How does viscosity affect volcanic eruptions

The advantages of a low Wviscosity number is obvious. The quicker the oil flows cold, the less dry running. Less dry running means much less engine wear. Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home Users' questions How does viscosity affect volcanic eruptions?

Users' questions. If the liquid part of the magma has a high viscosity, then the gas will not be able to expand very easily, and thus, pressure will build up inside of the gas bubble s. When this magma reaches the surface, the gas bubbles will have a high pressure inside, which will cause them to burst explosively on reaching atmospheric pressure. This will cause an explosive volcanic eruption.

Effusive Non-explosive Eruptions. Non explosive eruptions are favored by low gas content and low viscosity magmas basaltic to andesitic magmas.

If the viscosity is low, non-explosive eruptions usually begin with fire fountains due to release of dissolved gases. When magma reaches the surface of the earth, it is called lava. Since it its a liquid, it flows downhill in response to gravity as a lava flows. Different magma types behave differently as lava flows, depending on their temperature, viscosity, and gas content. Pahoehoe Flows - Basaltic lava flows with low viscosity start to cool when exposed to the low temperature of the atmosphere.

This causes a surface skin to form, although it is still very hot and behaves in a plastic fashion, capable of deformation. Such lava flows that initially have a smooth surface are called pahoehoe flows.

Initially the surface skin is smooth, but often inflates with molten lava and expands to form pahoehoe toes or rolls to form ropey pahoehoe. See figure 6. Pahoehoe flows tend to be thin and, because of their low viscosity travel long distances from the vent. A'A' Flows - Higher viscosity basaltic and andesitic lavas also initially develop a smooth surface skin, but this is quickly broken up by flow of the molten lava within and by gases that continue to escape from the lava.

This creates a rough, clinkery surface that is characteristic of an A'A' flow see figure 6. Pillow Lavas - When lava erupts on the sea floor or other body of water, the surface skin forms rapidly, and, like with pahoehoe toes inflates with molten lava. Eventually these inflated balloons of magma drop off and stack up like a pile of pillows and are called pillow lavas.

Ancient pillow lavas are readily recognizable because of their shape, their glassy margins and radial fractures that formed during cooling. Lava Domes or Volcanic Domes - result from the extrusion of highly viscous, gas poor andesitic and rhyolitic lava. Since the viscosity is so high, the lava does not flow away from the vent, but instead piles up over the vent. Blocks of nearly solid lava break off the outer surface of the dome and roll down its flanks to form a breccia around the margins of domes.

The surface of volcanic domes are generally very rough, with numerous spines that have been pushed up by the magma from below.

Explosive eruptions are favored by high gas content and high viscosity andesitic to rhyolitic magmas. Explosive bursting of bubbles will fragment the magma into clots of liquid that will cool as they fall through the air. These solid particles become pyroclasts meaning - hot fragments and tephra or volcanic ash, which refer to sand- sized or smaller fragments.

If the gas pressure inside the magma is directed outward instead of upward, a lateral blast can occur. Directed blasts often result from sudden exposure of the magma by a landslide or collapse of a lava dome.

Pyroclastic Deposits. Pyroclastic material ejected explosively from volcanoes becomes deposited on the land surface. The process of deposition leaves clues that allow geologists to interpret the mode of ejection from the volcano.

Pyroclastic flows are also sometimes called pyroclastic density currents PDCs. They can range from surges which can have a range of clast densities from low to high with generally low concentration of of solid clasts high amonts of gases to high clast concentration clouds of ash and gas pyroclastic flows.

As defined above, block and ash flows consist of an unsorted mixture of blocks and ash with the blocks being mostly rock fragments. Surges tend to hug the ground as they flow over the surface and thus tend to produce thicker deposits in valleys with thinner deposits over ridges.

This helps to distinguish surge deposits from flow deposits and fall deposits. Volcanic eruptions, especially explosive ones, are very dynamic phenomena. That is the behavior of the eruption is continually changing throughout the course of the eruption. This makes it very difficult to classify volcanic eruptions. Nevertheless they can be classified according to the principal types of behavior that they exhibit.

An important point to remember, however, is that during a given eruption the type of eruption may change between several different types. Hawaiian - These are eruptions of low viscosity basaltic magma. Gas discharge produces a fire fountain that shoots incandescent lava up to 1 km above the vent.

The lava, still molten when it returns to the surface flows away down slope as a lava flow. Hawaiian Eruptions are considered non-explosive eruptions. Very little pyroclastic material is produced. Strombolian - These eruptions are characterized by distinct blasts of basaltic to andesitic magma from the vent. These blasts produce incandescent bombs that fall near the vent, eventually building a small cone of tephra cinder cone.

Sometimes lava flows erupt from vents low on the flanks of the small cones. Strombolian eruptions are considered mildly explosive, and produce low elevation eruption columns and pyroclastic fall deposits. Vulcanian - These eruptions are characterized by sustained explosions of solidified or highly viscous andesite or rhyolite magma from a the vent. Eruption columns can reach several km above the vent, and often collapse to produce pyroclastic flows.

Widespread pyroclastic falls are common that contain mostly angular blocks. Vulcanian eruptions are considered very explosive. They may also produce surges with resulting surge deposits.

Pelean eruptions are considered violently explosive. Plinian - These eruptions result from a sustained ejection of andesitic to rhyolitic magma into eruption columns that may extend up to 45 km above the vent.

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Previous Article What are the characteristics of a shield volcano? Next Article What will happen to social media in the future? Back To Top. Crystal Content: Some magmas have already begun to crystallise by the time they reach the surface.

Again, this applies particularly to the cooler, more viscous magmas typical of destructive plate margins. Experiements The "Treacle Test" experiment is designed to enable students to investigate how temperature, volatiles and crystals may affect viscosity. It is suggested that viscosity is roughly measured by how long it takes the treacle to flow from one end of a boiling tube to the other.