HISTORY OF LAVA FLOW ERUPTIONS AND RAFTING EVENTS AT STRAWBERRY CRATER, NORTHERN ARIZONA, USA: RESULTS FROM THE SAN FRANCISCO VOLCANIC FIELD REU PROGRAM

The landscape evolution within a monogenetic volcanic field varies with the eruptive characteristics of each volcano. The San Francisco Volcanic Field (SFVF), located in northern Arizona, contains more than 600 volcanoes, most of which are cinder cones that range in age from approximately 6 million to less than 1000 years old. Strawberry Crater, a cinder cone in the northeastern part of the SFVF, does not follow the basic model of cinder cone eruptions because conditions in the conduit and crater promoted sector collapse and rafting of a part of the cone with the lava.

Measured sections and facies mapping of sections of the crater walls that were rafted on the flows provide evidence of three rafting events and flows. Measured sections of rafts compared to successions on the cone suggest a sequence of the rafting events. Rafts on the earliest flow, to the north- northeast of the cone, are small, less than 16 m³, and are made up of mostly cinders and red spatter. The second lava flow carried out larger pieces of the cone, as much as 450 m³, that consist of red agglutinate, spatter, and small quantities of rootless flow; this flow moved to the northeast of the cone along the southern margin of the first flow. Sections from these rafts match up to some of the lowest successions inside the crater of the cone suggesting that there was some buildup of red agglutinate and rootless flow following the first breach of the cone. Towards the end of the eruption the cone was breached once again rafting segments of the cone as large as 3600 m³ only a small distance from the cone. The rafts consist of red, purple, brown agglutinate, dacite xenoliths, and rootless flow that match successions dominantly from the crater rim. The rafts also match material from all stratigraphic parts of the cone. The eruption at Strawberry Crater formed an unusual topography with implications for understanding the complexity of cinder-cone eruptions.