Surprising discovery found deep under New Zealand’s Lake Rotorua

New findings have revealed a concealed hydrothermal system beneath Lake Rotorua in New Zealand, which holds a significant place in a well-known Māori love tale. Situated at the center of a vast ancient crater of a dormant volcano on New Zealand’s North Island, Lake Rotorua is steeped in history. According to legend, it is where the daughter of a prominent chief defied forbidden love by swimming across the lake to be with a young warrior. The Rotorua area is renowned for its hydrothermal activity, with Tourism New Zealand describing clouds of steam around the lake’s banks and sulfur causing a “enchanting green-blue” hue to the water. Researchers at GNS Science, a New Zealand research institute, have recently mapped the floor of Lake Rotorua in unprecedented detail, unveiling eruption craters, an ancient river, and a significant magnetic abnormality in the lake’s southern part. These detailed maps demonstrate for the first time that the mainland hydrothermal systems of Rotorua extend into the lake’s concealed depths.Image displaying the significant magnetic anomaly in the southern area of the lake. (Image credit: Institute of Geological and Nuclear Sciences Limited (GNS Science).)Cornel de Ronde, a principal scientist at GNS Science, told Live Science that seeing the maps was like wearing glasses for the first time when you didn’t realize you needed them. “You finally put those glasses on, and you can see the fine print,” he said.
Related: Over half of the world’s largest lakes and reservoirs are losing waterThe maps cover 21 square miles (55 square kilometers), which is about 68% of the lake’s floor, according to a statement from GNS Science. The Royal New Zealand Navy collected some of the data, mapping the lake floor’s physical features using a multibeam echo sounder — a type of sonar. They also carried out magnetic surveys, which revealed the magnetic anomaly. “Normally with volcanic rocks, when you run a magnetometer over the top of them, you get very positive anomalies, but in this case we’re getting negative anomalies, likely due to very low magnetic susceptibilities,” de Ronde said. Lake Rotorua is located in the crater of a dormant volcano on New Zealand’s North Island.  (Image credit: GLVImages via Getty Images)Volcanic rocks generally contain the highly magnetic mineral magnetite, but in Lake Rotorua, researchers believe hydrothermal fluids have passed through the rock and changed the magnetite into pyrite, or fool’s gold, which has almost no magnetic signal. This hydrothermal process would drastically reduce the magnetic signal and explain the negative anomaly.Researchers also found further signs of hydrothermal activity in the same general area as the magnetic anomaly. A heat flow map indicates heat, probably hot water, rising up to the lake floor from below. Craters are also visible in this same region, which de Ronde pointed out are likely hydrothermal eruption craters. Despite all this activity, water temperatures near the bottom of the lake typically hover around a cool 57 degrees Fahrenheit (14 degrees Celsius), as per de Ronde. This is due to the lake’s size, which allows enough cool water to counteract the heat rising from below, resulting in a temperature fluctuation of just about 1.8 degrees F (1 degree C) over a month.”Nobody swimming in the lake would notice it, but with instrumentation, we do,” de Ronde said. Editor’s note: Updated at 5:46 p.m. EST to note that the hydrothermal process would drastically reduce the magnetic signal, not flip it, as had previously been stated.

Author: OpenAI