Abstract Mount St. Helens (MSH) is one of the most active volcanoes in the Cascade Arc and a natural laboratory for subduction‐related volcanism. However, intense subsurface scattering has long hindered high‐resolution seismic imaging of its magma plumbing system. To overcome this challenge, we apply an improved matrix‐imaging method to generate a high‐resolution crustal reflectivity model beneath MSH. The resulting model reveals a multilayered architecture dominated by a laterally extensive reflector that coincides with the top of the Siletz terrane. This horizon likely acts as both a primary accumulation platform and a mechanically sensitive gate. Southeast‐directed reflectors spatially coincide with a mid‐lower‐crust low‐velocity column and delineate potential fluid/melt pathways. Episodic inputs along this corridor may recharge the shallow system. These processes could modulate eruptive style. Overall, our results illuminate candidate subsurface transport pathways, highlight targets for monitoring, and demonstrate the effectiveness of matrix imaging in scattering‐prone volcanic crust.

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