VOLCANIC TOPOGRAPHY COVARIES WITH SUBSURFACE MAGMATIC STRUCTURES THROUGH TIME IN THE CASCADES ARC OF THE WESTERN U.S

Topography of the Cascades Arc encodes a complex history of volcanism, tectonics, and erosion. Edifices range from cinder cones to calderas, stratovolcanoes, and compound volcanic complexes. Often, these features are spatially localized around magmatic centers, alluding to the underlying magma transport network. A new USGS database compiles the location, type, age, and composition of 3000 volcanic vents over the last 2 Myr (recording last vent activity). These data, combined with high-resolution topography across the arc provide unprecedented detail on the Quaternary volcanic history of the Cascades.

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.