Anisotropy of magnetic susceptibility variations in Icelandic columnar basalts

The anisotropy of magnetic susceptibility (AMS) has been determined for 81 samples from eleven horizontal columnar segments from two Icelandic near-vertical dikes. Near-vertical orientation of short AMS axes and corresponding long-axis horizontal orientations in most columns represents alignments consistent with compactive effects due to vertically directed forces exerted by overlying columns. These data are inconsistent with primary orientations resulting from thermal contractive stresses, but such stresses may be responsible for the secondary orientations observed.