Minerals affecting compass accuracy??

Sesoku

Sesoku

Joined
Oct 19, 1998
Messages
498
My dad just got back from hunting in the upper peninsula of Michigan at the Seney Wildlife refuge. He told me that last Thursday he was walking down a road in the refuge and decided to cut through the woods heading west to another road running parallel to the one he was on. To make a long story short he ended up coming out of the refuge several miles north of where he thought he was, luckily he came out on a main road. He told me that he was paying careful attention to his compass, and he wasn't sure what had happened. I know there is the possibility of operator error, or that something on his person may have affected the reading but he said that he talked to someone else that said there are mineral deposits around there that have thrown other people off also. That just made me wonder if anyone has had experience with this or heard of it occuring before.

He was also talking about getting a gps, he wants something relatively simple and easy to use. I suggested an etrex, does anyone here have opinions on them?

Thanks!
 
I personally haven't had experience with minerals affecting my compass, but my father has had the same thing happen to him. He was surveying and suddenly his compass went berserk. When he got back he checked some geologic maps and found out that there was a huge iron load under the area in which he was working. I know that the U.P. was a big iron mining area for a while, so that may have been the problem for your father as well. Or he may have forgotten to adjust his compass for declination. I have done that before and it can throw you quite a ways off depending on the declination of the area you're in. Re: GPS My brother and I gave my mom an Etrex last christmas to use for Sea Kayaking. The're fairly basic and are a decent system, but sometimes they have trouble finding satellites. On the other hand I live in a dead zone in the boonies of N.H. where nothing comes in anyway. Magellan also makes some nice systems.
Lagarto
 
The UP and northern MN are pretty well known for iron ore production. Your Dad could certainly have walked over an ore deposit (though I'm not familiar with the particular refuge you mentioned) that tweaked his compass bearings. It's common in iron rich areas, as I recall.

As for operator error, I was just reading some of Horace Kephart's "Camping and Woodcraft" and he tells a story about forgetting about the effect of steel and balancing his compass on top of his rifle barrel to take a bearing. Happens to the best of us, I guess :)

No advise about a particular GPS, but they are unaffected by changes in the local magnetic field.

Patrick T.
 
``crustal magnetic anomalies.'' do exist and can be a real pain as they are rarely marked on common TOPOs. I remember leading a group of twenty students across an area in the Sierra on the 2nd to last day of a nine day survival trip. For some odd reason the terrain didn't EXACTLY match the map but if I thought about it I could make a fit. I'd never hiked this area before. I did know that at a certain point I would end up at a stream for our last night. We hit the stream right on time. One problem... it was running the wrong direction! I had the students set up camp and I climbed a nearby mountain and got a GOOD triangulation that fit the terrain. I was about 4 miles East of my expected location. Well within walking range out but....

I did some research and learned that the area we had gone through had been an old volcanic area and was well plotted as an anamoly on flight maps. Duh!

The other big cause is, as someone already pointed out, ferrous metals in your watch, belt buckle, around the eraser on your pencil, your glasses and so forth. I once had a pair of metal rimmed glasses that would attract the needle when I held the compass up to my face to take a reading.

Ron
 
Yes I have one and yes I would recomend it to anyone. This small device is AWESOME! Definately worth the Money.
 
I had a professor who liked to tell a story about being in the infantry, and coming across a platoon of tanks, with one of the TCs balancing a compass on the gun barrel and trying to figure out why his map wasn't accurate.
 
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