dormant volcano definition
Hello. Welcome to solsarin. This post is about “dormant volcano definition“.
Volcano
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates are diverging or converging, and most are found underwater. For example, a mid-ocean ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust’s plates, such as in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande Rift in North America.
3,000 kilometers
Volcanism away from plate boundaries has been postulated to arise from upwelling diapirs from the core–mantle boundary, 3,000 kilometers (1,900 mi) deep in the Earth. This results in hotspot volcanism, of which the Hawaiian hotspot is an example. Volcanoes are usually not created where two tectonic plates slide past one another.
Large eruptions can affect atmospheric temperature as ash and droplets of sulfuric acid obscure the Sun and cool the Earth’s troposphere. Historically, large volcanic eruptions have been followed by volcanic winters which have caused catastrophic famines.
Etymology
The word volcano is derived from the name of Volcano, a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan, the god of fire in Roman mythology. The study of volcanoes is called volcanology, sometimes spelled vulcanology.
Plate tectonics
According to the theory of plate tectonics, Earth’s lithosphere, its rigid outer shell, is broken into sixteen larger and several smaller plates. These are in slow motion, due to convection in the underlying ductile mantle, and most volcanic activity on Earth takes place along plate boundaries, where plates are converging (and lithosphere is being destroyed) or are diverging (and new lithosphere is being created).
Divergent plate boundaries
At the mid-ocean ridges, two tectonic plates diverge from one another as hot mantle rock creeps upwards beneath the thinned oceanic crust. The decrease of pressure in the rising mantle rock leads to adiabatic expansion and the partial melting of the rock, causing volcanism and creating new oceanic crust. Most divergent plate boundaries are at the bottom of the oceans, and so most volcanic activity on the Earth is submarine, forming new seafloor. Black smokers (also known as deep sea vents) are evidence of this kind of volcanic activity. Where the mid-oceanic ridge is above sea level, volcanic islands are formed, such as Iceland.
Convergent plate boundaries
Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. The oceanic plate subducts (dives beneath the continental plate), forming a deep ocean trench just offshore. In a process called flux melting, water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, thus creating magma. This magma tends to be extremely viscous because of its high silica content, so it often does not reach the surface but cools and solidifies at depth.
When it does reach the surface, however, a volcano is formed. Thus subduction zones are bordered by chains of volcanoes called volcanic arcs. Typical examples are the volcanoes in the Pacific Ring of Fire, such as the Cascade Volcanoes or the Japanese Archipelago, or the Sunda Arc of Indonesia.
Hotspots
Hotspots are volcanic areas thought to be formed by mantle plumes, which are hypothesized to be columns of hot material rising from the core-mantle boundary. As with mid-ocean ridges, the rising mantle rock experiences decompression melting which generates large volumes of magma. Because tectonic plates move across mantle plumes, each volcano becomes inactive as it drifts off the plume, and new volcanoes are created where the plate advances over the plume. The Hawaiian Islands are thought to have been formed in such a manner, as has the Snake River Plain, with the Yellowstone Caldera being the part of the North American plate currently above the Yellowstone hotspot. However, the mantle plume hypothesis has been questioned.
What is the difference between active and dormant volcanoes?
Volcanoes are an impressive force of nature. Physically, they dominate the landscape, and have an active role in shaping our planet’s geography. When they are actively erupting, they are an extremely dangerous and destructive force. But when they are passive, the soil they enrich can become very fertile, leading to settlements and cities being built nearby.
Such is the nature of volcanoes, and is the reason why we distinguish between those that are “active” and those that are “dormant”. But what exactly is the differences between the two, and how do geologists tell? This is actually a complicated question, because there’s no way to know for sure if a volcano is all done erupting, or if it’s going to become active again. Put simply, the most popular way for classifying volcanoes comes down to the frequency of their eruption. Those that erupt regularly are called active, while those that have erupted in historical times but are now quiet are called dormant (or inactive). But in the end, knowing the difference all comes down to timing!
Active Volcano:
Currently, there is no consensus among volcanologists about what constitutes “active”. Volcanoes – like all geological features – can have very long lifespans, varying between months to even millions of years. In the past few thousand years, many of Earth’s volcanoes have erupted many times over, but currently show no signs of impending eruption.
As such, the term “active” can mean only active in terms of human lifespans. Which are entirely different from the lifespans of volcanoes. Hence why scientists often consider a volcano to be active only if it is showing signs of unrest (i.e. unusual earthquake activity or significant new gas emissions) that mean it is about to erupt.
The Smithsonian Global Volcanism Program defines a volcano as active only if it has erupted in the last 10,000 years. Another means for determining if a volcano is active comes from the International Association of Volcanology, who use historical time as a reference (i.e. recorded history).
If you want to know about “how did gatsby get rich“, click on it.
Where do Volcanoes occur?
The majority of volcanoes occur at plate boundaries. They can occur where plates separate, an example of this is Iceland. Here volcanoes are formed by the North American and Eurasian plates pulling apart. (see divergent plate boundaries)
They can also occur where plates collide. Mount Etna is formed by the subduction of the African plate under the Eurasian plate. The melting of the subducted plate causes an increase in pressure which leads to the formation of a magma chamber and in turn a volcano.
Volcanoes can also form at areas known as Hot-Spots. Hotspots are caused by magma of increased temperature from a mantle plume. This hot magma melts through the rock of the Earth’s crust and rises through the cracks to form a volcano.
452 of the world’s volcanoes can be found in what is known as the Pacific Ring of Fire. This is an area of intense volcanic activity due to plate tectonics. 75% of the world active and dormant volcanoes can be found here.
What causes volcanoes to erupt?
Rock from subducted plates melts to form molten magma which pushes its way towards the surface forming a magma chamber. Gasses that have been dissolved in the magma expand causing a massive increase in pressure. This increase in pressure causes the magma to rise and force its way through cracks/fissures in the volcano above. As it reaches the surface the pressure is released and an eruption occurs. During an eruption volcanic ash, rock particles, dust, gasses and lava are all ejected.
How violent the eruption is depends on the amount of silica present in the magma. Silica produces a thicker magma that is better at trapping gasses. The more gas present the greater the pressure. Therefore the more silica present in the magma the more violent the eruption will be.
Cone Volcanoes
Types of lava and their effect on the volcano structure
There are two types of lava, acidic and basic.
Acidic lava has a high silica content and this makes it thicker. This thick lava doesn’t travel far and due to the high level of dissolved gas it has violent eruptions. Combined these cause the volcano to have a steep sided cone. These are known as Cone Volcanoes.
Basic lava contains less silica, this allows the gasses to escape and gives a runny lava. Eruptions of this type of lava a gentler and this along with it being runny allows the lava to flow further. Volcanoes of this type of lava will have gently sloping sides. They are known as Shield volcanoes.
Ireland and Volcanoes
Ireland is not known for its high level volcanic activity in recent history. But by studying the landscape volcanoes from hundreds of millions of years ago can be still be seen.
There are a number of extinct volcanoes in Ireland these include Slieve Gullion in County Armagh, Croghan Hill in County Offaly, Mount Slemish in County Antrim, Lambay Island in Dublin and Loch Na Fooey in County Galway. These volcanoes are all extinct with the last eruption was approximately 60 million years ago.
60 million years ago
Other volcanic activity can also be identified here in Ireland. One of the world’s most famous Geoheritage sites The Giant’s Causeway, is a result of volcanic activity. Approximately 60 million years ago Antrim was at the heart of intense volcanic activity, magma from below the Earth’s surface forced its way up through fissures in the rock and formed a huge lava plateau. As this lava rapidly cooled it contracted forming the famous hexagonal columns.
Thank you for staying with this post “dormant volcano definition ” until the end.
