I recently finished doing two mag grids with a lot of remanent magnetic responses. Both of these grids were located on mountain peaks with highly magnetic Precambrian rocks. There wasn�t any real pattern to the remanent responses and they were of various sizes (ranging from 5 to 50 meter diameters). The overall magnetic field varied from about 30,000 to 70,000 gammas with the background at about 56,000.
At first, I thought the remanence was probably induced by lightning strikes. After finishing the survey, I compared the local grid responses and locations to a high resolution helicopter magnetic survey that was flown earlier over the same area. Both of the grids are located near a major contact and there did seem to be an overall motley appearance (lots of small bull�s eye highs and lows) in the helicopter magnetic data near the contact regardless of terrain elevation. Therefore I concluded the remanent responses in the ground mag were probably caused by hydrothermal alternation from metamorphic activity near the contact rather than by lightning strikes. This project forced me to realize how little I know about lightning strikes and remanent magnetism. How strong are the responses (both in changes to the magnetic field and aerial extent) likely to be? I am curious to know if there is anyone on this list who has had experience with this or knows of any published works regarding lightning strikes and magnetism. Sincerely, Clark Jorgensen Big Sky Geophysics P.O. Box 353 Bozeman, MT 59771 USA (406) 587-6330 phone (406) 587-6394 fax [EMAIL PROTECTED] _______________________________________________________ List archive: http://www.mail-archive.com/[email protected]
