Volcanoes

Volcanoes are awesome manifestations of the fiery power contained deep within the Earth. These formations are essentially vents on the Earth's surface where molten rock, debris, and gases from the planet's interior are emitted.When thick magma and large amounts of gas build up under the surface, eruptions can be explosive, expelling lava, rocks and ash into the air. Less gas and more viscous magma usually mean a less dramatic eruption, often causing streams of lava to ooze from the vent.he mountain-like mounds that we associate with volcanoes are what remain after the material spewed during eruptions has collected and hardened around the vent. This can happen over a period of weeks or many millions of years.A large eruption can be extremely dangerous for people living near a volcano. Flows of searing lava, which can reach 2,000 degrees Fahrenheit (1,250 degrees Celsius) or more, can be released, burning everything in its path, including whole towns. Boulders of hardening lava can rain down on villages. Mud flows from rapidly melting snow can strip mountains and valleys bare and bury towns. Ash and toxic gases can cause lung damage and other problems, particularly for infants and the elderly. Scientists estimate that more than 260,000 people have died in the past 300 years from volcanic eruptions and their aftermath.Volcanoes tend to exist along the edges between tectonic plates, massive rock slabs that make up Earth's surface. About 90 percent of all volcanoes exist within the Ring of Fire along the edges of the Pacific Ocean.

About 1,900 volcanoes on Earth are considered active, meaning they show some level of activity and are likely to explode again. Many other volcanoes are dormant, showing no current signs of exploding but likely to become active at some point in the future. Others are considered extinct.

A volcano is a place on the Earth's surface (or any other planet's or moon's surface) where molten rock, gases and pyroclastic debris erupt through the earth's crust. Volcanoes vary quite a bit in their structure - some are cracks in the earth's crust where lava erupts, and some are domes, shields, or mountain-like structures with a crater at the summit.

Magma is molten rock within the Earth's crust. When magma erupts through the earth's surface it is called lava. Lava can be thick and slow-moving or thin and fast-moving. Rock also comes from volcanoes in other forms, including ash (finely powdered rock that looks like dark smoke coming from the volcano), cinders (bits of fragmented lava), and pumice (light-weight rock that is full of air bubbles and is formed in explosive volcanic eruptions - this type of rock can float on water).

Volcanic eruptions can cause great damage and the loss of life and property.

The Word Volcano:
The word volcano comes from the Roman god of fire, Vulcan. Vulcan was said to have had a forge (a place to melt and shape iron) on Vulcano, an active volcano on the Lipari Islands in Italy.

Extreme Volcanoes:
The largest volcano on Earth is Hawaii's Mauna Loa. Mauna Loa is about 6 miles (10 km) tall from the sea floor to its summit (it rises about 4 km above sea level). It also has the greatest volume of any volcano, 10,200 cubic miles (42,500 cubic kilometers). The most active volcano in the continental USA is Mt. St. Helens (located in westernWashington state).

Types of Volcanoes

Many people are interested in ways to classify volcanoes. There is probably a natural human instinct to try and give labels to all things. This is not a bad instinct and many times it makes it easier to understand the particular thing that is being classified. For example, you start to identify patterns when you classify things and these patterns may lead to a better understanding of whatever it is you are classifying. However (and that is a big "however"), when you are classifying natural things (they might be fish, plants, birds, oceans, minerals, volcanoes, or whatever), you MUST remember that the classification scheme is made up by human beings and Nature might decide to not follow the rules exactly. There will ALWAYS be exceptions to your classification scheme and there will ALWAYS be things that fall into more than one category. As long as you realize this and it doesn't bother you, you'll be just fine. Certainly there are different ways to classify volcanoes and all of them have particular benefits and drawbacks. These include classifying by lava chemistry, tectonic setting, size, eruptive character, geographic location, present activity, and morphology. As an example of how these can get mixed together, note that there are basaltic strato volcanoes (i.e. Mt. Fuji), big basaltic calderas (i.e. Taal), big gradual-sloped basaltic shields (i.e. Mauna Loa) and big steep-sloped basaltic shields (i.e. Fernandina). Additionally, although most volcanoes associated with subduction zones are steep-sided andesite or dacite cones, there are a few basaltic shields along these zones as well (i.e. Masaya, Westdahl, Tolbachik). These examples highlight the above-mentioned hurdle that any student of the Earth needs to get over - Nature makes exceptions to human rules.

Unfortunately, there is one particular volcano classification system that many people think is the only system. Not only is it not the only system, it is not a very good system. This is the famous "3 types of volcanoes" (shield volcanoes, strato volcanoes, and cinder cones), and it is found in many textbooks from elementary school to college. Why is this 3-types scheme so bad? First, it has no place in it for large caldera complexes (such as Yellowstone), flood basalts, monogenetic fields, or mid-ocean spreading centers. These are important types of volcanoes that you would never hear about if you thought there were only 3 types. Second, although you can occasionally find a cinder cone sitting somewhere all by itself, it is way more common for a cinder cone to either be one of many vents on a large (polygenetic) volcano or a member of a monogenetic field. Finally, if you actually think about the system you run into logical problems, as a teacher from Pittsburgh pointedly complained to VolcanoWorld about: She wanted to know how Pu'u 'O'o could be a cinder cone on Kilauea if cinder cones are a type of volcano and Kilauea is a shield volcano. The answer is that Pu'u 'O'o is one of hundreds of vents on Kilauea, and it happens to be a cinder cone.

Who knows what the origin of this 3-volcano system is, but the sad thing is that many people use it without thinking as far as the Pittsburgh teacher did. The cinder cone part may come from the fact that some cinder cones have names such as "This Volcano" or "Volcan That" even when they are just vents on a larger volcano. In these cases the cinder cone is probably all that has ever erupted in the collective memory of the local folks. They logically consider it to be "the volcano" and may think of the larger structure that hasn't erupted since they've been around (and may in part be highly eroded or vegetated) to be "just" a mountain.

For most volcanological applications a classification based on morphology is probably the most useful. In their excellent book Volcanoes of the World, Tom Simkin and Lee Siebert list 26 morphological "types" of volcanoes. That's certainly thorough but kind of extreme. You can account for probably >90% of all volcanoes with 6 types. Additionally, any system will be more useful if you use modifiers from the other potential classification schemes with the morphological types (i.e. active andesite strato volcano, extincthotspot shield volcano, etc.).

The following descriptions of 6 morphological volcano types are really brief. They were originally written for an "ask-a-volcanologist" answer - if they tell you things you already know, please don't feel insulted. In most any good volcanology book you should be able to find more details and many more examples

The largest volcano in our Solar System is perhaps Olympus Mons on the planet Mars. This enormous volcano is 17 miles (27 km) tall and over 320 miles (520 km) across.

Mount Merapi Erupts

Photograph by Dwi Obli, Reuters

Smoke rises Monday from Indonesia's Mount Merapi, one of the world's most volatile and dangerous volcanoes. Thousands of people living on the volcano's fertile slopes began evacuating as Merapi started erupting Tuesday, sending hot ash and rocks high in the air. 

Scientists had been warning for days that pressure building in the rumbling volcano has the potential to set off an especially violent eruption.

"The energy is building up. ... We hope it will release slowly," Indonesian-government volcanologist Surono told reporters, according to the Associated Press. "Otherwise we're looking at a potentially huge eruption, bigger than anything we've seen in years."

Meanwhile, officials in western Indonesia are racing to deal with the aftermath of a deadly tsunami that struck the remote Mentawai Islands late Monday, killing at least 113 and leaving hundreds more missing. The killer wave, triggered by a magnitude 7.7 earthquake centered offshore of the island of Sumatra, had many recalling the December 2004 Indian Ocean tsunami, which devastated the same region.

While it's unclear whether Monday's earthquake and the Merapi volcano eruption are linked, neither event is uncommon in Indonesia. The archipelago sits along the Pacific Ring of Fire, a series of fault lines that stretches from the Pacific coasts of the Americas through Japan and into Southeast Asia. 

Three Volcanoes

Mount Semeru, seen with an ash plume, is the highest volcano on the Indonesian island of Java and has been in a constant eruption since 1967.  It lies at the southern end of the Tengger caldera, which contains smaller volcanoes Mount Bromo and Mount Batok (both seen in the foreground), and several others.

On Deep Sea Volcanoes and Ocean Warming: Reprint

Since we regularly get questions about this type of thing, I wanted to repost this excellent post from Erik Klemetti's blog 'Eruptions.'

"I recently read a post about how humans couldn't be to blame for the warming of the oceans.  
The "logic" of their post was this:

• We see water getting warmed by magma at volcanoes worldwide, like Taal andRuapehu.
• The bottom of the ocean is covered in volcanoes, whether it be seamounts or the mid-ocean ridge system.
• Volcanoes at the bottom of the ocean must heat up the ocean water (like in crater lakes), so humans aren't to blame.

There are a number of ways to attack this poor reasoning, but I'll try to go with the ones I think are most convincing.

• This argument suggests that volcanic activity (not just volcanoes) on the ocean floor must be increasing over the last few hundred years. We see no evidence of this - and the author of the post only uses evidence that we have discovered more volcanoes (up to 3.4 million) on the seafloor.
• The author claims "that 3,477,403 number, coming from two well-respected oceanographers, does reinforce my point rather nicely, namely, that underwater volcanoes are heating the seas." Sure, there might be a lot of volcanoes but he makes no mention of how many might be active enough to heat the ocean water. We can see at surface volcanoes that not all of them are erupting or puffing away simultaneously - 
• Finally, you would expect in this situation that ocean water would warm from the bottom (near the volcanoes) upwards, but it is actually the surface waters that are warming, not the deep ocean. This suggests that heating is coming from exchange with the atmosphere, not from some deep source on the ocean floor.

It is very easy to try to throw around some partially baked ideas about volcanism to try to explain the changing in the ocean temperature worldwide, but they would require extraordinary circumstances where ocean volcanic activity was increasing exactly when human carbon dioxide production was also increasing. Sorry, the subsurface volcanoes are no source for your ocean heating (and if I had the time, I'd calculate how much energy would take to heat all the oceans by 0.5C - it is bound to be more than you can get out of a few hundred thousand Ruapehus)."

Working on Volcanoes

  

The following section is meant to give you a flavor of what it is like to work on a volcano. It illustrates some of the techniques that are used to study active Hawaiian volcanoes, most of which are also used to study the rest of the world's volcanoes.   Keep in mind also, that there are lots of indoor techniques that are equally important for understanding what a volcano is doing. Important examples of these are the analysis of seismic signals and geochemical studies of erupted lavas and gases.