Thermoremanent Magnetisation (TRM)
Definition
Magnetic alignment locked into iron-bearing minerals as they cool through the Curie temperature after being heated. Burning soil can transform weakly magnetic iron oxides into more strongly magnetic magnetite or maghemite, enhancing susceptibility.
- Definition
- Magnetic alignment locked in on cooling past Curie point
- Trigger
- Heating, such as burning
- Effect on soil
- Weak iron oxides convert to magnetite or maghemite
- Detected by
- Magnetometry and susceptibility survey
Common questions
Why does burning make buried features easier to detect magnetically?+
Fire-altered soil gains a stronger, more stable magnetic signature than surrounding undisturbed soil, so a magnetometer survey can highlight burn pits, hearths, or burned clandestine graves against the background.
Does TRM require intense heat to form?+
No, even moderate sustained heating from small fires can convert some iron oxide minerals to more magnetic forms, though the degree of enhancement depends on the temperature reached and how long it was sustained.
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