Author: Fraser Cain

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Volcanoes can erupt with ash and rocks, but one of the most common images are great rivers of molten lava streaming from the volcano’s vent. This molten lava is made of rock, heated to more than 700 degrees C inside the Earth. Inside the Earth, it’s called magma, but when it reaches the surface, scientists call it molten lava.

You might be surprised to know that there are many different kinds of molten lava, depending on the chemical structure of the rock itself. This structure defines how viscous the lava is; how easily it flows. Think of the difference between water and syrup. Syrup is very viscous. Molten lava can be 100,000 times as viscous as water.

The least viscous lava can flow great distances from a volcano during an eruption, sometimes traveling many kilometers, destroying everything in its path. Volcanoes with this kind of molten lava are called shield volcanoes and they take on a very wide, low appearance, since the lava can flow so far. Other types of lava are thicker, or more viscous. It only travels a short distance in thick, crumbling flows. And some molten lava is so thick that it doesn’t really flow at all. It just piles up around the volcanic vent.

When it first erupts from the volcanic vent, molten lava can be anywhere from 700 to 1200 degrees Celsius. The thickness (or viscosity) defines how the lava behaves as it leaves the vent, and how far it can flow downhill before cooling and solidifying. Even though it looks solid, a lava flow can remain hot for weeks and even years before it finally cools.

As scary as it looks, molten lava really isn’t that dangerous for people. You can easily outrun a lava flow. Of course, buildings and trees aren’t so lucky since they’re attached to the ground.

We have written many articles about volcanoes for Universe Today. Here’s an article about the largest volcano in the Solar System, 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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When volcanoes erupt, they can release large quantities of lava, rocks, hot gasses and volcanic ash. This volcanic ash is made up of pulverized rock and glass particles smaller than 2 millimeters in diameter. Once ejected into the air, it can travel for hundreds of kilometers before coming back to Earth.

There are two kinds of volcanic ash: fine ash, with particles smaller than 0.063 mm, and course ash, with particles smaller than 2 mm. Larger rocks aren’t kept aloft and rain down around the volcano’s cone during an eruption. The largest rocks are called volcanic bombs, and they can be as large as 6 meters across.

Ash is created when solid rock shatters and magma separates into tiny particles during an explosive eruption. The violent eruption together with steam tears apart the rock surrounding the volcano’s vent, and fires it up into the air – sometimes many kilometers into the air.

Once the volcanic ash is in the air, obscures light from the Sun, turning the sky hazy and yellow. It can even make spectacular sunsets. A large enough eruption can spread volcanic ash around the world, cooling the Earth for several years. The smallest particles can be held aloft in the Earth’s atmosphere for years, and spread around the planet on high-altitude winds.

Volcanic ash is part of one of the biggest dangers with volcanoes: pyroclastic flows. These occur when hot gas and ash erupt from a volcano and flow down its flanks at high speed. These flows can have temperatures higher than 1,000 degrees C, and travel at more than 700 km/hour. It’s impossible to outrun a pyroclastic flow.

When the ash finally lands around a volcano, it can cause further problems. Just a few centimeters of ash is heavy enough to collapse roofs, and kill animals and crops. If there’s rain, the ash turns into a sticky, muddy mess that will take months to clean up.

We have written many articles about volcanoes for Universe Today. Here’s an article about different types of volcanoes, and here’s one 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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There are thousands and thousands of known volcanoes around the world. Many have no names, and most are located deep underneath the ocean at the point where the Earth’s tectonic plates are spreading apart. This is just a partial list.

List of Volcanoes
Fogo Caldera, SW Cape Verde Is. Atlantic Ocean
Merapi Volcano, Java, Indonesia
Batur Voclano, Bali, Indonesia
Rabaul Caldera, Papua New Guinea
Pinatubo Volcano, Central Luzon, Philippines
Mt Canlaon, Negros Islands, Philippines
Bulusan, Luzon, Philippines
Parker, Southern Mindanao, Philippines
Gemini Seamount, New Hebrides Island Arc, Vanuatu Islands
Aoba (Ambae Island), Vanuatu Islands
Barren Island, Andaman Islands, Indian Ocean, India
Mt Unzen, Japan
Bezymianny Volcano, Kamchatka, Russia
Karymsky Volcano, Kamchatka, Russia
Klyuchevskoi Volcano, Kamchatka, Russia
Avachinsky Volcano, Kamchatka, Russia
Kilauea Volcano, Hawaii
Loihi Seamount, Hawaii
Marianis Islands
Metis Shoal, Tonga
Ruapehu, New Zealand
Taupo Volcanic Zone, New Zealand
Akutan Volcano, Aleutian Islands
Shishaldin Volcano, Aleutian Islands
Mt Spurr, Alaska
Pavlof Volcano, Alaska Peninsula
Gorda Ridge, Northeast Pacific Ocean
Mount St. Helens
Mount Lassen, California
Lake Superior Ice Volcanoes, Michigan
Popocatepetl, Mexico
Santa María Volcano, Guatemala
Pacaya Volcano, Guatemala
Fuego Volcano, Guatemala
Tacaná Volcano, Guatemala
Cerro Quemado Volcano, Guatemala
Arenal Volcano, Costa Rica
Volcano Rincon de la Vieja, Costa Rica
Coatepeque, El Salvador
Ilopango, El Salvador
Izalco, El Salvador
San Miguel, El Salvador
San Salvador, El Salvador
San Vicente, El Salvador
Santa Ana, El Salvador
Cerro Negro, Nicaragua
Soufriere Hills, Montserrat, West Indies
Galeras, Nevado Cumbal, Dona Juana, Cerro Negro de Mayasquer, Azufral
Galapagos, Fernandina
Stromboli Volcano, Italy
Etna Volcano, Italy
Bardarbunga/Grimsvotn Volcanoes, Iceland
Askja Volcano, Iceland
Krafla Volcano, Iceland
Hekla Volcano, Iceland
Katla Volcano, Iceland
Vestmannaeyjar Volcano, Iceland
Mount Erebus, Antarctica

Thanks to the list at the MTU Volcanoes Page. The best list of volcanoes is located at the Oregon State University website. And another great list from NASA.

We have written many articles about volcanoes for Universe Today. Here’s an article about dormant volcanoes, and here’s an article about extinct 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.

There are three ways to describe a volcano’s activity; there can be active, dormant, or extinct volcanoes. Active volcanoes have erupted recently. A dormant volcano isn’t erupting right now, but vulcanologists expect it could erupt at any time. Extinct volcanoes haven’t erupted for tens of thousands of years, and aren’t expected to erupt again.

What causes volcanoes to go extinct? Simply put, they’re cut off from their supply of lava. This is where a chamber of magma underneath the surface of the Earth finds its way to the surface through weaknesses in the crust. A good example of this is the hotspot that created the chain of Hawaiian Islands. The tectonic plate carrying the islands is slowly moving, so that volcanoes are cut off from the hotspot underneath. Eventually they go extinct, while the hotspot creates a new volcano further to the East.

Some volcanoes look extinct, but it might just be a long time since they’ve erupted. For example, the Yellowstone Caldera in Yellowstone National Park hasn’t had a violent eruption in about 640,000 years, but scientists think it’s still active. There has been minor activity and lava flows as recently as 10,000 years ago. The region also has regular minor earthquakes and ground is lifting up in some areas, so scientists think that’s it’s still an active volcano.

Volcanoes thought to be extinct have erupted again. For example, Mount Vesuvius erupted famously in AD 79, destroying the towns of Herculaneum and Pompeii. And the Soufriere Hills volcano on the island of Montserrat resumed activity in 1995.

Other volcanoes are clearly extinct, with only the heavily eroded lava plug remaining.

We have written many articles about volcanoes for Universe Today. Here’s an article about shield volcanoes, which can sometimes be extinct. And here’s another about dormant 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.

Vulcanologists classify volcanoes into three groups: active, dormant and extinct. A dormant volcano is one that isn’t currently active or erupting, but geologists think that it’s still capable of erupting.

One of the best examples of a dormant volcano is Mauna Kea, one of the five volcanoes that make up the Big Island of Hawaii. The peak of Mauna Kea is 4,207 meters above sea level, but 10,203 meters above the base of the floor of the Pacific Ocean. Geologists classify Mauna Kea in the post-shield stage of volcanic evolution. It stopped being a shield volcano about 200,000 years ago. Mauna Kea’s last eruption is thought to be 2460 BC.

Volcanoes become dormant because the Earth’s plates are constantly shifting above volcanic hotspots. Each time the hotspot reaches the surface, it creates a new volcano. The tectonic plate continues to shift above the hotspot, and eventually the volcano is shut off from the magma chamber beneath. And so the magma finds a new source to the surface, creating a new active volcano. The older volcano stops erupting and becomes dormant. Here’s more information on the active volcanoes in the world.

Dormant volcanoes do still erupt from time to time, however, sometimes with devastating results for people who thought the volcano was completely extinct.

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 the most active volcanoes in the world.

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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Many volcanoes start out on land, rising above the surrounding landscape. But many more volcanoes get their start at the bottom of the ocean. These underwater volcanoes, or submarine volcanoes, can eventually grow into islands that rise above the surface of the ocean.

Geologists have identified more than 5,000 active underwater volcanoes, which account for more than 75% of the total lava that erupts every year. Most of these are located along the mid-ocean ridges, where the Earth’s tectonic plates are spreading apart. Most of these are very deep underwater, and difficult to study, but some are located in more shallow water.

An underwater volcano erupts differently than a surface volcano. This is because there is an unlimited amount of water to cool down the lava. A shell of rock hardens around the lava almost immediately, creating a type of formation called pillow lava. Deeper than about 2,000 meters, the pressure of the water is so high that it can’t boil, and so underwater volcanoes are difficult to find using hydrophones.

Underwater volcanoes build up over time, and can eventually reach the surface of the ocean. This is what happened to form the Hawaiian islands. The Earth’s crust has drifted above an active vent, creating each of the islands in turn. A new Hawaiian island, Lo’ihi, is forming under the ocean about 48 km off the southeast coast of Hawaii. It’s already taller than Mount St. Helens and will breech the surface in a few hundred thousand years.

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 how volcanoes form.

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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When you think of volcanoes, you immediately think of lava flows. These are the familiar rivers of lava pouring down the sides of the volcano, burning everything in their path, covering up building and generally ruining things. Well, you might be surprised to know that lava flows are the least hazardous way a volcano can kill you.

Molten rock is much thicker than a liquid like water. Even lava flows with the least viscosity (the least thick), will only flow at a maximum speed of a few kilometers per hour. You can easily out run a lava flow, and that’s why people are rarely killed by them. Building and trees, which are stuck to the ground, aren’t so lucky.

How far the lava flow goes depends on its viscosity. Lava flows made of basalt, like you might find in Hawaii, have very low viscosity, and so they can flow as much as 4 km away from the source and have a thickness of 10 meters. Thicker lava flows only get about 1 kilometer away from the source, but can be as thick as 100 meters.

People aren’t really at risk from lava flows, but they can do a tremendous amount of property damage. If the intense heat doesn’t set your house on fire, the slow moving wall of liquid rock will certainly knock it over and crush it to pieces. Entire towns built close to volcanoes have been overrun by lava flows, destroying houses and cars, encasing everything in meters of rock. Once an eruption is over, the lava flow can take days or even years to cool down.

Engineers have tried to battle nature, coming up with all kinds of ways to stop lava flows – few successful. In Italy, engineers have installed retaining walls to try and slow down lava flows coming down the side of Mount Etna, on the island of Sicily. These walls did slow down the lava flows enough that they didn’t reach inhabited land. In Hawaii, engineers bombed narrow lava tubes, forcing the lava to lose energy. And in Iceland, firefighters sprayed water on lava flows for nearly 5 months, cooling it so that it solidified early and didn’t block an important port.

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

Reference:
USGS Volcanoes: Lava Flows and Their Effects