What does magma with high silica content form?
High silica content produces a thick viscous lava that does not flow easily. Low silica content produces a lava that is more fluid and flows more easily. Lava is less dense than the surrounding rock and rises up to the surface through cracks and crevices under the Earth.
Which type of magma has more silica?
Felsic magma has more silica and alumina content, which makes magma more viscous. Mafic magma has less silica content and more iron and magnesium in it.
Which lava has the highest silica content?
As a result of its higher viscosity and gas content intermediate magma builds up pressure below the Earth's surface before it can be released as lava. Felsic magma has the highest silica content of all magma types between 65-70%. Thick viscous felsic magma can trap gas bubbles in a volcano's magma chamber.
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.
What type of volcano will be produced if the magma contains little amount of silica?
Over time low silica eruptions build a large broad cone. A typical low silica eruption produces large amounts of lava. Tectonic Setting for Low Silica Eruptions include Spreading Centers such as the Mid-Atlantic Ridge or African Rift Zone and Aseismic Ridges or Hot Spots such as the Hawaiian Islands.
Which has the most silica content?
Quartz; Quartz is the most abundant silica mineral. Pure Quartz is colorless and transparent. It occurs in most igneous and practically all metamorphic and sedimentary rocks. It is used as a component of numerous industrial materials.
What type of rock has the most silica?
The most significant variations are the amounts of silica (SiO2) present (see table). Most igneous rocks contain between 45 and 70 wt% silica. They range from lower-silica basalt and gabbro to higher-silica rhyolite and granite.
Does andesitic magma have high silica content?
Andesitic magma — SiO2 55-65 wt%, intermediate. in Fe, Mg, Ca, Na, K. Rhyolitic magma — SiO2 65-75%, low in Fe, Mg, Ca, high in K, Na.
Does silica make volcanoes more explosive?
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.
How does silica content affect viscosity?
A magma's silica content will not only control the rock type that forms, it also controls the relative viscosity of the magma. Differences in a magma's viscosity will determine the shape a volcano takes. High-silica (basalt) magma has a much lower viscosity. It flows much easier and over longer distances.
Which type of magma has the highest silica content and viscosity?
Explosive eruptions are favored by high gas content and high viscosity (andesitic to rhyolitic magmas)….Viscosity of Magmas.
| Summary Table | Magma Type | Rhyolitic |
|---|---|---|
| Solidified Rock | Rhyolite | |
| Chemical Composition | 65-75 SiO2 %, low in Fe, Mg, Ca, high in K, Na. | |
| Temperature | 650 – 800 oC | |
| Viscosity | High |
•Sep 14, 2015
What is silica magma?
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.
What rocks are high in silica?
Silicon is never found in its natural state, but rather in combination with oxygen as the silicate ion SiO44- in silica-rich rocks such as obsidian, granite, diorite, and sandstone. Feldspar and quartz are the most significant silicate minerals.
Does basalt have high silica content?
Basalt is a hard, black volcanic rock with less than about 52 weight percent silica (SiO2). Because of basalt's low silica content, it has a low viscosity (resistance to flow).
What kind of rock is silica?
siliceous rock, any of a group of sedimentary rocks that consist largely or almost entirely of silicon dioxide (SiO2), either as quartz or as amorphous silica and cristobalite; included are rocks that have formed as chemical precipitates and excluded are those of detrital or fragmental origin.
What is basaltic magma?
Basaltic (or mafic) magma predominates in nonexplosive volcanic eruptions. It is a high-temperature magma (1,200 °C (about 2,200 °F)) characterized by flowing lava, and it is made up of about 45–55 percent silica (SiO2) by weight.
What is rhyolitic magma?
Rhyolitic lavas are viscous and tend to form thick blocky lava flows or steep-sided piles of lava called lava domes. Rhyolite magmas tend to erupt explosively, commonly also producing abundant ash and pumice.
How does silica content control magma viscosity?
High-silica (basalt) magma has a much lower viscosity. It flows much easier and over longer distances. As low-silica magma cools, it hardens to rock, adding a new thin layer of rock to the volcano.
Why is silica content so important?
It is the silica content that controls the viscosity of the magma, and hence the nature of the volcanism that is seen. 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.
What type of magma has high viscosity?
The magma that has the highest viscosity is rhyolitic magma.
Which type of volcano the magma content is high?
Viscosity of Magmas
| Summary Table | ||
|---|---|---|
| Magma Type | Solidified Rock | Gas Content |
| Basaltic | Basalt | Low |
| Andesitic | Andesite | Intermediate |
| Rhyolitic | Rhyolite | High |
Sep 14, 2015
What is mafic magma?
Describes magma that contains lower amounts of silica and is generally less viscous and less gas-rich than silicic magma. Tends to erupt effusively, as lava flows. Includes andesites (57-63 percent SiO2), basaltic andesites (53-57 percent SiO2), and basalts (47-53 percent SiO2).
Is basaltic magma high silica?
Basalt is a hard, black volcanic rock with less than about 52 weight percent silica (SiO2). Because of basalt's low silica content, it has a low viscosity (resistance to flow). Therefore, basaltic lava can flow quickly and easily move >20 km from a vent.
Is andesitic magma high in silica?
Andesitic magma — SiO2 55-65 wt%, intermediate. in Fe, Mg, Ca, Na, K. Rhyolitic magma — SiO2 65-75%, low in Fe, Mg, Ca, high in K, Na.
Is rhyolite high in silica?
Rhyolite is a felsic extrusive rock. Due to the high silica content, rhyolite lava is very viscous. It flows slowly, like tooth paste squeezed out of a tube, and tends to pile up and form lava domes.
What does high silica content mean?
Lava with high silica content is thick and viscous and does not readily flow. Lava rises up toward the surface but is too thick to squeeze through the cracks and fissures in the Earth.
Which magma type has the highest silica and gas content?
MAGMA COMPOSITION AND ROCK TYPES
| SiO2 CONTENT | MAGMA TYPE | VOLCANIC ROCK |
|---|---|---|
| ~50% | Mafic | Basalt |
| ~60% | Intermediate | Andesite |
| ~65% | Felsic (low Si) | Dacite |
| ~70% | Felsic (high Si) | Rhyolite |
Which magma type has the lowest silica content?
Because basalt contains the least amount of silica and erupts at the highest temperature compared to the other types of lava, it has the lowest viscosity (the least resistance to flow). Thus, basalt lava moves over the ground easily, even down gentle slopes.
Is mafic high in silica?
In a widely accepted silica-content classification scheme, rocks with more than 65 percent silica are called felsic; those with between 55 and 65 percent silica are intermediate; those with between 45 and 55 percent silica are mafic; and those with less than 45 percent are ultramafic.
What is felsic magma?
Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Felsic magma or lava is higher in viscosity than mafic magma/lava. Felsic rocks are usually light in color and have specific gravities less than 3.