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Subglacial Volcano

 

A subglacial volcano is a volcano that is located either underneath a glacier itself or under the water in a lake which is inside a glacier. These volcanoes are very different from the other types in terms of shape as they usually have steep sides and a flat top. The exception is in the cases when the subglacial volcano produces enough heat to melt the ice layer above it, in which case its shape will be more conventional.

Because of their proximity to glaciers, these volcanoes are most common in Antarctica and Iceland although some older volcanoes can be found in Canada as well. These volcanoes can be very beautiful due to the snow and ice; however, these features make them very hard to access.

Eruption

Usually when a subglacial volcano erupts the heat associated with the flow of lava will cause the overlying ice to melt. When this happens, the water cools the lava very quickly in a manner similar to what happens with a submarine volcano and will therefore produce a flow with pillow shapes similar to an underwater eruption. With these eruptions however, the pillows will break off and fall down the slopes of the volcano, causing a formation of hyaloclastite, tuff breccia and pillow breccia (breccia is a type of sedimentary rock). Because of the water present during a subglacial volcano eruption, they can also produce lahars and dangerous floods.

Jökulhlaup

A jökulhlaup is an outburst flood that is produced from a glacier. They are most commonly associated with a subglacial volcano and will occur when the heat from the eruption causes the surrounding glacier to melt, creating the flood. Although the term originated in Iceland to describe this occurrence in relation to their volcanoes, it is now used by geologists around the world. A classic example of a jökulhlaup is when Katla in Iceland erupts, it causes the glacier Mýrdalsjökull to experience this phenomenon.

Antarctica

The most popular locations in the world to find a subglacial volcano is Antarctica. This is because volcanoes in this area can be found spanning around 5000 kilometers, going all the way from East Antarctica to the Antarctic Peninsula and all the way to the South Sandwich Islands which are sub-Antarctic. Because of the large quantity of volcanoes combined with the cold environment and presence of glaciers, it is no surprise that the area is home to a large proportion of the subglacial volcano population.

A subglacial volcano in Antarctica that was only recently discovered is actually over 20,000 square miles. Scientists believe that this volcano erupted over 2,000 years ago and the heat from the eruption actually created a hole in the ice sheet. They also believe that this volcano probably produced a large plume of gas and ash that reached 8 miles in the sky. The combination of factors leads the scientists believe that the eruption of this volcano was the largest eruption that took place in Antarctica within the previous 10,000 years.

The most interesting thing about this volcano is that it most likely still active, making scientists wonder what would happen to the surrounding glaciers if it were to erupt again.

Iceland

Due to its cold environment and large number of volcanoes, Iceland is another place to find these subglacial volcanoes. In fact, in 2010 the subglacial volcano Eyjafjallajökull began erupting after 200 years of being dormant. There is another similar volcano nearby named Katla, whose eruption from one of its fissures in 934 A.D. created one of the largest known lava flows to take place during the Holocene. Although this volcano was more active in historical times than at present, there is still occasional small activity.

 

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Submarine Volcano

 

A submarine volcano is different than all of the other types because they are found underwater. These volcanoes are in fact some of the most productive of the volcanic systems, producing around three quarters of the year’s output of magma but most people do not think of them because they are usually located around 8,500 feet underwater on average. Some scientists estimate that in the Pacific Ocean in just a million square kilometers of the ocean floor you will find around 4,000 volcanoes. Like other types, a submarine volcano can vary greatly in height, although it is estimated that around 75,000 of those in the Pacific Ocean rise half a mile over the ocean floor.

Eruptions

Although each submarine volcano is located underwater, it will still produce eruptions while active and the products of these eruptions are what shape the way the sea floor looks. Scientists estimate that out of the million or so of these volcanoes that can be found around the world, many thousands of them are active. Despite this because of their location underwater, it can be hard to catch a submarine volcano in the eruption process. However, scientists do know that most eruptions from these volcanoes will take place in shallow water although recent technological advances have helped scientists document those that take place in deeper water well.

Deposits

Because a submarine volcano is located underwater, the deposits that are created during the eruption can be very different than those of other types of volcanoes. Volcanologists are actually unsure if an explosive eruption of a submarine volcano is even possible. That is because due to the high pressure created by the water (250 times the atmospheric pressure) bubbles are hard to form in the magma and lava. Because the water will almost instantly quench the lava, the outer surface of volcanic flows becomes glass.

Lava Flows

The shape of the flows of a submarine volcano tends to be pillow-like as compared to the blocky flows that are typical of land volcanoes. These pillows are created when the crust of a flow will split causing the lava to ooze out at which point it flows a very short distance and solidifies. The process then repeats with the new piece of lava and ends up creating what seems to be a large stack of pillows. The lava flows can also take other shapes, such as sheet flows and tumuli, which is an inflation feature.

Volcanic Ecosystems

Like all volcanoes, a submarine volcano is associated with a unique volcanic ecosystem. These are usually located by hydrothermal vents, or black smokers, which have been located at all of the mid-ocean ridges around the world. At these vents, hydrogen sulfide and water in addition to other minerals exit these vents, creating an ecosystem of organisms that live using sulfur instead of sunlight. Here you can find tube worms, mussels, giant clams and other organisms.

Detection Of Eruptions

As mentioned earlier, despite recent advances in technology it is still difficult for scientists to detect the eruption of a submarine volcano. In fact, they have only been capable of detecting them at all since around the year 1990. Long before they were first detected, oceanographers and volcanologists alike were aware that submarine volcano eruptions were occurring but had no way to know where and when. In recent decades, however, they created a new system that measures the small earthquakes that are normally part of magma migration.

Instead of relying on feeling vibrations like they do with earthquakes on land, this system listens for them as the vibrations underwater will produce an acoustic wave. Since this system was created, it has been much easier for scientists to pinpoint the location of these underwater eruptions.

 

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