Question

What determines the viscosity of magma? What else determines whether a volcano will erupt violently or calmly 

Answer The two main factors that influence how a volcano will erupt are 

viscosity  and gas content. Both are related to the composition of the  magma . Hawaiian volcanoes tend to erupt  basalt , which is low in viscosity and low in gas content (about 0.5 weight percent). The gas that is present can readily escape and little pressure builds up in the magma. At the other extreme,  rhyolite  magmas are very viscous and can contain a lot of gas (up to 7-8 weight present). As the magma moves into the vent and the pressure drops, the gas wants to escape. The magma is very sticky and resists the expansion of the gas bubbles. Ultimately, enough bubbles grow and expand to blow the magma into ash size fragments and eject them violently into the atmosphere.

Answer 1

The viscosity of magma is influenced by its composition. Low silica magma has low viscosity, while high silica magma has high viscosity. Gas content also plays a role, with low gas content leading to calm eruptions and high gas content leading to violent eruptions.

Step-by-step explanation:

The viscosity of magma is influenced by its composition. Magma with a low silica content, such as basalt, has low viscosity, meaning it is more fluid and flows easily. On the other hand, magma with a high silica content, such as rhyolite, has high viscosity, meaning it is sticky and doesn't flow easily.

Another factor that determines how a volcano will erupt is the gas content of the magma. Basaltic magmas typically have low gas content, allowing the gas to escape easily and resulting in calm eruptions. In contrast, rhyolitic magmas can have high gas content, and the sticky magma resists the expansion of gas bubbles, leading to violent eruptions.

Answer 2

The viscosity of magma is determined by its silica content. Basalt magma, on the one hand, which is often of low viscosity, has a low silica content of approximately 50% or less. Rhyolite magma, on the other hand, has high viscosity due to the high silica content of approximately 70% and more.

Gas content and temperatures of the magma are the other factors that determine an explosive or nonexplosive eruption. High temperatures and high gas content (coupled with high viscosity) cause violent explosions.