“If we connect compositions and combinations [of pressure and temperature] to what happens inside the Earth, that might be able to help predict eruptions.”
Shelf Life Episode 18 – Under the Volcanoes
Probably one of the most classic eruptions in human history was the eruption of Mt. Vesuvius in 79 A.D.
Narrator (Pliny the Younger)
We had scarcely sat down to rest when darkness fell—not the dark of a moonless or cloudy night, but as if the lamp had been put out in a closed room.
It grew lighter, though that seemed not a return of day, but a sign that the fire was approaching.
At last, the cloud thinned out. The sight that met our still terrified eyes was a changed world, buried in ash like snow.
My name is Jim Webster and I'm a curator here at the American Museum. I'm the curator of mineral deposits, but it also bridges into volcanology.
[SHELF LIFE ID]
Since I've been at the Museum, about 28 years now, I've been fortunate. I've visited at least several dozen volcanos around the Earth. But I've focused most of my research attention on two particular volcanos—Mt. Vesuvius, Italy and Augustine volcano in Alaska.
Mt. Vesuvius is along the Bay of Naples. It has erupted roughly 20 times since the last huge eruption in the 1630s. The last eruption of Mt. Vesuvius was at the end of World War II.
Up from the crater of 4,000-foot-high Mount Vesuvius rise towering clouds of smoke and volcanic ash.
Now, Naples and the surrounding areas have two to three million inhabitants. Probably 600,000 live within what's called the Red Zone, the danger zone.
Augustine volcano is actually a volcanic island. It's located up away from populations, in Alaska. It is about 200 or so kilometers from Anchorage and Augustine is the most active volcano in the eastern Aleutian chain. It's erupted seven times in the last 200 years. Most recently in 2005, 2006.
And fortunately, I and a colleague here were able to go and do sampling in the summer after that eruption settled down.
All of these drawers are full of Augustine samples.
So, this is a volcanic rock from Augustine. There are dark and light crystals. So, these are minerals that crystallize out of the liquid rock. Sometimes, as these crystals grow, they may trap some of the molten rock inside of them.
The good part is it can preserve the information exactly when that melt was trapped. So, we can know what kind of compositions and combinations of pressure and temperature relate to certain types of eruptions.
My name is Shuo Ding. I'm a postdoc in the Museum, and my research is to investigate the pre-eruption stage of a volcano.
By conducting experiments, we can compare our experimental results to the samples produced from historic eruptions. And if we connect compositions and combinations to what happens inside the Earth that might be able to help predicting the eruptions.
We use expanding gases in an internally heated combustion engine to drive pistons and move cars. And we use expanding steam in turbines to drive electricity. And in volcanos, expanding gases drive explosive behavior.
So, highly explosive magmas have higher gas content.
It seemed to happen in an instant. The whole top of the mountain—tons of ash, rock, and ice rocket into the stratosphere.
Just like when you pop the top on a bottle of seltzer water and the bubbles form
But there's another factor and this gets into the chemistry. The most abundant element in all magmas is oxygen. The second most abundant is silicon. The more silica and oxygen in the magma, the more viscous, sticky, thick that magma becomes.
The more viscous the magma, the more difficult for it to release its gases.
So, if it's gas charged, basically, there are billions and trillions of little tiny gas bubbles. Each one has an explosive force. But there are so many that during the course of a single eruption, huge amounts of energy can be released during these eruptions.
And both Augustine volcano in Alaska and Mt. Vesuvius in Italy, they're both very gas-charged magmas. But there's something different between Mt. Vesuvius and Mt. Augustine. Vesuvius is higher in sodium and potassium.
The more sodium and potassium that's inside a magma, it tends to break up that structure. It weakens the magma. So, more in Vesuvius, less in Augustine and they actually have very different eruptive histories—Augustine, the last 200 years it's been every 10, 20, 30 years there's been an eruption. Whereas at Vesuvius, it's been very different.
So, for a rock sample from a given eruption, say the 2006 eruption, we can analyze its chemistry, but then we need data to compare that to. And that's what we do here in the lab.
I cook my rock. My experiment is mainly to replicate the conditions inside the Earth like 10 kilometers depth at the pre-eruption stage.
We'll take a powdered material of some- either natural rock or a synthetic equivalent, and we'll put them in a little capsule of gold. We use gold because it's relatively chemically inert. We'll add water. We'll add carbon dioxide. We'll add sulfur, and we'll add chlorine or fluorine in some form.
And I seal it to make sure nothing escapes. And then I put my capsule in one of these bombs. The bomb is like a pressure pot. You put things inside and heat it and pressurize it. I run all my runs at 800 degrees C. It's hot enough to melt the rock I'm using, but not hot enough to melt my capsule.
And then let it sit and cook typically days to weeks, sometimes. It might be a month for a given experiment.
And then turn off the heat, let it quench to a rock again. I will analyze it, analyze the composition and then we can compare the composition of the rocks from historic eruptions to my experimental results to see at what condition that natural sample was produced.
Mt Vesuvius was on a 40, 50-year cycle. So, the issue now—because it's been almost 75 years—is Vesuvius going into a resting period where potentially the next big eruption might be a huge eruption. Or is it just running a little bit late?
We're putting all this together. And I think we'll have a really good chance, you know, from one explosively erupting volcano to another, to understand prior eruptions and hopefully forecast future activities.
Two volcanoes loom large in Jim Webster’s research. Webster, the Museum’s curator of mineral deposits, studies both Mount Vesuvius, Italy—the site of one of the world’s most famous eruptions—and the lesser-known Mount Saint Augustine in Alaska. In 2006, only a few months after an eruption of Augustine, he flew with a small team of geologists to this remote volcanic island in the Aleutian chain. Every morning, they would load into a helicopter and be dropped off at a location on the volcano’s slopes. They’d work their way down, collecting samples along the way. “Hot rocks would occasionally come tumbling down the side of the volcano,” says Webster.
Webster brought some of those rocks back to New York, where he compares them to samples collected at Vesuvius and to artificial materials he synthesizes in his experimental petrology lab. Mt. Saint Augustine and Mt. Vesuvius have several things in common: they’re both young in geologic terms—less than 200,000 years old; they both have magmas rich in volatiles like water, carbon dioxide, sulfur, and chlorine; and both erupt gases that are highly charged with carbon dioxide and water. But, the two volcanoes have very different eruptive cycles. Webster and Kalbfleisch Postdoctoral Fellow Shuo Ding are re-creating pre-eruptive conditions inside the lab and comparing their results to the natural volcanic samples in the hopes that one day we may understand how the different “ingredients” in magma can make one volcano more explosive than another.
Find out what happens when an “extinct” volcano roars back to life
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