Mount Adams Electromagnetic and Magnetic Data

Hydrothermally altered rocks, particularly if water saturated, can weaken stratovolcanoes, thereby increasing the potential for catastrophic sector collapses that can lead to far-traveled, destructive debris flows, which are the largest volcanic hazards for Mount Adams and Mount Baker. Evaluating the hazards associated with such alteration is difficult because much of the alteration is obscured by ice and its depth extent is unknown. Intense hydrothermal alteration significantly reduces the resistivity and magnetization of volcanic rock and therefore hydrothermally altered rocks are identified with helicopter electromagnetic and magnetic measurements at Mount Baker and Mount Adams. High resolution magnetic and electromagnetic data were collected using the RESOLVE multi-coil, multi-frequency electromagnetic system supplemented by a high sensitivity cesium magnetometer. The survey took place out of over Mount Adams, Washington during May of 2002. The survey covers an area centered on Mount Adams. Data were collected along north-south flight lines with east-west tie lines. A nominal EM sensor flight height of 60 m was maintained, except where safety dictated a higher elevation. A total of 200 kilometers over 2 survey blocks (including the Mount Baker area) were flown. Three files are available in this publication and include flight line data for the magnetic survey, flight line data for the gravity gradiometry survey and a report describing the survey parameters, field operations, quality control and data reduction procedures.