12/29/2023 0 Comments Define viscosity volcano![]() For example, Iceland was formed where the mid-ocean ridge met with a mantle plume – a ‘hotspot’ of abnormally hot rock in the mantle – and eruptions of lava built volcanoes and filled rift valleys. This process can also form volcanic islands. ![]() The tectonic plates are spreading apart allowing soft molten rock to bubble up between the plates. It stretches all around the globe and is more than 64,000 kilometers (40,000 miles) long. The mid‐ocean ridge is a continuous, underwater seam of mountains and volcanoes that form where divergent tectonic plates meet. Hills covered by volcanic ashes, Great Rift Valley, Tanzania, East Africa. Spreading may have created East Africa's volcanic Great Rift Valley. When spreading centers develop within continents, they form new plate boundaries and trigger volcanic activity. Spreading centers can be found under the sea or on land. In these zones, plates move away from each other, decreasing the pressure on the underlying mantle, allowing it to rise and melt, forming magma. Volcanoes called rift volcanoes are formed in spreading centers. It does not store any personal data.Sorry, your browser doesn't support embedded videos. The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. The cookie is used to store the user consent for the cookies in the category "Performance". This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Other. The cookies is used to store the user consent for the cookies in the category "Necessary". The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". The cookie is used to store the user consent for the cookies in the category "Analytics". These cookies ensure basic functionalities and security features of the website, anonymously. ![]() Necessary cookies are absolutely essential for the website to function properly. Looking back through history, you can be sure that the largest eruptions (think Pinatubo, Krakatoa) will all have involved magma that is rhyolitic in nature. Eventually, the point is reached where the gases can no longer be contained, and a violent eruption ensues. As a result, pressure builds and and builds, with the gasses unable to escape. The reason for the difference is that the viscous magma is unable to escape from the chamber. They are much less frequent, but are typically highly explosive. This is because the pressure from gasses being built up below the surface from tectonic processes is constantly being released, which in turn is only possible since the magma is non-viscous, and so able to be ejected from the magma chamber easily.Įruptions like that seen at Mt St Helens, on the other hand, where the magma is rhyolitic, are generally much more dangerous. Also, they are not particularly explosive. Their eruptions are almost continuous, so are predictable. Types of Eruptionįor all the impressive photography that they attract, eruptions like those in Hawaii, or the Mediterranean island of Stromboli, are not particularly dangerous (from a human perspective, at least). In fact, the entire nature of the eruption is different. The effect of this viscosity is that flowing rivers of lava are not common. The magma is described as ‘rhyolitic’, and is far more viscous due to its higher silica content. The low levels of silica mean that Hawaiian magma has a low viscosity, which explains why we see lava readily cascading downslope, and being churned up in the air in great fire fountains.Īt the other end of the spectrum we have magma that is formed from ‘felsic’ volcanic rock, which has a much higher silicon content. It is the silica content that controls the viscosity of the magma, and hence the nature of the volcanism that is seen. Mafic rock contains relatively little silica. ![]() Hawaiian magma is ‘basaltic’, and is a prime example of what results from heating ‘mafic’ volcanic rock. However, the orange rivers flowing down the sides of Hawaiian volcanoes are not typical of what may be found elsewhere. Magma (or lava, as it is called when it reaches the surface) is molten rock, and you are probably already familiar with what it looks like. To understand this, we must first look at what effect silica has on magma. The role of silica is a subject in itself, however one aspect of silica is that it has an important role in controlling the nature of magma and volcanism. ![]()
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