Explosive eruptions If a lot of gas is trapped within magma, pressure will build and build until eventually the magma erupts explosively out of the volcano.
Why would a volcano erupt explosively?
Explosive eruptions occur where cooler, more viscous magmas (such as andesite) reach the surface. Dissolved gases cannot escape as easily, so pressure may build up until gas explosions blast rock and lava fragments into the air!
What does it mean when magma is high in silica?
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. As lava continues to rise upward, pressure continues to build.
What magma is most likely to erupt explosively?
Explosive eruptions are favored by high gas content & high viscosity magmas (andesitic to rhyolitic magmas).
What does it mean by higher silica content magma in terms of viscosity?
The higher the amount of silica in the magma, the higher is its viscosity. Viscosity is a liquid’s resistance to flow. Viscosity determines what the magma will do. Mafic magma is not viscous and will flow easily to the surface. Felsic magma is viscous and does not flow easily.
How does the magma chemical composition of silica affect its viscosity?
Viscosity of Magmas Viscosity depends on primarily on the composition of the magma, and temperature. Higher SiO2 (silica) content magmas have higher viscosity than lower SiO2 content magmas (viscosity increases with increasing SiO2 concentration in the magma).
What is the relationship between silica and the viscosity of the magma?
Viscosity is the resistance to flow (opposite of fluidity). Viscosity depends on primarily on the composition of the magma, and temperature. Higher SiO2 (silica) content magmas have higher viscosity than lower SiO2 content magmas (viscosity increases with increasing SiO2 concentration in the magma).
How does silica rich magma erupt?
Silica-Rich Magma Traps Explosive Gases Magma with a high silica content also tends to cause explosive eruptions. H. Silica-rich magma has a stiff consistency, so it flows slowly and tends to harden in a volcano’s vents. If enough pressure builds up, an explosive eruption takes place.
How does silica affect magma viscosity?
How does the silica content of magma affect how explosive an eruption is?
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.
Why does silica increase the viscosity of magma?
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.
Why does silica increase viscosity?
Water, for example, is a low viscosity fluid. Composition: he more felsic the lava (the more silica in the lava), the higher the viscosity because silica forms chains in the cooling lava even before it crystallizes. The more mafic the lava (the less silica in it), the lower the viscosity.
Why is silica rich magma highly explosive?
However, once this rock surfaces from an explosion, the liquid rock is known as magma. Silica-rich magma is highly explosive because the gases within the magma build up within the highly viscous magma and burst when pressure is too great.
What is low silica in a volcanic eruption?
Volcanic Eruptions: Low Silica. Magma is less dense than the surrounding rock and rises up to the surface through cracks and crevices under the Earth’s surface causing an eruption of lava . 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;
How does magma rise up?
Magma is less dense than the surrounding rock and rises up to the surface through cracks and crevices under the Earth’s surface causing an eruption of lava .
Why does lava not flow out of the ground?
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. As lava continues to rise upward, pressure continues to build.
