Today we went to Sunset Crater, which is part of the San Fransican Volcanic Field.
Our first stop was to get up close and personal with a cinder cone (a type of volcanic formation). On the way we stopped to examine the soil, which contained pyroxene, feldspar, and amphibole, as well as clays due to chemical weathering. Along the walk to the outer edge of the cinder cone, we saw that the rock was dominantly basalt and cemented together, which is called a pyroclastic flow. We also talked about how the apparent dip of each bed was different from the actual dip of the beds of rock, due to the erosional surface.
Our second stop, and the rest of our day, was spent discussing the formation of Sunset Crater and looking at the different types of lava flows. The primary type of lava flow we discussed was pahoehoe lava, which is undulating and results in rock that has many vesicles (or holes, like a sponge does). Ultimately, we learned that due to the formation of the Colorado Plateau and the extension that occurred during that time, this caused fractures where lava from the mantle could escape to the surface through a thinned crust, resulting in volcanism!
Fun fact: Sunset Crater is the youngest volcanic feature in the San Franciscan Volcanic Field, forming only 900 years ago. In geologic time, this is like it formed yesterday!
– Hannah and Emma