Classification of Volcanoes

Composite Cone Volcanoes

which are also called 'stratovolcanoes' or simply 'composite volcanoes,' are cone-shaped volcanoes composed of layers of lava, ash and rock debris. Composite cone volcanoes are grand sites and can grow to heights of 8,000 feet or more. Mount St. Helens and Mount Rainier, which are both found in Washington State, are impressive examples of composite volcanoes.

These steep-sided volcanoes erupt in an explosive manner. In fact, Mount Vesuvius is a composite volcano that is most famous for burying the ancient Roman city of Pompeii in up to 20 feet of volcanic ash in 79 AD. The explosiveness of their eruptions is due to the thick, highly viscous lava that is produced by composite cone volcanoes.

And, this viscous lava has a lot to do with why they are shaped the way they are. The thick lava cannot travel far down the slope of the volcano before it cools. This makes the sides of the composite volcano steep. These explosive volcanoes also spew out eruptions of small rock and ash, which gets deposited on the sides of the volcano. Therefore, we see that composite volcanoes are composed of alternating layers of hardened lava, volcanic ash and rock fragments, which is why they are called 'composite.'

FACTS:

Composite volcanoes are composite in three ways. They are composites of multiple eruptions. The eruptions that build up a composite volcano may be separated by hundreds of thousands of years. They are also composites of multiple materials. The eruptions that form these volcanoes lay down alternating layers of lava, ash and cinders. Thirdly, while this type of volcano might have only one vent, it also might be a composite of several vents.

Composite volcanoes have steep slopes and tend to be symmetrical in shape. They can be very tall, up to 8,000 feet in height. That’s over a mile and a half. They can become so tall that their steep slopes become unstable and collapse underneath their own weight. These volcanoes can become very wide as well, up to approximately five miles across.

Composite volcanoes are formed by viscous lava, which is relatively thick. Viscous is the opposite of runny. After this lava flows for a while, the eruption changes and starts ejecting ash and cinder that falls near the summit of the mountain, which is why these volcanoes have such steep sides. The eruption then changes back to lava, which cements the ash and cinder.

Most composite volcanoes occur in chains, rather than singly. The volcanoes that make up these chains can be separated by dozens of miles. These chains can form anywhere on earth, but are most numerous around the rim of the Pacific ocean, which is known as the “Rim of Fire” because of all the volcanoes that form there.

Shield Volcanoes

are broad, domed-shaped volcanoes with long, gently sloped sides. If you were to fly over top of a shield volcano, it would resemble a warrior's shield, hence the name. These volcanoes can cover large areas but never grow very tall. The reason these volcanoes tend to flatten out is due to the composition of the lava that flows from them, which is very fluid. This more fluid lava spreads out in all directions but cannot pile up in steep mounds.

Shield volcano eruptions are less explosive than composite volcanoes, as the lava tends to pour out of the volcano’s vent, creating the low-profile layers of lava that are characteristic of these volcanoes. The Hawaiian Islands are actually the tops of gigantic shield volcanoes riaing from the ocean basin.

Facts:

The way that a volcano gets its shape is determined by the lava. Shield volcanoes have low viscosity lava, described as being basaltic.

Shield volcanoes' low viscosity lava means that the lava is more liquid and flows more quickly than thick lava. Therefore it can spread further, building up thin layers that continue to accumulate and create the shield volcano's shape.

Shield volcanoes have lava tubes which are a type of cave-like structure made up of hardening lava that forms an insulating layer that allows the lava underneath to travel further.

A lava tube in Hawaii Volcanoes National Park called the Thurston Lava Tube, is a tourist attraction. It looks like a long tunnel.

When the lava from a shield volcano reaches water, the temperature of the lava meeting the water causes an explosive eruption of steam, ash, and sometimes rock. This type of eruption is called hydrovolcanic.

Mauna Loa in Hawaii is the world's largest subaerial (located on the earth's surface) volcano and the second largest overall volcano, at 13,680 feet above sea level, reaching another 8 miles below the surface of the water into the earth's crust. It is also the largest shield volcano on earth by volume.

Mauna Loa makes up more than 50% of Hawaii's surface area.

Mauna Kea is a shield volcano in Hawaii that is 120 feet taller than Mauna Loa, but is not as big overall. Mauna Kea is 4000 feet taller than Mount Everest.

Iceland has several shield volcanoes. The shield volcanoes there are smaller than in other parts of the world and are only 5,000 to 10,000 years old on average.

The Galapagos Islands are home to many shield volcanoes. The shield volcanoes there are much older than in Iceland, and are believed to be between 700,000 and 4.2 million years old. Fernandina Island is one of several shield volcano islands in the Galapagos Islands.

Shield volcanoes can be found in New Zealand (Rangitoto), United States (Belknap volcano and Newberry volcano).

Ethiopia, in Africa, has an active shield volcano called Erta Ale. Erta Ale has a lava lake in its caldera (crater). Africa has several shield volcanoes.

Shield volcanoes exist on other planets as well. Scientists have discovered them in evidence from space probes on Mars, and on Venus, and can exist on any planet or moon with a molten core.

Cinder cones

are the simplest type of volcano. They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings. Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world. A cinder cone, also called a scoria cone, is a volcano composed of volcanic cinders (scoria), or small, rough particles of hardened lava. When lava that is highly charged with gas bubbles erupts from a vent under pressure, it tends to shoot straight up into the air. This effect is called a fire fountain, and it can sometimes be hundreds of meters high. Blobs of the frothy lava break apart, cool quickly, and fall relatively close to the vent. Over time, a cone-shaped hill builds up around a circular crater.

FACTS:

Cinder cones it can develop as free-standing volcanoes, but can also grow around new vents on the slopes of existing shield volcanoes or stratovolcanoes.

Because the cinders that make up a cinder cone have already solidified by the time they hit the ground, the cone is just a pile of loose particles, pretty much like a sand dune - not cemented together by flowing lava. However, because each cinder has rough, jagged edges, the particles tend to lock together, and the pile is relatively stable at the angle of repose, about 33 degrees. But it's not strong enough or dense enough to support the quieter, 'un-fizzy' lava that emerges later in the eruption, so that lava often flows out under the base of the cinder cone and forms a smooth 'pad' for it to sit on.

Cinder cones can grow quickly, but they don't become giants. Big for a cinder cone is just a few hundred meters high. But cinder cones often 'piggyback' on much larger volcanoes.

Cinder cones are a 'friendly face' of volcanic activity - their fire-fountain eruptions are beautiful and dramatic, and because their lava tends to fall straight down and cool quickly, they don't endanger thousands of lives or lay waste to vast areas. It can be relatively safe to view these eruptions close-up - of course, with any erupting volcano, 'relatively' is an important word.

A cinder cone looks smooth and inviting to climb, and the view from the top can be great! But unless you stick to an established trail, make sure you have the right footwear. Scoria particles are glassy and sharp and will tear up your flip-flops in no time. Sturdy hiking boots are best. Also, it's smart to wear tough clothing that will give you some protection if you fall. A cinder cone may look a lot like a sand dune, but its harsh surface is no fun at all to roll down.

Lava domes

A lava dome is a mound that will form when lava piles up over a volcano’s vent instead of moving away. Since the eruption of lava is slow there is no chance for a lava flow to occur and therefore the lava dome will form. Most of the time the sides of a dome will be steep and they are usually composed of what’s called silica-rich lava which in some cases will contain pressurized gas so that explosions can occur. The domes can be described as a small bulbous mass of lava. As the lava cools down it becomes hard and the dome forms.

Size And Shape

The size and shape of a lava dome can change from one volcano to the next. However, you can expect them to be thick and steep sided. The thickness of the lava dome can vary from up to a kilometer in height to just a few meters. The length or diameter can also vary a lot from several kilometers to just a few meters. The shape of the dome can also be very different from one to the next with some of the more common shapes being circular, flat topped, spiny, piston shaped and even a combination. The form of the dome depends on different factors including the viscosity of lava, strength and the slope of the surrounding area it is being erupted onto.

Where Do They Form?

A lava dome can form anywhere there is any volcanic activity. Usually they can be found in the crater of larger volcanoes like Mount St. Helens. However they will not only appear at the craters. In some cases the domes will form on the sides or flanks of the volcano. In rare cases they can even form away from volcanic features. It all depends on the magmatic attributes of the area around them. There are domes on Mount St. Helens which are located on its flanks. These types of domes will eventually help rebuild the mountain.

What They Are Made Of?

There are different types of composition that a lava dome can have and those include anything from rhyolite to basalt. It is important to know however that most of the time the lava that will form a dome will have a higher content of silica (Si02). That composition is what makes the lava more viscous. While a dome can take one of many different types of textures, usually they tend to be blocky in nature.

Types

A lava dome can take many different shapes the first one of which is the Tortas kind. The reason for the name is the similarity that the shape has to a cake or otherwise known as a torta. This is a very common type of formation but it does happen more often in South America near the Andes Mountains.

The Peleean type of lava dome is probably the steepest of all domes. Typically they are similar to Tortas with the difference that they have smoother upper surfaces. They also have vertical spines and can collapse.

The Coulees are somewhere between a lava dome and a lava flow. This type of dome usually takes place on the side of a slope and that is why it can run down. It is rare for this type of dome to be very large but there are a few examples which are over 10 kilometers.

Finally you will be able to find what is called an Upheaved Plug which is a very interesting and very rare type of dome. The lava when it erupts tends to be stronger than that of other domes and because of that the lava is pushed up, almost like a piston. These extrusions can travel very high when compared to the surface.

Caldera

is a depression created after a volcano releases the majority of the contents of its magma chamber in an explosive eruption. Without any structural support below, the land around the erupting volcanic ventor vents collapses inwardly, creating the bowl-shaped caldera. Depending on their intensity and duration, volcanic eruptions can create calderas as much as 100 kilometers (62 miles) wide.

A caldera-causing eruption is the most devastating type of volcanic eruption. It permanently alters the environment of the surrounding area.

A caldera is not the same thing as a crater. Craters are formed by the outward explosion of rocks and other materials from a volcano. Calderas are formed by the inward collapse of a volcano. Craters are usually more circular than calderas. (Calderas may have parts of their sides missing because land collapses unevenly.) Craters are also usually much smaller than calderas, only extending to a maximum of one kilometer (less than a mile) in diameter.

Types of Calderas

Crater-Lake Calderas

Crater-lake calderas result from the collapse of a stratovolcano after a Plinian eruption, the most explosive type of volcanic eruption. Plinian eruptions release massive amounts of lava, volcanic ash, and rocks.

Crater Lake, in the U.S. state of Oregon, is in a crater-lake caldera, not a crater. The Crater Lake caldera is about 10 kilometers (6 miles) wide. Crater Lake is the deepest lake in the United States. It resulted from an eruption that occurred more than 7,000 years ago at the ancient Mount Mazama. The eruption completely emptied Mount Mazama’s magma chamber. The magma chamber’s roof then collapsed and filled with water from rain and snow, creating the lake. Subsequent eruptions of Mount Mazama built up Wizard Island, a volcanic cone that forms an island on the western end of the lake.

Deception Island, located off the coast of Antarctica, is another crater-lake caldera. Unlike Mount Mazama, the Deception volcano is still active. The Deception volcano experienced a violent eruption roughly 10,000 years ago that caused its summit to collapse and flood with seawater, forming a caldera about 7 kilometers (4.4 miles) wide. The caldera gives the island its unique horseshoe shape, which opens to the sea through a narrow channel. Deception Island’s unique geologic structure makes it one of the only places in the world where vessels can sail directly into an active volcano.

Shield Volcano Calderas

Shield volcano calderas do not result from singular explosive eruptions. They instead subside in gradual stages, due to the episodic release of lava. This less-explosive release of lava, known as lava fountaining, is characteristic of shield volcanoes. As a shield volcano periodically releases lava, it produces nested or terraced depressions rather than a large bowl-shaped caldera. As a result, shield volcano calderas are usually less than 5 kilometers (3.1 miles) in diameter.

Composed of dormant and active shield volcanoes, the islands of Hawaii have a number of impressive shield volcano calderas. Moku'aweoweo, the caldera at the summit of Mauna Loa on the “Big Island” of Hawaii, is actually comprised of three distinct depressions that overlap. In total, the caldera complex has an area of roughly 15 square kilometers (6 square miles) and reaches a depth of 180 meters (600 feet).

The Galápagos Islands are also a series of shield volcanoes with some summit calderas. Fernandina Island, the most volcanically active island in the chain, has a deep elliptical caldera that measures 4-by 6.5-kilometers (2.5-by 4-miles). In 1968, a massive volcanic eruption produced one of the largest caldera collapses in recent history. Like most shield volcano calderas, Fernandina caldera collapsed incrementally and asymmetrically, sinking in as much as 350 meters (1,150 feet) in some parts.

Resurgent Calderas

Resurgent calderas are the largest volcanic structures on Earth, ranging from 15 to 100 kilometers (9 to 62 miles) in diameter. They are not associated with one particular volcano, but instead result from the widespread collapse of vast magma chambers. This caldera collapse is produced by incredibly destructive eruptions known as pyroclastic sheet flows, the likes of which have not occurred in historic times.

The Toba Caldera on the Indonesian island of Sumatra is the newest resurgent caldera, created roughly 74,000 years ago by the largest volcanic eruption in the last 25 million years. This massive eruption ejected 2,800 cubic kilometers (1,740 cubic miles) of debris. The eruption left a caldera 100 kilometers (62 miles) long, 29 kilometers (18 miles) wide, and 508 meters (1,666 feet) deep, making it the largest volcanic structure on Earth. The caldera is now home to Lake Toba and Samosir Island. Samosir was formed by the uplift of the caldera floor due to magma pressure below. This uplift is common to all resurgent calderas as new magma fills in the empty magma chamber over thousands of years.

The Yellowstone Caldera, located in Yellowstone National Park in the U.S. state of Wyoming, is the result of the Yellowstone Supervolcano. This enormous volcano complex last erupted about 640,000 years ago. The Yellowstone Caldera is more than 72 kilometers (45 miles) long. Recent scientific analyses have revealed that the caldera’s magma chamber is 2.5 times larger than previously thought, measuring an incredible 90 kilometers by 30 kilometers (55 miles by 20 miles) and 10 kilometers (6 mi) deep. These new measurements put the magma chamber at roughly the same size it was during its last eruption.

Lava Plateau

are extensive areas of flood basalt which are formed by the extensive eruption of basaltic lava over a large area. Rifting of the continental crust is often responsible as the crust thins and allows magma from the mantle to erupt over an extensive area of fissures. The eruptions are often non explosive and continue for a long time building lava flow upon lava flow.

The Colombia river Flood Basalts are situated between the Casacades and Rocky Mountains in the NW USA. Over 10-15 million years during the Miocene ( 5-23 Ma ago) a 6000 feet thickness of basaltic lava was built up. As the lava erupted the crust sank into the cavity left by the eruption.

How does a lava plateau form?

Lava plateaus are formed when a landscape is covered by lava and volcanic ash. The huge volume of volcanic materials needed to produce a lava plateau comes from an event known as a flood basalt eruption, an eruption extreme in both extent and duration.

A flood basalt eruption may last tens of thousands or even millions of years. The ash and lava produced by these large-scale eruptions is typically carried a great distance and may eventually come to cover landscapes and areas that are far from the actual eruption. Volcanic rock produced by a flood basalt eruption can be hundreds of meters thick and typically features a top surface that is very flat.

The formation of lava plateaus may also be influenced by other forces. The distinction between a plateau formed by a flood basalt eruption and one formed by the expansion of the lithosphere or crustal shorting is not always clear, as many plateaus are formed by multiple forces that may be operating simultaneously. The most well-known example of a lava plateau in the United States is the Columbia Plateau, which covers large parts of Washington State and extends all the way to the Pacific Ocean and into parts of Oregon.

A plateau in general is an area which is raised to a small elevation from the surrounding regions with usually steep edges or some times a normal decline.

Not all plateaus are formed due to lava accumulations.

Lava plateaus are slow accumulations of lava eruptions from old volcanic regions or eruptions from open cracks or craters. The continuous flow of lava is made to get accumulated in the near by places.This gradually starts to cool,which later become as solid rocky structures.

Now, Imagine the following scenario, you are ordering dinner from Dominos pizza, and they give you a free Choco lava cake. Once you finish your pizza, you start to dig in the yummy dessert.

Here, the solid outer cake or the relatively cooled outer crust (imagine it as our Earth’s crust) which is still having relatively hot, still in semi fluid state chocolate lava inside it(Imagine this as the magma under our Earth’s crust). Once you dig in or crack the outer crust of the cake, the semi fluid chocolate flows out and flows as far as it can and stops. Then if you leave it as it is for some time, the hot chocolate lava cools off to form a solid crust like object.

This is exactly how lava flows from the crack or the opening in the Earth crust and flows over the land and eventually cools off to form an elevated, cooled, solid structure on the region where it flowed and gets accumulated.

This Basalt rock / lava plateau formations are one of the beautiful geological events happened on our Earth.

Example, our India’s Deccan plateau is one of the worlds largest lava plateau or volcanic basalt beds happened during Cretaseous period, between 65–70 Ma.

And the beautiful columnar joints or columned basalt rock formations in St.Mary’s Island in India, near Mangalore, Karnataka.

Above and the below pictures are the columnar joints in St.Mary’s Island, this was also formed by the same process, but the only difference is, lava plateaus nearer to the water resources will get cooled off at a faster rate than the one which flows away from the water resources.

Plateau means flat region, whatever the materiel is made up of (large extend) in the volcanic plateau which formed due to eruption of fludic basalt which can move fast and cover large extended area, the successive eruption will create thick pile and prolonged eruption will create lare geographical cover. Eg Deccan basalt plateau.

Credits:

http://study.com/academy/lesson/types-of-volcanoes-shield-cinder-cones-composite-cones.html

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http://www.softschools.com/facts/geography/shield_volcano_facts/2246/

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