VOLCANIC TOPOGRAPHY COVARIES WITH SUBSURFACE MAGMATIC STRUCTURES THROUGH TIME IN THE CASCADES ARC OF THE WESTERN U.S
We use spectral analysis over a range of wavelengths and existing topographic boundary identification methods to determine edifice boundaries within the Cascades from 10-m resolution DEMs, separating complex topography into nested volcanic structures. We combine these boundaries with the USGS vent database to quantify volumes and shapes of most (75%) edifices, which are a proxy for total eruptive output. Along-arc variations in volume associated with edifice type, age, and composition provide updated estimates for total eruptive output of ~760 km3/Myr, with significant differences between the Northern (47°-49°;~ 60 km3/Myr) and Southern (40°-47°; ~700 km3/Myr) Cascades.
We then compare Cascade edifice topography to a variety of geophysical data to understand the relationship between surface volcanism and underlying arc structure. We synthesize and interpolate tomography models, heat flow, gravity, and GPS-derived strain rates to edifice locations and compare with edifice shape, spatial density, and spatially-averaged erupted volume. We find that recently erupted edifices (Holocene and Late Pleistocene) are strongly correlated with crustal thickness, heat flux, and shallow (<20 km) Vs anomalies. However, correlation coefficient magnitudes systematically weaken with available data for older-eruption edifices (Mid-Early Pleistocene), suggesting subsurface magma migration away from edifices that last erupted in the early Quaternary. This provides a new perspective to better interpret arc-scale magmatism. By combining temporally-resolved surface volcanism with geophysics, an integrated, time-resolved perspective on magma transport may be possible.