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La Soufriere

Volcanoes are really big and really dangerous! Right now, one volcano in a big chain of volcanoes in the Caribbean is erupting. It’s called La Soufriere de Saint Vincent. We talked to Charlie Mandeville of the US Geological Survey’s Volcano Hazards Program about La Soufriere, and about volcanoes more generally.

Guest bio: Charlie Mandeville

Charles Mandeville is the Program Coordinator for the USGS Volcano Hazards Program (VHP) at USGS Headquarters in Reston, Virginia. He has been Program Coordinator for the Volcano Hazards Program since Sept. 2012. He was trained as a physical volcanologist and geochemist and has conducted research at the following volcanoes in his career, including Krakatau, and Galunggung in Indonesia, Mt. St. Helens in Washington, Crater Lake in Oregon and Augustine volcano in Alaska.  His Ph.D. research focused on all aspects of the Krakatau 1883 eruption in Indonesia and involved the study of both onshore and offshore submarine samples from that eruption in order to characterize the erupted material and to delineate the likely cause of lethal tsunamis generated during the eruption that resulted in over 36,000 fatalities. 

He now manages the USGS’ s Volcano Hazards Program (VHP) that operates volcano observatories in Hawaii, Alaska, Cascadia, California and Yellowstone, and the Volcano Disaster Assistance Program (in partnership with the US Agency for International Development), and supporting research and assistance projects. He develops the program’s science portfolio and capabilities and strategies and corresponding budget plans. He coordinates USGS volcano monitoring with the efforts of cooperative university and state geological survey partners. He represents the USGS VHP on interagency and international committees and meetings and advocates the importance of national volcano monitoring to members of Congress.

Transcript

ABBY: When I was a teenager, I went on a trip with my family to Grenada, which is an island in the Caribbean. I remember that the pilot of our very little plane told us that we had to take a different flight path unusual to get to Grenada because of Kick’em Jenny.

MAGGIE: What is Kick’em Jenny?

ABBY: It’s a volcano in the Caribbean Sea. It’s part of a chain of volcanoes in the Caribbean Sea. And at that time, scientists thought it might start erupting, and they didn’t want a plane flying over it and accidentally, well, you can imagine what might happen. Now, it didn’t erupt then. But right now, at this very moment, another volcano very close to Kick ’em Jenny is erupting.

MAGGIE: That volcano is called La Soufriere. And it’s the topic of today’s episode of

MAGGIE and ABBY: Big If True.

MAGGIE: where I, Maggie,

ABBY: and I, Abby,

MAGGIE: explore the truth about big things.

ABBY: Today, we’re going to talk about La Soufriere. But we’re also going to talk about volcanoes in general.

MAGGIE: So here’s our quiz question to test your knowledge.

ABBY: Lava can look like a lot of different things. What does the lava known as lava look like?

MAGGIE: A. a shiny smooth black rock; B. spines of a glass sea urchin; C. a sponge full of holes, or D. a rock with lots of shells and fossils in it.

ABBY: We’ll tell you the answer near the end of the show.

MAGGIE: Our expert today knows a lot about volcanoes. He’s been studying them for a long time.

CHARLIE MANDEVILLE: My name is Charlie Mandeville, and I’m the program coordinator for volcano hazards at the US Geological Survey.

MAGGIE: How did you get interested in volcanoes?

MANDEVILLE: I got interested in volcanoes, probably when I was first in college. But I was always pretty good at chemistry, and a lot of volcanoes is understanding chemistry of the Earth’s materials at high temperature. And the Earth’s materials can be anything from gaseous compounds like water and carbon dioxide and sulfur dioxide and hydrogen sulfide and hydrogen chloride and hydrogen fluoride to things like pure quartz, or things which are mixtures of quartz, and the oxides of other elements like aluminum, iron, magnesium, calcium, manganese, and phosphorus. And those are what the components that go into building rocks. And when you melt those components, you form magmas, the very thing that volcanoes erupt.

ABBY: It’s okay if you don’t know what all of those chemical compounds and elements are. The point is, they’re all parts of the earth, and they all show up in rocks.

MAGGIE: What is a volcano?

MANDEVILLE: A volcano is any place on the surface of the earth, and it can be the submarine surface of the earth or on land surface of the earth, where either magma comes to the surface in the form of lava, or it comes to the surface explosively in an ash and tephra producing eruption. And tephra is any fragmental material that the volcano produces as a result of gases ripping apart the magma and exploding it.

TEPHRA: solid material ejected into the air during a volcanic eruption

Merriam-Webster

MAGGIE: What is La Soufriere?

MANDEVILLE: It’s a popular name, believe it or not, in islands in the Lesser Antilles or the Windward Islands of the Caribbean, as they’re known, or the West Indies. And it’s generally a generic term that comes from the French, meaning a solfatara, or places where the ground is emitting gases, usually sulfurous gases.

SOLFATARA: a volcanic area or vent that yields only hot vapors and sulfurous gases

Merriam-Webster

And those sulfurous gases are doing other things to the ground. They’re locally acidifying the groundwater. And where the groundwater gets acidified, it actually eats rocks. So in many of these solfatara areas, or la soufriere, you actually have a lot of rotted rock. And the reason the rock is rotting away and corroding is it’s being eaten by acids. And the way the acids form is you combine the the CO2 that is coming, the sulfur dioxide coming out of the magma, or the hydrogen chloride coming out of the magma, and you dissolve it in groundwater that’s stored in the ground on the volcano, and you turn those waters to acid and that acid is very strong. So it eats rocks and corrodes the rocks. But in so doing, it actually creates opportunity for the gases coming from the magma to escape. So many of the islands in the Windward Islands or the Lesser Antilles have what’s called la soufriere on top at their summit. There happen to be a number of them in the Lesser Antilles, so there’s La Soufriere on the island of Guadalupe. But there’s also La Soufriere on the island of St. Vincent, which is now erupting.

You can see the crater of La Soufriere in the northern part of St. Vincent, the large island on the top of this map. Wikipedia.

MAGGIE: What makes La Soufriere on St. Vincent special or unique?

MANDEVILLE: The one in St. Vincent is unique because it’s erupted a number of times in recorded history, namely, in 1718, again, and 1902, 1971, 1979. And anytime one of these volcanoes which you know, maybe erupts every 30 to 50 years, tells us something about how volcanoes work. Not only that, it tells us something about how those islands formed originally, believe it or not, each of those islands in the Lesser Antilles started as a submarine volcano where it may have been 3000 to 4000 meters beneath the sea surface. So it’s literally a volcano that’s been growing on the sea floor for, you know, 10s of millions of years. And it finally breaks through to the surface above sea level, and starts creating an emergent island. As the island gets bigger, sometimes you have an amalgamation of two or three of those submarine volcanoes to form the main island. But typically, they’re not all active at the same time. You might have an island that’s composed of an old volcano that was active 20 million years ago, and the northern part of the island is constructed from a volcano that is still growing and active. And that’s the case at La Soufriere de St. Vincent.

ABBY: So this volcano gives volcanologists a lot of opportunities to study it.

MANDEVILLE: Of course, as volcanologists we’re opportunists to learn something new every time we can witness an eruption, and see what kind of events take place even before the eruption starts. And we learn something about how to predict those eruptions. Each time the volcano shows some level of unrest, it might show an increase in the number of earthquakes beneath, it might show us some change in the gases coming out of it, might show us some changes in the shape of its slopes. Is the volcano actually swelling like a blister? And is it deforming and deflating as the eruption ensues? We can send geologists to the island. And we can look at the products from its past eruptions and we can say something about the general style of eruptions that have taken place there. As volcanologists, we need to know that history, such that we can predict the hazards posed by that volcano and pose to the local population.

MAGGIE: How does a volcano grow?

MANDEVILLE: The volcano can actually grow from repeated eruptions, some of which comprise lava flows, which essentially armor the volcano and make it harder to erode. The other type of eruptions that occur are called explosive eruptions that generate ash, pyroclastic flows and surges and airfall deposits. And that material tends to accumulate around the volcano in steep slopes of about 25 to 30 degrees. So you’re literally forming a pile of grains around the vent opening of the volcano. Just like you build drip sand castles at the beach, you’re doing that with natural fragmental material, but that material is easily eroded. The best way to preserve it is to cover it with a subsequent lava flow, which makes it much more resistant to erosion, because the forces of wind and water and ice and freezing and thawing are always trying to degrade the volcano and reduce it to a level ball field. Whereas the eruptions tend to construct the volcano if you will, and armor it, particularly if it’s a lava forming eruption. Many of the volcanoes in the Lesser Antilles, they’re what are known as stratovolcanoes.

STRATOVOLCANO: a volcano composed of explosively erupted cinders and ash with occasional lava flows

Merriam-Webster

And stratovolcano is literally a volcanic mountain that’s been built with alternating layers of fragmental deposits, which lie at about 25 to 30 degrees slope, and form the nice cones like your drip castles at the beach versus lava flows, which tend to coat that cone and protect it from being eroded. So if you look at a cross section of a stratovolcano, you’ll see that it’s typically composed of many, many layers of alternating fragmental deposits, which are ash deposits and pumice fall deposits and lava flows. And that’s that composite material that comprises the flanks of the stratovolcano.

Schematic cross-section through a stratovolcano (synonym: composite volcano), showing the physical build-up. A: inflow of magma through central vent; B: central vent; C: pyroclastic cone on the flank of the volcano; D: lava flow; E: sill; F: pyroclastic deposits; G: crater and crater infill; H: old vent.
Schematic cross-section through a stratovolcano (synonym: composite volcano), showing the physical build-up. A: inflow of magma through central vent; B: central vent; C: pyroclastic cone on the flank of the volcano; D: lava flow; E: sill; F: pyroclastic deposits; G: crater and crater infill; H: old vent. Woudloper, CC BY-SA 3.0, via Wikimedia Commons.

MAGGIE: How long do volcanic eruptions last?

MANDEVILLE: An eruption can last anywhere from, you know, literally seconds, to as many as, you know, weeks, to many decades. Just to give you an idea, Kilauea was erupting from 1983, all the way to about 2017, for about 35 years, whereas eruptions that typically can take place during a lava dome explosion might last for a few 10s of seconds. And something like the May 18 eruption of Mount St. Helens that put a plume up to 35,000 feet, can actually last for several hours.

So there’s a complete range. Part of what is controlling it is are the gases allowed to escape from the magma easily are in fact are the gases being released because of an explosion. And the other big factor is how much lava or magma is available for eruption beneath the volcano. Because as soon as that connection to the surface is formed, all the magma in that chamber feels the effect of the pressure release.

MAGGIE: How do scientists know what a volcano is going to erupt?

MANDEVILLE: Typically, what it has to have is a series of ground based instruments on it to tell us something is escalating away from background. So typically, to get an eruption, you have to bring magma to the surface. And to bring magma to the surface means you have to literally break rock beneath the volcano. Well, if you’ve got a network of say, five to as many as 12 seismometers on the volcano coupled to the ground, they’ll actually feel those smaller earthquakes.

ABBY: Seismometers, by the way, are instruments that measure how big an earthquake is.

MANDEVILLE: And the earthquakes are happening because as the magma is buoyant, and rising to the surface, it’s actually fracturing the rock ahead of it. And those earthquakes tend to be small magnitude. But if you’ve got very sensitive seismometers stationed, say 20 kilometers from the summit of the volcano, you’ll hear and record those small earthquakes. And you can actually trace the foci or the hypocenters of those earthquakes. as it gets closer and closer to the surface. They’re literally tracing the path of the magma to the surface. The other thing that will happen is as the magma gets closer to the surface, and the container that is holding it breaks, some of the gases will start leaking and be easily measured at the surface. And of those gases, it’s the things like carbon dioxide, and sulfur dioxide and hydrogen sulfide, that are really telling us it’s magma that’s on its way to the surface, because those compounds have increased solubility in the magma at higher pressures. But as it comes as the magma ascends in the earth to lower pressures, those gases want to come out, just like the co2 wants to come out of the soda in the bottle. When you open the cap.

MAGGIE: Do volcanoes smell bad?

MANDEVILLE: Some volcanoes smell really bad! And not only that, that’s a great question, some of the gases that they emit like hydrogen sulfide actually deadens your sense of smell. So you can actually be fooled into breathing literally fatal levels of hydrogen sulfide, because your sense of smell is dead, and the more sulfur gases you inhale, so we actually have to resort to physical instruments to measure those gases to know that we’re not in harm, or we’re not exposed to those gases for too long. So the volcanologists actually wear face masks with chemical filters on them to separate out to prevent the intake of carbon dioxide and sulfur gases to keep us safe when we’re working near a volcano.

MAGGIE: Why do we need to know when volcanoes are going to erupt?

MANDEVILLE: The biggest reason we need to know when the volcanoes is going to erupt is because we don’t yet have the technology to stop a volcanic eruption. What we can do, though, is we can help the emergency responders get people evacuated to a safe place where they are no longer in harm’s way from the hazards that will happen as a result of the eruption.

MAGGIE: Volcanoes are very destructive. Do volcanoes have any benefits?

MANDEVILLE: Yes, I’m glad you asked that question. Some of the most fertile soils on earth originate on the slopes of volcanoes. In fact, in a country like Indonesia, or a country like Japan, or even places like Argentina, Colombia and Chile, you have agricultural activity way up on the flanks of the volcano. Because some of the most fertile and mineral rich soils are found there. As well as if you’re living in a tropical climate like Indonesia, the cooler temperatures in the evening are good for rice cultivation, coffee, growing tea, growing coconut plantations, rice plantations, and it makes living that much more tolerable. And you have fertile soil that is mineral rich, because the ash tends to break down pretty quickly. Then release its you know mineral nutrients to whatever plants can take advantage of it.

MAGGIE: This fertile soil comes from the ash from a volcano. What does lava look like when it’s cooled down?

MANDEVILLE: It can look like sometimes ropey textured, very hard shiny black or charcoal gray colored, and can have swirls in it, can have little crystals in it. Or other times it forms these deposits, which we call aa lava, which almost feel like you’re walking on a sea urchin, because there are spines of very, very sharp glass sticking out of it. Because this material is very, very viscous. And really viscous material tends to crust when it reaches the Earth’s surface. But the crust will repeatedly break as the rest of the lava that is underneath and still molten deforms that and literally breaks the crust. So these aa lavas are literally pieces of broken, sharp, glassy crust that will cut your boots and cut your hands and cut your knees really, really badly if you’re not watching out. That’s a Hawaiian term. And it’s really literally onomatopoeic: ah ah! I’ve fallen on a few aa lava flows in my day. And it’s not— it’s really nasty.

MAGGIE: Hey, there’s the answer to our quiz question. Aa lava looks like the spines of a glass sea urchin, and it hurts! Thank you, Charlie, for telling us all about volcanoes. We didn’t even have time to include all the cool things Charlie told us.

ABBY: Did you know that you can actually watch the St. Vincent la Soufriere erupt right now? And there are also lots of other volcanoes erupting around the world. We’ve linked to some of the webcams of these eruptions in our show notes. You should go check them out at bigiftrue.abbymullen.org.

MAGGIE: And that’s it for today. We’ll see you next time for another episode of

MAGGIE and ABBY: Big If True.

ABBY: Big If True is produced by me, Abby, and Maggie. Special thanks to our guest today, Charlie Mandeville of the USGS Volcano Hazards Program. Our theme music is composed by Andrew Cote.

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