Walking up Cinder Cones

Growing up, I never payed much attention to cinder cones, a type of volcano that surrounded my hometown of Flagstaff, Arizona. They always seemed like an uninteresting buildup of red, rocky material. Even though I learned a little bit about them in my introductory geology classes, they seemed simple and uninteresting. Little did I know that a single hike up the side of a cinder cone built 76 thousand years ago would change my perspective on them.

The day started out like any other, I was prepared with water, lunch, my notebook and copious amounts of sunscreen. The day promised to be hot, with no reprieve from clouds, but a small breeze provided a little bit of cooling. As we began the trek up the hill on a small, rocky trail, I admired the view of the sea on both sides. The view got better and better as we moved up the hill of what I immediately recognized as cinders. They were pebble sized, vesicular(a volcanic rock with a lot of holes) and appeared to be black (Figure 1).

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Figure 1: Side of Megalo Vouno cinder cone, note the color of the cinders.

As we hiked up the cone, I noticed a large object jutting out of the cinders right in front of me. This object, I soon found out, was lava that had traveled up through many layers of rock to reach the cinders, from the magma chamber to the surface. The name of this vertical object is a dike.

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Figure 2: Dike protruding from red, oxidized cinders, surrounded by black cinders.

The dike is surrounded by red cinders, the red color is caused by oxidation, which is a chemical reaction when the material is exposed to heat and oxygen. This shows that the cinders were in place before the dike intruded. The presence of the dikes provides an explanation as to how the cinder cone I am standing on came to be there.

When I first started this hike, the material I was walking on was sturdy rock from Peristria, which is a composite cone that formed 530,000 years ago. As I progressed up, the rocks beneath my feet rapidly changed to cinders. This is from one of two cinder cones that make up Megalo Vouno, which formed 76,000 years ago. The composite cone is made up of resistant, basaltic and andesitic rocks(see Figure 3). In order for magma to get to the top to form the cinder cones, it follows the path of least resistance through existing cracks in the Peristria lavas, and typically forms thin, vertical lines. These vertical lines are the dikes I spotted on the path. You can also see a dike in Figure 3, going up through the basaltic and andesitic lavas.

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Figure 3: Dark red and grey lava flows from the Peristria composite cone with an intruding dike.

The dike in Figure 3 looks neater than the one in Figure 2 because of the material it broke through. The dike in Figure 2 came up through cinders, which would be a very messy encounter. Imagine when you are trying to spread icing on a very crumbly cake, it ends up being very messy and the cake wants to stick to the icing. The cinders act in the same way, and stick to the flow while the magma is moving toward the surface. It eventually comes out in a very blob like way. The dike in Figure 3 is much more planer, because the material it pushed through was very sturdy basalt and andesite, keeping the flow more upright. Many of these dikes worked their way through the Peristria layer up to the surface to form the cinder cones. I decided not to attempt to count the numerous dikes from my watery view, the sheer amount of them overwhelmed me.

These many dikes created the cinder cone I walked on. When the magma of what is now a dike reaches the surface, it began with discrete bursts of a very dark cinders and ash. This builds up over time, creating large cones. Imagine the creation of the cinder cone like a popcorn machine. The magma is like the popcorn kernels, it is driven up by the expansion of gas bubbles that cause it to shoot out, and it builds up to form a cone shape(Figure 4). [1]

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Figure 4: Sketch of the upward travel of magma to the surface, where small explosions send cinders flying into the air around the vent.

The cinders crunched under my feet as I walked around the top of the Megalo Vouno cinder cone. My feet constantly rolled and sank into the round pieces of volcanic material, making it difficult to walk. I could imagine the magma pushing its way up through cracks in the hardened lava flows of Peristria, with cinders clinging to it like bees to honey once it reached the top, and more cinders popping out, forming the cone I hiked up. The hike was well worth it, for the new knowledge and appreciation of cinder cones, and the amazing views.

References:

[1] Volcano World. (n.d.). Retrieved June 16, 2016, from http://volcano.oregonstate.edu/cinder-cones

 

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2 thoughts on “Walking up Cinder Cones”

  1. Hi Jess – I know you have struggled to put together a personal narrative that you could maintain throughout the post. Well done this time. Your blog flows well, has a good amount of science, and I never feel like I’m reading a wikipedia page (or something) while I’m reading it. Great job. It’s been a pleasure having you on this trip.

  2. Hi Jessica,

    Your introduction is perfect for your post because you provided your readers with some background information, while also introducing your topic of discussion. You establish a strong narrative that is consistent throughout your post. Well done!

    I love your use of images in this post because they were referenced during your narrative, and you told your audience what to pay attention to. Drawing your readers’ attention to a specific component of the image is also important and helpful for outside audiences. This was a very smart use of images that effectively helped my understanding of this post.

    In addition to your images helping an outside audience’s understanding of the content, your explanations of the geological concepts were thorough and appropriate for that audience. I am mostly unfamiliar with cinder cones, and I appreciated your specific and succinct definitions. I was able to follow along with the information with no problems in understanding the content.

    Overall, this is an excellent post. Your narrative is consistent and engaging, and you presented the information in an appropriate way for an outside audience. In addition, your images provided strong support for your content and also helped an outside audience understand your content. Great job on your blog work this month!

    Marisa

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