Final answer:
Highly viscous lava is associated with rhyolitic or andesitic magma and can plug vents to create lava domes. This type of lava, having a high silica content, exhibits significantly lower flow rates compared to more fluid basaltic lava. Volcanic glass forms when such lava cools rapidly.
Step-by-step explanation:
Understanding Highly Viscous Lava
The type of lava described in the question is highly viscous, which means it does not flow easily and tends to plug the volcanic vent, forming what is often referred to as a lava dome. This kind of lava is typically associated with rhyolitic or andesitic magma due to its high silica content, which contributes to the increased viscosity. For example, pancake-shaped volcanoes on Venus consist of eruptions of this viscous, sludgy lava, indicating the presence of similar geological processes occurring on other planetary bodies.
Lava with high viscosity can create significant geological formations. The Galileo data from Io, one of Jupiter's moons, reveal that silicate lava eruptions there encounter frozen sulfur compounds, leading to impressive plumes and subsequent snowfalls of recondensed sulfur, which contrasts with the more fluid basaltic lava found in some of Earth's eruptions, including those that have shaped the landscapes of places like Hawaii.
Examples of less viscous flows include basaltic lava, which forms more fluid lava plains and aa lava flows that can sometimes overpower human-made barriers as evidenced in historical eruptions. In contrast, volcanic glass, such as obsidian, is created when viscous lava cools rapidly, preventing crystal formation.