Magnetic anomaly deep below New Zealand's lake reveals buried ancient secret

Magnetic anomaly deep below New Zealand’s lake reveals buried ancient secret

In a big revelation, scientists have unveiled a hidden hydrothermal system beneath the waters of Lake Rotorua, a site steeped in Maori legend and situated atop a dormant volcanic crater on New Zealand’s North Island.

This discovery not only adds a new chapter to the lake’s rich history but also marks a significant milestone in the understanding of subterranean geological phenomena.

Lake Rotorua, renowned for its geothermal marvels such as bubbling mud pools, shooting geysers, and natural hot springs, has long been a keeper of the Earth’s fiery power. But despite the intense geothermal activity, its temperature at the bottom remains cooler.

The lake itself is shallow, with an average depth of about 10 meters, and is part of the Taupo Volcanic Zone. It was formed when a magma chamber collapsed following a volcanic eruption, creating what is known as the Rotorua Caldera.

Researchers from GNS Science, a New Zealand research institute, have meticulously mapped approximately 68% of Lake Rotorua’s floor, covering 55 square kilometers. Their efforts have brought to light a series of eruption craters, traces of an ancient river, and a significant magnetic anomaly in the southern part of the lake.

These findings confirm for the first time that the well-known hydrothermal activity on the mainland extends into the submerged realm of Lake Rotorua.

The mapping project, which involved the Royal New Zealand Navy, utilised advanced multibeam echo sounder technology to chart the lake’s physical features. Magnetic surveys conducted during the exploration revealed the unexpected magnetic anomaly.

Typically, volcanic rocks exhibit strong positive magnetic responses due to the presence of magnetite. However, the anomaly detected suggests that hydrothermal fluids have altered the magnetite into pyrite, or fool’s gold, resulting in a significantly reduced magnetic signal.

Cornel de Ronde, a principal scientist at GNS Science, likened the clarity of these new maps to the experience of seeing through glasses for the first time. The detailed imaging has exposed a dynamic underwater landscape, where heat—likely from hot water—is rising to the lake’s floor, and hydrothermal eruption craters punctuate the terrain.

Despite the intense geothermal activity below, Lake Rotorua maintains a relatively cool temperature near its bottom, averaging around 14 degrees Celsius. The vast volume of the lake ensures that any heat emanating from the depths is effectively dissipated, keeping the overall temperature stable with only minor fluctuations.

As researchers continue to analyze the data, the secrets of Lake Rotorua’s underwater world will undoubtedly yield further wonders, deepening our understanding of the complex interplay between land, water, and the forces beneath the Earth’s crust.

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