Researchers have discovered a large amount of water trapped within the sediments and rocks of a lost volcanic plateau, currently located deep within the Earth’s crust.
Revealed through 3D seismic imaging, a ancient water reservoir lies 3.2 kilometers below the ocean floor off the coast of New Zealand, where it may act as a buffer for a major earthquake fault facing North Island, Phys.org reported on October 8.
Seismic imaging device towed behind the research vessel during the survey of the Hikurangi subduction zone in New Zealand. (Photo: Adrien Arnulf)
Faults often generate slow-moving earthquakes, referred to as slow slip events. These can release tectonic pressure harmlessly over days and weeks. Scientists want to understand why these events occur more frequently in some faults than others. Many slow slip earthquakes are believed to be associated with buried water. However, there has previously been no direct geological evidence pointing to such a large water reservoir existing at the fault in New Zealand.
“We haven’t been able to observe deeply enough to know exactly how it affects the fault, but we can see that the amount of water accumulating here is much higher than usual,” said Andrew Gase, the lead researcher and a postdoctoral fellow at the Institute for Geophysics at the University of Texas (UTIG).
The study, published in the journal Science Advances, is based on seismic surveys and ocean drilling conducted by the research team at UTIG. Gase, now a postdoctoral fellow at Western Washington University, called for deeper drilling to explore the reservoir’s depths so researchers can determine whether it influences the pressure around the fault. This information is crucial for a better understanding of significant earthquakes.
The location where researchers found the water reservoir is part of a vast volcanic region formed when a massive lava column the size of the United States rose to the Earth’s surface in the Pacific Ocean 125 million years ago. This event is one of the largest volcanic eruptions on Earth and caused upheaval for millions of years. Gase utilized seismic imaging to construct a 3D representation of the ancient volcanic plateau, revealing that sediments are largely thick around the buried volcano. Gase’s colleagues at UTIG conducted experiments with core samples of volcanic rock and found that water occupies nearly half of its volume.
Gase speculates that the shallow sea where the eruption occurred eroded part of the volcano into porous rock that stored water like an aquifer. Over time, rock and debris transformed into clay that accumulated even more water. This new discovery is significant because researchers believe that underground water pressure may be a key factor creating conditions for tectonic pressure release through slow slip earthquakes. This typically occurs when water-rich sediments are buried alongside the fault, retaining water underground. However, the fault in New Zealand contains very little of this typical oceanic sediment. Instead, the research team suggests that ancient volcanic rock and metamorphic clay carry large volumes of water when consumed by the fault.
