Universe Today

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Pelean eruptions, or Nuee Ardente eruptions occur when a large quantity of gas, dust, ash and lava fragments are blown out of a volcano’s central crater. This material falls back, and then travels down the side of the volcano at tremendous speeds – faster than 150 km/hour.

These eruptions are also known as pyroclastic flows, and they’re one of the most dangerous kinds of eruptions that volcanoes can do. Material blasted out in a Pelean eruption can tear through populated areas, killing thousands of people.

Pelean eruptions got their name from Mont Pelee, the volcano that caused tremendous destruction on Martinique, Lesser Antilles in 1902. The Pelean eruption and following pyroclastic flows killed more than 30,000 people in the worst volcanic disaster of the 20th century. The town of St. Pierre was effectively wiped off the map by a series of powerful eruptions.

We have written many articles about volcanoes for Universe Today. Here’s an article about Plinian eruptions, and here’s an article about Strombolian eruptions.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

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Volcanoes make bad neighbors. Between 1900 and 1986, volcanoes have killed an average of 845 people every year. And volcanoes have so many ways to kill you, from the hot lava flows and clogging ash to the rock bombs and toxic fumes. Let’s take a look at dangerous volcanoes, and their associated volcanic dangers.

One of the most familiar aspects of a volcanic eruption are the lava flows. You might be surprised to know that lava flows are actually one of the least dangerous ways that volcanoes can try to kill you. Lava flows rarely move faster than walking speed, so you can easily outrun and avoid them. Buildings, roads and trees aren’t so lucky; however, and can be destroyed by the crushing weight and burning temperature of a lava flow.

Poisonous volcanic gases are a danger from volcanoes too. During an eruption, volcanoes can release vast amounts of water vapor, carbon dioxide and sulfur dioxide. If you encounter a cloud of pure carbon dioxide, you can suffocate without air. Other volcanic gases are poisonous and people have even been killed by acidic gases (ouch).

During an explosive eruption, volcanic ash is hurled up to 45 km in the air. Several cubic kilometers of ash can rain down around the volcano, covering everything in a thick layer of ash. It might look a bit like snow, but it’s rock, and very heavy. Just a few centimeters of volcanic ash is heavy enough to collapse buildings and kill crops.

You also have to watch out for rocks hurled out of volcanoes during an eruption. These volcanic bombs can be meters across and be hurled hundreds of meters and even kilometers away from the volcanic vent. Imagine a rock the size of a house falling from the sky.

But the volcano danger that kills more people every year is known as a pyroclastic flow. In some eruptions, hot rock and gas flow down the side of the volcano at speeds greater than 700 km/hour. A wall of material as hot as 1,000 degrees C plunges down the side of the volcano and can travel hundreds of kilometers away from the vent, destroying anything in its path. This is what destroyed the ancient Roman town of Pompeii.

Volcanoes are beautiful sights, but they have their dangers too, so be careful.

We have written many articles about volcanoes for Universe Today. Here’s an article about lightning around Redoubt volcano in Alaska.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

References:
http://www.geo.mtu.edu/volcanoes/hazards/primer/
http://www.appstate.edu/~abbottrn/vlcns/

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Here on the surface of the Earth, the ground is cool and comfortable. But as you descend into the Earth, temperatures increase. By the time you get to the Earth’s mantle, temperatures can get more than 1000 degrees C. The high temperatures cause rocks to melt into magma. This magma collects together into large underground pools called magma chambers.

The molten rock in a magma chamber is under tremendous pressure. This pressure fractures the rock, and the magma seeps through these cracks, rising to the surface. When the magma finally reaches the surface, you get a volcanic eruption. What started out as magma inside the Earth becomes lava, ash, gas and volcanic rock.

Magma chambers are hard to detect. That’s because they can be deep underground. The magma chambers that scientists actually know about are only 1 to 10 km under the surface. Scientists can identify the location of magma chambers through seismology. They detect the minor earthquakes that happen as magma moves up through through the rock into and out of a magma chamber.

Once a volcano erupts, it empties out the magma chamber, causing the surrounding rock to collapse inward. If enough rock collapses, you can get a large depression at the surface of the Earth called a caldera.

In 2006, drillers in Hawaii accidently pierced into an active magma chamber. It was the first time that magma had ever been studied “in its natural habitat.” They were searching for geothermal energy sources at a depth of 2.5 km when their drill bit went into the magma chamber. Molten rock went back up the bore hole several meters and then solidified so the scientists could study it.

We have written many articles about volcanoes for Universe Today. Here’s an article about the difference between magma and lava. And here’s an article about different types of volcanoes.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

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The material that erupts out of a volcano starts as magma deep underground. Much of this magma is rock, but it can also contain pockets of volcanic gas dissolved into it. As the magma rises up, these dissolved gasses begin to form tiny bubbles as the pressure gets lower. As it gets closer to the surface, the bubbles increase in number and size creating additional pressure inside the volcano.

The volcanic gas undergoes a tremendous increase in volume when the magma reaches the surface and erupts. This expansion can be the driving force of explosive eruptions.

The primary components in volcanic gas are water vapor, carbon dioxide and sulfur (either sulfur dioxide or hydrogen sulfide). But you can also find nitrogen, argon, helium, neon, methane, carbon dioxide and hydrogen. Approximately 60% of total emissions released by volcanoes is water vapor, and carbon dioxide accounts for 10 to 40% of emissions. Although that sounds like a candidate for greenhouse gases, volcanoes actually contribute only 1% of the carbon dioxide released into the atmosphere every year.

You might be surprised to know that poisonous gases were responsible for about 3% of all volcano-related deaths from 1900 to 1986. Some people were killed by acidic corrosion (ouch) while others were asphyxiated.

We have written many articles about volcanoes for Universe Today. Here’s an article about different types of volcanoes, and here’s an article about the biggest volcano in the Solar System.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

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This mysterious, giant object existed at a time when the universe was only about 800 million years old. It stretches for 55 thousand light years, a record for that early point in time. Its length is comparable to the radius of the Milky Way’s disk.

Besides being a great candidate for a future “Where in the Universe Challenge,” what is it?

In general, objects such as this one are dubbed extended Lyman-Alpha blobs; they are huge bodies of gas that may be precursors to galaxies.

And this blob was named Himiko for a legendary, mysterious Japanese queen.

Beyond that, researchers remain puzzled. It could be ionized gas powered by a super-massive black hole; a primordial galaxy with large gas accretion; a collision of two large young galaxies; super wind from intensive star formation; or a single giant galaxy with a large mass of about 40 billion Suns. Because this mysterious and remarkable object was discovered early in the history of the universe in a Japanese Subaru field, the researchers named the object after the legendary, mysterious queen.

“The farther out we look into space, the farther we go back in time, ” explained lead author Masami Ouchi, a fellow at the Observatories of the Carnegie Institution who led an international team of astronomers from the United States, Japan and the United Kingdom. “I am very surprised by this discovery. I have never imagined that such a large object could exist at this early stage of the universe’s history.”

Ouchi adds that, according to Big Bang cosmology, small objects form first and then merge to produce larger systems. “This blob had a size of typical present-day galaxies when the age of the universe was about 800 million years old, only 6 percent of the age of today’s universe,” he said.

Extended blobs discovered before now have mostly been seen at a distance when the universe was 2 to 3 billion years old. No extended blobs have previously been found when the universe was younger. Himiko is located at a transition point in the evolution of the universe called the reionization epoch—it’s as far back as we can see to date. And at 55 thousand light years, Himiko is a big blob for that time.

This reionizing chapter in the universe was at the cosmic dawn, the epoch between about 200 million and one billion years after the Big Bang. During this period, neutral hydrogen began to form quasars, stars, and the first galaxies. Astronomers probe this era by searching for characteristic hydrogen signatures from the scattering of photons created by ionized gas clouds.

The team initially identified Himiko among 207 distant galaxy candidates seen at optical wavelengths using the Subaru telescope from the Subaru/XMM-Newton Deep Survey Field located in the constellation of Cetus. They then made spectroscopic observations to measure the distance with the Keck/DEIMOS and Carnegie’s Magellan/IMACS instrumentation.

Himiko was an extraordinarily bright and large candidate for a distant galaxy.

“We hesitated to spend our precious telescope time by taking spectra of this weird candidate. We never believed that this bright and large source was a real distant object. We thought it was a foreground interloper contaminating our galaxy sample,” said Ouchi. “But we tried anyway. Then, the spectra exhibited a characteristic hydrogen signature clearly indicating a remarkably large distance—12.9 billion light years!”

Using infrared data from NASA’s Spitzer Space Telescope and the United Kingdom Infrared Telescope, radio data from the VLA, and X-ray imaging from the XMM-Newton satellite, Ouchi and his colleagues have been able to estimate the star-formation rate and stellar mass of the galaxy and to search for an active nucleus powered by a super-massive black hole.

“We found that the stellar mass of Himiko is an order of magnitude larger than other objects known at a similar epoch, but we cannot as yet tell if the center houses an active and growing black hole,” said James Dunlop, a team member from the University of Edinburgh. 

Alan Dressler, a team member from the Carnegie Institution, said it’s possible that Himiko is a member of a whole class of objects yet to be discovered.

“Because this object is, to this point, one-of-a-kind, it makes it very hard to fit it into the prevailing model of how normal galaxies were assembled. On the other hand, that’s what makes it interesting,” he said.

Source: Carnegie Institution. The research appears in the May 10, 2009, issue of The Astrophysical Journal (here).

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Named after the volcano Stromboli in Siciliy, Strombolian eruptions are one of the most beautiful to watch; and fortunately, they’re one of the less dangerous types of eruptions. A Strombolian eruption has huge blobs of lava and hot rocks bursting from the volcano’s vent. As the lava hits on the sides of the volcano, it streams down the slopes in fiery rivers.

Strombolian eruptions occur when gas inside the volcano coalesces into bubbles, called slugs. These grow large enough to rise through the magma column. Once they reach the top of the magma column, they burst because of the lower air pressure, and throw magma into the air. Imagine a soap bubble popping, throwing soapy material everywhere. During an eruption, these gas bubbles can be popping every few minutes.

Since a Strombolian eruption doesn’t cause catastrophic damage to the volcano itself, they can keep going for years and years. In fact, Stromboli itself has been erupting this way for thousands of years. Another famous Strombolian volcano is Mount Erebus in Antarctica.

One of the best ways to experience a Strombolian eruption is to see it at night. That when the glowing blobs of magma are easily seen against the dark sky.

We have written many articles about volcanoes for Universe Today. Here’s an article about different types of volcanoes, and here’s an article about different types of lava.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

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Think about a classic volcanic eruption, with a huge cloud of volcanic ash rising up from a giant cinder cone. That’s a Plinian eruption, named after the Roman statesman Pliny the Younger, who witnessed the eruption of Italy’s Mount Vesuvius in 79 AD. As you probably know, that eruption desctroyed the downs of Pompeii and Herculaneum, killing thousands of people.

Plinian eruptions are associated with volatile-rich dacitic to rhyolitic lava, and they typically erupt from stratovolcanoes (think Mt. Fuji). A Plinian eruption can go on for hours or days, sustaining a giant eruptive column. The thrust of the expanding gases give the volcanic material an exit velocity of several hundred meters per second. Some of these eruptive columns can reach heights of 45 km.

What goes up has to come back down. The material thrown so high in a Plinian eruption rains back down over a large area, covering everything in a thick covering of ash. Cubic kilometers of ash can come down on the surrounding landscape.

Plinian eruptions can also generate one of the most dangerous events associated with volcanic eruptions: pyroclastic flows. This is where an eruptive column can collapse. Instead of flowing up high into the air, the hot gas, rock and ash coming from the volcano flows down its steep sides, reaching speeds of 700 km/hour. Everything in the path of the flow is destroyed by this high speed, superheated gas and rock. Pyroclastic flows have been known to travel hundreds of kilometers from an eruption site.

We have written many articles about the Earth for Universe Today. Here’s an article about different types of volcanoes, and here’s an article about different types of lava.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.