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Over thousands and thousands of years, the Earth’s higher layers have carried out a dance that has created mountains, volcanoes, continents, ridges and ocean trenches.
Tectonic plates play a key position on this course of. These big, irregular slabs of the Earth’s crust—the strong rock floor the place people dwell—and the higher a part of the underlying mantle “float” on a deeper, hotter layer of the mantle. When two plates meet, generally one provides means and finally ends up sinking little by little into the depths, in a course of generally known as subduction.
If the phenomenon happens alongside the whole size of the plate boundary, a line of volcanoes, generally known as a volcanic arc, varieties. There are volcanic arcs within the Andes of South America, Tonga within the South Pacific Ocean, the Aleutian Islands of Alaska, the Philippine Islands and Central America, amongst others — all of them a part of the Pacific Ring of Fire, the place earthquakes and volcanoes are widespread.
The Central American arc is comparatively small, simply 1,100 kilometers lengthy. But it accommodates an necessary number of several types of magmas, a few of that are distinctive on the planet. It is a “geological paradise” hiding secrets and techniques worthy of investigation, says Esteban Gazel, a geochemist at Cornell University in Ithaca, New York. “Central America has a rich combination of conditions that allow the comparison of different natural experiments in magma generation,” he and his two coauthors wrote in a evaluation revealed within the 2021 Annual Review of Earth and Planetary Sciences.
Central America was born on what used to be an oceanic plate, as a consequence of the subduction of tectonic plates. About 150 million years in the past, a gradual course of started that regularly allowed volcanic islands to develop between the continental plenty of northern and southern America. About 3 million years in the past, the world now comprising Costa Rica and Panama was lastly joined to the north of present-day South America, making a single landmass from Alaska to Tierra del Fuego.
In the final 11,000 years, 70 volcanoes have been energetic on this a part of the Ring of Fire. Just as volcanoes have created fertile lands the place agriculture and cattle-raising have flourished, they’ve additionally introduced dying and displaced populations. In 1902, for instance, following a collection of earthquakes within the area, the Santa Maria volcano in Guatemala recorded one of many largest and most explosive eruptions of the twentieth century. In 1968, an eruption of the Arenal volcano in Costa Rica left 78 useless; and in 2018, the Fuego volcano in Guatemala erupted, killing greater than 100.
Gazel carried out his first research as a geochemist in Costa Rica, his dwelling nation. In this interview, edited for size and readability, he explains how the geology of Central America helps us perceive the evolution of our planet.
What is the Central American volcanic arc?
It is an alignment of dozens of volcanoes, not all of that are at present energetic, stretching from the border between Mexico and northern Guatemala to central Costa Rica. Among them are the volcanoes of Fuego and Tajumulco in Guatemala, Santa Ana in El Salvador, Masaya and Momotombo in Nicaragua, and Arenal and Poás in Costa Rica. This arc is the results of the subduction of the Cocos plate underneath the Caribbean plate. The Cocos plate is produced in a ridge within the Pacific Ocean. The ridges are submarine fractures via which magma emanates. When magma comes out at a ridge, it pushes the plates, cools, crystallizes and creates new crust.
When the plate subducts, it’s full of unstable parts, primarily water and carbon dioxide. At about 60 kilometers deep they develop into unstable. Because of the excessive stress and temperature situations at these depths, the minerals will break down and the volatiles will come out in a really particular kind: a hybrid between a liquid and a gasoline, which is called a supercritical fluid or a soften. This fluid interacts with the remainder of the supplies and fuses the rocks of the mantle. This is the method that generates the magma that comes to the floor within the type of lava.
When did this course of start?
We have a historical past of volcanism in Central America going again many thousands and thousands of years. The arc has been rising and evolving, creating totally different variations. It started to kind about 150 million years in the past, on the time of the dinosaurs.
The tectonic system strikes and accommodates itself. For instance, the Cocos plate doesn’t have the identical subduction angle alongside the arc’s 1,100 kilometers; the best way through which it enters underneath the Caribbean plate—its entry angle—is totally different in numerous areas. This impacts the formation of the arc.
For instance, some 20 million years in the past, the arc was the place the San Carlos plains are—north of what’s now Costa Ric —and to the east of immediately’s Nicaragua Lake. It resembled immediately’s Mariana Islands [a group of islands aligned north to south, close to each other and located southeast of Japan]. The arc continued to the place Chiapas is immediately, in Mexico.
Today, the arc is nearer to the Pacific coast in northern Central America and towards central Costa Rica. Most of the volcanoes you see immediately are 500,000 to 250,000 years outdated. But there are additionally youthful volcanoes. Nicaragua’s Cerro Negro is the youngest, relationship from 1867.
The Earth evolves and leaves outdated variations. The pages of the evolution of the planet are written on these rocks.
What makes the Central American volcanic arc distinctive?
It is one thing unbelievable. The geochemical variations from Nicaragua to Costa Rica are essentially the most excessive on the planet. Throughout Italy there are magmas comparable in chemical composition to these of Costa Rica, however all these volcanoes in Italy are going to be very comparable to one another.
In the Mariana Trench within the western Pacific Ocean, the magmas are very comparable to these of Nicaragua, however all of the volcanoes within the Marianas produce magmas very comparable to one another.
Italy and the Mariana Trench are separated by 1000’s of kilometers, whereas Costa Rica and Nicaragua present necessary geochemical variations of their magmas despite the fact that they’re very shut. The excessive quantity of variation in such a small space makes Central America the one place on the planet with these traits, and due to this fact a singular pure laboratory.
Why is there a lot variation?
The regional variation is managed by the angle of subduction and the composition of the subducted materials. The native variations of Central American volcanoes are managed by the amount of the volcano. Very giant volcanoes have extra molten materials coming from the mantle and fewer variability. In distinction, smaller volcanoes have far more geochemical variation. Large volumes of magma homogenize the sign, and smaller volumes present us extra extremes.
Central America additionally has a mix of denser oceanic crust and lighter continental crust. What does this imply and what does it educate us?
It is one thing very distinctive to Central America. In the Mariana Trench, the entire arc is developed in oceanic crust. In the Andes, in South America, the whole arc develops in continental crust. In Central America, the arc begins in continental crust in Chiapas and Guatemala, and once we enter Costa Rica, we enter the oceanic crust. All the magmas in Costa Rica are oceanic arc magmas that look very very similar to the Marianas, till about 15 million years in the past when issues begin to change once more, and the magmas in Costa Rica begin to look extra like continental crust. This tells us that it is a very dynamic zone.
Why does this occur?
Fifteen million years in the past, a a lot youthful crust started to attain what’s now Costa Rica, with the Galapagos seamounts—submerged oceanic islands within the Pacific Ocean that when had been like what at the moment are the Galapagos Islands of Ecuador. That is what is called a scorching spot, a thermal anomaly that brings materials from the Earth’s decrease mantle. These islands journey with the plate, submerge, and ultimately collide and enter the Costa Rica-Panama subduction zone, the place the Cocos plate dives underneath the Caribbean plate.
This plate has a singular geochemical signature that exhibits up within the volcanoes of Costa Rica and Panama. The conclusion from quite a lot of my work through the years is that Costa Rica was not continental crust, and since about 15 million years in the past one of many youngest continental crustal terranes [fragments consisting of a distinct and recognizable series of rock formations that has been transported by plate tectonic processes] on the whole planet has been fashioned by the melting of those seamounts within the subduction system. So additionally it is a pure laboratory.
Cocos Island [an island and national park located in the Pacific Ocean, some 500 kilometers off the Costa Rican coast] is a part of a collection of seamounts. These mountains are getting into the subduction zone and are melting. As the crust advanced from oceanic to continental, its density was decreased, permitting Costa Rica and Panama to emerge from the ocean. This course of contributed to the closure of the Central American isthmus, which lastly occurred about 3 million years in the past. The beginning of the volcanic arc helped to generate sediments within the space, and tectonic exercise raised the floor till a whole closure occurred.
So, is Cocos Island getting nearer to the mainland?
Yes. In a number of million years, it is going to subduct after which come out once more as a volcano like Poás or Irazú in central Costa Rica immediately, the place the Galapagos signature is extraordinarily evident.
What are the instruments you utilize to examine volcanic arcs?
The important instruments are the volcanic rocks, obtained after an eruption, as a result of their chemical composition is managed by these processes. We analyze them utilizing electron microscopes, spectroscopes and mass spectrometry to infer their origin, age and evolution.
How has your area advanced through the years?
I began doing analysis in volcanology and geochemistry on the Nuclear Research Center of the University of Costa Rica. I began there as a result of geology and volcanology at the moment had been very descriptive. The nuclear physics researchers applied extra quantitative measurements. When I began my profession within the United States, my science advanced to be far more numerical and fewer descriptive.
In the final decade, and particularly the final 5 years, as a neighborhood we’ve got moved to a volcanology that’s extremely exact and quantitative.
That’s solely going to proceed to develop. We’re already at a degree the place to be a contemporary geologist you might have to find out about geochemistry tools, about programming, about statistics. Now there may be machine studying and synthetic intelligence, and all these instruments are getting used together with area and laboratory knowledge.
Geologically, what does the longer term maintain for this area?
What we should perceive is that in Central America we dwell in a tectonic and volcanically energetic zone. Prevention and good building actually make a big distinction to save lives within the face of eruptions and earthquakes. Because volcanoes are going to maintain erupting and earthquakes are going to maintain taking place. It is the pure technique of evolution.
What new analysis is arising?
In January 2024, a gaggle with professionals from totally different components of the world will go to Poás volcano in Costa Rica to check new applied sciences to examine volcanic processes and with the purpose of sometime having a greater thought of how to forecast a volcanic eruption. The particular person organizing it from the United States was my post-doc mentor.
And my lab was simply funded by the US National Science Foundation to examine Plinian eruptions of mafic composition. Plinian eruptions are the highest-magnitude eruptions, just like the Vesuvius eruption that destroyed Pompeii. They are usually felsic, that means they’re excessive in silica. However, there’s a group of mafic eruptions which might be excessive in magnesium and iron that even have that magnitude. In Central America, Nicaragua’s Masaya volcano holds a document for one such eruption.
How can Central America educate us about Earth’s formation extra broadly?
If we would like to perceive how the continents had been fashioned within the early a part of the Earth’s evolution, among the best locations to work is Central America.
If we would like to examine the method of subduction, the way it begins and the way the composition of continents adjustments, we’ve got that historical past in Central America.
If we would like to examine samples of supplies that traveled to the inside of the Earth, that “visited” the mantle in a subduction zone and got here up once more, they’re uncovered in Guatemala.
If we would like to perceive the mechanisms that begin very high-intensity eruptions, we’ve got a document of eruptions in Nicaragua and Costa Rica.
So Central America is already a pure laboratory, and it’ll proceed to be a spot the place many geological processes could be studied.
Additional examples the place Costa Rica has one thing that may be very distinctive are the uncovered oceanic crust on the Nicoya Peninsula and the uncovered mantle on the Santa Elena Peninsula. In Santa Elena, we’ve got the terrestrial mantle uncovered, and also you see rocks, generally known as peridotites, which fashioned at depths of fifty to 70 kilometers and had been introduced to the floor by tectonic exercise. These are extremely distinctive and really attention-grabbing sections, which have been the main focus of a few years of analysis which have allowed us to higher perceive the construction, composition and historical past of the mantle.
Central America will proceed to be studied for its variety: a geological paradise.
Article translated by Debbie Ponchner
This story is a part of the Knowable en español collection on science that impacts or is carried out by Latinos within the United States, supported by HHMI’s Science and Educational Media Group.
This article initially appeared in Knowable Magazine, an impartial journalistic endeavor from Annual Reviews. Sign up for the e-newsletter.