Magnets: I like to think of them as gravity’s little cousin. (Really? This guy gonna talk about magnets for 10 minutes?) Well, fine, how about volcanoes? (Yeah, exploding mountains!) Would you have ever guessed that a mere magnet could dethrone the largest volcano on this planet, possibly even in this solar system!? Oh, magnets just got a lot more interesting, huh. (yeah cool – when does it blow up?) Okay, stay with me now…
That former-king of volcanoes is called Tamu Massif, and “massif” it is! It sprawls over an area of 120,000 square miles! For comparison, that’s about the size of New Mexico, the 5th largest state in the US. Hmm, can’t recall hearing about any volcanoes the size of an already sizeable state, but maybe I wasn’t paying attention… Oh, it’s an extinct volcano sleeping at the bottom of the Pacific Ocean 1,000 miles east of Japan. That explains it! Its record-breaking size results partly from its location, as the volcano sits at the intersection of 3 underwater fault lines.
Those, in turn, happen to be part of a larger system geologists call the Ring of Fire. (Hey, that rings a bell!) Where and how it formed explains why it’s so ginormous, but I’ll get into that later. For now, what’s with the exotic-sounding name? It must mean something epic like “Fire Master” in a language I don’t know. Eh, not quite: “Tamu” is simply an acronym for Texas A&M University, while “Massif” is a French word used in geology to describe certain types of mountains based on how they form. It’s also French for “massive” because what else were they gonna call it? On the long list of famous volcanoes we all know since grade school (Vesuvius, St. Helens, Fuji, Krakatoa!), why haven’t most people heard of Tamu Massif? It’s supposedly the largest of them all! The thing is, this sleeping giant hasn’t erupted in a long looong time. I’m talking 150 million years – back during the peak of dinosaur times! But just because this volcano has apparently decided to retire, that doesn’t mean nothing’s happening there. Mainly, it’s a massive source of magnetic anomalies.
That’s the fancy way of saying disruptions in the Earth’s magnetism. You see, the molten layers beneath the planet’s crust are rich in metals like iron, nickel, and cobalt. All of those are known for their magnetic properties. So when you get a whole bunch of them (mmm, say, 120,000 square miles-worth), you’re bound to produce a magnetic anomaly! Wait, rewind, let’s go back to “molten layers beneath Earth’s crust.” You might remember hearing about magma back in school when you were learning about volcanoes and making those cool exploding models. (My class never did that, by the way. I still feel robbed of my childhood to this day…) Magma is a sort of gooey hot semi-liquid beneath or within the Earth’s crust. Yep, it’s under your feet right now! (“Oh, ah, hot!”) Since it’s less dense than solid rock, it naturally flows upward, sometimes finding an exit through a volcano.
It might ooze out or explode in a fiery rage depending on the gaseous pressure behind it. Once a volcano erupts, those magnetically charged metals (iron, nickel, and cobalt) come to the surface in large amounts. A volcano as big as Tamu Massif is going to have some outstanding eruptions, especially when it’s in a geological hotspot like the Ring of Fire. The question that drew many scientists to the scene was exactly how large these eruptions were and how many there were in all. Enter Dr. William Sager, the marine geophysicist who discovered the volcano when he was a professor at Texas A&M. When he and his team released the first measurements of Tamu Massif in 2013, the undersea volcano skyrocketed to the top of the scoreboard. Not only did it dethrone Hawaii’s Mauna Loa as the largest volcano on Earth, it even surpassed Olympus Mons on Mars to become the biggest known volcano in the Solar System! Well, as far as surface area goes. Impressive for a mountain nobody even knew existed until recently. Unfortunately for the new reigning champ, its glory would be short-lived… Back when it won Mount Universe 2013, researchers were pretty sure a single massive eruption had formed Tamu Massif before the volcano burned itself out. But like all good scientists, Dr. Sager and his team wanted to test their theory and make sure.
So, they began studying the volcano’s magnetic anomalies. You see, the Earth’s magnetic field goes through natural cycles over the course of several million years. You can imagine our planet like a giant magnet. Right now, the North Pole is positively charged, while the South is negative. That’s why a compass will still point North even in the Southern Hemisphere. However, the poles will gradually reverse over millions of years, and lost hikers will be confused to no end! When a volcano erupts, the expelled lava carries with it the magnetic charge it had when it was part of the earth’s mantle. It also keeps that charge even as the Earth’s magnetic field continues to shift. By examining these magnetic anomalies, researchers hoped to get a better understanding of Tamu Massif’s lifecycle. What they found was that this thing isn’t exactly a volcano… at least not a single one. As the physicist Ricky Ricardo might say: Let me ‘splain. Originally, they thought it was a regular shield volcano, only much bigger than any others on this planet. Shield volcanoes form when magma oozes out, piles up on itself, and cools over time. This forms a giant mound that looks like a shield lying on the ground, hence the name. The mound would have uniform magnetism throughout since the magma that spilled up and over would cover it entirely and spread those magnetic metals out evenly. But that’s not the case with Tamu Massif. It has “stripes” of magnetic anomalies that point to it popping up a different way.
They now think that it’s a sort of volcanic system formed through seafloor spreading. This is when an ocean ridge spreads apart, new material forms in the center, and the older stuff goes out to the edges. New material wells up from the middle instead of being added to the top in the form of dried lava like in shield volcanoes. Tamu Massif’s striped magnetic anomalies point to gradual seafloor spreading over a couple million years, not volcanic formation from hardened lava. In short, the crown went back to Hawaii’s Mauna Loa. (Yea!) Tamu Massif is still getting a lot of attention from geologists. While bulges in the earth’s crust exist all over, this is the only known example with a massive volcanic system sitting on top! So, Tamu, don’t feel bad about losing your spot as Earth’s biggest volcano – you’re still one of a kind! (I feel better.) Then again, there are plenty of other volcanoes that are just as unique and puzzling. Heading over to the Atlantic, geologists recently found something very exciting just off the shores of Bermuda. All the ships and planes that disappeared in its infamous triangle? Not exactly, but still just as newsworthy! Most volcanoes in the Caribbean sprang up along fault lines. You know, just like how the Pacific Plate is bumping elbows with its neighbors, creating the Ring of Fire.
But the undersea volcano that created the island of Bermuda is well within the North American tectonic plate. Odd, indeed! For many years, geologists assumed that Bermuda had formed over a volcanic hotspot, just like Hawaii. To prove that long-held theory, scientists from around the world got together to examine a 2,600-foot sample drilled from the center of the dormant volcano. What they found ended up being something nobody had ever seen in this world. Atlantis? If only! They discovered that the island formed due to unusual activity in what geologists call the Transition Zone. It’s a region of the Earth’s Mantle about 250 miles below sea level. The researchers noticed that the chemical composition of the rocks resembles those found at that extreme depth. They have much more water and crystalized minerals than are usually found in the relatively shallower Upper Mantle, which is where most volcanic magma originates. Because Earth’s molten interior is constantly shifting, an upwelling occurred around 60 million years ago.
That material from the Transition Zone found itself sucked into the Upper Mantle. From there, the pressure moved it toward the surface, and the molten rock eventually burned its way through the crust. This phenomenon created a temporary hotspot from which the volcano, and later the island of Bermuda itself, could form. No one knew that volcanoes could come about this way. Now that we do know they can, scientists are scrambling to find more examples of this strange phenomenon. They’re confident that if such an event could occur once, it must’ve happened before. In fact, it’s likely that many existing volcanoes have been misidentified as having formed in a more conventional way! Between this and the revelation of Tamu Massif’s true nature, it’s an exciting time for geologists. Just when you think there’s nothing left to discover, our world continues to surprise us! Hey, have you ever seen a volcano in real life? Would you want to?