All rights reserved. If a lot of gas is trapped within magma, pressure will build and build until eventually the magma erupts explosively out of the volcano. This builds pressure inside the bottle and when you release the pressure by opening the bottle, the gas rushes out of the top carrying some of the liquid with it.
Phreatomagmatic eruptions are a type of explosive eruption that results from magma erupting through water. Some submarine volcanoes are phreatomagmatic if the magma is gas-rich, for example Surtsey in Iceland. This eruption formed a new island. Explosive eruptions can form pyroclastic flows that sweep down valleys, destroying everything in their path. They also send ash high into the atmosphere, forming plumes. If a magma has low viscosity it is runny , gas can escape easily, so when the magma erupts at the surface it forms lava flows.
These eruptions are relatively! If a magma rises very slowly within the conduit. By December the growth rate was 10 m 3 per second — in other words, enough lava to fill a minibus was produced every second.
Aerial view of the Holuhraun lava field, Iceland, September The effect of temperature on viscosity is intuitive. Like most liquids, the higher the temperature, the more fluid a substance becomes, thus lowering its viscosity. Composition plays an even greater role in determining a magma's viscosity.
A magma's resistance to flow is a function of its "internal friction" derived from the generation of chemical bonds within the liquid.
Chemical bonds are created between negatively charged and positively charged ions anions and cations , respectively. Of the ten most abundant elements found in magmas see above , oxygen is the only anion.
Silicon, on the other hand, is the most abundant cation. Thus, the Si-O bond is the single most important factor in determining the degree of a magma's viscosity. These two elements bond together to form "floating radicals" in the magma, while it is still in its liquid state i.
These floating radicals contain a small silicon atom surrounded by four larger oxygen atoms SiO 4. This atomic configuration is in the shape of a tetrahedron. The radicals are therefore called silicon-oxygen tetrahedra , as shown here. These floating tetrahedra are electrically charged compounds.
As such, they they are electrically attracted to other Si-O tetrahedra. The outer oxygen atoms in each tetrahedron can share electrons with the outer oxygen atoms of other tetrahedra. The sharing of electrons in this manner results in the development of covalent bonds between tetrahedra. In this way Si-O tetrahedra can link together to form a variety shapes: double tetrahedra shown here, C , chains of tetrahedra, double chains of tetrahedra, and complicated networks of tetrahedra.
As the magma cools, more and more bonds are created, which eventually leads to the development of crystals within the liquid medium.
Thus, the Si-O tetrahedra form the building blocks to the common silicate minerals found in all igneous rocks. However, while still in the liquid state, the bonding of tetrahedra results in the polymerization of the liquid, which increases the "internal friction" of the magma, so that it more readily resists flow.
Magmas that have a high silica content will therefore exhibit greater degrees of polymerization, and have higher viscosities, than those with low-silica contents. The amount of dissolved gases in the magma can also affect it's viscosity, but in a more ambiguous way than temperature and silica content.
When gases begin to escape exsolve from the magma, the effect of gas bubbles on the bulk viscosity is variable. Although the growing gas bubbles will exhibit low viscosity, the viscosity of the residual liquid will increase as gas escapes. The overall bulk viscosity of the bubble-liquid mixture depends on both the size and distribution of the bubbles. Although gas bubbles do have an effect on the viscosity, the more important role of these exsolving volatiles is that they provide the driving force for the eruption.
For example Diamond has a melting point of about C. It will not melt when touched by lava. Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home Essay Which type of magma is known for the most violent eruptions?
Ben Davis May 2, Which type of magma is known for the most violent eruptions? Which volcano produces the most violent eruptions and why? What magma causes powerful explosive eruptions? What are the composition of magma that contributes to eruption of volcano? What are the top two composition of magma answer? Is water considered Lava?
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