Paper No. 1
Presentation Time: 9:00 AM


ANDRY, Eloise, Geosciences, Williams College, Williamstown, MA 01267, RIGGS, Nancy, Geology, School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, AZ 86011-4099, CASARES, Heather, Geology, Arizona Western College, 2020 S. Avenue, P.O. Box 929, Yuma, AZ 85365 and PULIDO, Courtney, Geology, Northern Arizona University, 516 W. Cherry #4, Flagstaff, AZ 86001,

Strawberry Crater is an ~50 ka cinder cone located in the eastern portion of the intra-plate, monogenetic San Francisco Volcanic Field. This volcanic field contains over 600 scoria cones and stratovolcanoes that range in age from 6 Ma to ~900 ybp. Scoria cone formation is usually modeled as an explosive cone-building phase followed by a lava flow and occasional breaching of the cone. Strawberry Crater deviates from this model with a complex eruption history reflecting changes in vent conditions.

Facies analysis of the cone and lava flows shows three lava flows, each with an associated breaching and rafting event, directed rootless flow and agglutinate deposition on the rim, and rootless flows that acted as slip-surfaces for fallen blocks inside the crater. The eruption began with a scoria-producing Strombolian eruption that was followed by eruption of a lava flow that breached the eastern section of the cone. Vertical eruptions continued, but the height of the eruptive column decreased and overall, Hawaiian-style eruptions became predominant, depositing rootless flow and agglutinate on the inside and outside of the crater. A second lava flow breached the cone, emplacing rafted blocks against the first lava flow. Unstable blocks of agglutinate and rootless flow slipped from the rim, creating unconformities with younger deposits. The vent became directional, causing thick agglutinate layers to be deposited on the northwestern section of the crater. A final lava flow breached the cone, again rafting out blocks and forming a dam against the second flow. This forced the lava to flow to the east and south of previous flows, weakening the southern portion of the crater. This breaching caused the unstable agglutinate to slip in large blocks from the rim, leaving slickensides along the interior rootless flows. A landslide to the west removed a portion of the southern crater rim, leaving a pronounced topographic saddle.

The eruptive history of Strawberry Crater demonstrates that cinder cone formation can be a highly complex process, consisting of multiple eruptive styles with various depositional products, small scale landslides, and changing vent conditions. Unique to Strawberry Crater is that evidence for these events has been preserved, primarily due to the prominence of resistant rootless flow and agglutinate layers.