Lake Rotorua in New Zealand has always been known for its mysterious and ethereal qualities, thanks to the geothermal activity that lies below and around its waters. However, recent research conducted by experts at the country's GNS Science research institute has unveiled an even more intriguing aspect of this legendary lake. In an unprecedented mapping effort, scientists have discovered that Lake Rotorua's hydrothermal systems extend into its hidden depths.
Formed by a colossal volcanic eruption around 200,000 years ago, Lake Rotorua sits at the center of a massive crater on New Zealand's North Island. The collapse of a magma chamber formed a 16km-wide circular caldera, which later filled with water. Despite the passage of millennia, the lake's water still possesses a high sulphur content, resulting in a mesmerizing green-blue coloration. Clouds of steam continuously waft around its shores, accentuating its enchanting allure.
The recent mapping effort, which covers around 68 percent of the lake's floor, was carried out using a variety of techniques. Data was collected by The Royal New Zealand Navy, which employed a multibeam echo sounder to study the lake floor. Magnetic surveys were also conducted, revealing a large magnetic anomaly. Surprisingly, instead of the expected positive anomalies typically associated with volcanic rocks, the researchers found negative anomalies, which can be attributed to the low magnetic susceptibilities of the rocks.
According to Cornel de Ronde, a principal scientist at GNS Science, this unexpected finding suggests that hydrothermal fluids have passed through the rock, transforming highly magnetic minerals into pyrite (commonly known as fool's gold) with negligible magnetic signals. This hydrothermal process drastically reduces the magnetic signal, explaining the negative anomaly observed.
Furthermore, the research team found other evidence of hydrothermal activity in the same area. A heat flow map indicated the presence of rising heat, most likely in the form of hot water, from beneath the lake floor. Additionally, craters, likely created by hydrothermal eruptions, were discovered. Interestingly, water temperatures near the bottom of Lake Rotorua measure around 14°C (57°F), which is not typically associated with hydrothermal blasts. De Ronde explains that the lake's vast size allows its cool waters to counteract the rising heat, making the hydrothermal activity virtually imperceptible to swimmers.
While the geological discoveries beneath Lake Rotorua are astonishing, it is worth touching upon the lake's cultural significance as well. The lake is intricately tied to an ancient Maori love story that takes place on Mokoia Island—a dome formed by solidified lava in the center of the lake. The tale revolves around a beautiful maiden named Hinemoa and a warrior named Tutanekai. Despite their forbidden love, Hinemoa defies societal expectations and swims across the lake to be with Tutanekai on Mokoia Island. In a surprising turn of events, Hinemoa's tribe eventually accepts Tutanekai as her husband, and the couple lives happily ever after.
The recent discoveries beneath Lake Rotorua add another layer of intrigue to its already captivating allure. As scientists continue to delve into the hidden depths of this ancient lake, the mysteries hidden beneath its shimmering, ethereal surface are sure to enthrall us for years to come.
