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Course: American Museum of Natural History > Unit 4
Lesson 2: Volcanoes- Volcanoes 101
- Volcanoes: Magma Rising
- Monitoring Mount Etna: Magma on the Move
- Follow the Magma
- Yellowstone—Monitoring the Fire Below
- Yellowstone National Park is a Volcano
- Scientists at Work: Hawaii
- Quiz: Volcanoes
- Exploration Questions: Volcanoes
- Answers to Exploration Questions: Volcanoes
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Volcanoes: Magma Rising
Some volcanoes explode with the force of an atomic bomb. Others spill rivers of gently flowing lava. What causes volcanoes to erupt? How do scientists study them? Let’s explore one of the most powerful, destructive volcanic eruptions in history.
More than a century ago, the city of Saint-Pierre was known as the Paris of the Caribbean. Located on the island of Martinique, Saint-Pierre was a center of trade in rum, sugar, cocoa, and coffee. Its boulevards were lined with beautiful homes and shops.
But in the Spring of 1902, All of That Changed…
On the morning of May 8, the nearby volcano Mt. Pelée exploded in a burst. A swirling cloud of hot gas, ash, and rocks, called a pyroclastic flow, rushed down the mountainside at 480 kilometers per hour (300 mph). It burned everything in its path, including the town of Saint-Pierre and nearly all the ships in the harbor. Within two minutes, close to 30,000 people were dead.
How Does Subduction Cause Volcanoes To Form?
- When an oceanic plate collides with a continental plate, it sinks into the mantle below.
- As the oceanic plate sinks, fluid (shown in purple) is squeezed out of it.
- The fluid flows up into the mantle rock above and changes its chemistry, causing it to melt. This forms magma (molten rock).
- The magma rises and collects in chambers within the crust.
- As magma fills the chamber, pressure grows. If the pressure gets high enough, the magma can break through the crust and spew out in a volcanic eruption. Most explosive volcanoes occur above subduction zones.
Why Are Some Volcanoes So Explosive?
It’s all a matter of chemistry. The way a volcano erupts depends on the amount of gas and silica (a molecule of silicon oxygen) in the magma below. Magma with lots of silica is thick and gooey, while magma low in silica is thin and runny. And in magma with lots of gas, bubbles form as it rises. The more bubbles that form, the more explosive the eruption!
Explore How Different Shapes of Volcanoes Have Different Kinds of Eruptions.
How Do Scientists Study Volcanoes?
Around the world, there are about 1,500 active volcanoes. Active volcanoes are those that have erupted in the past, and could erupt again. About twenty are probably erupting right now.
These days, eruptions rarely come as a surprise. Scientists are keeping a watchful eye on active volcanoes. They want to find out if magma is rising beneath a volcano — a sign that it could erupt. The goal? Reduce the risk to humans who live near them.
Check out some of the tools that scientists use to monitor volcanoes.
Want to join the conversation?
- How does the lava go from the mantle to the bottom of the volcano through all the rocks in the way?(8 votes)
- The magma coming up from the core is so hot it melts the rock around it. The magma is also less dense than the rock around it, so it floats to the top.(11 votes)
- How does the lava go from the mantle to the bottom of the volcano through all the rocks in the way??(2 votes)
- it desolves and developes a new subtance.(1 vote)
- I saw that silica is similar to viscosity are they the same thing?(0 votes)
- Silica is related to viscosity. Viscosity is the measurement of how fast a liquid flows. So something like honey will have a high viscosity, and water would have a low viscosity.
In terms of volcanoes however, the more silica there is (silica is similar to rubber, imagine rubber/silicon in a liquid form, how thick would that be!) the more viscous it is.(4 votes)
- When there is a volcano that erupts highly viscous magma, does that mean the eruption is gradual and think; or that it is fast and watery?(1 vote)
- Does the volcano form due to the plates colliding (and subduction) or is it just a mountain with magma forcing it's way out of the mountain?(1 vote)
- if their are 20 volcanoes that are erupting right now how do scientists know which one is erupting.(0 votes)
- There's always a team or so of scientists closely monitoring groups of volcanoes to see if there's any signs of immediate eruption, so they would know.(2 votes)
- I don't even get how volcanoes form...?(0 votes)
- a volcano forms from the subduction zone (oceanic plate and continental plate collides the oceanic plate sink because it heavier than the continental plate as shown in the diagram)(2 votes)
- So, I read about the spider in this article, and i'm curious as to how exactly it works Do they drop it in, and if so, wouldn't it just melt?(1 vote)
- Volcanologists have "Spider-Legs" 'crawl' into the crater of a volcano to take gas emissions, temperature measurements, and video footage. One good example is shown in the crater scene from "Dante's Peak" (1997).(1 vote)
- why does the volcanoes erupt out of no were(1 vote)
- Why do volcanoes erupt out of no where? Well, as the article says, the volcanoes don't just "erupt out of nowhere". Scientists everywhere monitor all the volcanoes that aren't extinct. They know when one might erupt.(1 vote)
- Like lava, can pyroclastic material harden turn into rock?(0 votes)
- Usually not. Although most pyroclastic debris hardens from being semi-molten, the solidified material can maintain temperatures of 500 degrees Fahrenheit for days. A prime example of this occurred several days of the 1980 Mount St. Helens eruption, on the shores of Spirit Lake.(1 vote)