Dancing compass needles in Kiruna?

Kiruna has the world second largest magnetic anomaly!

But what is normal and why is it anormal in Kiruna?

The magnetic field of earth:
If you align a compass (in Central Europe), the needle points north.

Not to the geographic north pole (N90 °), but to one of the two magnetic poles of the earth. Since both poles (as seen from Central Europe) are close to each other, it is relatively easy to determine the north direction with the aid of a compass (the magnetic declination amounts to 2-4°E in Germany, 6-8°E in northern Sweden and 20-30°W in Greenland (in summer of 2019)).

Between the magnetic north and south pole, the magnetic field of the earth spans.

In contrast to the geographic north and south pole the two magnetic poles are not fixed but moving. Since the beginning of observation in 1590, the northern magnetic Pole has long zigzagged through northern Canada, since the mid-19th century, it took its current course across the Artic Ocean to the Russian peninsula Taimyr and sets ever larger distances per year (in 2000 56km ).

The diagram below illustrates this:

Movement of the magnetic north pole: positions from 1831 to 2007 are marked as yellow quadrats, molded positions from 1590 to 2020 as circles changing colour from blue to yellow. (Source: NOAA)

In the course of geological history, the Earth's magnetic field has reversed several times.

The earth's magnetic field surrounds and penetrates the earth. It consists of three components:
1.) Geodynamo in the liquid outer core (95%)(responsable for the moving of the poles)
2.) electric currents in the ionosphere and the magnetosphere (1-3%)
This is due to winds in the ionosphere or effects of the magnetized plasma of the solar wind.
3.) local components in the upper crust, e.g. mineral deposits. Such an interference field can make up locally several percent of the total field.

The magnetic anomaly in Kiruna

Such a magnatical disorder exists in Kiruna!
The city lies between the two iron mountains Kiirunavaara (749m) and Luossavaara (729m). There high quality iron ore was found
The Kiruna seam has a very high magnetite content, which is responsible for the second largest magnetic anomaly in the world. The seam is about 4km long and 80m wide (in the depth even up to 180m wide) and extends at least 2km in depth.
The seam is mined by the mining company LKAB since 1888, currently in a depth of 1365m (in 2018).
The seam was formed about 1.6 billion years ago after intensive volcanic activity due to the precipitation of iron-rich solutions on a syenite porphyry foundation. The seam was overlaid by further volcanic deposits of rhyolite and sediments before it was tipped into its present state. It forms an angle of 60 °.

The seam consists almost exclusively of magnetite and apatite. The rock contains up to 60% iron and an average of 0.9% phosphorus, which is a very high quality ore. Kiruna is home of the largest magnitite deposit in the world.

Magnetite
Magnetite is ferrite with the chemical formula Fe3+2Fe2+O4; the composition contains 72,36% F and therefore it is relatively pure.
Often it has crystals that are octahedral. The surfaces are usually striped. The color is iron black, sometimes bluish on the crystal surfaces. The hardness is 5.6-6, the density 4.9-5.2 that means is it relatively heavy. Magnetite is strongly magnetic, at 580 ° C this property disappears, but reappears on cooling. The melting point is 1527 ° C.
With the help of a magnet you can easily find out if you have found magnetite: It will stick to it!


A: Kiruna-Magnetite (by broiler)
B: Test for Magnetite (by broiler)

To log this cache as a found:
1.) go tho the co-ordinates and consult your compass! Tell me how it behaves (for example pointing north, pointing to the mountain, turning in circles, pointing between mountain and north ...) and what device (real compass, GPS ...) you take for meassurement.
2.) Search with your magnet magnetite. Tell me what it feels like, color, texture, crystals, heavy or light ... If you do not find magnetite, give me a possible cause.
3.) Optional: if you should stay in Kiruna overnight and stay up at 1:15am (or set an alarm), listen to the night with all your senses and e-mail me what happens at 1:20am. Tell me what your observation has to do with magnetite.
4.) Optional: if you leave Kiruna, consult your compass from time to time. E-maile me the co-ordinates where it works "normal" works again.

Of course, we are also happy about photos!

Please log in directly after you have e-mailed us. If there are several teams in your group, please send an e-mail for each nickname (it could be the same of course).