Magnetic profiles obtained by deep submersible ALVIN across a newly erupted lava flow on the Juan de Fuca Ridge (JDFR) show strong magnetic anomaly fields (>20,000 nT) and high crustal magnetization (>50 A/m contrast) relative to the surrounding older lavas. These results are consistent with previous ideas that extrusive crust is initially highly magnetized. Within the high amplitude magnetic anomaly over the center of the flow, there is a clearly defined deep, ''notch-like'' magnetic low. This notch may indicate thermal demagnetization associated with a subsurface feeder dike, weakly magnetized intrusives or altered extrusive rock. If the former mechanism is active, the notch should disappear with time as the dike cools. ¿ American Geophysical Union 1995