Sunset Crater and many of the other cinder cones erupted through weak spots in the crust around the central volcano, these are also called vents because they are an extension of the central volcano. Our first stop of the trip took us to the first main eruptive lava flow on the west side of the volcano. The flow first erupted in 1180 A.D. and is made up of basalt and scoria igneous rocks. As stated in Picture 3, the flow is made up of pahoehoe and aa lava flows. Both of these terms are Hawaiian in origin.
Pahoehoe lava is usually at the beginning of a lava flow and appears smooth, thin, and runny.
As the lava cools and degasses more, the flow becomes jagged, thicker, and slower moving. Xenoliths in Bonito Lava Flow. Our second stop of the trip took us to a part of the Bonito Lava Flow where parts of the underlying Kaibab Limestone layer is visible within the basaltic lava. When pieces of the underlying rock get mixed in the the lava the piece is called a xenolith. There are at least three visible in the area we looked at.