Jonathon,

Magnetic susceptibility is the significant variable in magnetic anomaly maps, playing the same role as density in gravity, for example. Since magnetic anomalies are entirely caused by the amount of magnetic minerals contained in the rocks, it is necessary to thinking about these minerals, and the magnetic susceptibility.

In each case the susceptibility depends only upon the amount of ferrimagnetic minerals, such as magnetite, ilmenite and pyrrhotite.

Although there is a great variation in the susceptibility, even for a particular rock, and a wide overlapping between different types (sedimentary the lowest average values) the fact that magnetic susceptibility in volcanic rocks are very high (several magnitude – order) than sedimentary or metamorphic rocks, I think that

it is possible to locate the magnetic anomaly associated with the current generated by lava fluid flow. But it is not simple to find inclinations of magnetic minerals, individually? as you need.

It is not simple due that the nature of the Earth´s magnetic field: you must correct the answers according with your own latitude, inclination, declination, depth of the sources, if your tube are horizontal or not, the azimuth respect the North magnetic pole, the azimuth of your tube respect the survey lines of the acquisition, the uniforme or not magnetic response, pole-dipole, for instance.

Therefore, in view of these limitations,

I recommend to modelling the magnetic responses of very simple geometrical models or simple-shaped geometric source bodies such as point source, sheet, sphere, horizontal and vertical cylinders, and prism. It means: synthetic simulations with and without noise, and trying to estimate model parameters such as source-depth and inclination. Maybe other way to try is when you have another geophysical observation, such as gravity or seismic survey, to minimize the ambiguity of the responses.

This paper: "Standard curves for interpretation of magnetic anomalies due to thin dykes of finite depth extent" by Haigh and Smith (1975, Australian Bureau of Mineral Resources, Geology and Geophysics) that I attached to you I think is an excellent contribution for your questions.

Best wishes, Mario E. Sigismondi

Magnetism is a property created in solid-state metals

Jonathon,

As Mario mentioned, in a lava tube your main anomaly will be produced by the amount of magnetic minerals present, that will be a lot!! However, since lava is still molten, it won't create a magnetic field, properly speaking. Temperature of lava will be somewhere between 700 to 1200ºC. Magentite's Curie temperature is about 520ºC, so basically, solid rock around the lava tube will form a magnetic field, assuming it is an active volcano, you basically will expect to have an anomaly with the same declination and inclination as todays. I also agree with Mario, I will try to produce a very simple 2-D model, with a circle with a very high magnetic susceptibly and the background with "reported" parameters from Hawaii or Island active volcanic field.

Check Bob Butler's Paleomag book, it's free on the web, you'll find the basics there:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwjEysGa45_lAhURxVkKHSZfDvIQFjAAegQIAhAC&url=https%3A%2F%2Fwebsites.pmc.ucsc.edu%2F~njarboe%2Fpmagresource%2FButlerPaleomagnetismBook.pdf&usg=AOvVaw2N8qUVzFX8izYvdrtJS6Zl