Bonito Lava Flow
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Stop 18 Bonito Lava Flow
Location: Sunset Crater National Monument
Date: March 10, 2007

Lava that broke out the side of the cinder cone formed structurally complex flows some nearly two miles in length composed of basalt.  On the lava flow trail there are two types of lava visible, Aa and pahoehoe. Flows typically start as pahoehoe, thin and runny, forming a smooth ropy texture when cooled. As the lava cools and becomes thicker it changes into an Aa flow. Aa flows are characterized by their jagged, blocky texture. The majority of the lava here at the lava flow trail is Aa lava.


Bonito Lava Flow Trail


From this location one can see all three main types of volcanoes. San Francisco Peak is a composite volcano and the highest point in Arizona at 12,633 feet, and may have been as high as 16,000 feet before a Mount St. Helens style of eruption in the past.  O’Leary peak is a dome volcano and Sunset Crater is a cinder cone.


View of San Francisco Peak from the Lava Flow trail.  San Francisco Peak is a composite volcano.

O’Leary Peak is a dome volcano

Sunset Crater Volcano is a cinder cone. Note the scars visible on the cinder cone. This is a result from the
public hiking up the volcano, before being banned in the 1970’s, causing subsidence in the cinders
and are still visible today.



By W. Patrick Dryer