Magnetic Anomaly Discovered Under Historic New Zealand Lake

But in a recent study conducted by GNS Science, they’ve found out that beneath the calm surface is a large magnetic anomaly, making Lake Rotorua truly one of a kind.

Because the eruption created a circular depression in the earth’s surface that filled with water, Lake Rotorua is actually a caldera, and the floor of the lake is made up of volcanic rock.

However, when the rocks beneath Lake Rotorua were examined, experts found that they were lacking that expected positive magnetic charge and, instead, showed negative anomalies.

While they were mapping, they also performed magnetic surveys, and that’s where things got incredibly interesting.

The lack of positive magnetic activity led the researchers to believe that the mineral magnetite once found in the volcanic rock on the floor of the caldera had been transformed into mineral pyrite, which has almost no magnetic signal.

But it wasn’t the only indicator. In fact, within their research, they also noted pockmarks on the lake’s floor that led to a fascinating realization.

They then deduced that these pockmarks are locations of gas discharge, as the gas bubbles from within the Earth’s core have disturbed the sediment in specific areas. And the craters they formed release hot water and gas into the rest of the lake.

They also noted just how important these craters are to understanding the geology of the lake and the surrounding landscape. GNS researchers wrote, “These craters, now venting hot water and gas, are clear evidence of the various inputs into the lake that affect its ecosystem.”

They report, “The depiction of a river provides a tangible link to the landscape that predates the formation of Lake Rotorua, which is linked to when the Rotorua Caldera last subsided ~220,000 years ago.”

Within GNS’ report, they explained that the river they found slowly makes its way from Sulphur Point at the bottom of the lake toward the west side of the famous island before curving toward the northeast corner.

In the mythical tale, a beautiful maiden and daughter to a local chief, Hinemora, fell in love with a warrior, Tutanekai. However, Tutanekai was of a lower class and wasn’t considered worthy of the chief’s daughter. The story goes that Tutanekai sat solemnly on the island until one day, Hinemoa fashioned a floatation device from empty gourds and swam to him, and her tribe accepted him as her husband.

Reports say that those who visit the lake won’t notice the change in temperature of the hydrothermal craters, but the fact that they are there will change the way scientists see and understand the entire region.

In the case of Lake Rotorua, this process lied beneath the magnetic anomaly discussed above. A comprehensive exploration of this process is essential for a true, nuanced understanding of what is going on under Rotorua’s surface.

As pyrite undergoes gradual oxidation from the hydrothermal vents to the ocean interior, it liberates iron, providing a continuous supply to marine organisms. This process can be likened to an ongoing iron supplement for the ocean, comparable to how humans take vitamins.

The investigation aimed to unravel the intricacies and kinetics governing this replacement process.

However, as the temperature continues to rise, reaching up to 210°C, the replacement rate experiences a decline. Another crucial factor is the pH dependence of the process, revealing a nuanced connection between the replacement rate and pH levels. Specifically, the rate intensifies with a decrease in pH, ranging from 6 to 1.

Additionally, the specific surface area of the minerals involved holds significance in determining the rate of replacement. As the specific surface area varies, it correlates directly with the efficacy of the replacement process.

Grasping the intricacies of magnetite-to-pyrite replacement significantly augments our comprehension of ore-forming mechanisms and mineralization processes.