly two weeks. It's obviously field season! I've actually been home for a couple of weeks, but other projects took precedence, not the least of which was a lot of weeding. I spent most of the last month discussing the active volcanoes of the Hawaiian Islands, and I will return to that project soon. For the moment I am taking the blogger's perogative to change the subject. I have come close to completing a year-long project on the geology of the Colorado Plateau, and there is a matter of some serious volcanic activity in Cenozoic time across the plateau country.

The Plateau is above all about horizontal rocks. They may form cliffs, but it a simple truth that the landscape is dominated by sedimentary layers of sand, silt, clay and lime. Throughout Paleozoic and Mesozoic time, thousands of feet of rock were laid down, but in Cenozoic time things were changing. The land was rising and buckling so that the last sediments formed on the plateau were in freshwater lake basins of somewhat limited extent that form the colorful rocks of Bryce Canyon and Cedar Breaks today. The Laramide Orogeny, which had lifted the Rocky Mountains, was also responsible for the vast changes in this region as well. The tectonic conditions responsible for the deformation was to have one other effect on the land: volcanism.

Driving across this strange and scenic landscape, one is struck every so often by the sight of rocks just sticking up into the sky. The ancients were pretty sure that these were the remains of monsters who had been frozen in stone. Although geologists have a wonderful time debating the reasons, the fact is that from about 30 million years to around 20 million years ago, volcanism swept across the region, leaving behind all manner of volcanoes, calderas, volcanic necks, and strange laccolithic mountains (see the next post).

Today's pictures include a couple of volcanic necks, including Shiprock in New Mexico. These are the cores of volcanoes that have been exposed by intense erosion.