A “magnetic anomaly” was discovered at the bottom of a legendary volcanic lake in New Zealand

Once upon a time, the daughter of an influential chief overcame forbidden love by swimming across a lake to join the chosen one of her heart, a young warrior… This lake mentioned by the Maori people in their legends is Lake Rotorua, in northern New Zealand.

More realistically, the place is now frequented by tourists for its stunning beauty – in the heart of a dormant volcano, the sulfur gives the water an almost fluorescent green hue, even more vibrant in the park's smaller lakes. In neighboring Waiotapu – just for its proximity to thermal springs where you can recharge your batteries.

Can the secret of this legendary lake finally be revealed? “Researchers from GNS Science, a New Zealand research institute, have mapped the floor of Lake Rotorua in unprecedented detail.”Regard Live Science.

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Pseudo-gold, the metal that is the origin of magnetic anomalies

These new maps cover an area of ​​55 square kilometres, or approximately 68% of the lake floor, using data collected in part by the Royal New Zealand Navy using a type of sonar. “Proves for the first time that continental hydrothermal systems at Rotorua extend into the hidden depths of the lake.”emphasized our colleagues.

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Thus the analysis reveals “explosion craters”, “Old River”…especially, “A large magnetic anomaly in the southern part of the lake”.

“Typically, with volcanic rocks, when you pass the magnetometer [appareil de mesure du champ magnétique] Above, we get very positive anomalies, but in this case, we get negative anomalies.”Cornel de Ronde of GNS Science told LiveScience.

Igneous rocks generally contain magnetite, which, as its name suggests, is a highly magnetic mineral, our colleagues explain.

But in Lake Rotorua, researchers believe hydrothermal fluids passed through the rocks and turned magnetite into pyrite. However, this metal – nicknamed “fool's gold” because of its resemblance to real gold – has no magnetic signal. Hence the negative anomaly that researchers measure.

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“Hydrothermal eruptions”

Furthermore, the map of heat flows reveals directed flow from the basement to the lake floor, possibly hot water, the authors believe. For Cornel de Ronde, the craters visible in this area would not bear witness to the rise of magma, however “Hydrothermal eruptions”.

However, the princess of Maori legend had to brave the cold, because despite this intense hydrothermal activity, the water temperature at the bottom of the lake does not deviate much from 14 degrees Celsius. In fact, the lake is very wide “There is enough cold water to balance the heat rising from the bottom.” What don't we do for love…