An underwater plateau larger than Idaho in the Pacific Ocean first began to form during volcanic eruptions during the Cretaceous period. (145-66 million years ago) and continues to grow today.

According to a new study published Jan. 15 in the journal Earth and Planetary Science Letters, the Melanesian Border Plateau, located east of the Solomon Islands, was formed as a result of four separate pulses of volcanism, each with different root causes.

This chronology is important because giant volcanic features under the ocean are often poorly understood, said study leader Kevin Conrad, an earth scientist at the University of Nevada, Las Vegas. In some cases they form in a single magma flow, in which case they are known as major eruption sites. These massive, long-lasting volcanic events are so dramatic that they often alter the climate and are associated with mass extinctions.

But in other cases, features that resemble major eruption sites are actually created over long periods when multiple volcanic events deposited rock like a layer cake. It can be difficult to distinguish with limited rock samples.

“There are some features in the Pacific basin. [вчені] “We only have one example, and it looks like one very large, massive event,” Konrad told LiveScience. said. “Sometimes when we examine these features in detail, we realize that they were actually formed from a few impacts over tens of millions of years and would not have had a significant impact on the environment.”

Conrad and his colleagues had the opportunity to explore the Melanesian Border Plateau in detail during a five-week research mission in 2013. They used large chain machines to remove rocks from the slopes of the seamounts and volcanoes that make up the plateau.

By studying the age and chemical composition of these rocks, they learned that the plateau probably began to form 120 million years ago. The part of the plateau beneath other rocks, known as Robbie Ridge, was probably formed by the eruption of large amounts of basaltic lava during this period. This created a large underwater plateau that probably did not reach sea level.

Then, 45 million years ago, this piece of the Pacific Ocean drifted over a hot spot in the mantle. Hotspots are plumes of heated material that rise from the mantle and cause volcanoes to form in the middle of tectonic plates. Hawaii is an example of an island chain formed by a hotspot.

The culprit in this case was the Rurutu-Arago hotspot, which still exists today under French Polynesia. This formed a chain of underwater mountains called seamounts, with islands rising above the ocean surface. These islands were eroded, but 13 million years ago a seamount drifted over another hotspot, the Samoan Hotspot, which today forms the Samoa Islands.

“All of the channels that magma passed through 45 million years ago are now weak points through which magma could begin to pass 13 million years ago,” Konrad said. said.

This created new islands that eventually sank below sea level again. Finally, tectonic movements in the Tonga Trench over the last three million years have triggered new volcanic eruptions on the plateau; This mechanism was quite different from the hotspot volcanism that preceded it.

According to Conrad, there are many hotspots in the South Pacific, so it’s likely that other seamounts have built up in similarly complex shapes over time. The nonprofit organization Ocean Exploration Trust and the National Oceanographic and Atmospheric Administration collect samples from such seamounts in the United States.

Conrad and colleagues at the University of Maryland and Cal State University Long Beach will soon sample Central Pacific mountains that may have been formed by overlapping hotspots. Konrad proposes calling these features “mid-ocean plate superstructures” to distinguish them from large igneous regions formed by a single massive volcanic event.

“As we analyze the samples in more detail, we will encounter an even more complex situation,” Conrad said.