Kamal Ghorui
Among all volcanic systems known to humans today, one of the most interesting is located at the bottom of the Pacific Ocean. It was called the Tamu Massif, which came into the spotlight when geologists started discussing the possibility that it may be the largest volcano on our planet. However, additional information raised doubts about the initial hypothesis.The giant structure can be found at the bottom of the Shatsky Rise area of the northwest Pacific. Similar to many other underwater structures, Tamu Massif cannot be observed using visual techniques. Nevertheless, geologists study it using various methods, including seismic exploration, rock drilling, and bathymetric mapping.Why geologists believe that Tamu Massif is the largest volcanoOne of the main discoveries connected with the structure under discussion took place in 2013 when several scientists published an article about the Tamu Massif in Nature Geoscience. In particular, they concluded that the object appeared to be a large-scale shield volcano based on data obtained from multichannel seismic profiles and rock drilling.Scientists believed that the massif formed slowly as lava spread over large expanses of the seafloor. In the research, it was reported that the volcano had covered a region similar in size to that of New Mexico. This became a sensation, since it indicated that our planet could form volcanic systems even more extensive than those seen before.The authors stated in their publication that the presence of outward-dipping lava flows is one of the most convincing indicators of a shield volcano morphology.Why the Pacific Ocean seafloor keeps secretsExamining underwater volcanoes is significantly more challenging than exploring terrestrial volcanoes. The Pacific oceanic crust is covered by several kilometres of seawater, making direct observations costly and laborious.Geophysical methods such as seismic reflection imaging help here. This shows the stratification of rocks underneath. Magnetic anomalies contain information about cooling and motion in the past. Samples are obtained using drills. The result is a concealed chronicle of planetary geological evolution stored within the Pacific seafloor.A Nature commentary observed that the Tamu Massif was not only unique due to its massive size but also because it may turn out to be “a single volcanic edifice.
Underwater volcanoes are significantly more challenging. Image credit – Wikimedia
The magnetic evidence that turned everything upside downSome time after this first discovery, an additional scientific study brought confusion to the issue. According to the researchers who published their findings in Nature Geoscience in 2019, the Tamu Massif may not have been the product of one perfectly centralised volcano.Scientists analysed the magnetic anomalies present in the oceanic crust. The process of forming magnetic stripes occurs as lava solidifies and captures the state of Earth’s magnetic field. As it appeared, this formation process is likely connected to seafloor spreading rather than to growing out of one vent.This conclusion meant that instead of being a regular shield volcano, Tamu Massif may have been shaped under the influence of a variety of factors, including volcanism and tectonic activity of seafloor spreading. According to the authors of the study, the formation of the Tamu Massif was “closely related to ridge processes”.Why Tamu Massif still countsDespite the controversy, one thing remains clear: Tamu Massif is still considered one of the biggest volcano-like structures on the planet. Its significance lies more in how it helps scientists learn about the deep ocean bedrock. According to the Tamu Massif, huge volcanic structures could be formed by a complex process involving multiple geological activities instead of just one activity.William Sager, the marine geologist at the University of Houston involved in initial studies about the massif, once noted that the Tamu Massif had a unique shape, making it different from other seamount chains. Its shape remains significant in further studies.This case study also serves to show how scientific knowledge advances. Initially, seismic evidence backed one hypothesis. Then, magnetic studies introduced another idea. It is not that the previous study was incorrect. Instead, both sets of data gave a more complete picture of how gigantic underwater mountains form.
The massive undersea mountain beneath the Pacific changed how scientists define giant volcanoes. Image credit – Wikimedia
Giant volcano lying dormant under the PacificAlthough the Tamu Massif resists easy categorisation, this very resistance is the reason why researchers remain interested in it. This mountain cannot be called an ideal volcano, although it can claim a place among the largest volcanic constructs discovered on our planet. What is more important, the existence of the Tamu Massif serves as evidence of the existence of some geological phenomena on the bottom of the Pacific Ocean that can surprise scientists.
