Ash from the May 1980 eruption of Mount St. Helens deposited from air faithfully records the direction of the local geomagnetic field in eastern Washington, whereas ash settled from suspension in water in fluvial environments exhibits significant inclination and current-rotation errors in magnetic direction similar to those reported in other subaqueously deposited sediments. The current-rotation errors are associated with partial alignment of the major axes of magnetic susceptibility in the direction of water currents. Subaerial deposition produces strong stable remanent magnetization in ash with or without postdepositional wetting by rain.