Gravity evidence for a shallow intrusion under Medicine Lake volcano, California

A positive gravity anomaly is associated with Medicine Lake volcano, California. Trials with different Bouguer reduction densities indicate that this positive anomaly cannot be explained by an inappropriate choice of Bouguer reduction density but must be caused by a subvolcanic body. After separating the Medicine Lake gravity high from the regional field, we were able to fit the 27-mgal positive residual anomaly with a large, shallow body of high density contrast (+0.41 g/cm³) and a thickness of 2.5 km. We interpret this body to be an intrusion of dense material emplaced within the several-kilometres-thick older volcanic layer that probably underlies Medicine Lake volcano.