1 Distributed volcanic fields of the southwestern U.S.
This session invites submissions from various disciplines (e.g., petrology, tectonics, geophysics, geochronology) that explore distributed volcanism in the southwestern U.S. Topics of interest include spatio-temporal trends, magma compositions, and mantle and/or crustal controls on volcanism.
Monday, 18 May 2026
8:00 AM - 12:00 PM
Alvarado A
Disambiguating Spatial and Temporal Trends in the San Francisco Volcanic Field
Paper number: 1-11
Program: Technical Sessions
Time: 11:15 AM – 11:35 AM
Authors
Abstract
The San Francisco volcanic field contains over 600 individual cones, many of them scoria cones that vary in shape and size. Previous studies have attributed the primary control on shape as degradation over time based on connecting the cone’s inferred age group with the flank slope, crater width, and crater depth. This study takes a new look at the spatial distributions of shape characteristics to discern whether all effects are from progressive degradation combined with spatial shifts in eruption location.
This study combines classical morphometric datasets (Hooper 1994, Wood 1980) with ages compiled by a USGS vent list and new measurements of plan view shape character and supplementary morphometric parameters. A series of spatial distribution maps show that morphometric indicators (maximum slope,average slope, flatness, planview shape) do not typically follow an eastward shifting pattern in accordance with known temporal patterns of eruption despite the clear temporal changes in population means for maximum and average flank slope. Planview shape is primarily an indicator of eruption style, suggesting that some morphometric parameters may be more sensitive to eruption style than degradation. This motivates a deeper dive into the causes of temporal changes.
Preliminary analyses suggest flatness (crater width/cone width) may increase with age. Eruption style is a major control on flatness, as explosivity and openness of craters affect the initial wideness of the crater and how it responds to erosion. Typical erosion models depict craters filling in and eventually disappearing but not necessarily widening or shrinking before disappearing. However, open craters may not fill, providing one explanation for retaining wide craters. Alternatively, ground water or magma volatile content may have changed over time.
Geological Society of America Abstracts with Programs. Vol. 58, No. 4
doi: 10.1130/abs/2026RM-410679
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