Magnetotelluric data, with both electric and magnetic field references for noise cancellation, were collected at accessible locations around and as close as possible to the Mount Hood andesite-dacite volcano. The purpose of the study was to identify and map conductive features and to relate them to the thermal regime of the region. Several conductors could be discerned. The shallowest, at a depth of around 500 m below the surface, was identified as a flow of heated water moving away from the summit: the deepest (~50 km) might be a melt zone in the upper mantle. Of particular interest is an elongate conductor that strikes N 10¿ W and extends from a depth of 12 km down to 22 km. Because the conductor strike is close to the trend of the chain of Cascade volcanoes and because of the high conductive thermal gradients reported for the area, this feature was initially believed to be a zone of partial melt following the volcanic axis. However, because no teleseismic P wave velocity anomaly has been found, the cause of the conductor is more problematic. While the existence of small zones of melt cannot be ruled out, it is possible that the conductor is caused by a large volume of intensely deformed rocks with brine-filled microfractures. |