How does silica change the shape of a volcano?

As low-silica magma cools, it hardens to rock, adding a new thin layer of rock to the volcano. Over time, these long thin layers build up into a volcano that is wide (many are more than 10 miles) with shallow sloping sides. These are called shield volcanoes due to their shield-like shape.

What happens if a volcanoes magma is high in silica?

Magmas with high silica content have a high viscosity (resistance to flow) and are generally more explosive when eruptions occur. All magmas also contain some degree of trapped gasses (CO2 & H2O ). The more trapped gas the more violent the explosion. All magma that reaches the surface can be classified as Lava.

What affects the shape of a volcano?

The shape of a volcano is largely determined by the type of lava that has erupted, and importantly, its viscosity. Viscosity is a fluid’s resistance to flow. … The cooler the lava, the higher the viscosity (the thicker it is).

How do volcanoes get their shape?

Volcanoes have several shapes, which are controlled by the composition of the magma and the nature of its eruption. If a volcano produces very fluid lava (low in the compound SiO2, or silica), the magma flows a long distance before it cools, making a flat, shield-shaped volcano.

Why does magma have high silica content?

As the magma cools, more and more bonds are created, which eventually leads to the development of crystals within the liquid medium. … Magmas that have a high silica content will therefore exhibit greater degrees of polymerization, and have higher viscosities, than those with low-silica contents.

How does silica content affect the viscosity of magma?

The higher the amount of silica in the magma, the higher is its viscosity. Viscosity is a liquid’s resistance to flow. … Mafic magma is not viscous and will flow easily to the surface. Felsic magma is viscous and does not flow easily.

What is the shape of volcano?

Volcanoes are classified by the eruption type and by the volcanic cone shape. There are three basic cone shapes and six eruption types. The three cone shapes are cinder cones, shield cones, and composite cones or stratovolcanoes.

Why do volcanoes differ in shape?

Volcanoes differ in appearance because of the composition of their magma and the processes that originally created them. The tall cone shape you usually think of when you think of a volcano describes a composite volcano, one common form of volcanoes.

How do the dissolved gases and viscosity of magma affect the explosivity of a volcanic eruption?

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.

How does lava form in a volcano?

Lava forms when magma erupts from a volcano. As pressure is released gases, dissolved in the magma, bubble out so the composition of lava changes. Most lava flows are formed by the eruption of hot (around 1200oC) basalt magma, (see video clip above).

Why are volcanoes cone shaped?

They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone.

What are the three main shapes of a volcano?

There are three types of volcanoes: cinder cones (also called spatter cones), composite volcanoes (also called stratovolcanoes), and shield volcanoes. Figure 11.22 illustrates the size and shape differences amongst these volcanoes. Shield volcanoes, which get their name from their broad rounded shape, are the largest.

What effect does silica have on viscosity?

Higher silica content means higher viscosity.

But lower temperatures and low gas content mean higher viscosity. Hence, lower viscosity and low gas content mean higher temperature of magma.

How is magma turned into lava?

Since it is lighter than the solid rock around it, magma rises and collects in magma chambers. Eventually, some of the magma pushes through vents and fissures to the Earth’s surface. Magma that has erupted is called lava.

How does magma rise through the crust?

The magma rises and collects in chambers within the crust. As magma fills the chamber, pressure grows. If the pressure gets high enough, the magma can break through the crust and spew out in a volcanic eruption. Most explosive volcanoes occur above subduction zones.

How does silica relate to volcanoes?

Silica: Influences lava viscosity and overall shape of the volcano. Silica molecules form a strong bond that permits entrapment of volcanic gases and promotes explosive volcanic eruptions. Low-silican magmas allow rapid escape of gases and low-explosivity eruptions.

What is volcanic silica?

Silicon dioxide, the most abundant rock-forming compound on Earth and the predominant molecular constituent of volcanic rocks and magmas. It tends to polymerize into molecular chains, increasing the viscosity of the magma.

How does viscosity affect the movement of magma?

How does viscosity affects the movement of magma? Heating reduces viscosity (warm syrup flows more easily than cold.) High viscosity lavas flow slowly and typically cover small areas. In contrast, low viscosity magmas flow more rapidly and form lava flows that cover thousands of square kilometers.

What is the effect of silica content to volcanic eruption?

The silica content of the magma determines how thick the magma is, how easily it flows and how easily dissolved gases within the magma can escape; therefore the silica content determines the characteristic of the volcanic eruption and the shape and size of the resulting volcanic cone.

How does silica content affect the viscosity of magma quizlet?

A more viscous (thick) magma will produce a more violent eruption This is controlled in part by the concentration of silica in the magma. A magma with low silica (<45%) will be runny and so the eruption will not be explosive. A magma with high silica (>60%) will be quite viscous and so the eruption will be violent.