This text was initially featured on Knowable Magazine.
Over hundreds of 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 enormous, irregular slabs of the Earth’s crust—the stable rock floor the place people stay—and the higher a part of the underlying mantle “float” on a deeper, hotter layer of the mantle. When two plates meet, typically one offers method and finally ends up sinking little by little into the depths, in a course of often known as subduction.
If the phenomenon happens alongside your complete size of the plate boundary, a line of volcanoes, often known as a volcanic arc, kinds. 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 surely incorporates an necessary number of several types of magmas, a few of that are distinctive on the planet. It’s a “geological paradise” hiding secrets and techniques worthy of investigation, says Esteban Gazel, a geochemist at Cornell College in Ithaca, New York. “Central America has a wealthy mixture of circumstances that permit the comparability of various pure experiments in magma era,” he and his two coauthors wrote in a overview revealed within the 2021 Annual Review of Earth and Planetary Sciences.
Central America was born on what was an oceanic plate, as a consequence of the subduction of tectonic plates. About 150 million years in the past, a sluggish course of started that steadily 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.
Within the final 11,000 years, 70 volcanoes have been lively on this a part of the Ring of Hearth. Simply as volcanoes have created fertile lands the place agriculture and cattle-raising have flourished, they’ve additionally introduced loss of life and displaced populations. In 1902, for instance, following a sequence of earthquakes within the area, the Santa Maria volcano in Guatemala recorded one of the largest and most explosive eruptions of the 20th 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 residence nation. On this interview, edited for size and readability, he explains how the geology of Central America helps us perceive the evolution of our planet.
What’s the Central American volcanic arc?
It’s an alignment of dozens of volcanoes, not all of that are presently lively, stretching from the border between Mexico and northern Guatemala to central Costa Rica. Amongst 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 beneath the Caribbean plate. The Cocos plate is produced in a ridge within the Pacific Ocean. The ridges are submarine fractures by means of 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 stuffed with risky components, primarily water and carbon dioxide. At about 60 kilometers deep they turn into unstable. Due to the excessive stress and temperature circumstances 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 fuel, 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. That is the method that generates the magma that involves the floor within the type of lava.
When did this course of start?
We’ve got a historical past of volcanism in Central America going again many hundreds of thousands of years. The arc has been rising and evolving, creating completely 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 way in which wherein it enters beneath the Caribbean plate—its entry angle—is completely 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 as we speak’s Nicaragua Lake. It resembled as we speak’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 as we speak, in Mexico.
Right this moment, the arc is nearer to the Pacific coast in northern Central America and towards central Costa Rica. Many of the volcanoes you see as we speak are 500,000 to 250,000 years previous. However there are additionally youthful volcanoes. Nicaragua’s Cerro Negro is the youngest, courting from 1867.
The Earth evolves and leaves previous variations. The pages of the evolution of the planet are written on these rocks.
What makes the Central American volcanic arc distinctive?
It’s one thing unimaginable. The geochemical variations from Nicaragua to Costa Rica are probably the most excessive on the planet. All through Italy there are magmas comparable in chemical composition to these of Costa Rica, however all these volcanoes in Italy are going to be similar to one another.
Within the Mariana Trench within the western Pacific Ocean, the magmas are similar to these of Nicaragua, however all of the volcanoes within the Marianas produce magmas similar to one another.
Italy and the Mariana Trench are separated by hundreds of kilometers, whereas Costa Rica and Nicaragua present necessary geochemical variations of their magmas regardless that they’re very shut. The acute quantity of variation in such a small space makes Central America the one place on the planet with these traits, and subsequently 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 quantity of the volcano. Very massive volcanoes have extra molten materials coming from the mantle and fewer variability. In distinction, smaller volcanoes have far more geochemical variation. Giant 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’s one thing very distinctive to Central America. Within the Mariana Trench, the entire arc is developed in oceanic crust. Within the Andes, in South America, your complete arc develops in continental crust. In Central America, the arc begins in continental crust in Chiapas and Guatemala, and after we enter Costa Rica, we enter the oceanic crust. All of 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 this can be a very dynamic zone.
Why does this occur?
Fifteen million years in the past, a a lot youthful crust started to succeed in what’s now Costa Rica, with the Galapagos seamounts—submerged oceanic islands within the Pacific Ocean that after have been like what at the moment are the Galapagos Islands of Ecuador. That’s what is called a sizzling spot, a thermal anomaly that brings materials from the Earth’s decrease mantle. These islands journey with the plate, submerge, and finally collide and enter the Costa Rica-Panama subduction zone, the place the Cocos plate dives beneath the Caribbean plate.
This plate has a singular geochemical signature that reveals up within the volcanoes of Costa Rica and Panama. The conclusion from plenty 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 your complete planet has been fashioned by the melting of those seamounts within the subduction system. So it is usually 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 sequence of seamounts. These mountains are getting into the subduction zone and are melting. Because the crust developed 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 delivery 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?
Sure. In a number of million years, it’ll subduct after which come out once more as a volcano like Poás or Irazú in central Costa Rica as we speak, the place the Galapagos signature is extraordinarily evident.
What are the instruments you utilize to research volcanic arcs?
The primary 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 deduce their origin, age and evolution.
How has your subject developed through the years?
I began doing analysis in volcanology and geochemistry on the Nuclear Research Center of the College of Costa Rica. I began there as a result of geology and volcanology at the moment have been very descriptive. The nuclear physics researchers carried out extra quantitative measurements. After I began my profession in america, my science developed to be far more numerical and fewer descriptive.
Within the final decade, and particularly the final 5 years, as a neighborhood we’ve moved to a volcanology that’s extremely exact and quantitative.
That’s solely going to proceed to increase. We’re already at a degree the place to be a contemporary geologist it’s important to find out about geochemistry gear, about programming, about statistics. Now there’s machine learning and synthetic intelligence, and all these instruments are getting used together with subject and laboratory knowledge.
Geologically, what does the longer term maintain for this area?
What we should perceive is that in Central America we stay in a tectonic and volcanically lively zone. Prevention and good development actually make a big distinction to save lots of lives within the face of eruptions and earthquakes. As a result of volcanoes are going to maintain erupting and earthquakes are going to maintain taking place. It’s the pure technique of evolution.
What new analysis is arising?
In January 2024, a bunch with professionals from completely different elements of the world will go to Poás volcano in Costa Rica to check new applied sciences to review volcanic processes and with the objective of sometime having a greater concept of tips on how to forecast a volcanic eruption. The individual organizing it from america was my post-doc mentor.
And my lab was simply funded by the US Nationwide Science Basis to review Plinian eruptions of mafic composition. Plinian eruptions are the highest-magnitude eruptions, just like the Vesuvius eruption that destroyed Pompeii. They’re usually felsic, which means they’re excessive in silica. Nonetheless, there’s a group of mafic eruptions which are excessive in magnesium and iron that even have that magnitude. In Central America, Nicaragua’s Masaya volcano holds a file for one such eruption.
How can Central America educate us about Earth’s formation extra broadly?
If we need to perceive how the continents have been fashioned within the early a part of the Earth’s evolution, the most effective locations to work is Central America.
If we need to examine the method of subduction, the way it begins and the way the composition of continents adjustments, we’ve that historical past in Central America.
If we need 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 need to perceive the mechanisms that begin very high-intensity eruptions, we’ve a file 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 might be studied.
Extra 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 the terrestrial mantle uncovered, and also you see rocks, often known as peridotites, which fashioned at depths of fifty to 70 kilometers and have been dropped at the floor by tectonic exercise. These are extremely distinctive and really fascinating sections, which have been the main target of a few years of analysis which have allowed us to raised perceive the construction, composition and historical past of the mantle.
Central America will proceed to be studied for its range: a geological paradise.
Article translated by Debbie Ponchner
This story is a part of the Knowable en español sequence on science that impacts or is performed by Latinos in america, supported by HHMI’s Science and Academic Media Group.
This text initially appeared in Knowable Magazine, an impartial journalistic endeavor from Annual Opinions. Join the newsletter.
