High resolution magnetic susceptibility imaging is a new technique for studying the magnetic properties of geological thin sections. The two‐dimensional distribution of both remanent and induced magnetization can be determined with a spatial resolution (< 1.0 mm) that is similar to the size of phenocrysts in the sample. Amongst many problems in rock magnetism to which it could be applied, the technique holds great potential for understanding the origin of the anisotropy of magnetic susceptibility in pyroclastic flows. Preliminary tests on a single sample of ignimbrite indicate that secondary iron‐titanium oxide particles deposited within vesicle walls prior to their collapse are responsible for the bulk susceptibility.