Discovery of a magnetic anomaly in a volcanic lake

Lake Rotorua, famous in Maori folklore, is located in the heart of an extinct volcano in New Zealand. However, the bottom of this lake has been mapped for the first time by a local research institute. Then scientists noticed a magnetic anomaly there.

Unpublished maps of Lake New Zealand

It is known that he is in the heart Maori legend From Hinemoa and Tutanikai, Rotorua is a body of fresh water covering an area of ​​79.8 square kilometres. This legendary lake is located in northern New Zealand The average depth is only ten metres. It was formed from the crater of a large volcano in the Taupo volcanic region, and has not been mapped until today.

in Detailed Report Published on January 25, 2024, but New Zealand's GNS Science Institute has published several new maps. The production of these documents was made possible thanks in part to data collected using a type of sonar by the Royal New Zealand Navy. However let us emphasize that the cards are in question It concerns only 68% of the lake bottom.

Large magnetic anomaly

According to GNS Science researchers, these new maps prove for the first time that Rotorua's continental hydrothermal systems extend deep into the hidden depths of the lake. Their analysis reveals the presence of an ancient river, eruption craters, and, most surprisingly, a A large magnetic anomaly in the southern part of the lake. You should know that usually passing a magnetometer over volcanic rocks results in very positive anomalies. However, in the case of Lake Rotorua, there are negative anomalies.

But researchers have an explanation. Normally, volcanic rocks already contain magnetite, but in Lake New Zealand, it contains the same magnetite It has been transformed into pyrite. It is a metal called “fool's gold” because of its resemblance to classic gold. Pyrite consists mainly of iron disulfide and traces of precious metals, and is not actually generated Almost no magnetic signal. So it's not surprising to learn that researchers at GNS Science have observed negative anomalies.

One of the cards also reveals a It flows from the basement to the bottom of the lake. For researchers, it might be hot water. Thus, the craters visible in the area do not indicate magma rising, but rather hydrothermal eruptions. However, despite this significant hydrothermal activity, the water temperature It remains around 14°C continuously. In fact, the lake contains enough cold water to balance out the effect of hot water coming from the basement.