A diagram of the Earth’s magnetic field as influenced by the Sun.
Research published March 16 in the Proceedings of the National Academy of Sciences (PNAS) reveals that about 800 years ago, a significant anomaly in the magnetic field of Southeast Asia occurred.
The team came to this conclusion by examining residues such as slag from an iron ore smelter called Tonle Bak, located in what is now Cambodia.
Many iron smelters were built in Tonle Bak between about the 11th and 14th centuries, when the area was part of the Khmer Empire. As a part of the production process, workers took the residues of iron making to a nearby location for dumping at regular intervals. Over Time, they piled up 50 hills formed by the waste slag.
Because these hills contained large amounts of iron ore, they were a local magnet for a long time afterwards. This study extracted remnants from inside several of the hills to learn more about the magnetic field in the area between 1034 and 1391.
The researchers found that in the nearly 100 years between 1200 and 1300, the direction of the magnetic field in Southeast Asia changed by about 0.05 degrees per year, with the tilt decreasing from about 30 degrees to only 5 degrees and the strength of the field decreasing significantly.
The researchers say this indicates a significant anomaly in the magnetic field in a localized area of Southeast Asia about 800 years ago. They estimate that this is part of a larger anomalous region, and that the entire magnetic field weakening may extend all the way to the equatorial region.
The researchers believe that this is a “flux expulsion” (flux expulsion) phenomenon that exists at low latitudes. It is not yet possible to explain the specific cause of this anomaly, except that it is estimated to be related to some kind of turbulence between the core and the mantle layer.
The study mentions that several other regions also have this anomaly, such as the region below the southern Atlantic Ocean, where this phenomenon now also occurs.
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