The magnetism of the north and south poles are what make a compass work. But the pull of those poles is affected by the ground beneath your feet. WHY?
A magnetic anomaly at the eastern tip of Lake Ontario means that a compass reading there may be wrong by as much as 16° in either direction—east or west. How much it changes depends on exactly where you measure. Boats using autopilot can suddenly swerve into the nearby shoals because the readings change so much! Some call this the Bermuda Triangle of the north.
Researchers measured the anomaly to find its strongest point, just 800 m offshore from Gord Downie Pier, in Kingston. Right there, they found a negative effect to the right (making a compass point farther west) and a positive effect to the left (making a compass point farther east).
Shipwrecking History
The Great Lakes are littered with shipwrecks, and areas like the Thousand Islands (just past the end of the lake) claimed dozens of boats over the years. So it's no surprise that this area has about 200 shipwrecks.
A little farther out from shore is an area called the graveyard of Lake Ontario!
Why Do Compasses Waggle Wildly?
The minerals in the rock underground causes compasses to wiggle, but why is that mineral there?
There's evidence of a large meteor impact farther off shore, creating a crater 1 km long. Metals in that meteorite may be magnetic, and about 460 million years old. But that crater isn't close to the centre of the anomaly. Could another meteor be involved?
Other Anomalies
There are magnetic anomalies in many other places.
There's even another one 19 km further south from Kingston, at Charity Shoal. You can see the circle outline of the crater in satellite pictures!
Staying in Ontario, look up the one in Temagami!
Read More
L. R. Newitt, L.R. and Dawson, E. "Kingston Harbour Magnetic Anomaly," The Canadian Surveyor.
