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The expansion of gases in lava caused by decreasing pressure as it rises to the surface can make for very explosive eruptions, such as the last eruption of Mt. St. Helens.

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A characteristic of lava that determines the force of a volcanic eruption is?

The silica content of the lava plays a key role in determining the force of a volcanic eruption. High silica content makes lava more viscous, leading to more explosive eruptions, while low silica content results in less viscous lava and less explosive eruptions.


What are the characteristics of viscous lava flows?

Viscous lava flows are typically thicker and move more slowly than less viscous lava flows. They have a higher silica content, which makes them more resistant to flow. Viscous lava flows tend to form steep-sided volcanoes and are associated with explosive eruptions.


Is phroclastic material likely to form from low - viscosity lava or high - viscosity lava?

Pyroclastic material is more likely to form from high-viscosity lava. This is because high-viscosity lava traps gases more effectively, leading to explosive eruptions that fragment the lava into ash, pumice, and other pyroclastic materials. In contrast, low-viscosity lava tends to flow more easily and is less explosive, resulting in less pyroclastic activity.


Why is rhyolitic lava more expolsive than basaltic lava?

Rhyolitic lava is extremely viscous. This means it can hold more gas under pressure. The magma travels upward slowly until the gas, which has been held in place, comes out of solution pretty much all at one, resulting in an explosion. The high viscosity also means that the magma can build over time only to be released suddenly. Basaltic lava, which does not resist flow as much, can be extruded more gradually.


How are the slope of a volcano and the type of lava that forms the volcano related?

The slope of a volcano can affect the type of lava that erupts. Steeper slopes typically result in more explosive eruptions with thicker, more viscous lava that can lead to pyroclastic flows and ash clouds. Meanwhile, gentler slopes tend to produce less explosive eruptions with runnier, less viscous lava that flows further and can create lava flows.


What is mafic lava like?

Mafic lava is low in silica and high in iron and magnesium, which makes it less viscous and more fluid compared to felsic lava. It tends to flow easily and often forms basaltic rocks when it cools. Mafic lava eruptions typically result in gentle, effusive lava flows rather than explosive eruptions.


Is basaltic lava less fluid than andesitic lava?

No, basaltic lava is typically more fluid than andesitic lava due to its lower silica content. This results in basaltic lava flowing more easily and spreading over larger areas compared to andesitic lava.


How are volcanic eruptions affected by the type of lava?

The more silaceous the lava, (higher silica content), the more explosive the eruption.


Difference between viscous and non viscous lava?

Viscous lava is very sticky and thick and is more felsic (ie it contains more silica) than non-viscous lava. This type of lava makes for a very explosive volcano, because it's so sticky that it sticks to itself and can't exit the volcano until it explodes violently. Non-viscous lava is more runny and is more mafic (has more iron, less silica). Volcanoes with non-viscous lava are less explosive because the lava just runs out slowly and no pressure builds. The Hawaiian islands are formed from volcanoes with non-viscous lava.


Why can lava be explosive or non explosive?

Lava can be explosive if it is high in gas content, such as dissolved water vapor or carbon dioxide, which can cause pressure to build up and lead to explosive eruptions. On the other hand, lava can be non-explosive if it is low in gas content and flows more easily without building up pressure, resulting in effusive eruptions with slower lava flows.


Is a non-explosive volcanic eruption more likely to produce lava or pyroclastic material?

Lava because pyroclastic material explodes from a volcano, Lava just runs down the surface of the volcano nonexplosive or explosive.


Why is blocky lava an important clue to the explosiveness of volcano?

Blocky lava, known as andesitic or rhyolitic lava, typically indicates a high-viscosity magma that traps gases, leading to explosive eruptions. The angular, jagged formations of blocky lava suggest that the lava cools and solidifies relatively quickly, often in a more viscous state. This behavior contrasts with fluid basaltic lava, which tends to flow smoothly and produce less explosive eruptions. Therefore, the presence of blocky lava can signal a volcano's potential for more violent eruptive activity.