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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. Each TeachEngineering lesson or activity is correlated to one or more K science, technology, engineering or math STEM educational standards.
In the ASN, standards are hierarchically structured: first by source; e. View aligned curriculum. Do you agree with this alignment? Thanks for your feedback! Students learn about the causes, composition and types of volcanoes. They begin with an overview of the Earth's interior and how volcanoes form. Once students know how volcanoes function, they learn how engineers predict eruptions.
While learning about volcanoes, magma and lava flows, students learn about the properties of liquid movement, coming to understand viscosity and other factors that increase and decrease liquid flow. They also learn about lava composition and its risk to human settlements. Students observe an in-classroom visual representation of a volcanic eruption. During the activity, students observe, measure and sketch the volcano, seeing how its behavior provides engineers with indicators used to predict an eruption.
Students are introduced to natural disasters and learn the difference between natural hazards and natural disasters. Students should have a basic understanding of volcanoes and volcanic eruptions and be familiar with fluid behaviors in situations of flow and static equilibrium, understanding that these behaviors may vary based on temperature and fluid composition.
Students should also be familiar with the concept of gas exerting pressure inside a closed container. Today we are going to talk about something that we all know about, but that is still a great mystery to us in many ways. What do you know about volcanoes? Listen to student answers. Expect students to answer with a general description of a volcano as a large landmass that is prone to eruptions. I heard you mention lava, magma, eruptions and heat.
Today, we are going to delve into some characteristics that make each volcano unique by looking at certain features that cause them to behave differently. Volcanoes have long fascinated humans with their immense—sometimes incredibly destructive—power and impact. Would any of you like to live near a volcano? Expect students to respond by mentioning the dangers of being close to an active volcano, including the potential for death and destruction caused by eruptions.
Heat, fire, hot magma, etc. Commonly, people associate volcanoes with eruptions of a violent nature, but many volcanoes do not pose a catastrophic risk to their surrounding environments because they do not erupt violently.
During some eruptions, lava, as well as volcanic ash, gas and rock fragments, are sent miles into the air and surrounding areas, posing a large environmental hazard.
Volcanoes are dangerous because of the extreme temperatures of the molten melted rock involved in eruptions. Complex processes happen inside magma, and that is our focus today. Figure 1. Myers and S. Brantley, U. First, it is important to note that pressure is incredibly high under the surface of volcanoes.
We measure pressure in units of Pascals, just like we measure length in meters. At that point, a volcano can erupt in one of two main ways: an effusive eruption or an explosive eruption. Explosive eruptions pose huge dangers to nearby communities. Eruption intensity can also vary depending on how much pressure is inside the bubbles.
We must understand these two concepts to understand violent volcanic eruptions and ultimately what we can do to engineer solutions to the inevitable hazards they pose. A thorough understanding of volcanoes made this feat possible in the form of engineered tools that monitored and predicted the volcanic eruption.
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