Lava tubes and magnetic reversals

[Patricia N Kambesis]

I found that it does takes on the average about a meter distance to get
away from the magnetic affect of a piece of  magnetic breakdown
(sometimes one can get away with less).  

To answer Paul on affects of magnetic reversals - all iron bearing
materials (lava, sediments, rocks being formed etc.) will take on the
existing magentic direction of the time (first humanly observed from sea
floor dredgings which showed "stripes" of sea floor basalt with reversed
magnetic directions. ) These stripes formed at spreading zones at plate
margins.  The basalts took on the magentic direction of the poles  during
the time that the basalts were being deposited.

Paleomagnetic dating that is done on laminated cave sediments uses the
magnetic reversals to determine despoitional times of those sediments.  

The last magnetic reversal happened some 780,000 years ago - so if one
were to find lavas with reversed polarity, then the lavas would be at
least that old. I have no idea if there are any lava tubes out there of
this age and if there were, what effect, if any the reversed polarity
would have on a compass.

pk