Category: Astronomy

There are several different types of volcanoes: steep stratovolcanoes, wide shield volcanoes, and mounded lava domes. The shape of a volcano actually depends on the types of lava that it’s made up of. And so, there are several different types of lava.

The type of lava coming out of a volcano depends on its mineral content. Some lava is very thin, and can flow out of a volcano in great rivers that go for dozens of kilometers. Other lava is very thick, and only flows for a short distance before cooling and hardening. And some lava is so thick that it barely “flows” at all, and can plug up the plumbing of a volcano.

The main types of lava have been given Hawaiian names, because of the volcanic nature of the Hawaiian islands. You can find examples of different kinds of lava flows on the island.

A’a
Pronounced “ah-ah”, this is a basaltic lava that doesn’t flow very quickly. It looks like a slowly moving mass of hot jello, with cooler, rough surface. Once it hardens, the sharp spiny surface of a’a lava is extremely difficult to walk across. These types of lava erupt at temperatures above 1000 to 1100 degrees C.

Pahoehoe
Pronounced “pa-ho-ho”, this type of lava is much thinner and less viscous than a’a. It can flow down the slopes of a volcano in vast rivers. The surface of the lava congeals into a thin crust that looks very smooth. Pahoehoe lava can also form lava tubes, where the rock hardens around a fast-moving liquid core. When that core flows out of the tube, a long tunnel remains. Pahoehoe erupts at temperatures of 1100 to 1200 C.

Pillow Lava
Pillow lava is typically found erupting from underwater volcano vents. As soon as the lava contacts the water, it’s cooled down and forms a hardened shell. As more lava issues from the vent, the shell of lava cracks and more “pillows” come out of these cracks.

We have written many articles about volcanoes for Universe Today. Here’s an article about the temperature 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.

The temperature of lava when it is first ejected from a volcanic vent can vary between 700 and 1,200 degrees C (1,300 to 2,200 F).

As you probably know, lava is molten rock that comes out of a volcano during an eruption. Although the Earth’s mantle is solid, it’s so hot that puddles of molten rock can form between the mantle and the Earth’s crust. This lava is less dense than the surrounding rocks, and so it makes its way to the surface through cracks and faults in the Earth’s crust. Eventually, it erupts to the surface.

Even though lava is much thicker than water, it can flow great distances across the surface of the Earth before it cools and hardens. Some lava is very thin, and can flow many kilometers, while other lava is thick and doesn’t flow at all; it just piles up around the volcanic vent.

Whether lava is thick or thin doesn’t depend on the temperature of the lava. Instead it’s caused by the minerals in the lava. The coolest lava are felsic lavas, which can erupt at temperatures as low as 650-750 C. Next are the andesitic lavas, which erupt in the range of 750-950 C. Basaltic lavas typically erupt at temperatures above 950 C.

We have written many articles about volcanoes for Universe Today. Here’s an article about the recent eruption of Alaska’s Redoubt volcano, and here’s an article about the biggest volcano on Earth.

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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Stratovolcanoes, or composite volcanoes, are some of the largest, most familiar mountains on Earth. Perhaps you’ve heard of Mount Fuji, Mount Kilimanjaro, or Mount Rainier? These are stratovolcanoes. They’ve got that familiar shape with the gently sloping lower sides and then the sharp cone shape at the top. They make up 60% of the Earth’s individual volcanoes.

They typically have a layered or stratified appearance, with alternating lava flows, mudflows, fallen ash, and other debris. They usually form along the margins of the Earth’s tectonic plates, where one plate is pushing beneath another, or they’re sliding together. This creates weaknesses in the Earth’s crust, where magma from beneath the surface can escape.

Stratovolcanoes will usually have a central caldera, or crater, at the top, but they will also have a network of vents. They can have many lava domes and smaller vents where eruptions can occur; not just from the top. The lava flows out of them is extremely thick, and sometimes it barely flows at all. This lava plugs up the plumbing in stratovolcanoes, allowing them to build up tremendous amounts of pressure.

Of all the volcanoes on Earth, stratovolcanoes are the most dangerous. They can erupt with little warning, releasing enormous amounts of material. And they don’t always erupt nicely from their tops. As we saw with Mount Saint Helens, they can blast out material from the side, creating pyroclastic flows the hurtle down the volcano’s flanks at enormous speeds. Some classic eruptions of stratovolcanoes include the island of Krakatoa, which detonated in 1883, sending ash 80 km into the atmosphere.

We have written many articles about volcanoes for Universe Today. Here’s an article about how a volcano triggered a lightning storm. And here’s an article about the largest 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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Not all volcanoes are the familiar cone-shaped mountains with lava spewing out of the top. Sometimes you can get a very slow eruption, underneath the ground, where a mound of earth rises up above the surroundings. These are called lava domes.

Lava domes form when you have slow eruption of very thick lava, or multiple eruptions of different kinds of lava. Instead of breaking through to the surface, the material builds up underneath the ground, causing the huge lava dome mound to form. It’s so thick that the lava can’t flow very far at all, it just hardens quickly, extruding new material around the vent. They can grow for months or years, eventually building up to several hundred meters in height. Large composite volcanoes can have hundreds of lava domes across their flanks.

The sides of lava domes are very steep, and can cause rockslides around because of the extrusion of new lava. This can bury the surrounding landscape, and even start forest fires if the rocks are still hot. The surfaces of lava domes are rough and blocky because of the fragmentation of rock shell as the dome grows.

As you can probably guess, this buildup of lava and gas can be dangerous. Although people can avoid the growth of a lava dome, they can be a problem for buildings that can’t be moved. But an even more dangerous problem with lava domes is the fact that they can explode violently, without warning, releasing pyroclastic flows of ash and mud for more than 20 km around the dome itself. In 1902, an eruption from a dome on Mont Pelee in Martinique killed 30,000 people with high-velocity ash flow and poisonous gasses.

We have written many articles about volcanoes for Universe Today. Here’s an article about how a volcano in Chile triggered a lightning storm, and here’s an article about cinder cone 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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Some of the most dramatic mountains in the world are volcanoes. Volcanoes can grow to enormous heights quickly, sometimes just a few years. But have you ever wondered, how are volcanoes formed?

As you probably know, you’re standing on the Earth’s crust; a relatively thin layer of solid Earth. Beneath this is the mantle, an extremely hot region just a few dozen kilometers beneath your feet. Although the mantle is almost entirely solid, it can form small pockets of liquid rock and hot gasses. It’s hard to think of this way, but the molten rock – called magma – is more buoyant than the surrounding solid rock. It slowly forces its way upward through weaknesses in the Earth’s crust. These become volcanoes.

When the magma reaches the surface, it wells out onto the surface forming a volcano. What kind of volcano forms depends on the size of the crack in the crust, and the kind of lava that comes out. Some lava is very fluid, and can flow for long distances. This kind of lava creates shield volcanoes, like in the Hawaiian islands. Other lava is very thick, and doesn’t travel very far, creating the more familiar cinder cone shaped volcanoes.

Some very energetic volcanoes will spew rock, ash and magma high into the air. This material falls back down around the vent, and this is how the volcano builds up. The volcano is like a big debris pile surrounding the volcanic vent.

The largest, most dramatic volcanoes in the world are composite volcanoes, or stratovolcanoes. These can have vast networks of volcanic vents and chambers, with many openings to the surface. They can be made up of lava flows and deposits of ash that build up into huge mountains over millions of years. Some of the most dramatic mountains in the world are composite volcanoes: Mt. Fuji, Mt Kilimanjaro, and Mt. Rainier, for example.

We have written many articles about the volcanoes for Universe Today. Here’s an article about the biggest volcano on Earth, and here’s the tallest volcano.

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 are mountains. But unlike most mountains in the world, formed from folding continental plates, uplift and erosion, volcanoes are created when material from inside the Earth escapes to the surface. Let’s answer the question, “what are volcanoes”.

As you probably know, the ground you’re standing on is the Earth’s crust. It varies in depth between 10 km under the oceans and 30 km beneath the continental plates. Beneath the crust is a vast region called the Earth’s mantle. The mantle is made up of molten rock called magma. At the boundaries between continental plates, volcanic vents can open up, where magma and gasses from inside the Earth can escape.

When it’s still underground, the molten rock is called magma. Although most of the Earth’s mantle is solid, it can create pockets of liquid which escape from underneath through weaknesses in the Earth’s crust. After it escapes to the surface, it’s called lava. Lava has different levels of viscosity – how easily it flows downhill. The least viscous (easy flowing) lava creates shield volcanoes. The lava can flow for great distances in huge rivers, and creates wide volcanoes with gently sloping sides. The most viscous (thickest) lava piles up around the volcanic vent created the familiar cone-shaped volcanoes.

The simplest volcanoes where a single vent breaks through a weakness in the crust, releasing lava, ash and rocks. After being blasted out of the vent, it piles up around on the surface, allowing the volcano to grow up quickly. Some of the largest, most familiar volcanoes are composite, or stratovolcanoes. These are built up of multiple layers of ash and lava, and can have vast networks of vents.

The word volcano comes from the island of Vulcano in the Mediterranean Sea off Sicily. Ancient people thought that this island was the chimney of the forge of Vulcan, the Roman god of blacksmithing.

We have written many articles about volcanoes for Universe Today. Here’s an article about the biggest volcano on Earth, and here’s one about the tallest volcano.

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.

Most volcanoes are dormant. They erupted millions of years ago, but then the Earth’s plate tectonics closed the vent or caused it to drift away. But some volcanoes are still active and erupt on a regular basis. Here are a list of the most active volcanoes in the world.

The most active volcano on Earth is Kilauea volcano on Hawaii. It’s the most recent of a series of volcanoes that created the Hawaiian archipelago of islands. They formed as a string of islands because the Pacific plate is slowly moving over the Hawaii hotspot. That’s why the islands of Kauai and Oahu are no longer active, but Kilauea is. This volcano only rises 1,247 meters above sea level, but it’s still growing. 90% of the surface of Kilauea is less than 1,100 years old, and there were 45 eruptions of the volcano in the 20th century alone. Even in 2008, there were explosive eruptions from Kilauea.

The second most active volcano in the world is Mount Etna, a composite volcano on the east coast of Sicily. It’s the largest active volcano in Europe, with an altitude of 3,329 meters. It’s in an almost constant state of eruption, but despite this, its flanks support extensive vineyards and orchards. Over the last few thousand years, it has experienced many eruptions. Ash from its eruptions have been found as far away as Rome, 800 km away. There are more than 300 volcanic vents across Mount Etna, ranging in size from small holes to massive craters, hundreds of meters across.

The third most active volcano is Piton de la Fournaise, which is French for the “Peak of the Furnace”. This is a shield volcano on the eastern side of Renunion island in the Indian Ocean. It has erupted in 2006, 2007 and in 2008 – with more than 150 eruptions since the 17th century. Piton de la Fournaise is referred locally as “le Volcan”, and stands at a height of 2,631 meters tall. It has many craters and cinder cones inside the volcano’s caldera and around its outer flanks.

We have written many articles about volcanoes for Universe Today. Here’s an article about how the dinosaurs might have been killed by both volcanoes and asteroids, and how they helped slow the ocean warming trend.

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:
USGS Volcanoes Page: Kilauea
NASA Earth Observatory
USGS Volcanoes Page: Piton de la Fournaise